APPLE
Malus sylvestris Mill., family Rosaceae
In 1969, about 6.7 billion pounds of apples, valued at $274.4 million, were produced in the United States. In the six States where almost two- thirds of the entire crop was produced, the volume, in million pounds, was: Washington, 1,675; New York, 855; Michigan, 720; California, 540; Pennsylvania, 525; and Virginia, 472.
Hedrick (1938*) stated that 4,000 to 5,000 cultivars of apples were described, but Henderson et al. (1969) showed that fewer than two dozen cultivars account for 95 percent of the total crop. The leading cultivar is 'Delicious', which accounts for 30 percent of the total production. 'Golden Delicious' ranks second and accounts for 13 percent. Other leading cultivars and their percentages of the total crop are: 'McIntosh', 10 percent; 'Rome Beauty', 8 percent; 'Jonathan', 6 percent; and 'York Imperial', 5 percent.
Plant:
The apple tree may reach a height of 40 feet or more; however, for various cultural reasons, commercial apple growers keep their trees of standard rootstock less than half that high. Trees on the recently developed dwarf (fig. 37) and semidwarf rootstock (Tydeman 1955) in the newer orchards and replants may be less than 10 feet. This development of dwarf apples is so changing apple production that much of the older information on culture, pollination, and harvest of this crop may no longer be applicable. An example of the difference in the size and planting rate of apple trees is given in table 7.
Many of the older trees were spaced 40 by 40 feet (27 per acre) and took 25 years to reach their maximum production of 500 bushels ( a bushel weighs about 44 pounds) per acre (Anonymous 1969). Snyder (1968) reported production of 113 to 377 bu/acre on 21 farms observed in western New York, where the number of trees ranged from 70 to 182 and averaged 91 per acre. Kelly ( n.d. ) reported 313 bu/acre on 18 farms in Pennsylvania, where over 50 percent of the trees were standard cultivars,. Henderson et al. (1969) reported an agerage of 592 bu/acre for California.
By using dwarf apple trees, the growers can have as many as 1,000 trees per acre, and expect a maximum production of 900 bushels in 6 years on 'Jonathan' trees, or as much as 1,300 bu/acre on 'Golden Delicious' (Anonymous 1971). The smaller trees yield more per acre, reach maximum production at a much earlier age, are more easily pruned and sprayed, and the fruit is much more accessible for thinning and harvesting (Shoemaker and Teskey 1959, Gaylord 1965).
Norton (1971) considered the density of the trees per acre as follows: Low 75 to 150 trees; medium, 200 to 300 trees; high, 400 to 800 trees; ultra-high, 1,000 or more trees.
[gfx] FIGURE 37. - Dwarf apple tree in blossom.
TABLE 7. - Difference in the size and planting rate of apple trees1
____________________________________________________________________________________________________________________________________________
tree
Inflorescence:
The apple flower cluster, made up of about six flowers, is produced on a 1- to 3-year-old woody shoot, l/2 inch to 2 inches long, called a spur. The clusters are usually found at the tip of the spur in the axils of leaves, and are formed the previous summer (Bradford 1915, Latimer 1933). The primary or "king" bud opens first, and usually produces the choicest fruit. If the king bloom fails, the lateral blooms, which open a day or more later, can also produce fruit. Howlett (1926a) showed, however, that the lateral flowers are much more likely to shed, making the preservation of the king bud still more important. The five pinkish-white petals of the 1- to 1 1/2-inch broad and pleasantly scented blossom (fig. 38) shed a few days after they open, but the five green sepals persist in a dried shriveled state in the blossom end of the mature fruit.
The five stigmas, which unite into a common style that leads to the ovary, are surrounded by 20 to 25 erect pollen-bearing stamens. Nectar is secreted between the bases of the stamens and the style.
The ovary is divided into five compartments, each containing two ovules (four in the case of the cultivar 'Northern Spy') so that 10 (or 20 in 'Northern Spy') seeds may develop (Goff 1899, 1901).
The apple flower produces both nectar and pollen in abundance, more nectar than most of our other deciduous fruit trees produce (Smith and Bradt 1967*). Apple pollen and nectar are eagerly collected by honey bees, and are important contributors to spring buildup in honey bee colonies. Colonies usually arrive in the orchard low on stores and relatively weak, the period of bloom is short, and frequently the weather is unfavorable for bee activity. This prevents the storage of surplus honey, so that apple honey on the market is rare. The amount that the bees are able to collect is left in the hive for food reserves.
The average blossoming period for apples is about 9 days. Cool weather lengthens and warm or dry windy weather shortens this period (Morris 1921). Bee activity on apples during the day is usually greatest about 9 a.m. (Brittain 1933). Although numerous blossoms appear on the apple tree, a set of only 5 percent will produce a fair apple crop (McDaniels and Heinicke 1929, Brittain 1935).
[gfx] FIGURE 38. - Longitudinal section of 'Delicious' apple blossom x 6.
Pollination Requirements:
The pollination of apples has been of interest since Cooke (1745) stated that the "farina" (pollen) of one apple tree influenced the fruit of another. Eventually, Wicks (1918) showed that foreign pollen does not bestow a benefit to the fruit in either size, shape, color, or quality. The pollen stimulates development of the seed, which in turn produces an auxin that stimulates adjoining tissue to develop. Of course, the pollen influences the offspring that develops from the seed.
The fertilization of every ovule in the ovary is not essential to fruit development, but the larger the number fertilized the greater the likelihood that the fruit will succeed in the competition for the plant's nutrients and remain on the tree until harvest (Brittain 1933, Tydeman 1943). Usually, the more seeds that develop in the apple, the larger it is (Murneek and Schowengert 1935). About six or seven seeds are necessary for good fruit set (Hartman and Howlett 19S4). Some apple selections set seedless fruit without pollination, but no commercial cultivar has this characteristic (Chan and Cain 1967).
The research by Waite (1895, 1899) produced the first concrete evidence that apples and other pomaceous fruits benefit from the interplanting of and cross-pollination between cultivars, and that pollinating insects are essential for transferring the pollen between compatible cultivars. This research led scores of other scientists to study the pollination requirements of apples, both in the United States and abroad. These studies have been reviewed by Hutson (1926), Brittain (1933), and Free (1960, 1970*), who also conducted research on the subject.
Griggs (1970*) stated that all apple cultivars are self-incompatible to some degree. Some set no fruit at all when self-pollinated; others set various proportions of a commercial crop under favorable conditions. He also stated that the self-fuitfulness of an individual cultivar may vary in different parts of the country, but apple specialists generally agree that no apple cultivar is sufficiently self-fertile to be dependably productive when planted alone. The grower, then, has no choice except to interplant. His problem is to find the most satisfactory and profitable combination of cultivars to produce his crop.
Studies, in particular by Brittain (1933), Burrell and Parker (1931), Latimer (1931), MacDaniels and Heinecke (1929), and Overholser (1927), proved that interplanting of cultivars was necessary, but that all cultivars were not equally compatible. The best pollenizer cultivar is one that has the most compatible pollen, and it blooms at the same time as the main cultivar. Although numerous studies have been made on the pollination of apples, we may not have full information on these points for all major cultivars in all apple-growing regions.
In selecting appropriate cultivars for interplanting, the grower should choose those that flower at the same time. Way (1971) showed that, at least in New York, flowering of early, midseason, and late cultivars generally overlaps sufficiently for their use as pollinators of any commercial cultivar. In the southern section of the apple-growing regions, this difference between cultivars increases, and an overlapping of flowering dates is less likely to occur. This increases the importance of selecting cultivars that flower at the appropriate time. Compatible cultivars should, of course, also be chosen.
The importance of compatibility of cultivars, even when they flower at the right time, was shown by Overholser (1927). The cultivar 'Newtown' set 51.5 percent of its blossoms when cross-pollinated with 'Bellflower' (under a tent enclosing a colony of honey bees, which, presumably, provided maximum cross-pollination), but 'Bellflower' set only 4.3 percent of its flowers that were cross-pollinated with 'Newtown'.
Frost:
The damaging effect of frost is sometimes blamed for poor yields, when, actually, the problem is inadequate cross-pollination. However, blossoms that have been pollinated are believed to be less susceptible to frost damage than nonpollinated ones. The grower should strive, therefore, to get the flowers pollinated as soon as possible after they open. This increased effort to get the flowers pollinated may result in excessive set of fruit some seasons, but excess fruit can be thinned. There is no way to put fruit on the tree after flowering has ceased. As Rom (1970) stated, "Pollination is without question the most critical event in the yearly production cycle [of apples]."
Problems with Interplanting for Cross-Pollination:
In one planting pattern that has been used, every third tree in every third row is a pollenizer. This places every tree of the main cultivar next to a pollenizer. This plan was satisfactory, from both the pollination and the harvesting standpoint, with standard cultivars and separated trees.
In high-density orchards, the trees within the row frequently form a hedge. If pollenizers are planted within the row, the pickers or picking machines fail to separate the fruit from the two cultivars, which may be necessary for the packaging of uniform fruit. If the pollenizer trees are planted on separate rows, the bees, being inclined to forage only within the row rather than to cross the intervening space between rows, become ineffective.
In an attempt to solve this problem, some growers are seeking a small pyramidal crabapple selection that might serve within the row as a pollenizer, occupying little space, furnishing compatible pollen for the main cultivar, yet producing fruit unlikely to be harvested with that of the main cultivar. This should be a satisfactory solution, if the flowers are equally attractive, so that the bees will forage indiscriminately between flowers.
Beekeeper Problems with Dwarf Trees:
Beekeepers who provide colonies for the pollination of apples claim that the narrow spacing between rows of dwarf apple trees creates a maneuvering problem for large vehicles used in transporting bee colonies. Some beekeepers deliver the colonies to the edge of the orchard; then the grower, using a forklift or other small vehicle, distributes the colonies within the orchard.
Pollinators:
The need for an appropriate agent to transfer poller from one self- incompatible cultivar to another was established by Waite (1895, 1899), although growers had associated insect pollination with increased production for years.
Wind has been suggested and disproved at various times as a possible agent in the transfer of apple pollen (Lewis and Vincent 1909, Free 1966). It is no longer considered of significance for this task.
Various wild bees have been mentioned as important pollinators of apples, including the genera Andrena, Bombus, Halictus, and Osmia (Brittain 1933,1936; Free 1964; Glukhov 1955; Hutson 1926; Kitamura and Maeta 1969; Loken 1958; Phillips 1933; Horticultural Education Association 1967). Some wild bees, for, example Osmia, visit flowers at lower temperatures than do honey bees. At times and in some areas, wild bees are sufficiently abundant to set an apple crop. In general however, wild bees cannot be depended upon to adequately pollinate the blossoms of a commercial apple orchard in the United States.
Honey bees are easily handled, and they can be concentrated within the orchard the degree desired. As a result, commercial apple growers have come to depend upon the honey bee as their apple pollinating agent.
The precise method of utilizing honey bees on apples for maximum economic production is less well defined than the appropriate agent. Free and Spencer-Booth (1963) showed that bees were consistently fewer between groups of nine colonies in the center of 9-acre blocks but not when they were in groups of four or singly at one colony per acre. The strength, placement, and manipulation of colonies, the effects of competing plants, soil, and weather, and other factors both within the colony and in the environment contribute to the effectiveness of honey bees.
Smith and Bradt (1967*) mentioned, as had various others before them, that when the honey bee visits an apple blossom for nectar its proboscis is sometimes inserted at the base of the stamens, leaving the anthers and stigma untouched (fig. 39B). When this is done, little pollination occurs. By contrast, the larger bumble bee clambers over the anthers and stigma when foraging and cannot help but transfer pollen from flower to flower. Preston (1949) found that bees visited one cultivar four times as frequently as another. He associated this difference in visitation to the accessibility of nectar in the flowers. The filaments of the 'Delicious' apple are in a narrow upright cluster, more so, according to Roberts (1945), than other cultivars. This permits the bee to alight on the petal, insert its proboscis between the upright filaments, and collect nectar without touching the stigma. For this reason, he recommended that more colonies be used to pollinate 'Delicious' than would be needed on other cultivars. When honey bees are collecting apple pollen, their pollinating efficiency on apples is much greater than when they are collecting nectar.
Beekeepers also mention that dwarf trees have more blooms per acre than trees on standard rootstock; therefore, more bees are needed on the dwarf plantings.
Griggs (1970*) stated that growers who previously worried about overpollination now favor it, knowing that no adequate set can be otherwise obtained. Then, when there is too much fruit set, they thin with chemical sprays to the desired set of fruit, which prevents alternate bearing.
Viable, compatible pollen has been distributed by hand, airplane, or other mechanical means, even by pollen dispensers attached to the entrance of beehives (Bullock and Snyder 1946, Corner et al. 1964, Jaycox 1971, Snyder 1946). When pollen is applied by any of these methods, the grower expects the pollinating insect to pick up the pollen and redistribute it to flowers that were not directly applied with the pollen. Since insects are thus required, the grower would generally get more satisfactory pollination if he would utilize more pollinating insects. A study of pollen tube growth in relation to marginal temperatures (which frequently stimulate growers to use artificial means of pollination) would be of interest. If the tube does not grow at such temperatures, the grower would be wasting his investment in these methods.
[gfx] PN-3768 FIGURE 39. -honey bee on apple blossom. A, collecting nectar; B, collecting pollen.
Pollination Recommendations and Practices:
There are no recommendations for use of wild bees on apples in the United States, but scores of papers have recommended the use of honey bees. These recommendations have changed considerably since Doolittle (1893) first suggested that apiaries of 100 colonies should be placed every few miles. The recommended placement of the colonies now is near or distributed within the orchard (fig. 40), and the recommended number of colonies has increased. These have varied from (1) one colony per 2 to 4 acres (Hooper 1913, Howlett 1926b, Kelty 1929, Kurrenoi 1969, Luce and Morris 1928, West 1912); to (2) one colony per acre (Brittain 1933, Griggs 1953*, Hutson 1926, Jaycox 1968, Lundie 1927, Phillips 1930, Philp and Vansell 1932); to (3) two or more colonies per acre (Benson 1896, Burrell and MacDaniel 1930, Rom 1970).
Many of the recommendations are based more on grower experience with use of bees than precise experimental results. The recommendations stress "strong" colonies, but the growers often leave colony strength to the discretion of the beekeeper.
Woodrow (1933, 1934) and Gooderham (1950) showed that populous colonies of honey bees were much more effective in apple pollination than weaker ones, and overwintered colonies superior to packages of bees. MacDaniels (1929) supported the value of strong colonies particularly in the ability of such colonies to effectively pollinate an orchard when only a few hours of weather were favorable for bee flight.
Even the appropriate number of bees per blossom has not been established with certainty; however, Palmer Jones and Clinch (1968) indicated that there should be one bee for each 1,000 blossoms. Petkov and Panov (1967) reported that the percentage of 'Jonathan' flowers that set increased with bee visits up to six visits per flower. They also associated larger fruit with increased numbers of bee visits.
The effectiveness of the bee is determined by the cross-visits it makes between compatible varieties. If the visits are confined to one variety they are not effective. Repeated cross-pollination of the flowers must occur to produce the optimum set. If a sufficiently large bee population is created, it superimposes over the fixed population a number of wandering bees. These wanderers consist of a few old bees driven on by competition and a larger number of young bees that have not yet become fixed to any particular area of the crop. These wanderers, which are forced to "shop around" from tree to tree to obtain their load of food, are the most valuable to the grower.
When temperatures are marginal for bee flight, bees tend to visit only the blossoms that are near the hive, and also those blossoms on the warm or leeward side of the tree. This preferential visitation can be substantially overcome by the use of strong healthy colonies and by thorough distribution of the colonies in the orchard. If the weather is fair and calm and the temperatures range into the seventies or above, a single group of colonies might adequately pollinate an orchard of many acres in a single day. With cold, cloudy, or windy days, the bees are likely to visit only trees within a few hundred feet of the hives.
The grower should expect the best but prepare for the worst. This includes providing plenty of strong colonies, appropriately distributed for getting ample pollination and a maximum harvest of highest quality fruit even under unfavorable conditions.
[gfx] FIGURE 40.- Honey bee colonies in apple orchard.
LITERATURE CITED:
ANONYMOUS.
1969. ORCHARDS GOING COMPACT TO KEEP APPLES COMPETITIVE. Food and Life
Sciences (New York). N.Y. (Cornell) Agr. Expt. Sta. 2(3): 21.
_____ 1971. DEVELOPING DWARF APPLE TREES. Mich. Agr. Expt. Sta. ''Science in Action," ser. 17,16 pp.
BENTON, F.
1896. THE HONEY BEE - A MANUAL OF INSTRUCTION IN APICULTURE U.S. Dept.
Agr., Div. Ent. Bul. 1, n.s., rev., 118 pp.
BRADFORD, F. C.
1915. THE POLLINATION OF THE POMACEOUS FRUITS. Oreg. Agr. Expt. Sta. Bul.
129,16 pp.
BRITTAIN, W. H.
1933. APPLE POLLINATION STUDIES IN THE ANNAPOLIS VALLEY N.S., CANADA, 1928-1932.
Canada Dept. Agr. Bul. 162, n.s., 198 pp.
BRITTAIN, W. H.
1935. STUDIES IN BEE ACTIVITY DURING APPLE BLOOM. Jour. Econ. Ent. 28:
553-559.
BULLOCK, R. M., and SNYDER J. C.
1946. SOME METHODS OF TREE FRUIT POLLINATION. Wash. State Hort. Assoc.
42d Ann. Mtg., pp. 215-226.
BURRELL, A. B., and MACDANIELS, L. H.
1931. FURTHER POLLINATION STUDIES WITH THE MCINTOSH APPLE IN THE CHAMPLAIN
VALLEY OF NEW YORK. Amer. Soc. Hort. Sci. Proc. (1930): 374-385.
_____ and PARKER, R. G.
1932. POLLINATION OF THE MCINTOSH APPLE IN THE CHAMPLAIN VALLEY. Third
Progress Report. Amer. Soc. Hort. Sci. Proc. (1931) 28: 78-84.
CHAN, B. G., and CAIN, J. C.
1967. THE EFFECT OF SEED FORMATION ON SUBSEQUENT FLOWERING IN THE APPLE.
Amer. Soc. Hort. Sci. Proc. 91: 63 - 68.
COOKE, B.
1745. CONCERNING THE EFFECT WHICH THE FARINA OF THE BLOSSOMS OF DIFFERENT
SORTS OF APPLE-TREES HAD ON THE FRUIT OF A NEIGHBORING TREE. Phil. Trans.
43: 169.
CORNER, J., LAPINS, K. O., and ARRAND, J. C.
1964. ORCHARD AND HONEY BEE MANAGEMENT IN PLANNED TREE-FRUIT POLLINATION.
Min. Agr. Apiary Cir. 14, 18 pp. Victoria, Brit. Columbia.
DOOLITTLE, G. M.
1893. FRUIT-BLOOM FERTILIZATION. Gleanings Bee Cult. 21: 427-428.
FREE, J. B.
1960. THE POLLINATION OF FRUIT TREES. Bee World 41(6): 141-151; (7): 169-186.
____ 1964. COMPARISON OF THE IMPORTANCE OF INSECT AND WIND POLLINATION OF APPLE TREES. Nature 201(4920): 726 - 727.
____ 1966. THE POLLINATING EFFICIENCY OF HONEY BEE VISITS TO APPLE FLOWERS. Jour. Hort. Sci. 41: 91 - 94.
____ and SPENCER-BOOTH, Y.
1963. THE FORAGING AREAS OF HONEY-BEE COLONIES IN FRUIT ORCHARDS. Jour.
Hort. Sci. 38(2): 129 - 137.
GAYLORD, P.
1965. HOW WE GROW SEMI-DWARF APPLES AND THE YIELDS OBTAINED. N.Y. State
Hort. Soc. Proc., 110th Ann. Mtg.: 172-175.
GLUKHOV, M. M.
1955. [HONEY PLANTS.] Izd. 6, Perer. i Dop. Moskva, Gos. Izd-vo Selkhoz
Lit-ry. 512 pp. [In Russian.]
GOFF, E. S.
1899-1901. THE ORIGIN AND EARLY DEVELOPMENT OF THE FLOWERS IN THE CHERRY,
PLUM, APPLE AND PEAR. 1899,16th Ann. Rpt. Wis. Agr. Expt. Sta.: 289 - 303;
1900, 17th Ann. Rpt. Wis. Agr. Expt. Sta.: 266 - 285; 1901, 18th Ann. Rpt.
Wis. Agr. Expt. Sta.: 304-316.
GOFF, E. S.
1901. ORIGIN AND DEVELOPMENT OF THE APPLE BLOSSOM. Amer. Gard. 22: 330,
346-347.
GOODERHAM, C. B.
1950. OVERWINTERED COLONIES VERSUS PACKAGE BEES FOR ORCHARD POLLINATION.
Canada Dept. Agr. Dominion Apiarist Prog. Rpt., 1937-48. (Abs.) Bee World
31: 96.
HARTMAN, F. O., and HOWLETT, F. S.
1954. FRUIT SETTING OF THE DELICIOUS APPLE. Ohio Agr. Expt. Sta. Bul. 745,
64 pp.
HENDERSON, W. W., KTTTERMAN, J. M., and NELSON, G. A.
1969. COMMERCIAL APPLES, UNITED STATES APPLE PRODUCTION BY VARIETIES. Calif.
Crop and Livestock Rptg. Serv., 2 pp. Sacramento.
HOOPER, C. H.
1913. THE POLLINATION AND SETTING OF FRUIT BLOSSOMS AND THEIR INSECT VISITORS.
Roy. Hort. Soc. Jour. 38: 238 - 248.
HORTICULTURAL EDUCATION ASSOCIATION.
1967. THE POLLINATION OF FRUIT CROPS. 68 pp. Hort. Ed. Assoc. Fruit Com.,
Res. Sta., Long Ashton, Bristol, England. Reprinted from Sci. Hort. 14
126-150 (1960); 15: 82-122 (1961).
HOWLETT. F. S.
1926a. SOME FACTORS OF IMPORTANCE IN FRUIT SETTING STUDIES WITH APPLE VARIETIES.
Amer. Soc. Hort. Sci. Proc. 59: 307-315.
____ 1926b. POLLINATION STUDIES IN OHIO. Ohio State Hort. SOc. Proc. 59: 197-200.
HUTCHINSON, A.
1964. ROOTSTOCKS FOR TREE FRUITS. Ontario Dept. Agr. Pub. 334, 18 pp.,
Toronto.
HUTSON, R.
1926. RELATION OF THE HONEYBEE TO FRUIT POLLINATION IN NEW JERSEY. N.J.
Agr. Expt. Sta. Bull 434, 32 pp.
JAYCOX, E. R.
1968. EVALUATING HONEY BEE COLONIES FOR POLLINATION. Fruit Growing 20,
3 pp., rev.
____ 1971. POLLEN INSERTS FOR APPLE POLLINATION. Fruit Growing 22, 3 pp., rev.
KELLY, B. W.
[n.d.] FACTORS RELATED TO THE COST OF PRODUCING APPLES IN PENNSYLVANIA,
1959-1963. Farm Mangt. 18 (Pa. Agr. Ext. Serv.), 20 pp.
KELTY, R. H.
1929. RENTING OR KEEPING BEES FOR USE IN THE ORCHARD. Mich. Agr. Col. Ext.
Bul. 56, 11 pp.
KITAMURA T., and MAETA, Y.
1969. STUDIES ON THE POLLINATION OF APPLE BY OSMIA. III. PRELIMINARY REPORT
ON THE HOMING ABILITY OF OSMIA CORNIFRONS (RADOSZKOWSKI) AND O. PEDICORNIS
COCKERELL. Kontyu 37(1): 83 - 90. AA-80/71.
KURRENOI, N. M.
1969. [THE ROLE OF HONEY BEES IN REGULAR FRUIT BEARING OF THE APPLE TREE.]
In 22d Internatl. Apic. Cong. Proc., Munich, pp. 483-485. [In Russian,
English abstract.]
LATIMER, L. P.
1931. POLLINATION STUDIES WITH THE MCINTOSH APPLE IN NEW HAMPSHIRE. Amer.
SOC. Hort. Sci. Proc. 1930: 386-396.
____ 1933. POLLINATION AND FRUIT SETTING IN THE APPLE. N.H. Agr. Expt. Sta. Bull 274, 38 pp.
LEWIS, C. I., and VINCENT, C. C.
1909. POLLINATION OF THE APPLE. Oreg. Agr. Expt. Sta. BuL 104, 40 pp.
LOKEN, A.
1958. POLLINATION STUDIES IN APPLE ORCHARDS OF WESTERN NORWAY. In 10th
Internatl. Cong. Ent. Proc. 4: 961-965. Aug. 17-25, 1956, Montreal.
LUCE, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223,
22 pp.
LUNDIE, A. E.
1927. THE HONEY-BEE AND THE FRUIT GROWER. HOW THE FLOWERS ARE FERTILIZED.
Farming in So. Africa 1(10): 384 - 387.
MACDANIELS, L. H.
1929. POLLINATION STUDIES IN NEW YORK STATE. Amer. Soc. Hort. Sci. Proc.
1928: 129-137.
____ and HEINICKE, A. J.
1929. POLLINATION AND OTHER FACTORS AFFECTING THE SET OF FRUIT, WITH SPECIAL
REFERENCE TO THE APPLE. N.Y. (Cornell) Agr. Expt. Sta. Bul. 497, 47 pp.
MORRIS, O. M.
1921. STUDIES IN APPLE POLLINATION. Wash. Agr. Expt. Sta. Bul. 163, 32
pp.
MURNEEK, A. E., and SCHOWENGERT, G. C.
1935. A STUDY OF THE RELATION OF SIZE OF APPLES TO NUMBER OF SEEDS AND
WEIGHT OF SPUR LEAVES. Amer. Soc. Hort. Sci. Proc. 33: 4 - 6.
NORTON, R. L.
1971. WHAT YOU MUST KNOW ABOUT HIGH-DENSITY PLANTINGS. Amer. Fruit Grower
91(5): 14-15, 24; (6): 20-23; (7): 10-11.
OVERHOLSER, E. L.
1927. APPLE POLLINATION STUDIES IN CALIFORNIA. Calif. Agr. Expt. Sta. Bul.
426, 17 pp.
PALMER-JONES, T., and CLINCH, P. G.
1968. HONEY BEES ESSENTIAL FOR POLLINATION OF APPLE TREES. New Zeal. Jour.
Agr. 11(5): 32 - 33.
PETKOV, V. G., and PANOV, V.
1967. STUDY ON THE EFFICIENCY OF APPLE POLLINATION BY BEES. In 21st InternatL
Apic. Cong. Proc., College Park, Md., pp. 432- 436.
PHILLIPS, E. F.
1930. HONEY BEES FOR THE ORCHARD. N.Y. (Cornell) Agr. Ext. Serv. Bul. 190,
24 pp.
_____ 1933. INSECTS COLLECTED ON APPLE BLOSSOMS IN WESTERN NEW YORK. Jour. Agr. Res. 46: 851 -862.
PHILP, G. L., and VANSELL, G. H.
1932. POLLINATION OF DECIDUOUS FRUITS BY BEES. Calif. Agr. Ext. Serv. Cir.
62, 27 pp.
PRESTON A. P.
l949. AN OBSERVATION ON APPLE BL0SSOM MORPH0L0GY IN RELATION TO VISITS
FROM HONEYBEES (APIS MELLIFERA). East Malling Res. Sta. Ann. Rpt. (1948),
pp.64-67. (Abs.) Bee World 31: 24,1950.
ROBERTS, R. H.
1945. BEE P0LLINATION OF DELICIOUS. Amer. Fruit Grower 65(4): 16.
ROM, R. C.
1970. VARIETY AND CULTURAL CONSIDERATIONS NECESSARY TO ASSURE ADEQUATE
P0LLINATION IN APPLE ORCHARDS. In The Indispensable Pollinators, Ark. Agr.
Ext. Serv. Misc. Pub. 127, pp.219 - 225.
SHOEMAKER, J. S., and TESKEY, B. J. E.
1959. TREE FRUIT PRODUCTION. 456 pp. John Wiley & Sons, Inc., New York.
SNYDER, D. P.
1968. AN ECONOMIC STUDY OF APPLE PRODUCTION ON SIZE CONTR0LLED TREES. N.Y.
(Cornell) Agr. Expt. Sta., Dept. Agr. Econ., Agr. Econ. Res. 233,20 pp.
SYNDER. J. C.
1946. P0LLINATION OF TREE FRUITS AND NUTS. Wash. Agr. Ext. Serv. Bull 342,20
pp.
TYDEMAN, H. M.
1943. THE INFLUENCE OF DIFFERENT P0LLENS ON THE GROWTH AND DEVEL0PMENT
OF THE FRUIT IN APPLES AND PEARS. East Malling Res. Sta. Ann. Rpt., pp.
31 - 34.
TYDEMAN, H. M.
1965. DESCRIPTION OF THE MALLING APPLE ROOTSTOCKS. East Malling Res. Sta.
Ann. Rpt., pp. 64 - 66.
WAITE M. B.
1895. THE P0LLINATION OF PEAR FL0WERS. U.S. Dept. Agr., Div. Veg. Path.
Bul. 5,86 pp.
____ 1899. P0LLINATION OF POMACEOUS FRUIT U.S. Dept. Agr. Yearbook 1898: 167 - 180.
WAY, R. D.
1971. APPLE CULTIVARS. Search - Agr. Pomol. I (1): 1-84.
WEST, G. H.
1912. THE P0LLINATION OF APPLES AND PEARS. Kans. State Hort. Soc. Trans.
32: 38 - 50.
WICKS W. H.
1918. THE EFFECT OF CROSS-P0LLINATION ON SIZE, C0L0R, SHAPE, AND QUALITY
OF THE APPLE. Ark. Agr. Expt. Sta. Bul. 143,32 pp.
WOODROW, A. W.
1933. THE COMPARATIVE VALUE OF DIFFERENT C0L0NIES OF BEES FOR FRUIT P0LLINATION.
N.Y. (Cornell) Agr. Expt. Sta. Mem. 147,29 pp.
____ 1934. THE EFFECT OF C0L0NY SIZE ON THE FLIGHT RATES OF HONEYBEES DURING THE PERIOD OF FRUIT BL00M. Jour. Econ. Ent. 27: 624-629.
APRICOT
Prunus armenica L., family Rosaceae
Apricots are produced primarily in California. In 1969, 223,000 tons were produced as compared with 3,050 tons in Washington and 4,500 tons in Utah. The estimated value of the total 1969 apricot crop was $33.5 million.
Plant:
In appearance, the apricot tree, fruit, and flower seem to be somewhat intermediate between the plum and the peach. The tree may be larger than a plum tree but spreads like the peach. The flowers are usually white like plum flowers, but they are not borne in clusters. The pit is smooth, somewhat like that of the plum but broader, flatter, and more winged, and intermediate in size between that of the peach and plum (fig. 41). The fruit is peach shaped (Cullinan 1937).
Inflorescence:
The white flower is borne either singly or doubly at a node on very short stems. There are about 30 stamens with one pistil, again like both the plum and the peach (fig. 42). The flowers are attractive to bees for both pollen and nectar. The cultivars of apricots were discussed by Coe (1934) and Hesse (1952).
[gfx] FIGURE 42.- Longitudinal section of 'Royal' apricot flower, x 6.
Pollination Requirements:
The literature on pollination of apricots is meager an not in complete
agreement. Cook and Green (1894 reported that the best set of fruit was
obtained from bagged flowers, with the next best from flowers in bags with
honey bees, and the lowest set in the open. They did not comment on the
activity of the bees either in the bags or on the open flowers. Cullinan
(1937) stated that the apricot is self-fruitful. He did not indicate whether
he meant the flowers would pollinate themselves or that they would set
only if pollinated with their own pollen. Jusubov (1957) reported that
some cultivars were self-fertile and some were completely self-sterile.
Kostina
(1966) also found variation in degrees of fertility between cultivars.
When Schultz (1948) bagged flowers on different cultivars, he reported
good sets on 'Blenheim', 'Royal', 'Tilton', and 'Wenatchee Moorpark'. Schultz
(1948) and Griggs (1970*) identified two self- incompatible cvs., 'Perfection'
and 'Riland'. Slate (1970) stated that some cultivars are self-unfruitful.
Luce and Morris (1928) stated that visits to blossoms by insects "seem
to increase the set of fruit even in larger blocks of a single variety."
Corner et al. (1964) reported that half of the Canadian cultivars were
self-sterile. Hootman (1935) stated ". . . even self-fertile varieties
produce better crops when interplanting is practiced."
The rather meager data indicate that some apricot cultivars must be cross-pollinated and other cultivars are benefited by cross-pollination.
[gfx] FIGURE 41. - Harvesting apricots from fruit-laden tree.
Pollinators:
There seems to be little question as to which pollinating agents are effective on apricots. Jorgensen and Drage (1953) stated that wind is not an effective pollinating agent. Instead, they said that the sticky pollen needs the help of insects to carry it from the stamens to the stigma. Murneek (1937) also concluded that, whether a cultivar is self-sterile or self-fertile, insects are equally necessary for proper pollination and setting of fruit.
The chief pollinators are bees. Stark (1944) stated: "Other insects may be responsible for the pollination of an occasional flower but would not begin to do the job for a commercial crop of fruit."
These observations and statements show that insect pollination is required on self-sterile cultivars and is at least beneficial to the self- fertile cultivars. Honey bees are the primary pollinating agents.
Pollination Recommendations and Practices:
The available literature indicates that the apricot, like the peach and nectarine, depends upon pollinating insects to set a commercial crop on all cultivars. A heavy population of bees may be unnecessary, but they should be distributed throughout the orchard. Thus, since the bees are required but not in large numbers, the recommendation by Corner et al. (1964) of a colony of honey bees per acre would seem adequate, providing the colonies were distributed in small groups in the orchard.
LITERATURE CITED:
COE, E. M.
1934. APRICOT VARIETES. Utah Agr. Expt. Sta. Bul. 251,59 pp.
COOK, A. J., and GREEN, E. C.
1894. SYMPOSIUM ON BEES AND FRUIT-FERTILIZATION, AGAIN. Gleanings Bee Cult.
22: 448-451.
CORNER, J., LAPINS K O.. and ARRAND. J. C.
1964. ORCHARD AND HONEY BEE MANAGEMENT IN PLANNED TREE-FRUIT POLLINATION.
Min. Agr., Victoria, British Columbia, Apiary Cir. 14,18 pp.
CULLINAN, E. P.
1937. IMPROVEMENT OF STONE FRUITS. U.S. Dept. Agr. Yearbook 1937: 665-748.
HESSE, C. O.
1952. APRICOT CULTURE IN CALIFORNIA Calif. Agr. Expt. Sta. Cir. 412,58
pp.
HOOTMAN, H. D.
1935. IMPORTANCE OF POLLINATION AND THE HONEY-BEE IN FRUIT YIELDS. Midwest
Fruitman 8(9): 3-4,9-10.
JORGENSEN, C., and DRAGE, C. M.
1953. POLLINATION OF COLORADO FRUIT. Colo. Agr. Expt. Sta. and Ext. Serv.
Bul. 427-A, 13pp.
JUSUBOV, A. M.
1957. [POLLINATORS FOR NEW APRICOT VARIETIES IN THE CENTRAL BELT.] Sad
i Ogorod 2: 47-48. [In Russian.] Plant Breeding Abs. 27(4): 4367, p.721,
1957.
KOSTINA, K. F.
1966. [THE DEGREE OF SELF-FERTILIZATION IN APRICOT VARIETIES AND HYBRIDS
OF DIFFERENT ECOLOGICAL-GEOGRAPHICAL GROUPS.] Sel'skokhoz. Biol. 1(3):
352-355. [In Russian, English summary.]
LUCK, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223,22
pp.
MURNEEK, A. E.
1937. POLLINATION AND FRUIT SETTING. Midwest Fruitman 10(5): 8-9.
SCHULTZ, J. H.
1948. SELF-INCOMPATIBILITY IN APRICOTS. Amer. Soc. Hort. Sci. Proc. 51:
171-174.
SLATE, G. L.
1970. APRICOTS, NECTARINES AND ALMONDS. Horticulture 48(5): 42,47-48.
STARK, A. L.
1944. FRUIT POLLINATION - A PROBLEM IN UTAH. Farm and Home Sci. 5(4): 5-6.
AVOCADO
Persea americana Mill., family Lauraceae
The avocado is grown primarily in California, to a lesser extent in Florida, and on only a few acres in Hawaii, Puerto Rico, and southern Texas. Crop production in 1970 amounted to 83,400 tons valued at $30 million. California produced 64,600 tons and Florida produced 18,800 tons.
On mature trees, about 2 tons of fruit per acre are harvested, although productive orchards will yield 3 to 6 tons. Year-to-year production varies, depending upon many factors, but a year of high production is frequently followed by a year of low production. Weather has a strong impact upon production. Prolonged cool weather, subfreezing weather, low humidity, strong winds at flowering time, or tornadoes can all result in low set of fruit and low production. The most critical effect of temperature occurs during flowering.
Plant:
The avocado is a tropical evergreen, upright shrub or tree that grows to 60 feet high, but usually between 15 and 30 feet in height (fig. 46). Its dark green leaves are 4 to 10 inches long and 2 to 3 inches wide. The plant may exhibit two or more growth flushes during the year in contrast to the single growth period of most deciduous plants. It may flower in summer or in winter, and may have a flowering period lasting 6 months. It is less tolerant of cold than lemons or navel oranges and prefers high humidity and calm weather. The fruit, which can remain on the tree for several months after maturity, is a nutritious, fresh food rich in oil and high in calories and vitamin E. A few seedling dooryard trees are estimated to be 100 years old, but commercial trees last about 35 years (Goodall et al. 1970).
Hundreds of cultivars have been tried in the United States, but about two dozen are of commercial importance (Rowland 1970).
The cv. 'Fuerte' has for years provided the bulk of the avocado crop (Bergh et al. 1966, Rock and Platt 1968, Rowland 1970). Its fruit weighs 8 to 16 ounces and contains 18 to 28 percent oil. It is cold resistant and ripens over a long period - December to May. By comparison, the Florida cv., 'Pollock', weighs 30 to 50 ounces and contains only 3 to 5 percent oil. The 'Haas' cv. is second in importance to 'Fuerte.' Its fruit weighs only 6 to 12 ounces. Other important California cvs. include the 'Bacon', 'Zutano', 'Rincon', 'Nabal', 'McArthur', 'Anaheim', 'Carlsbad', 'Dickinson', and 'Puebla'. In Florida, the most important cultivars include 'Booth 8', 'Lula', 'Booth 7', 'Waldin', 'Pollock', end 'Hickson' (Rowland 1970).
Avocados can be grown from seed, but the plants are usually propagated by grafting. They are set in the grove 20 to 40 feet apart depending upon whether the type of growth is spreading or upright. Sometimes they are set at 15 to 20 feet with the alternate plants removed after a few years. Older orchards with spreading trees may have as few as 40 trees per acre. Orchards with upright trees may have 150 trees per acre. About 90 trees per acre is average (Lee and Burns 1967). Fruit bearing begins at 3 to 6 years of age and may continue for 50 or more years.
The honey bee is attracted to the plant for both the nectar and the pollen, although citrus, mustard, and many other plants that flower at the same time as avocado are much more attractive to bees than are avocado flowers. Pellett (1926, 1947*) reported that bees collect only a small amount of avocado honey. Vansell (1931) stated that avocados are visited moderately by bees for nectar and pollen. In general beekeepers consider the plant as a source of buildup for their bees rather than as a source of surplus honey.
[gfx] FIGURE 46. - Avocado orchard in bloom.
FIGURE 47. - Closeup of avocado tree in full bloom.
Inflorescence:
A full-grown avocado tree may bear a million flowers in a season, the flowers occurring in panicles of severe dozen to several hundred on the ends of the numerous branches (Robinson and Savage 1926) (fig. 47).
The relatively inconspicuous blossom is about one half inch in both width and depth. Three sepals and three similar-appearing green petals make up the perianth. The single pistil has a simple, bulbous, smooth ovary and a somewhat elongated style terminated by a slightly enlarged stigma. There are nine stamens inserted in two whorls. The inner whorl consists of three stamens, with three prominent, orange, nectar-producing staminodes (sterile or abortive stamens) alternating between them. Opposite each stamen and staminode of the inner whorl is one of the six stamens of the outer whorl. There is an orange nectary, slightly smaller than the staminode, on each side of each outer stamen.
The flower opens twice, on subsequent days or in two stages (fig. 48). In stage 1, the first day, the petals separate and bend outward. The stigma is whitish, fresh, and receptive to pollination (Hodgson 1930), but the stamens, bent out at right angles to the pistil, release no pollen. Some nectar appears on the staminodes. After a few hours, the flower closes.
In stage 2, the second day, the flower opens again. This time, nectar on the six true nectaries is secreted more profusely than occurred on the staminodes. The pistil is shriveled and dark and no longer receptive. The stamens are longer and larger, the inner three overtopping the stigma but facing away from it, and the outer stamens at about a 45 deg angle from the style and facing it, and both sets releasing sticky clumps of pollen. Each stamen has four pollen sacs, the valves of which hinge at the top.
When the flower closes the second day, it never reopens. It is therefore, structurally bisexual but functionally unisexual. This dichogamous condition was first noticed by Nirody (1922) and enlarged upon by Stout and Savage (1925) and Peterson (1955a, b, 1956).
The unusual part about the avocado flower is that in some cultivars stage 1 occurs in the morning of the first day and stage 2 in the afternoon of the second day. These cultivars are referred to as type A. In other cultivars, referred to as type B, stage 1 occurs in the afternoon, and stage 2 occurs the following morning. If cultivars of both types are interplanted within the same orchard, pollen should always be available when the stigmas are receptive (Stout 1932, Robinson 1930, 1933, Ward 1933, Bergh and Gustafson 1958, Bergh and Garber 1964). At least one cv., 'Collinson', produces no pollen; therefore, it is incapable of setting fruit unless pollen is transferred to it from other cultivars that release pollen when its stigmas are receptive (Anonymous 1930).
If the temperature is too low, some flowers, for example, those on the 'Fuerte' cv., may fail to open in the female stage, making fruit set impossible. On the other hand, hot weather and low humidity are not conducive to fruit set. Also, too much disturbance of the flowers by wind can cause shedding. A mild climate with calm humid days is best for the flower.
Bergh (1968) showed that trees set more fruit when there are flowers of different avocado cultivars nearby. This may not be true for all cultivars or all years, but such effects have been thoroughly demonstrated. For example, he showed that the 'Fuerte' and the 'MacArthur', which are considered to be self-fertile, increased production as much as 50 percent when exposed to pollen of other interplanted cultivars.
Avocado flowering may extend from one to several months depending upon conditions affecting fruit setting. A sufficient supply of pollinating agents will tend to shorten the period of flowering. The number of flowers that may set fruit has been variously estimated by different people. Purseglove (1968*) stated that only one in 5,000 flowers produces a fruit. Gustafson and Bergh (1966) considered that a set of less than 1 percent of the flowers is usually sufficient for a good fruit crop. Chandler (1958*) stated that flower clusters containing 1,000 or more flowers may be found on a branch less than a foot long in space enough for no more than two fruit. He stated that less than one flower in 500 on a 'Fuerte' tree set fruit. If a tree produces a million flowers and there are 90 trees per acre, 90 million flowers should be produced. If one flower in 5,000 produces a fruit that weighs 12 ounces, the grower should harvest 18,000 fruits, or over 6 tons per acre. That this is seldom done is a good indication that only a small fraction of 1 percent of the flowers produce fruit.
FIGURE 48. - Longitudinal section of 'fuerte' avocado flower, x 18. A, Stage 1: stigma receptive, but stamens bent outward and anthers not dehisced; B, stage 2, the second day, with stigma no longer receptive, but stamens upright and anthers dehisced.
Pollination Requirements:
Peterson (1955b) showed that the pistillate stage, or stage 1, of the 'Rincon' cv. was open for 3 hours 40 minutes, the maximum time in which pollination of this cultivar could take place. He showed that the flower was incapable of selfing because first flowering began at 7:25 a.m. and ended by 11 a.m.; whereas the second stage of the 2-day-old flower did not begin until 11 a.m., by which time the current-day stigma had withered and was no longer receptive. In the 'Zutano' cv., stage 1 extended from 2:50 p.m. to 6:20 p.m., and stage 2 (the next morning) from 8:40 a.m. until after 11 a.m. Therefore, when the flowers of type A, for example, 'Rincon' cv., are receptive to pollination, the pollen is being shed by flowers of type B, for example,'Zutano' cv.. and when flowers of the 'Rincon' are shedding pollen, flowers of the 'Zutano' are receptive to pollination. This condition is considered by horticulturists to be highly fluid and influenced by the cultivars involved and various environmental conditions.
Peterson (1955a) showed that at least the 'Zutano' and the 'Haas' cvs. were capable of setting fruit when isolated from other cultivars if honey bees were present in abundance. He caged four individual trees, two of each cultivar with one tree of each group in a cage with honey bees during the flowering period. When flowering was over, the bees and cages were removed and the fruit counted. The results concerning the treatment and fruit produced were as follows:
Cultivar Bees in cage No bees in cage 'Zutano'..............................................4 120 ÔHaasÕ..................................................5 284
Whether the pollen was carried over on the bees from the normal time of anther opening until the time of stigma receptivity, whether the opening phases overlapped, or whether the bees forced open the anthers when the stigma was still receptive was not determined, but in any event the effect of the bees was striking.
The evidence is clear that avocados must be insect-pollinated, and that production is best when varieties are interplanted. Bees usually transfer avocado pollen no greater distance than two avocado rows (Bergh 1961). The varieties should intermesh in their blooming dates so that pollen is available on one cultivar when the stigmas on another are receptive, and vectors should be available to move the pollen to the receptive stigmas. Maximum set can only be achieved through adequate provision for cross-pollination - the interplanting of appropriate flowering types and the availability of adequate pollinating agents (Bergh 1969).
Pollinators:
Various pollinating agents visit the avocado flowers for nectar and pollen. These include the honey bee, various species of wild bees, wasps, flies, and hummingbirds (Chapman 1964*).
The consensus of various research workers who have studied the flowering and fruiting of the avocado is that only honey bees are sufficiently abundant on the blossoms at all times to set satisfactory crops of fruit (Clark 1923,1924; Clark and Clark 1926; Boyden 1930; Traub et al. 1941; Lemmerts 1942; Lesley and Bringhurst 1951; Winslow and Enderud 1955; Lecomte 1961; Popenoe 1963).
Many observers have noted that a bee tends to visit a single tree and thus fails to afford the cross-pollination desired. This can occur when the trees are separated by some distance, for example, when they are small or spaced too far apart (Bergh 1966). It also occurs when there is an insufficiency of bees in relation to the number of blooms available.
When the flowers per bee ratio is low, the bees are required to visit many flowers to obtain a load of food and their efficiency as cross-pollinating agents is increased. Ruehle (1958) stated that good crops are set consistently in groves a considerable distance from any bee hives hut that the presence of trees would increase production. Wolfe et al. (1942, 1946) stated that it is quite possible that a hive of bees per acre with sets of five in the middle of each 5-acre tract would materially increase production. Popenoe (1963) stated that honey bees are probably necessary for good pollination unless there is an abundance of wild bees in the area.
In an excellent survey of the reasons for low yield of avocados in California, Bergh (1967) unequivocally stated: "Practically every avocado fruit set means that a honey bee transferred pollen to that flower from some other flower. Gravity or wind may act, but they are so rare they can be ignored by the practical avocado grower." Further on, he stated, "At the present time the California avocado industry is dependent upon the honey bee. The greater the bee population, the more likely the bees are to travel from flower to flower and so make the best of such inter-flower overlap in male and female stages as may be present. This is probably the chief source of avocado set in California."
Pollination Recommendations and Practices:
Peterson (1955a) stated that there was no evidence that addition of bees to the "natural population of wild bees and other large insects" would increase fruit set. He gave no indication as to the population of wild bees honey bees, or other large insects present on the trees. Wolfenbarger (1954) showed that honey bees were more abundant within 375 feet of a 64-colony apiary than at more remote distances, and more avocados were harvested per tree within 250 feet of the apiary than at a distance of 1,000 feet. Wolfe et al. (1946) and Ruehle (1958) recommended that one colony of bees per acre be used with five colonies set in the middle of each 5-acre tract. Stout (1923) recommended providing "bees in abundance" and control of other plants in the area that might attract the bees. LeComte (1961) suggested one colony per acre. Stout (1933) went even further by stating that one hive per acre for other fruit is satisfactory, but the flowering habits of the avocado make it desirable to employ more than one hive per acre to supply the honey bees in abundance.
Bergh (1967) stated that the average California avocado grower would have better crops if he would use more honey bees. He recommended that growers use two to three strong colonies per acre, the colonies placed in groups no more than one-quarter mile apart with 0.1 mile being preferable.
Bergh (1967) made the following recommendations: (1) Place hives or have them placed by the beekeeper after the avocados begin blooming so the bees will "get the avocado habit" right away; (2) place hives in the grove if possible, at least avoid locations where the bees must fly past citrus or other attractive pasturage; (3) control other blooms, such as mustard; (4) avoid use of insecticides during the blooming season, (5) and for cross-pollination, interplant types A and B to increase production 50 to 150 percent.
Thus, after careful study of the research by these scientists, one must conclude that for commercial production of avocados bees are essential, that honey bees are the primary pollinators, and that two to three colonies per acre should be used, the colonies placed within or alongside the groves, and that steps should be taken to insure protection of the bees and discouragement of associated plants attractive to them.
The majority of avocado growers only passively encourage the keeping of bees in the area of their groves. Few if any actively contract for the bees or pay any type of pollination fee to insure the presence of adequate numbers. Many of them know that beekeepers usually move the colonies to the avocado growing areas to obtain nectar and pollen for buildup of the colonies. The bee population the beekeeper desires on the flowers for colony buildup, however, is far short of the population needed for maximum avocado pollination. Colonies vary enormously in strength and pollination effectiveness. Also, unless contracted for, the colonies may be transported to avocados when forest, range, or desert conditions are unfavorable for beekeeping, but may be placed elsewhere at avocado flowering time if the other flora is more favorable. For dependable pollination and maximum avocado fruit set, the grower should see that his trees are amply supplied with strong colonies of honey bees.
LITERATURE CITED:
ANONYMOUS.
1930. NEW AVOCADO HAS NO POLLEN. Off Rec. 9(43): 3
BERGH, B. O.
1961. BREEDING AVOCADOS AT C.R.C. Calif. Avocado Soc. Yearbook 45: 67-74.
______ 1966. AVOCADO TREE ARRANGEMENT AND THINNING IN RELATION TO CROSS-P0LLINATION. Calif. Avocado Soc. Yearbook 50: 52-61.
______ 1967. REASONS FOR LOW YIELDS OF AVOCADOS. Calif. Avocado Soc. Yearbook 51: 161-172.
______ 1968. CROSSP0LLINATION INCREASES AVOCADO SET. Calif. Citrog. 52(3): 97-100.
______ 1969. AVOCADO In Ferwerda, F. P., and Wit, F., eds. Outlines of Perennial Crop Breeding in the Tropics, pp. 23-51. H. Veenman and Zonen, N. V. Wageningen, The Netherlands.
______and GARBER, M. J. 1964. 1964 AVOCADO YIELDS INCREASED BY INTER- PLANTING DIFFERENT VARIETIES. Calif. Avocado Soc. Yearbook 48: 78-85. ______ and GUSTAFSON, C. D. 1958. FUERTE FRUIT SET AS INFLUENCED BY CROSS-POLLINATION. Calif. Avocado Soc. Yearbook 42: 64-66.
______GARBER, M. J., and GUSTAFSON C. D. 1966. THE EFFECT OF ADJACENT TREES OF OTHER AVOCADO VARIETIES ON FUERTE FRUIT-SET. Amer. Soc. Hort. Sci. Proc. 89: 167-174.
BOYDEN, A. L., CO.
1930. THE IMPORTANCE OF THE HONEYBEE TO AVOCADO CULTURE. A. L. Boyden Co.,
Alhambra, Calif. Leaflet, 4 pp.
CLARK, O. I.
1923. AVOCADO POLLINATION AND BEES. Calif. Avocado Assoc. Ann. Rpt. 1922-1923:
57-62. 98
CLARK, O. I.
1924. AVOCADO POLLINATION TESTS. Calif. Avocado Assoc. Ann. Rpt. 1923-1924:
16-22.
______and CLARK, A. B.
1926. RESULTS OF POLLINATION AND OTHER EXPERIMENTS ON AVOCADOS AT THE ORCHARDS
OF THE POINT LOMA HOMESTEAD. Calif. Avocado Assoc. Ann. Rpt. 1925-1926:
85-94.
GOODALL, G. E.
1970. CAN YOU AFFORD TO GROW AVOCADOS? Calif. Avocado Soc. Yearbook 54:
43-45.
______LITTLE, T. M., ROCK, R. C., and others.
1970. USEFUL LIFE OF AVOCADO TREES IN COMMERCIAL ORCHARDS IN CALIF. Calif.
Avocado Soc. Yearbook 54: 33-36.
GUSTAFSON, C. D., and BERGH, B. O.
1966. HISTORY AND REVIEW OF STUDIES ON CROSS-POLLINATION OF AVOCADOS. Calif.
Avocado Soc. Yearbook 50: 39-49.
HODGSON, R. W.
1930. CROSS-POLLINATION. Calif. Avocado Assoc. Yearbook 1930: 30-31.
LECOMTE, J.
1961. [OBSERVATIONS ON POLLINATION OF THE AVOCADO IN THE FRENCH ANTILLES.]
Fruits 16(8): 411-414. [In French]
LEE, B. W., and BURNS, R. M.
1967. AVOCADOS IN VENTURA COUNTY. Calif. Citrog. 52(12): 520-522.
LEMMERTS, W. E.
1942. PROGRESS REPORT ON AVOCADO BREEDING. Calif. Avocado Soc. Yearbook
1942: 36-41.
LESLEY, J. W., and BRINGHURST, R. S.
1951. ENVIRONMENTAL CONDITIONS AFFECTING POLLINATION OF AVOCADOS. Calif.
Avocado Soc. Yearbook 1951: 169-173.
NIRODY, B. S.
1922. INVESTIGATIONS IN AVOCADO BREEDING. Calif. Avocado Assoc. Ann. Rpt.
1921-1922: 65-68.
PELLETT, F. C.
1926. THE AVOCADO FOR BEES. Amer. Bee Jour. 66: 11.
PETERSON, P. A.
1955a. AVOCADO FLOWER POLLINATION AND FRUIT SET. Calif. Avocado Soc. Yearbook
39: 163-169.
______ 1955b. DUAL CYCLE OF AVOCADO FLOWERS: STUDY OF THE CONTINUOUS DUAL OPENING CYCLE OF THE AVOCADO FLOWER SHOWS NEED OF LARGE FLYING INSECTS FOR POLLINATION. Calif. Agr. 9(10): 6-7, 13.
______ 1956. FLOWERING TYPES IN THE AVOCADO WITH RELATION TO FRUIT PRODUCTION. Calif. Avocado Soc. Yearbook 40: 174-179.
POPENOE, J.
1963. THE RUEHLE AVOCADO. Fla. Agr. Expt. Sta. Cir. S-144, 4 pp.
ROBINSON, T. R.
1930. SETTING OF FRUIT POLLINATION; SOME ABERRANT FORMS OF FLOWER MECHANISM
IN THE AVOCADO. Calif. Avocado Assoc. Yearbook 1930: 107-111.
______ 1933. POLLINATION AND OTHER FACTORS INFLUENCING THE PRODUCTION OF AVOCADOS. Fla. State Hort. Soc. Proc. 46: 109-114.
ROBINSON T. R., and SAVAGE, E. M.
1926. POLLINATION OF THE AVOCADO. U.S. Dept. Agr. Cir. 387, 16 pp.
ROCK, R. C., and PLATT, R. G.
1968. ECONOMIC ASPECTS OF MARKETING CALIFORNIA AVOCADOS. Calif. Agr. Ext.
Serv. AXT 279, 22 pp.
ROWLAND, W. A.
1970. AVOCADOS. Fruit and Veg. Facts and Pointers, 12 pp.
RUEHLE, G. D.
1958. THE FLORIDA AVOCADO INDUSTRY. Fla. Agr. Expt. Sta. Bul. 602, 100
pp.
STOUT, A. B.
1923. A STUDY IN CROSS-POLLINATION OF AVOCADOS IN SOUTHERN CALIF. Calif.
Avocado Assoc. Ann. Rpt. 1922-23: 29-45.
______ 1932. SEX IN AVOCADOS AND POLLINATION. Calif. Avocado Assoc. Yearbook 1932: 172-173.
______ 1933. THE POLLINATION OF AVOCADOS. Fla. Agr. Expt. Sta. Bul. 257, 44 pp.
______and SAVAGE, E. M.
1925. THE FLOWER BEHAVIOR OF AVOCADOS WITH SPECIAL REFERENCE TO INTERPLANTING.
Fla. State Hort. Soc. Proc. 38: 80-91.
TRAUB, H. P., POMEROY, C. S., ROBINSON, T. R., and ALDRICH, W. W.
1941. AVOCADO PRODUCTION IN THE UNITED STATES. U.S. Dept. Agr. Cir. 620,
28 pp.
VANSELL, C. H.
1931. NECTAR AND POLLEN PLANTS OF CALIFORNIA. Calif. Agr. Expt. Sta. Bul.
517, 60 pp.
WARD W. F.
1933. PRACTICAL HINTS TO COMMERCIAL AVOCADO GROWERS. Fla. State Hort. Soc.
Proc. 46: 139-142.
WINSLOW, M. M., and ENDERUD J.
1955. FLOWERING BEHAVIOR AND YIELDS OF SOME AVOCADO VARIETIES AT RIVERSIDE.
Calif. Avocado Soc. Yearbook 39: 133-135.
WOLFE, H. S., TOY, L. R., and STAHL, A. L.
1942. AVOCADO PRODUCTION IN FLORIDA. Fla. Agr. Ext. Serv. Bul. 112, 111
pp.
______TOY L. R., and STAHL, A. L
1946. AVOCADO PRODUCTION IN FLORIDA. Fla. Agr. Ext. Serv. Bul. 129, 107
pp.
WOLFENBARGER, D. O.
1954. BIOLOGY AND CONTROL OF INSECTS AFFECTING SUB-TROPICAL FRUITS. Fla.
Agr. Expt. Sta. Ann. Rpt., p. 290.
CACAO
Theobroma cacao L., family Sterculiaceae
Cocoa is the processed product derived from the beans of the cacao plant.
World production of cocoa exceeds a million tons, with Ghana producing 429,000 tons; Nigeria, 201,000 tons; Ivory Coast, 105,000 tons; Cameroon, 73,000 tons; Brazil, 94,000 tons; and Equador, 35,000 tons, with other countries of North and South America, Africa, Asia, and Oceania producing the balance. Of this amount, the United States consumes 25 percent; Germany, 13 percent; United Kingdom, 10 percent; and the Netherlands, 9 percent ( Purseglove 1968*). Europe, as a whole, takes over 50 percent and the American countries, about 40 percent of the entire crop.
Plant:
The evergreen cacao tree grows 15 to 25 feet primarily between latitudes 10 deg N to 10 deg S, usually below 1,000 feet in altitude, and in areas with a monthly average rainfall of about 4 inches. Various cultivars, propagated by seed, are grown. The oblong or oval fruit (fig. 58), commonly called a pod, is 4 to 12 inches long, and green when immature, but may be yellow, red, purple, or green when ripe. It contains afrom 20 to 60 reddish-brown beans 3/4 to 1/2 by 1/2 to 1 inch in size, usually arranged in five rows (fig. 59). Pods are produced throughout the year, but the main harvest usually begins at the end of the wet season and may extend for 3 months. From 7 to 14 pods will produce a pound of dry beans. Yeilds range from 200 to 3,000 pounds dry beans per acre, but 600 lb/acre is considdered a good yield (Purseglove 1968).
Inflorescence:
The cacao flowers arise in groups directly from old wood of the main stem or older branches at points which were originally leaf axils (fig. 60). Each flower has five prominent pink sepals, five smaller yellowish petals, each of which forms a pouch, an outer whorl of five staminodes, and an inner whorl of five double stamens, each stamen bearing up to four anthers. The staminodes are about as tall to twice as tall as the upright style and form a "fence" around the style. The stamens are curled so that the anthers develop inside the petal pouches. The ovary consists of five united carpels each having four to 12 locules, and one style that has several linear stigmatic lobes (van Hall 1932). According to Cheeseman (1932) and Urquhart (1961), the flower produces no nectar and has no discernible scent. However, Stejskal (1969) stated that there are two types of microscopic nectaries, ( 1 ) the cylindrical multicellular ones, 60 to 450 microns in size, on the pedicels, sepals, and ovaries, and (2) the conical unicellar ones 20 to 25 microns in size, located on the "guide lines" of the petals and on the staminodia. He showed that they secrete nectar, which has an odor that attracts male mosquitoes and lepidopterous insects.
The flower opens about dawn, and the anthers dehisce just before sunrise. The stigma is usually pollinated 2 to 3 hours later but is receptive from sunrise to sunset of the day of opening (Cheeseman 1932). The stigma is receptive to pollen along its whole length, and not merely at the apex as in most flowers. If the flower is not pollinated, it usually sheds the following day (Sumner 1962). Pollination before noon is best (Chats 1953).
[gfx]
FIGURE 58.- Maturing cacao fruit on the tree.
FIGURE 59.- Ripe cacao fruit opened to show the beans.
FIGURE 60.- Cacao flower cluster growing on the trunk of the tree, showing
the open flower, a flower ready to open, and a small fruit.
Pollination Requirements:
Although the full story of cacao pollination is not yet known, there seems little doubt that the flower is not self-pollinating, as flowers bagged to exclude insects invariably shed (Gnanaratnam 1954). Also, some plants are self-incompatible but set fruit well if pollinated with pollen from compatible trees (Chats 1953, Cope 1958, Knight and Rogers 1955). The method of the transfer of the pollen in nature is the somewhat questionable factor. The sticky pollen is not carried by the wind. Furthermore, it is produced and released in the petal pouches where wind is unlikely to disturb it (Cobley 1966*, Gnanaratnam 1954). Glendenning (1962) noted that pollen found on a stigma was usually from more than one flower, but the amount of foreign pollen depended on proximity to other plants. Little pollen seemed to move more than a couple of trees' distance.
Pollinators:
There is general belief that small insects are the primary pollinating agents of cacao, but no general agreement as to which insects are responsible. Numerous authorities credit midges, especially Forcipomyia quasiingrami Macfie and Lasiohela nana Macfie (Barroga 1964, Chatt 1953, Fontanilla-Barroga 1965, Macfie 1944, Saunders 1959, Toxopeus 1969). Others credit ants (Crematogaster spp.), aphids (Aphis gossypii Glover and Toxoptera spp.), thrips (Frankliniella parvula Hood), and unidentified wild bees (Billes 1941; Cope 1940; Harland 1925a, b; Hernandez 1966; Jones 1912; Muntzing 1947; Posnette 1942a, b, 1944, 1950; Posnette and Entwistle 1957; Urquhart 1961; Voelcker 1940).
Thrips and aphids move about but slightly from tree to tree, yet Glendenning (1958) reported, after a study of albino trees, that a considerable proportion of pollination takes place across two intervening trees, though less than over shorter distances. This would indicate an agent with considerable movement between trees.
The ants Wasmannia suropunctata (Roger) and Solenopsis geminata (F.) and the wild bee Trigona jaty Smith were occasional visitors. Glendenning (1958) concluded that the midges (Forcipomyia spp.) were the main pollinators, accounting for twice the pollination service performed by all of the other species combined. This was verified in various experiments with different numbers of insects per cage over cacao flowers. Hernandez (1965) reported pollination percentages ranging from 1 to 52 percent when he used midges, bees, thrips, and ants. However, Hernandez did not, indicate how pollination was accomplished.
Although midges seem to get the most credit as pollinators of cacao, there is clearly a lack of knowledge as to which insects are responsible in the different areas for the commercial set of fruit of this important crop.
Harland (1925a) found that of 5 percent of the flowers on trees not infested by ants and aphids, only 0.3 percent set fruit; whereas, on trees heavily infested by these insects, 35 percent of the flowers were pollinated and 2 percent set. At the same time, 5 percent of the hand pollinated flowers set fruit.
Little has been said about the adequacy of pollination of the individual flower or the minimum number of seed in relation to fruit set or shedding. However, at least as many pollen grains must fall upon the stigma as there are subsequently developed seeds. Thus, a minimum of 60 pollen grains is necessary to set the highest number of seed.
Many of the flowers are never pollinated (Harland 1925b), at least under Trinidad conditions. Apparently, wherever the crop is grown the lack of adequate pollination is a strongly limiting factor in production of the beans. Sumner (1962) stated that most of the pollination occurs 2 to 3 hours after dawn with a second much smaller peak in the afternoon, but only 2 to 5 percent of the flowers ever get pollinated, and these may not set if pollinated too late or with incompatible pollen. Urquhart (1961) stated that only about 5 percent of the stigmas ever get pollinated; Harland (1925b) found only 9 percent to be pollinated. Because some plants are self-incompatible - some are male sterile or sterile (Gnanaratnam 1954) - many of the flowers would appear to be doomed to shed. Knoke and Saunders (1966) tried a mist blower for mechanical transfer of pollen but achieved uneconomical success.
The use of honey bees under saturated pollination conditions has never been tried, probably because the blossom has no aroma and produces no nectar. Quite conceivably, however, honey bee colonies could be concentrated in numbers sufficient to exhaust the supply of pollen and nectar on competing plants and the bees induced to visit the flowers of this important crop for pollen and increase the percentage of cross- pollination and fruit set. A search for a selection of cacao pollen-loving honey bees might produce an acceptable and controllable pollinating agent. One or more of the various species of pollen-foraging wild bees might be found that could be controlled and used as a profitable pollinating agent of cacao.
Pollination Recommendations and Practices:
There are no recommendations on the use or manipulation of insect pollinators of cacao. According to Faegri and van der Pijl (1966*), the Forcipomyia spp in Africa breed mainly in decaying pods. If the pods are removed by too scrupulous cleaning of the plantations, these midges might also be removed. This would result in deficient pollination of the flowers. Otherwise, the presence or numbers of insect pollinators are left entirely to chance on this billion-dollar crop.
LITERATURE CITED:
BARROGA S. F.
1964. PROGRESS REPORT ON THE STUDY OF INSECTS, PARTICULARLY MIDGES ASSOCIATED
WITH POLLINATION OF THEOBROMA CACAO, APRIL 1963. Philippine Jour. Plant
Indus. 29(3/4): 123 - 133.
BILLES, D. J.
1941. POLLINATION OF THEOBROMA CACAO L. IN TRINIDAD, B.W.L Trop. Agr. [Trinidad]
18: 151-156.
CHATT, E. M.
1953. COCOA. 302 pp. Interscience Publishers Inc., New York.
CHEESEMAN, E. E.
1932. THE ECONOMIC BOTANY OF CACAO. A CRITICAL SURVEY OF THE LITERATURE
TO THE END OF 1930. Trop. Agr. [Trinidad] Sup., v. 9, June, 16 pp.
COPE, F. W.
1940. AGENTS OF POLLINATION IN CACAO. St. Augustine, Trinidad, Imperial
College of Tropical Agr. [Trinidad], Ninth Ann. Rpt. on Cacao Res. 1939:
13-19.
______ 1958. INCOMPATIBILITY IN THEOBROMA CACAO. Nature 181: 279.
FONTANILLA-BARROGA, S.
1965. A PROGRESS REPORT ON THE STUDY OF INSECTS ASSOCIATED WITH POLLINATION
OF THEOBROMA CACAO WITH SPECIAL EMPHASIS ON MIDGES. Philippine Jour. Agr.
27(3/4): 147-159.
GLENDINNING, D. R.
1958. PLANT BREEDING AND SELECTION. Cocoa Res. Inst. Rpt. of West Africa,
1957-58, pp. 50-54.
______ 1962. NATURAL POLLINATION OF COCOA. Nature 193(4822): 1305.
GNANARATNAM, J. K.
1954. POLLINATION MECHANISM OF THE CACAO FLOWER. Trop. Agr. [Ceylon] 110:
98 - 104.
HALL, C. J. J. VAN.
1932. CACAO Ed. 2, 514 pp. Macmillan, London.
HARLAND, S. C.
1925a. STUDIES IN CACAO. THE METHOD OF POLLINATION. Ninth West Indian Agr.
Conf. Proc. Kingston, Jamaica, 1924: 61 - 69.
______ 1925b. STUDIES IN CACAO. PART I. THE METHOD OF POLLINATION. Ann. Appl. Biol. 12: 403-409.
HERNANDEZ, B. J.
1965. INSECT POLLINATION OF CACAO (THEOBROMA CACAO L.) IN COSTA RICA. 173
pp. Ph.D. thesis and Diss. Abs. 28(1): 2B-3B, 1967, AA-257/71, Wis, Univ.,
Madison.
JONES, G. A.
1912. THE STRUCTURE AND POLLINATION OF THE CACAO FLOWER. West Indian Bull
12: 347 - 350.
KNIGHT, R., and ROGERS, H. H.
1955. INCOMPATIBILITY IN THEOBROMA CACAO. Heredity 9: 69 - 77.
KNOKE J. K., and SAUNDERS, J. L.
1966. INDUCED FRUIT SET OF THEOBROMA CACAO BY MISTBLOWER APPLICATIONS OF
INSECTICIDES. Jour. Econ. Ent. 59: 1427-1430.
MACFIE, J. W. S.
1944. CERATOPOGONIDAE COLLECTED IN TRINIDAD FROM CACAO FLOWERS. Bul.:Ent.
Res. [England] 35: 297 - 300.
MUNTZING, A.
1947. SOME OBSERVATIONS ON POLLINATION AND FRUIT-SETTING IN ECUADORIAN
CACAO. Hereditas 33: 397 - 404.
POSNETTE, A. F.
1924a. NATURAL POLLINATION OF COCOA, THEOBROMA LEIOCARPA, ON THE GOLD COAST.
Trop. Agr. [Trinidad] 19: 12-16.
______ 1942b. NATURAL POLLINATION OF COCOA. THEOBROMA LEIOCARPA, BERN., ON THE GOLD COAST II. Trop. Agr. [Trinidad] 19(10): 188-191.
______ 1944. POLLINATION OF CACAO IN TRINIDAD. Trop. Agr. [Trinidad] 21(6): 115-118.
______ 1950. THE POLLINATION OF CACAO IN THE GOLD COAST. Jour. Hort. Sci. 25: 155 - 168.
______and ENTWISTLE, H. M. 1957. THE POLLINATION OF COCOA FLOWERS. Rpt. Cocoa Conf. Grosvenor House, London, Sept. 10-12, pp. 66-69. (Abs.) Plant Breeding 28(4): 4550. Oct. 1958.
SAUNDERS, L. G.
1959. METHODS FOR STUDYING FORCIPOMYIA MIDGES, WITH SPECIAL REFERENCE TO
CACAO-POLLINATING SPECIES (DIPTERA, CERATOPOGONIDAE). Canad. Jour. Zool.
37: 33-51.
STEJSKAL, M.
1969. [NECTAR AND AROMA OF THE CACAO FLOWER.] Oriente Agropecuario 1(2):
75-92. [In Spanish, English summary.]
SUMNER, H. M.
1962. [COCOA] POLLINATION. In Wills, J. B., ed., Agriculture and Land Use
in Ghana, pp. 260 - 261. Oxford University Press, London, Accra, New York.
TOXOPEUS, H.
1969. CACAO. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial
Crop Breeding in the Tropics, pp. 79-109. H. Veenman and Zonen, N. V. Wageningen,
The Netherlands.
URQUHART. D. H.
1961. COCOA. Ed. 2, 293 pp. Longmans, Green & Co., Ltd., London.
VOELCKER, O. J.
1940. THE DEGREE OF CROSS-POLLINATION IN CACAO IN NIGERIA. Trop. Agr. [Trinidad]
17: 184-186.
CASHEW
Anacardium occidentale L., family Anacardiaceae
The cashew is a hardy drought-resistant tropical or subtropical tree. This limits its growth to the area of our continent from Mexico to Peru and Brazil, but includes Hawaii, Puerto Rico, and favored parts of the southern tip of Florida. Worldwide, India is the leading producer; other producing countries include Mozambique and Tanzania (Mutter and Bigger 1961, Purseglove 1968*).
Plant:
The cashew is a somewhat straggly evergreen tree, 12 to 15 m in height, seldom taller, with oblong 6- to 7-inch leathery green leaves and terminal, many flowered panicles. It is cultivated for its delicious 1- inch-long, kidney-shaped nut (fig. 65). The nut is inedible when raw and must be roasted to drive off the highly irritating volatile oil. The nut is produced on the end of a greatly enlarged fleshy pedicel disk and receptacle, called the cashew apple. The cashew apple is about 2 inches wide and 3 to 4 inches long (Kennarc and Winters 1960*), and when ripe it is shiny, red or yellow, soft, and juicy. It is used as a fresh fruit or in juices, jellies, or for making wine (Ochse et al. 1961*) The tree bark provides an indelible ink, and the shell provides an insect-repelling vesicant oil (Purseglove 1968 *).
The fruit ripens in 2 to 3 months and is harvested from the tree or picked up soon after falling. The nut is removed from the apple, dried or roasted in the shell, then hulled and vacuum packed.
Cashew plants are usually grown from seed and thinned to 30 by 30 feet. They begin bearing the second year, are in full production by the 10th year, and continue bearing for another 20 years. The yield varies from 1 to 100 pounds per tree (Purseglove 1968*, Haarer 1954).
[gfx]
FIGURE 65. - Cashew fruit. A, Cashew apple; B, cashew nut.
Inflorescence:
The cashew inflorescence is a sweet-scented lax terminal, many- flowered panicle 4 to 8 inches long. Both male and hermaphrodite flowers occur on the same inflorescence (fig. 66). In Tanganyika, Bigger (1960) found as many as 767 panicles on a single tree, with 63 to 67 hermaphrodite and 250 to 400 male flowers per panicle. In Mangalore, Madhava Rao and Vazir Hassan (1957) counted 329 florets on a panicle, 316 of which were staminate and 13 hermaphrodite. Only about 5 percent of the hermaphrodite flowers produce fruit (Anonymous, 1964). In general, the fewer the hermaphrodite flowers the lower the percent set. Usually from one to less than half a dozen fruits mature per cluster (Ochse et al. 1961 *, Northwood 1966).
The five reflexed petals of the l/3 to l/2-inch flower are pale green with red stripes, later turning to solid red (Morton 1961). In the male flower, about nine stamens are 4 mm long and one stamen, 12 mm, not all of which may be functional. The hermaphrodite flower also has nine short stamens and one about 8 mm long. The one-ovule ovary contains a style that extends above its own anthers to the same height as the long anther of the male flowers. About six flowers open per day on an inflorescence (Northwood 1966).
The flower opens almost any time of the day, but the peak period of opening is 11 am. to 12:30 p.m. The stigma is receptive as soon as the flower opens, but the anthers do not dehisce until 5 hours later, giving opportunity for crossing. The stigma is receptive for only 1 day (Madhava Rao and Vazir Hassan. 1957). The flower produces an abundance of nectar, which is highly attractive to flies, bees, ants, and other insects (Morton 1961, Free 1970*).
[gfx]
FIGURE 66.- Longitudinal section of cashew flower, x 7. A, Hermaphrodite
flower with elongated style and short stamens; B, male flower with abortive
pistil and elongated stamen.
Pollination Requirements:
The hermaphrodite flowers are self-fertile but not self-pollinating as indicated by the fact that bagged flowers set no fruit, but when flowers were hand self-pollinated a set of about five fruits per inflorescence was obtained (Northwood 1966). Madhava Rao and Vazir Hassan (1957) obtained a set of 55.5 percent of self-pollinated flowers. Because only one ovule in one ovary exists per flower, there is no need for a large amount of pollen on the stigma.
Pollinators:
Madhava Rao and Vazir Hassan (1957) indicated that the cashew was wind pollinated, with insects being unimportant, and Bigger (1960) also concluded that the high percentage of male flowers suggested that wind was the pollinating agent. The study by Northwood (1966), however, leaves little doubt that fruit setting is the result of insect activity. He considered that flies and ants were the principal pollinators. Madhava Rao and Vazir Hassan (1957) stated that only black and red ants visited the flowers, but Wulfrath and Speck (no date) stated that the flowers are attractive to bees all day for their rich nectar. Smith (1960) stated that cashew can be added to the Iist of plants benefiting from insect pollination. Personal correspondence from bee specialists in Ghana indicates that when bees are moved to cashews the production is increased.
Pollination Recommendations and Practices:
There are no recommendations on the use of insects in the pollination of cashew. The evidence strongly indicates that concentration of honey bee colonies in cashew plantings during flowering would at least alleviate the problem of poor setting of fruit. Selection for clones with a higher percentage of hermaphrodite flowers would doubtless enhance fruit production.
LITERATURE CITED:
ANONYMOUS.
1964. ADMINISTRATION REPORT OF THE AGRICULTURE DEPARTMENT, GOVERNMENT OF
KERALE, FOR THE YEAR 1962-1963. 325 PP. Plant Breed. Abs. 35: 3772 (1965).
BIGGER, M.
1960. SELENOTHRIPS RUBROCINCTUS GIARD AND THE FLORAL BIOLOGY OF CASHEW
IN TANGANYIKA. East Africa Agr. Jour. 25: 229-234.
HAARER, A. E.
1954. THE CASHEW (ANACARDIUM OCCIDENTALE LTNN.) NUT. World Crops 6: 95-96,
98.
MADHAVA RAO, V. N., and VAZIR HASSAN, M.
1957. PRELIMINARY STUDIES ON THE FLORAL BIOLOGY OF CASHEW (ANACARDIUM OCCIDENTALE
LINN.). Indian Jour. Agr. Sci. 27: 277 - 288.
MORTON, J.
1961. THE CASHEW'S BRIGHTER FUTURE. Econ. Bot. 15: 57 - 78.
MUTTER, N. E. S., and BIGGER, M.
1961. CASHEW. Tanganyika Min. Agr. Bul. 11, 5 pp.
NORTHWOOD, P. J.
1966. SOME OBSERVATIONS ON FLOWERING AND FRUIT-SETTING IN THE CASHEW, ANACARDIUM
OCCIDENTALE L. Trop. Agr. [Trinidad] 43(1): 35-42.
SMITH, F. G.
1960. BEEKEEPING IN THE TROPICS. 265 pp. Longmans, New York.
WULFRATH, A., and SPECK, J. J.
[n.d.] [LA FLORA MELIFERA.] Enciclopedia Apicola, Folleto 28, ed. 2, 96
pp. Ediciones Mexicanas, Mexico, D. F. [In Spanish.]
CHERRY
Prunus spp., family Rosaceae
Cherries grown commercially in the United States include sweet cherries (P. avium L.); tart, sour, or pie cherries (P. cerasus L.); and Dukes (probably P. gondouinii (Poit. & Turp.) Rehder). The mahaleb (P. mahaleb L.) and the mazzard, a wild or seedling form of P. avium, are used as rootstock upon which the fruiting types are grafted. The mahaleb is used much more extensively than the mazzard (Howe 1926, USDA 1967).
In 1970, 121,650 tons of sweet cherries, including Dukes (usually grouped with the sweet cherries), were produced, primarily on the West Coast. Oregon produced 40,000 tons; Washington, 25,800; California, 25,400; and Michigan, 21,000 tons. There were 118,640 tons of tart cherries produced - 79,000 in Michigan and 18,200 tons in New York. Several other States produced smaller amounts of both kinds.
The value of the 1970 sweet cherry crop was $43.2 million, compared to $17.9 million for the tart cherries.
Plant:
The deciduous cherry tree does not thrive where summers are long and hot, yet the blossoms are susceptible to injury by cold spring weather (Cullinan 1937). For these reasons, the growing areas are limited to the more northerly States, except for some areas of high altitude and temperatures moderated by large bodies of water such as the oceans or the Great Lakes.
The trees are planted at various distances apart but most commonly 20 feet for tart cherries and 25 to 32 feet for sweet cherries. They are usually planted at equal distances apart, except when the contour or hedgerow systems are used (Griggs 1970*).
When hedgerow planting is used in California, the trees are placed 6 feet apart in the row and the rows are spaced 4 feet apart. The pollenizer trees are placed at every eleventh location in every other row, offset by five trees, about one pollenizer for each 20 recipient trees (Ryugo and Mikuckis 1969).
Inflorescence:
When in bloom the cherry tree displays white, faintly fragrant flowers in clusters of two to five on short lateral spurs on the many branches (fig. 71). The five petals of the flower are oval, white, and rather widely spread. There is a single upright pistil and about 30 loose stamens (fig. 72). The sweet cherry flower is about an inch across, the tart cherry slightly smaller. The flower remains open 7 to 8 days. When the flower opens the stigma is receptive, but the anthers are closed. Anthers begin opening shortly after flowers open and continue into the second day (Knuth 1908*, p. 703; Srivastava and Singh 1970). Nectar is secreted on the inner surface of the receptacle. Eaton (1959) stated that pollination on the first day after anthesis was much more effective than pollination on the second day, and he stressed the importance of the earliest possible pollination particularly in cultivars such as 'Schmidt'.
Both pollen and nectar are attractive to insects, particularly bees, throughout the day if weather permits. The sweet cherry nectar is much richer in sugar (55 percent sugar) than the tart cherry nectar (28 percent) (Vansell 1942*). Pellett (1947*) stated that in California the cherry is one of the best fruit trees for honey production. Because of the time of year that cherries bloom, colonies are frequently not sufficiently strong to store surplus amounts and cherry honey is practically unknown. There are usually few other floral visitors except honey bees, although Nevkryta (O.M.) (1957) reported that only 60 percent of the insects on flowering sweet cherries were honey bees.
[gfx]
FIGURE 71. - Fruiting branch of cherry, showing spurs and clusters of flowers.
FIGURE 72. - Longitudinal section of a 'Bing' cherry flower, x 7.
Pollination Requirements:
The sweet cherry was shown by Gardner (1913), Anonymous (1926), Overholser and Overley (1931), Crane and Brown (1937), and Way (1968) to be self-sterile or self-unfruitful, and, furthermore, the most important cvs., 'Bing', 'Lambert', and 'Napoleon' ('Royal Ann'), were shown to be interincompatible. This interincompatibility continues to be a problem (Griggs 1970*), although Lapins (1971) reported that the 'Stella' cv. was a self-compatible sweet cherry, derived from a radiation-induced self- fertile selection obtained from England.
The attitude toward the pollination of tart cherries has changed over the years. Crane (1925), Dujardin (1921), Hooper (1924), and Schuster (1925) stated that the tart cherry was self-sterile or nearly so. Einset (1932) said that there was a continuous range from complete self- fruitfulness to complete self-unfruitfulness. Roberts (1922) and Marshall et al. (1929) said the blossoms were self-fertile and that insect pollinators were not needed. Murneek (1930) said they were self-fertile but benefited from insect pollination in unfavorable seasons. However, Hootman (1931, 1933) showed that only 4 percent of screened blooms (of 'Montmorency' cv.) produced fruit as compared to 49 percent that were hand pollinated. Lagasse (1928) and later Vansell and Griggs (1952*) stated that the commercially important tart cherry cultivars are self- fruitful if enough pollinizing insects are available, but better crops can be expected if the orchard contains more than one cultivar. The knowledge is now fairly well accepted that all of the important tart cherry cultivars will set fruit with their own pollen, but only after it is transferred by some outside agency from the anthers to the stigma.
The amount of fruit set expected on cherries has been mentioned by various research workers. All concede that set of every blossom is undesirable. Shoemaker (1928) reported a range of 13 to 60 percent with an average of 35 percent set of sweets, 21 to 42 percent with an average of 33 percent for tart cherries, and 10 to 53 percent with an average of 20 percent set for Dukes. As previously mentioned, Hootman (1931) obtained 49 percent set of hand-pollinated 'Montmorency' tart cherries. Gardner (1913) stated that 50 percent of the sweet cherry flowers should set. Griggs et al. (1952*) reported an overall average for several seasons of good crops at 21 to 32 percent set. Griggs (1970*) stated that self- fruitful cultivars of sweet cherries may be undesirable if they tend to set too heavily. Also, the fruit fails to develop adequate size without expensive thinning practices.
Luce and Morris (1928) stated that if the cherry blossom is not pollinated, the fruit develops to the size of a garden pea, then drops to the ground.
Tukey (1925), Free and Spencer-Booth (1964), and numerous others have reported decreasing production with increased distance from the pollenizer row of sweet cherries.
In summary, all cherries are basically incapable of automatic self- pollination. Tart cherries will set fruit if the pollen is transferred from anthers to stigma of the same flower but will set more fruit if other cultivars are interplanted in the orchard. Compatible cultivars can only be determined by tests (Griggs 1953*). Sweet cherries, with the exception of the 'Stella' cv. (Lapins 1970), will not set fruit with their own pollen, only with pollen of certain other cultivars.
Way and Gilmer (1963) showed that healthy trees are important in the set of cherries. When they used pollen from trees infected with tart cherry yellows disease, fruit set was only 25 to 90 percent of that with pollen from healthy trees. Such pollen would either decrease production or create a demand for more insect pollinators.
Pollinators:
Wind is not a factor in cherry pollination, as has been clearly and repeatedly established over the years (Roberts 1922, Burtner 1923, Murneek 1930, Claypool et al. 1931, and Brown 1968). Most researchers and growers give the primary credit for the pollination of cherries to honey bees. A heavy pollinator population is needed and flowering occurs too early in the year for other insects to be plentiful. Hendrickson (1922) stated that as early as 1894 a government report showed that a cherry crop near Vacaville, Calif., was greatly increased when several colonies of honey bees were placed in the orchard. Morrill (1899) also reported that bees increased cherry production. Gardner (1913) was the first to establish scientifically the need for pollination, and he stressed the importance of bees. This was supported with further research by various others, including Wellington (1923), Tuft and Philp (1925), Hooper (1930). Claypool et al. (1932), Weiss (1957), Skrebtsova and Iakovlev (1969), Eaton (1959), and Brown. 21
The fact that possibly only one pollen grain is needed to pollinate a cherry flower would indicate that repeated bee visits may be unnecessary, providing the pollen grain is compatible and successful fertilization of the ovule ensues. To play safe, the grower should insure the transfer of many pollen grains to the stigma. Tart cherry pollen may come from the same flower or the same tree, although greater benefit is usually derived if pollen comes from another cultivar. Sweet cherry pollen must come from another - and compatible - cultivar; therefore, a high degree of bee activity on the tree and between trees is required to adequately pollinate the crop.
The proper pollinator population is not easy to establish. Griggs et
al. (1952*) counted 30 to 40 bees per sweet cherry tree that had been in
production several years. The number of colonies per acre necessary to
provide this population was not given. Skrebtsova and Iakovlev (1959) spoke
of "saturation pollination" of cherries, but their data indicated
that even with their maximum of 3.8 colonies per hectare (less than two
colonies per acre) maximum set of all flowers was not achieved.
__________
21 Brown, K. BEES FOR SWEET CHERRY POLLINATION-
UNDER WILLAMETTE VALLEY FONDITIONS. Polk County (Oregon) Agr. Ext. Serv.
Agent, 2 pp. 1969. [Mimeographed.]
Pollination Recommendations and Practices:
Schuster (1925) recommended one strong colony for each 1 to 2 acres
"if the stands are strong." Tufts and Philp (1925) recommended
at least one colony per acre. Marshall et al. (1929), Murneek (1930), Philp
(1930, 1947), and Stephen (1961) concurred with the one-colony-per-acre
recommendation. Hooper (1930) recommended that colonies be placed in the
orchard during flowering. Brown (1968)22 recommended four to five colonies
per acre for his area of Oregon, the colonies placed in groups on each
5 to 10 acres of the orchard. Eaton (1962) stated that strong colonies
should be brought into the sweet cherry orchard on or before the day the
first flowers open, because placement in the orchard even 1 day late could
result in a reduced crop. Auchter and Knapp (1937*) recommended one colony
containing 7 to 9 pounds of bees to every 3 to 4 acres but conceded that
many growers use one colony for each acre or two. Coe (1934) and EIoffman
(1965) urged the use of bees but did not designate the concentration. Nevkryta
(A. N.) (1957) recommended four to five colonies per hectare (about two
colonies per acre). Skrebtsova and Iakovlev (1959) recommended "saturation
pollination" of the orchard, and showed that with 3.8 colonies per
hectare, 15 percent of all flowers set fruit but with 2.8 colonies only
13 percent set. Luce and Morris (1928) recommended one colony per acre.
Schuster (1925) also reported, "It is becoming the practice for cherry
growers either to keep their own bees or to hire stands of bees during
the blooming season." To take advantage of this needed cross-pollination
between cultivars, various planting plans of trees in the orchard were
recommended, ranging from one pollenizer and nine recipient trees to a
1:1 ratio. This recommended usage of bees barely seems to be accepted by
the growers. Kelly (n. d.) reported that during 1959 - 63, tart cherry
growers in Pennsylvania spent only 28 cents per acre for pollination fees;
when colonies were rented, the fee was $4.50 per colony. Considering the
pollination needs of this crop and the apparent lack of effort expended
by these growers, one is not too surprised at his statement: "In the
last decade sour cherry production and growers have both declined 31 percent."
However, pollination is probably not the only reason for this decline.
In a similar study made in Michigan on 37 tart cherry farms, Kelsey (1964)
reported that growers paid an average of $1.33 per acre for bee pollination.
The number of colonies of honey bees utilized, for which there was no remuneration,
was not disclosed. In general, most cherry growers make some attempt to
have bees present in their cherry orchards at flowering time. Frequently,
if bees are rented and there are 2 or 3 days of good weather for bee flight,
the tart cherry grower is ready for the bees to be removed. The number,
strength, and placement of colonies necessary to provide 50-percent set
of cherry flowers (Gardner 1913, Hootman 1931) is not known but should
be determined. Also, the difference in the need of bee pollination between
sweet and tart cherries should be determined. For highest production of
cherriesÑthe setting of the maximum number of blooms for greatest
production of sizeable fruitÑcross- compatible cultivars that flower
at the proper time must be interplanted in sweet cherry orchards, and possibly
also in tart cherry orchards, although large solid blocks are known to
produce satisfactory crops. For highest production of either sweet or tart
cherries as many as five strong colonies of honey bees per acre should
be placed on each 5 to 10 acres just before flowering time. The colonies
should contain 600 in2 or more of brood and 7 to 9 pounds of bees.
__________
22 Brown, K. POLLINATION OF ROYAL ANN (A-10) IN
THE WILLAMETTE VALLEY. Polk County (Oregon) Agr. Ext. Serv. Agent, 4 pp.
1968. [ Mimeographed.]
LITERATURE CITED:
ANONYMOUS.
1926. CROSS POLLINATION OF THE WINDSOR VARIETY. Amer. Fruit Grower Mag.
46(3): 26.
BURTNER J. C.
1923. LATEST CHERRY POLLINATION STUDIES. Better Fruit 182: 5 - 6, 23 -
24.
CLAYPOOL, L. L., OVERLEY, F. L., and OVERHOLSER, E. L.
1932. SWEET CHERRY POLLINATION IN WASHINGTON FOR 1931. Amer. Soc. Hort.
Sci. Proc. 28: 67-70.
____ OVERLEY, F. L., and OVERHOLSER, E. L.
1931. WASHINGTON SWEET CHERRY POLLINATION STUDIES IN 1931. 27th Ann. Mtg.
Wash. State Hort. Assoc. Proc. December 1, 2, and 3 at Yakima, Wash., pp.
171-174.
COE, F. M.
1934. CHERRY POLLINATION STUDIES IN UTAH. Utah Agr. Expt. Sta. Bul. 245,
53 pp.
CRANE M. B.
1925. SELF-STERILITY AND CROSS INCOMPATIBILITY IN PLUMS AND CHERRIES. Jour.
Genet. 15: 301, 322.
____ and BROWN, A. G.
1937. INCOMPATIBILITY AND STERILITY IN THE SWEET CHERRY. Jour. Pomol. and
Hort. Sci. 15: 86 - 116.
CULLINAN, F. P.
1937. IMPROVEMENT OF STONE FRUITS. U.s. Dept. Agr. Yearbook 1937: 724 -
737.
DUJARDIN F.
1921. [POLLINATION OF TREE FRUITS.] Rev. Hort. [Paris] 93: 300-302. [In
French.]
EATON, G. W.
1959. A STUDY OF THE MEGAGAMETOPHYTE IN PRUNUS AVIUM AND ITS RELATION TO
FRUIT SETTING. Canad. Jour. Plant Sci. 39: 466-476.
____ 1962. SWEET CHERRY POLLINATION, FRUITSET, AND VARIETIES. Mich State Hort. Soc. Ann. Rpt. 92: 102 - 104.
EINSET, O.
1932. EXPERIMENTS IN CHERRY POLLINATION. N.Y. Agr. Expt. Sta. (Geneva)
Bul. 617, 13 pp.
FREE, J. B. and SPENCER-BOOTH, Y.
1964. THE EFFECT OF DISTANCE FROM POLLENIZER VARIETIES ON THE FRUIT SET
OF APPLE, PEAR AND SWEET-CHERRY TREES. Jour. Hort. Sci. 39: 54 - 60.
GARDNER, V. R.
1913. A PRELIMINARY REPORT ON THE POLLINATION OF THE SWEET CHERRY. Oreg.
Agr. Expt. Sta. Bul. 116, 37 pp.
HENDRICKSON, A. H.
1922. WONDER WORK OF BEES. THEY MAKE MILLIONS FOR THE FRUIT GROWERS. BEES
THAT RETURNED TO THE ORCHARDIST $100 PER COLONY. Gleanings Bee Cult. 50:
226-229.
HOFFMAN, M. B.
1965. POLLINATION AND FRUIT DEVELOPMENT OF TREE FRUITS. N.Y. (Cornell)
Agr. Ext. Serv. Bul. 1146, 8 pp.
HOOPER, C. H.
1924. NOTES ON THE POLLINATION OF CHERRIES APPLIED TO COMMERCIAL CHERRY
GROWING. Jour. Pomol. and Hort. Soc. 3: 185-190.
____ 1930. THE STUDY OF POLLINATION IN RELATION TO CHERRY ORCHARDS. Gardners' Chron. 88(2293): 475 - 476.
HOOTMAN, H. D.
1930. RECENT DISCOVERIES IN POLLINATION METHODS AND PRACTICES AND THEIR
INFLUENCE UPON GREATER YIELDS OF DESIRABLE FRUIT. Md. Agr. Soc. Farm Burl
Fed. Rpt. 15,170-182; also in Md. State Hort. Soc. Proc. 33: 24-36.
____ 1933. THE IMPORTANCE OF POLLINATION AND THE HONEYBEE IN FRUIT YIELDS. Mo. State Hort. Soc. Proc. 1930/1932: 59-67.
HOWE, G. H.
1926. RELATIVE MERITS OF MAZZARD AND MAHALEB ROOT-STOCKS FOR CHERRIES.
Amer. Soc. Hort. Sci. Proc. 23d Ann. Mtg., pp. 53-55.
KELLY, B. W.
[ n.d. ] FACTORS RELATED TO THE COST OF PRODUCING CHERRIES IN PENNSYLVANIA,
1959-1963. Farm Mangt. 20, (Pa. Agr. Ext. Serv.), 17 pp.
KELSEY, M. P.
1964. THE COST OF GROWING TART CHERRIES IN THE VARIOUS AREAS OF MICHIGAN
AND HOW THEY WERE DETERMINED. Mich. State Hort. Soc. 94th Ann. Rpt., pp.
90 - 94.
LAGASSE, F. S.
1928. PROPER POLLINATION OF FRUIT BLOSSOMS. Del. Agr. Expt. Sta. Bul. 15,
20 pp.
LAPINS, K. O.
1971. 'STELLA', A SELF-FRUITFUL SWEET CHERRY. Canad. Jour. Plant Sci. 51:
252-253.
LUCE, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223,
22 pp.
MARSHALL, R. E., JOHNSTON, S., HOOTMAN, H. D. and WELLS, H. M.
1929. POLLINATION OF ORCHARD FRUITS IN MICHIGAN. Mich. Agr. Expt. Sta.
Spec. Bul. 188, 38 pp.
MORRILL, F. L.
1899. BEES AND FRUIT. Gleanings Bee Cult. 27: 430 - 431.
MURNEEK, A. E.
1930. FRUIT POLLINATION. Mo. Agr. Expt. Sta. Bul. 283, 12 pp.
NEVKRYTA, A. N.
1957. [DISTRIBUTION OF APIARIES FOR POLLINATING CHERRIES.] PchelovodstVo
34(4): 34-38. [In Russian.] AA-373l58.
NEVKRYTA, O. M.
1957. [INSECT POLLINATORS OF WILD AND CULTIVATED CHERRY IN THE UKRAINE.]
Zbirn. Prats Zool. Muz. 28: 49-61. [In Ukrainian, Russian summary.] AA-418/65.
OVERHOLSER, E. L., and OVERLAY, F. L.
1931. CHERRY POLLINATION STUDIES IN WASHINGTON FOR 1930. Amer. Soc. Hort.
Sci. Proc. 27: 400 - 403.
PHILP, G. L.
1930. CHERRY CULTURE IN CALIFORNIA. Calif. Agr. Ext. Serv. Cir. 46, 43
pp.
____ 1947. CHERRY CULTURE IN CALIFORNIA. Rev. Calif. Agr. Ext. Serv. Cir. 46, 51 pp.
ROBERTS, R. H.
1922. BETTER CHERRY YIELDS. Wis. Agr. Expt. Sta. Bul. 344, 30 pp.
RYUGO, K., and MIKUCKIS, F.
1969. SWEET CHERRY HEDGEROW PLANTING. Calif. Agr. 23(11): 14 - 15.
SCHUSTER, C. E.
1925. POLLINATION AND GROWING OF THE CHERRY. Oreg. Agr. Col. Expt. Sta.
Bul. 212, 40 pp.
SHOEMAKER, J. S.
1928. CHERRY POLLINATION. Ohio Agr. Expt. Sta. Bul. 422, 34 pp.
SKREBTSOVA, N. D., and IAKOVLEV, A. S.
1959. [EFFECTIVENESS OF SATURATED POLLINATION OF CHERRIES BY BEES.] Pchelovodstvo
36(5): 25 - 26. [ In Russian. ] AA-154/61.
SRIVASTAVA, R. P., and SINGH, I.
1970. FLORAL BIOLOGY, FRUIT-SET, FRUIT-DROP, AND PHYSICO- CHEMICAL CHARACTERS
OF SWEET-CHERRY (PRUNUS AVIUM L.). Indian Jour. Agr. Sci. 40: 400-420.
STEPHEN, W. P.
1961. BEES AND POLLINATION OF STONE FRUITS. Oreg. State Hort. Soc. Ann.
Rpt. 53: 78 - 79.
TUFTS, W. P., and PHILP, G. L.
1925. POLLINATION OF THE SWEET CHERRY. Calif. Agr. Expt. Sta. Bul. 385,
28 pp.
TUKEY, H. B.
1925. AN EXPERIENCE WITH POLLENIZERS FOR CHERRIES. Amer. Soc. Hort. Sci.
Proc. 21: 69-73.
UNITED STATES DEPARTMENT OF AGRICULTURE.
1967. GROWING CHERRIES EAST OF THE ROCKY MOUNTAINS. U.S. Dept. Agr. Farmers'
Bul. 2185, 30 pp.
WAY, R. D.
1968. POLLEN INCOMPATIBILITY GROUPS OF SWEET CHERRY CLONES. Amer. Soc.
Hort. Sci. Proc. 92: 119-123.
____ and GILMER, R. M.
1963. REDUCTIONS IN FRUIT SETS ON CHERRY TREES POLLINATED WITH POLLEN FROM
TREES WITH SOUR CHERRY YELLOWS. Phytopathology 53: 399-401.
WEISS, K.
1957. [THE DEPENDENCE OF THE CHERRY HARVEST ON THE NUMBER OF COLONIES PRESENT.]
Deut. Bienenw. 8(7): 124-126. [In German. ] AA-374/58.
WELLINGTON, R. [A.]
1923. SELF-STERILITY AND SELF-FERTILITY OF FRUIT VARIETIES GROWN IN NEW
YORK. N.Y. (Geneva) Agr. Expt. Sta. Cir. 71, 6 pp.
CHESTNUT
Castanea spp., family Fagaceae
Chestnut trees are cultivated for their nuts or as ornamentals. Probably the most notable species was the large and graceful ornamental American chestnut (C. dentata (Marsh.) Borkh.) (fig. 73), which extended from Maine southwest to Arkansas (Munns 1938). It has been almost completely destroyed by blight. The Japanese chestnut (C. crenata Sieb. and Zucc.) and the Chinese chestnut (C. mollisima Blume) are both cultivated for their nuts.
[gfx]
FIGURE 73. - American chestnut tree. (Photograph taken in 1915.)
Plant:
Chestnut is a deciduous tree or shrub, which is cultivated in a similar manner to other deciduous nut trees. It bears brown nuts, about an inch in diameter, which are usually consumed after they are roasted. From one to nine nuts are produced in a spiny involucre or burr (fig. 74).
[gfx]
FIGURE 74.- Burrs and nuts of Chinese chestnuts.
Inflorescence:
The fragrant inflorescence is about 12 inches long (fig. 75). It consists of a group of catkins 4 to 8 inches long. Catkins bearing only staminate florets make up the bulk of the inflorescence. Those produced near the base bear both staminate and pistillate florets. The latter, near the base of the catkin, are few in number. Usually three pistillate florets make up an involucre, each floret capable of producing three nuts.
Bees visit the staminate flowers for both nectar and pollen (Hazslinszky 1955, McKay 1939, Pellett 1947*). the degree of visitation depending upon competition from other flowers. The bees do not intentionally visit the pistillate flowers, but may accidentally come in contact with them while visiting the staminate flowers.
[gfx]
FIGURE. - Chestnut inflorescence.
Pollination Requirements:
Reed (1941) concluded that chestnut is self-sterile. He noted that isolated trees bear few nuts or even a fair crop, but best results are invariably obtained from trees in a mixed orchard where good pollen is available. McKay (1939) reported finding a C. crenata tree that was completely male-sterile. Its nectar production was normal, and it produced a normal crop of nuts. He also reported male sterility in C. sativa Mill. and C. sativa X C. dentata. Later, McKay (1942) reported that when flowers of C. mollissima were self-pollinated only 1.3 percent of the flowers set fruit, when they were cross-pollinated 34.9 percent set, but when they were open-pollinated 68.1 percent set. This showed the need for transfer of pollen between plants.
Crane et al. (1937) stated: "As a rule all chestnuts are more or less self-sterile and they bear better when interplanted with other cultivars."
Kawagoe (1955) stated that the stigmas may remain receptive as much as 45 days and that cross-pollination was best effected 8 to 22 days after stigma emergence.
Ohno et al. (1958), considering the effect of rain on the pollination of chestnuts, tested the effect of water on the pollen. They found that 17 to 19 percent of their pollen germinated even after soaking in water in the laboratory for 9 hours. In the field, this pollen caused 48 to 50 percent set of fruit if cross-pollinated but only 3 to 9 percent set if it came from the same plant.
Watanabe et al. (1964) reported much higher bur-set on adjoining rows to the pollenizer row than on the (decreasing) 3d to 10th rows. They recommended that pollenizer cultivars be set in the ratio of 1 to 1 or 1 to 2 of the main cultivar.
Pollinators:
Crane et al. (1937) and Clapper (1954) stated that chestnut pollen is produced in great abundance and is carried by wind. However, J. W. McKay (personal commun., 1972) questioned this. He indicated that honey bees, rose chafers, and wild bees are highly beneficial to chestnut in the transfer of pollen, and they frequently visit the staminate flowers in large numbers. He also considered that for highest production on younger trees, a high population of pollinators is especially needed. If production of newer cultivars and hybrids expands, the value of insects in cross- pollination for maximum set should be more fully explored.
Pollination Recommendations and Practices:
There are no recommendations on the use of pollinating insects on chestnut although evidence shows they are needed.
LITERATURE CITED:
CLAPPER, R. B.
1954. CHESTNUT BREEDING, TECHNIQUES AND RESULTS. II. INHERITANCE OF CHARACTERS,
BREEDING FOR VIGOR AND MUTATIONS Jour. Hered. 45: 201-208.
CRANE, H. L., REED, C. A., and WOOD, M. N.
1937. NUT BREEDING. U.S. Dept. Agr. Yearbook 1937: 827 - 889.
HAZSLINSZKY, B.
1955. [THE IMPORTANCE OF THE CHESTNUT TREE FOR BEEKEEPING.] Meheszet 3(6):
109 - 110. [ In Hungarian.] AA-171/57.
KAWAGOE, H.
1955. [STUDIES ON THE PERIOD DURING WHICH THE CAPACITY FOR FERTILIZATION
OF THE CHESTNUT PERSISTS.] Okayama Nogaku Shikenjo Rinji Hokoku/Spec. Bul.
Okayama Agr. Expt. stat 53: 141 - 154. [In Japanese.] Abs. in Plant Breed.
28(4): 826. 1958.
McKAY, J. W.
1939. MALE STERILITY IN CASTANEA. Amer. soc. Hort. Sci. Proc. 37: 509-510.
______ 1942. SELF-STERILITY IN THE CHINESE CHESTNUT (CASTANEA MELLISSIMA). Amer. Soc. Hort. Sci. Proc. 41: 156-160.
______ 1972. POLLINATION OF CHESTNUT BY HONEY BEES. North. Nut Growers' Assoc. Ann. Rpt. 63: 83-86.
MCKAY, J. W. and CRANE, H. L.
1953. CHINESE CHESTNUTS A PROMISING NEW ORCHARD CROP. Econ. Bot. 7(3):
228 - 242.
MUNNS, E. N.
1938. THE DISTRIBUTION OF IMPORTANT FOREST TREES OF THE UNITED STATES.
U. S. Dept. Agr. Misc. Pub. 287, 176 pp.
OHNO M., SATO, s., and SAWABE, H.
1958. [THE STUDY OF CHESTNUT POLLINATION. 1. THE FRUIT SET OF CHESTNUTS
WHICH WERE POLLINIZED BY THE WETTING POLLEN.l Chiba Univ. Faculty Hort.
Tech. Bul. 6: 129-135. [In Japanese, English summary.]
REED, C. A.
1941. THE PRESENT STATUS OF CHESTNUT GROWING IN THE UNITED STATES. Amer.
soc. Hort. Sci. Proc. 39: 147-152.
WATANABE, Y., ADACHI, M., and HIYAMA, H.
1964. [STUDIES ON THE POLLINATION IN CHESTNUT TREES. 1. INFLUENCE OF DISTANCE
FROM THE POLLINIZER UPON BUR-SET IN VARIETY GINYOSE.] Ibaraki Hort. Expt.
stat Bul. l: 7-12. [In Japanese, English summary.]
CITRUS
Citrus spp., family Rutaceae
The kind of citrus crop produced, its volume, area of profusion; and dollar value are shown in table 8. As this table shows, the bulk of the citrus crop is produced in Florida, and oranges and grapefruit account for more than 80 percent of all fruit produced.
[gfx]
TABLE 8. - Estimated U.S. production of citrus by State, type, number of
boxes, and total value in 1970-71
Plant:
The cultivated citrus plants are mostly shrubs or small trees with dense foliage; sweet-smelling, whitish to purple flowers that are often produced in great profusion; and greenish to golden fruit. The trees may live for more than 100 years, but citrus groves more than 50 years old are rare. Depending on the kind involved, the fruit may mature from fall until summer of the year following flower development. Some fruits, for example certain mandarins, fall shortly after they mature. Others, such as the 'Valencia' orange or the grapefruit, will remain on the tree several months after maturity. Citrus has little cold resistance and is not grown in areas where the temperature is likely to fall below 20 deg F.
A high degree of cross-fertility exists between the species of Citrus as well as between the genera of Citrus, Fortunella, and Poncirus. This has permitted breeders to develop the various simple and multiple hybrids, some of which have become of considerable economic importance (Cameron and Soost 1969).
The common and scientific names of the more well-known cultivars are shown in table 9. The species frequently mentioned but of minor value or used as rootstock or in breeding work are as follows:
Common name Scientific name:
Calamondin..........................................................Citrus reticulata var. austera Swingle X Fortunella spp. Citrange................................................................C. sinensis X Poncirus trifoliata Citrangequat.......................................................P. Trifoliata X Citrus spp. X Fortunella spp. Citron....................................................................Citrus medica L.Common nameÑ(Con.) Scientific nameÑ(Con.) Cleopatra mandarin............................................................C. reticulata Blanco Kumquat.................................................................................. Fortunella margarita (Lour.) Swingle Meyer lemon...........................................................................Citrus limon x C. medica Pummelo (Shaddock)..........................................................C. grandis (L.) Osbeck Rough lemon...........................................................................C. Iimon (L.) Burm. Sour Orange............................................................................C. aurantium L. Trifoliate orange.................................................................Poncirus trifoliata (L.) Raf. TABLE 9.ÑCommon and scientific names and important cultivars of U.S. citrus crops __________________________________________________________ Common Scientific Important name name cultivars __________________________________________________________ Grapefruit Citrus paradisi ÔBurgundyÕ, DuncanÕ,ÔMarshÕ, Macf. ÔRedblushÕ, ÔThompsonÕ. Lemon C. limon (L.) ÔEurekaÕ, ÔLisbonÕ Burm. f. Lime C. aurantifolia ÔKeyÕ (Mexican or West (Christm.) Indian group), ÔBearssÕ Swingle (Tahiti or Persian group). Orange (sweet) C. sinensis (L.) ÔHamlinÕ, ÔMediterranean Osbeck SweetÕ, ÔParson BrownÕ, ÔPineappleÕ, ÔValenciaÕ, ÔWashington NavelÕ. Mandarin and ÔAlgerianÕ (ÔClementineÕ) mandarin-hybrid ÔDancyÕ, ÔKinnowÕ, ÔK- complex EarlyÕ, ÔMinneolaÕ, ÔMurcottÕ, ÔOrlandoÕ, ÔPageÕ, ÔRobinsonÕ, ÔTempleÕ, ÔWilkingÕ. __________________________________________________________
Inflorescence:
The outstanding characteristics of citrus flowers are the pleasant fragrance, the pleasing contrast between the whitish (to pink or purple in lemons) petals and the dark-green background of the leaves, and the attractiveness of the flowers to bees. Blossom size varies in grapefruit, lemon, lime, orange, and the mandarin and mandarin-hybrid complex, ranging from about three-quarters of an inch for the smaller flowers to 1 1/2 inches for the largest (fig. 78).
The flowers usually open in one great flush of bloom in the spring, although lemons and acid limes are particularly noted for their tendency to flower throughout much of the year. The flowers are mostly hermaphrodite, releasing pollen when the stigma is receptive; however, staminate flowers occur in the lime, lemon, and citron (Purseglove 1968*) and pistillate flowers occur in 'Satsumas' (Kihara 1951). The pollenless flowers of the 'Washington Navel' are well known for their ability to set parthenocarpic fruit (Webber et al. 1943).
The flowers are in small clusters in the leaf axil of a preceding growth flush but single in the axils of a just-completed growth flush (Coit 1916, Chandler 1958*, Reece 1945). The four to eight, but usually five, oblong, glossy, flared petals arise from the base of the sexual column. The staminate portion consists of 20 to 40 upright white filaments, sometimes united into several groups at the base, with yellow anthers on the tip.
The globose yellowish stigma terminates the style. At the base, the style unites with the greenish ovary, with its 9 to 13 locules, which stands well above the disk.
Nectar is secreted from the nectary or floral disk just within and above the point of attachment of the stamens. Vansell et al. (1942) stated that secretion of nectar continues at least 48 hours after flower opening. Also, a thick viscous stigmatic fluid is secreted from papillose hairs on the stigma. This material serves to catch and hold pollen grains and provides suitable media for their germination. A similar material can sometimes be seen inside the style, apparently providing a route and media by which the pollen tube may reach the ovary.
The flowers open primarily from 9 a.m. to 4 p.m. with the peak period about noon (Randhawa et al. 1961). They never close; the petals merely shed a few days later. The stigma becomes receptive just before the bud breaks open, but the stamens usually do not release pollen until several hours later, after the flower is fully open (Wright 1937).
To determine if bee visitation altered the period of time the flower is open, I kept records of development on 20 'Clementine' ('Algerian') tangerine flowers at Yuma, Ariz., in 1954 (previously unpublished data). Ten flowers were on a tree enclosed in a cage with a colony of honey bees and 10 on a tree in a cage that excluded bees. Shedding of the petals and stamens in the no-bee cage was slightly slower than in the cage with bees but only because they became stuck in the uncollected nectar. Anther dehiscence was completed by the end of the second day, and normal petal fall was completed on the third day. Whether this applies to all other citrus or even to the same cultivar in other areas is not known but probably it is similar.
The difference in the appearance of the stigmas in the cages was significant. Pollination apparently occurred shortly after flower opening in the bee cage, after which the stigma color changed to brown. In the no- bee cage, the stigmas remained cream-colored and apparently receptive at least 4 days. This might explain the observation by Climenko (1936) that stigmas are receptive for 6 to 8 days.
Citrus generally yields nectar copiously. Vansell et al. (1942) stated that some blossoms contained 1.5 bee-loads of nectar, averaging 20 microliters, compared to 0.8 to 2.4 microliters per blossom for an alfalfa flower, another important nectar source. Because of the large amount and superior quality of honey that citrus blossoms produce, many beekeepers place their colonies in or near most groves.
The value of citrus as a source of pollen is influenced by the kind involved. Hamakawa (1967) reported that less than 1 percent of the bees foraging on 'Satsuma' mandarin (C. unshiu Marc.) carried pollen loads as compared to 95 percent on 'Hassaku' orange (C. hassaku Hort. ex. Y. Tanaka). In general, citrus is not considered to be an excellent source of pollen by beekeepers. Only a small percentage of citrus flowers set and develop into mature fruit. For example, Reuther et al. (1968) showed that one 'Washington Navel' tree had 102,350 blooms but matured only 419 fruit, and a 'Valencia' tree with 47,112 blooms matured 708 fruit. Reed (1919) reported 4,440 buds on one lemon tree, 52 percent of which set, but only 6.6 percent (294 fruit) reached maturity.
Moss (1971) studied the relation of flowering and the tendency toward biennial bearing in the sweet orange. He recorded twice as many flowers on the trees in "on" years as in "off" years, but the percentage of flowers that set was the same. Although more flowers usually equal more fruit, if the grower can take steps to increase this percentage during the "off" years, he should do so.
[gfx]
FIGURE 78. - Longitudinal section of citrus flowers, x 3. A, 'Red Blush'
grapefruit; b, 'Meyer' lemon; C, 'Algerian ('Clementine') tangerine; D,
'Washington Navel' orange.
Pollination Requirements:
In general, citrus has been considered as a crop with little or no need for insect pollination. However, that which was said about a crop years ago may not be true today for, as Webber et al. (1943) pointed out, no variety is likely to remain entirely static over long periods, even when propagated asexually. The likelihood that pollination requirements of citrus have changed in this way is minor. More likely, our increased knowledge, obtained through continued studies, has enlightened us as to the range of pollination needs.
Furthermore, economic conditions may require maximum production of a crop if a net profit is to be realized. Under such conditions, a slight benefit, derived from better pollination of the crop, can become highly significant economically. Considerable attention has been given to citrus pollination recently. Krezdorn (1970) stated that a growing number of citrus cultivars are known to be self-incompatible and, in some cases, cross incompatible. With such cultivars, an appropriate pollen supply and pollinating agents is needed.
The pollination requirements of the different kinds of citrus are quite diverse. In some there is almost complete self-sterility. Pollen must be transferred to these flowers from those of another compatible type for maximum fruit production. In others, the plant is benefited if pollen is moved from flower to flower within the cultivar or within the species. In still others, there is no known benefit from transfer of pollen to the stigma by external agents over production caused by the plant's own pollen coming into contact with the stigma without the aid of such insects. In addition, there are varying degrees of parthenocarpic development of the fruit. Because of such diversity, the more important kinds of citrus are discussed separately.
GRAPEFRUIT:
Authorities on citrus in the United States have consistently stated that cross-pollination is not required in grapefruit, and that grapefruit production presents no pollination problem (Coit 1915, Frost and Soost 1968, Krezdorn 1970, 1972, Soost 1963, Webber 1930). This does not necessarily mean that no benefit is derived from insect transfer of pollen within the cultivar.
Wright (1937) studied the effect of cross-pollination on seed development and fruit set of the 'Marsh' grapefruit. Although some of his data on unpollinated (emasculated and bagged) flowers are open to question, he reported that open pollinated flowers set about twice as many seeds, but more importantly four times as many fruit, as selfed flowers. The presence of seeds is generally undesired by the canners and other consumers, although the 'Duncan' grapefruit is preferred by canners in spite of its seeds. The difference in fruit set could be of considerable economic importance. Satisfactory crops of grapefruit are normally harvested from solid blocks of a single cultivar.
LEMONS:
Richter (1916) stated that without question (but also without showing data) all the blooms of the lemon could be protected from insect visitation without the slightest reduction in set of mature fruit. Webber (1930) also concluded that pollination by bees was probably a negligible factor in the production of citrus fruits, at least for the 'Eureka' and 'Lisbon' lemons, the 'Valencia' and 'Washington Navel' oranges, and the 'Marsh' grapefruit. However, Webber et al. (1943) stated that although self-pollination occurs rather commonly without insects, seedlessness sometimes results, and seedlessness is rather generally a handicap to setting of fruit. Frost and Soost (1968) and Soost (1963) concluded that supplying pollen of another variety does not appear necessary for most of the major types of citrus.
In Russia, however, where numerous tests have been conducted on caged citrus trees, Glukhov (1955) stated that lemon trees isolated from bees produced only one-fourth as much fruit as trees exposed to cross- pollination by bees. Burnaeva (1956) reported that lemons receiving supplemental pollen from other cultivars or citrus species, produced more than trees not exposed to cross-pollination. Zavrashvili (1964) reported that lemon trees caged without bees produced 42.5 percent less than open-pollinated trees, whereas the trees caged with bees produced only 10 percent less, indicating that bees contribute by distributing the self- pollen on the tree. Later, Zavrashvili (1967b) stated that the 'Novogrusinskii' requires cross-pollination by bees for fruit production. Randhawa et. al. (1961) obtained four mature 'Malta' lemon fruit from 25 cross-pollinated flowers but none from 50 selfed flowers.
LIMES:
There has been little research on the pollination requirements of limes. Krezdorn (1970) stated that the Tahiti lime is strongly parthenocarpic, and, although cross-pollination might increase the number of seed, the increase in production of fruit, if any, would be negligible. However, Motial (1964) reported that 80 to 100 percent of the open pollinated flowers he observed on sweet limes (C. limettoides Tan.) set fruit, but only 40 to 60 percent of the emasculated and hand pollinated flowers set. This indicates that strong pollinator activity might increase the set and total production of sweet limes. Motial concluded, however, that sweet lime is not self-incompatible but is merely a shy bearer because of the high percentage of staminate flowers the plant produces.
ORANGES:
A general statement about the pollination of oranges is difficult because of the variation among cultivars. Coit (1915) stated that certain oranges require pollination to set fruit, others will set fruit parthenocarpically without the stimulus of pollination, and some will not accept pollen from some other cultivars. Because of this difference, the 'Washington Navel' and 'Valencia' and other sweet oranges will be discussed separately.
'Washington Navel'. - The anthers of 'Washington Navel' blossoms produce no pollen and the embryo sac may degenerate before tubes of pollen from other cultivars can penetrate to it, yet fruit sets and develops if conditions are favorable. However, if the tree is stressed by desiccating winds or moisture shortage, drop of young fruit can be severe. Surr (1922) caged six 'Washington Navel' trees to increase the humidity around them, which also excluded pollinating insects. He found that by doing this the production was not increased but instead decreased as much as 86 percent. The cages may have influenced fruit set for reasons other than pollination. Krezdorn (1970) stated that cross-pollination in 'Washington Navels' does not increase the yield, yet he (1965) obtained the following results from hand-pollinating the flowers, which would indicate that cross-pollination might influence set:
[gfx] (fix table):
No. of flowers No. of Pollen Source pollinated fruit set 'Pineapple' orange 1,000 2 'Temple' orange 1,000 3 'Duncan' grapefruit 1,000 5 Self (None) 3,000 0
El-Tomi (1964, 1957) reported that cross-pollination of 'Washington Navels' significantly minimized the dropping of immature fruit.
An interesting report on pollination made by Zavrashvili (1967b) stated that 'Washington Navel' trees caged to exclude bees yielded fewer fruits than trees caged with bees or open plots. The flowers set the most fruit when crossed with the 'Grusinian' orange. He also reported that the transfer of stigmatic fluid between stigmas increased the percentage of set. No reason for this effect was given, and its significance has not been determined.
The effect of pollination on production of 'Washington Navel' oranges seemed to be summed up by Atkins (1963), who stated that there is a possibility that cross-pollination by bees may cause them to retain more fruit.
'Valencias.' - Richter (1916) stated, without showing data, that if all insects were kept off 'Valencia' flowers there would be no less production. Francke et al. (1969) also concluded that bees have no effect on production of 'Valencias', but Cameron et al. (1960) reported that fruit size of 'Valencias' was increased as the seed number increased and that 'Pearl' tangelo pollen may increase both seed number and fruit set on 'Valencias'. This would indicate that, with cross-pollination, fruit size and possibly number of fruit set might be increased.
Other sweet oranges. - Soost (1963) stated that commercial plantings show no obvious reduction of yield in the absence of other varieties, but this does not mean that cross-pollination is of no benefit. Khan and Chandhri (1964) concluded that five unidentified cultivars were self-pollinating. Oppenheimer (1935) (cited by Oppenheimer 1948) came to the conclusion that "citrus can be planted in large blocks with no admixtures of other varieties, without the least misgiving."
Conversely, Glukhov (1955) reported that orange trees (cultivar not given) pollinated by bees produced four times as much fruit as trees isolated from bees. Zavrashvili (1964) reported that the orange crop in cages without bees was 54.4 percent lower than that on trees in the open. The cultivar was not identified nor was there a measure of cage effect on the plant other than pollination effect. Wafa and Ibrahim (1960) obtained 31 percent increase in set of fruit on the 'Elfelaha' orange, 22 percent increase in fruit weight, 33 percent more juice, and 36 percent more seeds from fruits on trees visited by bees than on trees from which bees were excluded. Zacharia (1951) reported partial self-incompatibility in the 'Shamouti' orange.
Hassanein and Ibrahim (1959) reported a set of 2.6 percent of flowers of the 'Khalili' orange where insects were excluded, 10.4 percent set where honey bees were present, and 7.4 percent on control (open) blooms. Krezdorn (1967) showed that the 'Hamlin', 'Parson Brown', 'Pineapple', and 'Valencia' orange size increased linearly with fruit set.
Although the results of tests are meager, some beneficial effects of pollination on oranges are indicated.
PUMMELO:
Soost (1963, 1964), working with 11 different accessions and Nauriyal (1952) concluded that the pummelo, which is grown commercially only in the Orient, is self-incompatible.
Aala (1953) conducted pollination studies on the Siamese pummelo 'Siamese 3442' in the Philippines. It produces both complete and staminate flowers. Some of the flowers were left to visits by bees, some were selfed, and some were crossed with pollen of 'Sour', 'Siaver 14', and 'Valencia' orange, and 'Batanga' mandarin. He concluded that most pummelo trees were self-incompatible and should be inter-planted with other cultivars. He stated: "Bees or other insects are necessary for proper pollination and setting of fruits, whether a cultivar is self-fertile or self-sterile." He also noticed that a higher percent set of open-pollinated flowers was obtained during off seasons than regular seasons, which may indicate that an inadequate pollinator population existed at flowering time. Of course, it could also mean there was an interaction with unfavorable environmental or physiological factors.
MANDARIN AND MANDARIN-HYBRID COMPLEX:
More research has been conducted on the pollination requirements of this group than of all the other citrus species combined, because the pollination problem is more acute. The problem has been recognized since Lacarelle and Miedzyrzecki (1937) reported that fewer fruits of the 'Clementine' mandarin set on a tree enclosed for self-pollination without bees than on 30 others enclosed with bees, either with or without pollen of other cultivars. Oppenheimer ( 1948) also showed that production of the 'Clementine' tangerine was increased when it was cross-pollinated by bees with pollen from 'Dancy', 'Temple', 'Duncan', or some other seedy cultivars. He found that the 'Valencia', 'Eureka', 'Marsh Seedless', and 'Satsuma' were ineffective pollinators.
Van Horn and Todd (1954) caged 'Clementine' ('Algerian') tangerine trees with and without pollinating insects (honey bees) and with and without bouquets of other cultivars. They showed that trees having both bees and bouquets yielded 16 times as many tangerines as those with no bees, had double the yield of those provided with bees only, and had better fruit quality. Miwa (1951) showed that the 'Hyuganatsu' mandarin was self-sterile but cross-fertile. Lynch and Mustard (1955), Coste and Gagnard (1956), Soost (1956,1963), Mustard et al. (1957), and Barbier (1964) concluded that the 'Clementine' tangerine was self-incompatible. Minessy (1959) found that grapefruit pollen was highly effective in fertilizing 'Clementines'. Blondel and Barbier ( 1963) accepted the fact that pollination increased production but stated that it also increased the pips or seeds present. Hilgeman and Rodney (1961) and Krezdorn (1970, 1972) stated that yields of 'Clementine' can be improved with bee pollination.
Hearn et al. (1969) reported that the 'Lee', 'Page', 'Nova', and 'Robinson' were self-incompatible, but Reece and Register (1961) stated that the 'Osceola' was not completely so. Furr (1964) and Moffett and Rodney (1971b) reported that cross-pollination was necessary and should be provided for 'Fairchild'. Later (1973) they reported that bees increased the yield of 'Orlando' tangelo. Also, Moffett and Rodney (1973) showed that honey bee visits increased yields of 'Orlando' tangelo. Hearn et al. (1968, 1969) and Hearn and Reece (1967), concluded that the 'Lee', 'Nova', 'Page', and 'Robinson' were all self-incompatible. Krezdorn (1972) included the 'Orlando', 'Minneola', and 'Osceola' in this group, but questioned the inclusion of the 'Lee'. Hearn et al. (1969) also reported that the 'Page' fruits were larger if they developed from 'Lee' pollen, the first well-defined metazenic effects reported in citrus.
Krezdorn and Robinson (1958) showed that crossing 'Orlando' with pollen from 'Temple' or 'Dancy' increased yields. Krezdorn (1959, 1967) also reported a significant correlation between fruit size and number of seeds of the 'Orlando'. Krezdorn (1970) stated that the 'Orlando', and 'Minneola' were self-incompatible, the 'Nova', 'Osceola', and 'Robinson' require cross-pollination, and at least in the 'Orlando' the fruit size increases with seed number. Soost (1963) reported that 'Minneola', 'Orlando', 'Osceola', and 'Robinson' were self-incompatible and that 'Lee' and 'Osceola' were suspect. Krezdorn (1970) stated that there is a growing number of self-incompatible cultivars.
The 'Satsuma' is variously referred to as 'Satsuma' mandarin (Hamakawa 1967), 'Satsuma' orange, 'Unshiu' orange (Kresdorn 1970), or 'Unshiu' tangerine (Mchedlishvili 1962). Several tests indicate that it is benefited by bees- 6.3 percent according to Zhgenti (1956); 7 to 11 percent, Zavrashvili (1967a, b). Soost (1963) recommended that the plants be set in solid blocks, although there was some risk of excessive fruit drop under some conditions. Mchedlishvili (1962) showed the importance of insect pollination. At varying distances from an apiary, he observed that near the apiary 42.5 percent of the flowers set and 14.6 percent were harvested. At 150 m from the apiary, 29.3 percent of the flowers set and 10.6 percent were harvested. At 350 m from the apiary, however, only 13.6 percent of the flowers set, and 5 percent were eventually harvested. This showed the value of having the colonies of bees near the trees to be pollinated. Although a few research workers have obtained substantially the same set of fruit from no pollination, self-pollination, and cross- pollination of 'Satsuma', the data indicate that for best production, an ample bee population is needed.
CALAMONDIN, CITRANGE, CITRON, KUMQUAT, MEYER LEMON, PONDEROSA LEMON, SOUR ORANGE, AND TRIFOLIATE ORANGE:
No pollination problems have been observed on citron, kumquat, Meyer lemon, and trifoliate orange, but there have been problems of seed set in 'Morton' end 'Troyer' citrange (Soost 1963).
In summary, insect transfer of pollen within the flower, between flowers of a cultivar, or between cultivars may be of slight value to oranges, grapefruit, and lemons. Many, if not all, of the mandarin and mandarin-hybrid complex are dependent upon or greatly benefited by insect pollination. The pummelo is dependent upon pollinating insects.
Pollinators:
The honey bee is unquestionably the primary pollinating agent of citrus; wind is not a major factor. Other pollinating insects are minor. Beekeepers readily place their colonies near citrus groves for the delicious honey the bees store. and citrus specialists frequently intimate that an ample supply of bees is always in the groves (Krezdorn 1972). Moffett and Rodney (1971a) showed this may not be true. They observed an average of slightly less than one bee per 100 blossoms at Yuma, Ariz., and concluded that the population was so low that growers of most orchards needing insect pollination should have rented colonies for that purpose. During the peak bloom, the ratio was much less than one bee per 100 flowers. Such a population would not be likely to visit individual flowers more often than about once per hour. By contrast, Mchedlishvili (1962) reported 12 bee visits per blossom per hour.
P. M. Packard (personal commun., 1972), State apiary inspector for Florida, estimated that only 220,000 colonies of honey bees were in the prime citrus area during bloom time in 1972Ñabout one colony per 4 acres. He stated distribution is not systematic, with some areas overcrowded with bees and others having practically none.
Butcher (1955) observed a zonal production effect in relation to distance of 'Minneola' tangelos from the apiary with the most marked effect 200 to 300 feet away. However, Robinson (1958) stated that honey bees worked equally well in all directions and were evenly spread to 400 feet.
Honey bees collect both pollen (if it is produced) an nectar from citrus. The flower is so constructed that if the bee has visited a previous pollen-producing flower, some pollen is likely to be transferred to the next stigma visited.
Depending upon the cultivars involved, the results of insect pollination may have no effect, increase the number of fruits set, increase the size of the fruit, cause seed to be present, increase the number of seeds, or cause an overloading of the tree.
Pollination Recommendations and Practices:
Little work has been done on the number of bee visits per flower, or the effect of cross-visitation between cultivars in relation to fruit set on citrus cultivars either dependent upon or benefited by bee pollination. Some recommendations have been made, without support or data, on colonies per acre and suggested placement.
Oppenheimer (1948) suggested bringing bees in, if they were not present, to pollinate 'Clementine' mandarins in Palestine. He did not indicate how many bees should be brought in or where the colonies should be placed.
The placement of colonies of bees in citrus orchards for pollination has often been recommended. Baldwin (1916) without concrete data to support his statement recommended five colonies per acre. Van Horn and Todd (1954) recommended one colony per acre of 'Clementines'. The Florida Agricultural Extension Service (1961) recommended the use of bees and pollenizer cultivars to increase the number and size of tangelos. Robinson and Krezdorn (1962) recommended a minimum of one strong colony of honey bees per acre of 'Orlando' tangelos. Soost (1963) stated that most commercial kinds of citrus set adequate crops without cross-pollination, but where insect pollination is needed "one hive per 2 acres may be sufficient although this is not certain." Zavrashnli (1967b) stated that one colony per 2.5 acres doubled the crop. His research dealt with 'Washington Navels', 'Novogrusinskii' lemons, and 'Unshiu' tangerines. Haynie (1968) recommended one colony per 2 acres, the colonies in groups and properly spaced, for cultivars benefiting from bee pollination.
There seems to be no uniformity in these recommendations, probably because each dealt with only one or a few cultivars in different areas of the citrus world and under different conditions.
The weakness of the recommendations is that there is no indication given as to the relative bee population per unit of flowers and also no relation is shown between colonies per acre and bees per flower.
For most efficient pollination of citrus, the meager data indicate that if bees are needed they should be distributed at the rate of one-half to five colonies per acre at about 1/4- to l/10-mile intervals. Consideration in the recommendation should be given to vigor of the colonies, other colonies in the area, acres of citrus, and other nearby plants attractive to bees, size of the citrus trees, and blooms per tree. For greatest benefit, the colonies probably should be present throughout the citrus flowering period.
Beekeepers place their bees near citrus groves for the honey they obtain; however, these colonies may not be placed strategically or in aufficient numbers for most effective pollination of all areas of a particular grove. The grower would profit most by arranging for the appropriate number of strong colonies properly placed and managed for citrus pollination although the honey obtained could be a factor in relation to locations and pollination fees. The citrus grower can gain far more than the beekeeper from such an arrangement.
LITERATURE CITED:
AALA, F. T.
1953. EFFECTS OF HAND POLLINATION ON THE PRODUCTION OF SIAMESE PUMMELO.
Philippine Jour. Agr. 18(1-4): 101 - 113.
ATKINS, E. L.
1963. HONEYBEES AND AGRICULTURE. Calif. Citrog. 49(2): 81 - 82.
BALDWIN, E. G.
1916. PERFECT POLLINATION OF CITRUS GROVES. Gleanings Bee Cult. 44: 269-271.
BARBIER, E. [C. ]
1964. [POLLINATION AND FRUITING OF THE CLEMENTINE (ORANGE).] Ann. de l'Abeille
7(1): 63-80. [In French, English summary.]
BLONDEL, L., and BARBIER, E. [C.]
1963. [THE PROBLEM OF PIPS IN CLEMEMTINE ORANGES.] Fruits et Primeurs de
l'Afrique du Nord 33(2): 153-156 [In French.] AA-538/64.
BURNAEVA, N. L.
1956. [AN EXPERIMENT ON SUPPLEMENTARY POLLINATION OF CITRUS FRUITS.] Agrobiologiya
3: 124-128. [In Russian, abstract translated.]
BUTCHER, F. G.
1955. HONEY BEES AS POLLINATORS OF MINNEOLA TANGELOS. Fla. Hort. Soc. Proc.
68: 313.
CAMERON, J. W., and SOOST, R. K
1969. CITRUS. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial
Crop Breeding in the Tropics, pp. 129-162. H. Veenman and Zonen, N. V.
Wageningen, The Netherlands.
______COLE, D., JR.. and NAUER, E. M.
1960. FRUIT SIZE IN RELATION TO SEED NUMBER IN THE VALENCIA ORANGE AND
SOME OTHER CITRUS VARIETIES. Amer. Soc. Hort. Sci. Proc. 76: 170 - 180.
CLIMENKO, K.
1936. [PERIODICITY OR THE RECEPTIVITY OF STIGMAS OF ORANGES.] Batum Subtrop.
Bot. Gard. Bull 1: 127-129. [In Russian, English summary.]
COIT, J. E.
1915. CITRUS FRUITS. 520 pp. The Macmillan Co., New York.
COSTE, A., and GAGNARD, J. M.
1956. [STUDIES ON THE POLLINATION OF CLEMENTINES.] Fruits et Primeurs de
l'Afrique du Nord 26: 246 - 252. [In French.] Cited by Reuther, Batchelor,
and Webber (1968).
EL-TOMI, A. L.
1954. EFFECT OF CROSS-POLLINATION ON FRUIT SETTING IN WASHINGTON NAVAL
ORANGE. Citrus lndus. 35(8): 5-6.
______ 1957. EFFECT OF CROSS-POLLINATION OF JUNE-DROP PRE-HARVEST DROP, AND CROPPING IN WASHINGTON NAVEL ORANGE. Ann. Agr. Sci. 2(2): 249 - 265.
FLORIDA AGRICULTURAL EXTENSION SERVICE.
1961. YOUR 1961 AGRICULTURAL EXTENSION SERVICE ANNUAL REPORT. Fla. Agr.
Ext. Serv., Gainesville, 7 pp.
FRANCKE, R., JORGE, A., and MATHIEU, J. M.
1969. [EFFECTS OF INSECT POLLINATORS ON THE PRODUCTION OF VALENCIA ORANGES:
THE HONEY BEE AND ITS EFFECT ON CITRUS PRODUCTION.] Agronomia (Monterrey)
122, 7 pp. [ In Spanish. ]
FROST, H. W., and SOOST, R. K.
1968. SEED REPRODUCTION: DEVELOPMENT OF GAMETES AND EMBRYOS. In Reuther,
W., Batchelor, L. D., and Webber, H. J. The Citrus Industry, V. 2, pp.
290-324. The University of California Press, Berkeley and Los Angeles.
FURR, J. R.
1964. NEW TANGERINES FOR THE DESERT. Calif. Citrog. 49(7): 266.
GLUKHOV, M. M.
1955. [HONEY PLANTS.] 512 pp. Izd. 6, Perer. i Dop. Moskva, Gos. Izd-vo
Selkhoz Lit-ry. [In Russian.]
HAMAKAWA, H.
1967. [ON THE BEHAVIOUR OF HONEYBEES IN CITRUS FLOWERS OF FOUR SPECIES.]
Jap. Jour. Breed. 17 Suppl. 2: 143-144. [In Japanese.] AA-368/71.
HASSANEIN. M. H., and IBRAHIM, M. M.
1959. STUDIES ON THE IMPORTANCE OF INSECTS, ESPECIALLY THE HONEY BEE IN
POLLINATION OF CITRUS IN EGYPT. Agr. Res. Rev. 37(3): 390-409.
HAYNIE, J. D.
1968. BEES AND CITRUS BLOSSOMS. Amer. Bee Jour. 108: 397. 156
HEARN C. J., and REECE, P. C.
1967. POLLINATION NEEDS OF PAGE, LEE, NOVA AND ROBINSON CITRUS HYBRIDS.
Citrus lndus. 48(4): 19, 23.
______REECE, P. C., and FENTON, R.
1968. EFFECT OF POLLEN SOURCE ON FRUIT CHARACTERISTICS AND SET OF 4 CITRUS
HYBRIDS. Fla. State Hort. Soc. Proc. 81: 94-98.
______REECE, P. C., and FENTON, R.
1969. SELF-INCOMPATIBILITY AND THE EFFECTS OF DIFFERENT POLLEN SOURCES
UPON FRUIT CHARACTERISTICS OF FOUR CITRUS HYBRIDS. 1st Internatl. Citrus
Symposium Proc. 1: 183 - 187.
HILGEMAN R. H., and RODNEY, D. R.
1961 COMMERCIAL CITRUS PRODUCTION IN ARIZONA. Ariz. Agr. Expt. Sta., and
Ext. Serv. Spec. Rpt. 7, 31 pp.
KHAN, M., and CHANDHRI, M. K. H.
1964. POLLINATION STUDIES IN CITRUS SINENSIS. Punjab Fruit Jour. (Lyallpur)
1962-64: 26-27, 97-107.
KIHARA, H.
1951. TRIPLOID WATERMELONS. Amer. Soc. Hort. Sci. Proc. 58: 217-230.
KREZDORN, A. H.
1959. FACTORS AFFECTING THE UNFRUITFULNESS OF TANGELOS. Fla. Agr. Expt.
Sta. Ann. Rpt.: 228-229, 1960: 207.
______ 1965. FRUIT SETTING PROBLEMS IN CITRUS. Amer. Soc. Hort. Sci. Carribean Reg. Proc. 9(13): 85-92.
______ 1967. THE INFLUENCE OF SEEDS AND POLLEN SOURCE ON THE SIZE OF FRUIT. Fla. State Hort. Soc. Proc. 80: 37-43.
______ 1970. POLLINATION REQUIREMENTS OF CITRUS. In The Indispensable Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 211-218.
______ 1972. POLLINATION REQUIREMENTS OF CITRUS Citrus Indus. 53: 5 - 7, 28.
______and ROBINSON, F. A.
1958. UNFPUITFULNESS IN THE ORLANDO TANGELO. Fla. Hort. Soc. Proc. 71:
86 - 91.
LACARELLE, A., and MIEDZYRZECKI, C.
1937. [NEW CONTRIBUTIONS ON THE STUDY OF CLEMENTINES IN MOROCCO.] Experimentation
Fruitiere et Maraichere, Rabat, Morocco. Edition Terre Marocaine, 22 pp.
[In French.] Cited by Webber et al. (1943).
LYNCH, S. J., and MUSTARD M. J.
1955. STUDIES ON THE UNFRUITFULNESS OF MINNEOLA TANGELOS IN DADE COUNTY.
Fla. State Hort. Soc. Proc. 68: 299-301.
MCHEDLISHVILI, G. I.
1962. [POLLINATION OF CITRUS TREES BY BEES.] Pchelovodstvo 39(9): 17. [In
Russian.]
MINESSY, F. A.
1959. EFFECT OF DIFFERENT POLLINIZERS ON YIELD AND SEEDINESS IN CLEMENTINE
TANGERINE. Alexandria Jour. Agr. Res. 7: 279-287.
MIWA, T.
1951. [ON POLLINATION, FERTILIZATION PHENOMENA AND PROBLEMS CONNECTED WITH
FRUIT DROP IN THE HYUGANATSU MANDARIN.] Miyazaki Daigaku Jiho (Shizenkagaku)
Bul. Miyazaki Univ. (Nat. Sci.) 2: 2 - 67. [In Japanese, English summary,
pp. 66-67.]
MOFFETT J. O., and RODNEY, D. R.
1971a. HONEY BEE VISITS TO CITRUS FLOWERS. Ariz. Acad. Sci. 6: 254-259.
______and RODNEY, D. R.
1972b. FAIRCHILD TANGERINES NEED BOTH: HONEY BEES, POLLINATOR TREES. Prog.
Agr. in Ariz. 23(5): 6 - 7.
______and RODNEY, D. R.
1973. HONEY BEE VISITS INCREASE YIELDS OF `ORLANDO' TANGELO. Hort Science
8: 100
MOSS, G. I.
1971. EFFECT OF FRUIT ON FLOWERING IN RELATION TO BIENNIAL BEARING IN SWEET
ORANGE (CITRUS SINENSIS). Jour. Hort. Sci. 46: 177 - 184.
MOTIAL, V. S.
1964. FRUIT-SET STUDIES IN SWEET LIME. Indian Acad. Sci. Proc. Sect. B.
60(6): 371 - 379.
MUSTARD, M. J., LYNCH, S. J., and NELSON, R. O.
1957. POLLINATION AND FLORAL STUDIES OF THE MINNEOLA TANGELO. Fla. State
Hort. Soc. Proc. 69: 277 - 281, 1956.
NAURIYAL, J. P.
1952. SELF-INCOMPATIBILITY IN PUMELO (CITRUS MAXIMA MERR.). Current Sci.
[India] 21: 347.
OPPENHEIMER, C.
1935. ON CITRUS FERTILIZATION WITH SPECIAL REFERENCE TO SEEDINESS AND SEEDLESSNESS
OF THE JAFFA ORANGE. Hadar 8(10): 261-262, 265-267 (11): 291-292, 295-296.
OPPENHEIMER, H. R.
1948. EXPERIMENTS WITH UNFRUITFUL CLEMENTINE MANDARINS IN PALESTINE. Agr.
Res. Sta. Rehovoth (Israel) Bul. 48: 1-63.
RANDHAWA, G. S., NATH, N., and CHOUDHURY, S. S.
1961. FLOWERING AND POLLINATION STUDIES IN CITRUS WITH SPECIAL REFERENCE
TO LEMON (CITRUS LIMON BURM.). Indian Jour. Hort. 18: 135-147.
REECE P. C.
1945. FRUIT SET IN THE SWEET ORANGE IN RELATION TO FLOWERING HABIT. Amer.
Soc. Hort. Sci. Proc. 46: 81.
______and REGISTER, R. D.
1961. INFLUENCE OF POLLINATORS ON FRUIT SET OF ROBINSON AND OSCEOLA TANGERINE
HYBRIDS. Fla. State Hort. Soc. Proc. 74: 64-106.
REED, H. S.
1919. CERTAIN RELATIONSHIPS BETWEEN THE FLOWERS AND FRUITS OF THE LEMON.
Jour. Agr. Res. 17: 143 - 166.
REUTHER, W., BATCHELOR, L. D., and WEBBER, H. J.
1968. THE CITRUS INDUSTRY. 2 v., rev. University of California Press, Berkeley
and Los Angeles.
RICHTER, C. M.
1916. FROM THE CALIFORNIA STANDPOINT. Gleanines Bee Cult. 44: 271.
ROBINSON F. A.
1958. FACTORS AFFECTING THE UNFRUITFULNESS OF TANGELO. Fla. Agr. Expt.
Sta. Rpt. 1957-58: 102.
______and KREZDORN. A. H.
1962. POLLINATION OF THE ORLANDO TANGELO. Amer. Bee. Jour. 102: 132-133.
SOOST, R. K
1956. UNFRUITFULNESS IN THE CLEMENTINE MANDARIN. Amer. Soc. Hort. Sci.
Proc. 67: 171 - 175.
______ 1963. CITRUS POLLINATION. Calif. Citrog. 48: 447 - 452.
______ 1964. SELF-INCOMPATIBILITY IN CITRUS GRANDIS (LINN.) OSBECK. Amer. Soc. Hort. Sci. Proc. 84: 137-140.
SURR, G.
1922. GROWING ORANGE TREES IN TENTS. Calif. Citrog. 7: 103, 125.
VAN HORN, C. W., and TODD. F. E.
1954. BEES, BOUQUETS AND BETTER TANGERINES. Prog. Agr. Ariz. 6(1): 11.
VANSELL, G. H., WATKINS, W. G., and BISHOP, R. K.
1942. ORANGE NECTAR AND POLLEN IN RELATION TO BEE ACTIVITY. Jour. Econ.
Ent. 35: 321-323.
WAFA, A. K, and IBRAHIM, S. H.
1960. [EFFECT OF THE HONEYBEE AS A POLLLNATING AGENT ON THE YIELD OF ORANGE.]
Elfelaha (Jan.-Feb.), 18 pp. Cairo University, Egypt. [In Arabic. ] AA-448/63.
WEBBER, H. J.
1930. INFLUENCE OF POLLINATION ON SET OF FRUIT IN CITRUS. Calif. Citrog.
15(7): 304, 322-323.
WEBBER, J., BATCHELOR, L.D., and collaborators.
1943. THE CITRUS INDUSTRY. Ed. l, 2 v. University of California Press,
Berkeley and Los Angeles.
WRIGHT, N.
1937. POLLINATION AND THE SEEDINESS OF MARSH GRAPEFRUIT. Agr. Soc. Trinidad
and Tobago, Proc. 51-60.
ZACHARIA, D. B.
1951. FLOWERING AND FRUIT SETTING OF THE SHAMOUTI ORANGE. Palestine Jour.
Bot. (Rehovoth) 8: 84-94.
ZAVRASHVILI, R. M.
1964. [BEES AND THE CITRUS CROP.] Pchelovodstvo 84(8): 19. [In Russian.
] AA-347/66.
______ 1967a. [IMPORTANCE OF NECTAR IN FLOWERS OF MANDARIN ORANGE UNSHIU.] Akad. Nauk. Gruz. SSR Soobshch. [Tiflis] 45(1): 205-212. [In Georgian, Russian summary.] AA-789/70.
______ 1967b. [INFLUENCE OF BEES ON THE YIELD OF CITRUS TREES ON THE COMMERCIAL PLANTATIONS OF GEORGIA.] In 21st Internatl. Apic. Cong. Proc., College Park, Md. Aug., pp. 450-451. [In Russian, EngIish summary.]
ZHGENTI, S. K.
1956. [POLLINATION OF THE JAPANESE PERSIMMON AND MANDARIN ORANGE.] In Krishchunas,
I.V. and Gubin, A. F., [Pollination Of Agricultural Plants.] pp. 193-199.
MoskVa, Goz. Izd-vo. Sel-khoz. Lit-ry. [In Russian.]
COCONUT
Cocos nucifera L., family Palmaceae
The coconut is found along tropical seashores around the world, and in some areas it is cultivated far inland. It provides man with food, drink, fuel oil, and many other products.
There are about 8.5 million acres of coconuts, of which 2.45 million are in the Philippines, 1.59 in India, 1.5 in Indonesia, 1.07 in Ceylon, 0.6 in Malaya, 0.6 in other south sea islands, and 0.7 million acres elsewhere (Minon and Pandalai 1958, Woodruff 1970). Apacible (1968) indicated that there were 4.5 million acres in 1967 as against 2.4 million in 1958. Apacible (1968) also stated that coconut production has increased at the rate of 5 percent a year for the last 50 years. In the United States, coconuts are found in Florida, Hawaii, and Puerto Rico. The largest coconut plantation in the United States consists of about 30,000 trees in Key Biscayne, Fla. (Woodruff 1970).
Plant:
The usually leaning, branchless trunk may reach a height of 100 feet (fig. 79). However, selections of dwarf plants as low as 6 feet are now being cultivated (fig. 80). Wrigley (1969) stated, however, that dwarf coconuts are short lived and inferior in copra production. The top, head, or crown consists of 20 to 30 mature feather-shaped leaves 15 to 20 feet long and 1 to 3 feet wide, with additional developing leaves. A leaf requires 1 1/2 years to reach full size, then it will last for 2 more years. A new leaf and an inflorescence forms about once each month (Chandler 1958*). The inflorescence produces from 1 to 20, but usually about half a dozen nuts, each nut weighing up to several pounds. The nut is enclosed in a thick fibrous husk, that when removed reveals the well-known brownish fiber-coated coconut, comprising the hard shell which contains the edible meat and milk. One tree may yield 100 fruits per year, and about 90 trees per acre are used (Woodruff 1970). The plant will withstand a light frost, but is basically a tropical crop.
[gfx]
FIGURE 79. - Grove of "standard- height" coconuts
FIGURE 80. - Fruit of the dwarf coconut can be harvested from the ground.
Inflorescence:
The coconut is monoecious, having both staminate and pistillate florets on the same many-branched inflorescence, the 2- to 4-foot long spadix or fleshy panicle in the leaf axil. As many as 8,000 staminate flowers may make up most of the inflorescence, with 1 to 30 pistillate flowers near the base (Aldaba 1921, Ochse et al. 1961*).
Flowering of larger plants begins at 5 to 8 years of age (Chandler 1958*), but on dwarf plants it begins in the third or fourth year (Woodruff 1970). Flowering occurs on the plant throughout the year.
The individual staminate flower described by Juliano and Quisumbing (1931), which is open only 1 day primarily between 6 a.m. and noon, and is only a few millimeters in size, has three cream-colored petals and six stamens. The stamens shed large amounts of pollen, some of it before the flower is open and altogether as much as 6.1 g per inflorescence (Whitehead 1963). There is also an abortive pistil whose stigmatic area is divided into three parts each bearing an active nectar gland. The much larger 1/2- to 1-inch oval pistillate flower has three stigmas on a short style and three ovules, two of which always abort. Sholdt and Mitchell (1967) mentioned that honey bees collect nectar from "the nectary orifices and stigmatic region." Menon and Pandalai ( 1958) stated that nectar secretion is most profuse between the stigma and the base of the ovary. Whitehead (1965) stated that considerable quantities of nectar were produced from three nectaries in the pistillate flower.
Patel (1938) stated that when the stigma is receptive a clear sweet fluid is profusely secreted in four places, at the base of the stigma and at three pores on the pericarp toward the top of the ovary.
Not all of the pistillate flowers mature fruit. Lever (1961) stated that there is a normal shed, comparable to the "June drop" of fruit trees, and also a shedding caused by harmful insects.
Usually only one spadix at a time opens on a plant. Furthermore, the staminate flowers frequently complete their flowering 3 to 6 days before the pistillate flowers open; therefore, crossing between flowers on a spadix or even a plant is unlikely, although the flowering periods tend to overlap in the newer dwarf selections (Woodruff 1970, Ochse et al. 1961*).
The period of staminate flowering on a spadix may extend from 18 to 38 days; the pistillate phase, from 2 to 12 days; and the interval between spadices, from 10 to 57 days, averaging 18 days (Kidavu and Nambiyar 1925). Overlapping of phases on a plant ranges from "seldom" to 20 percent of the time (Sholdt and Mitchell 1967, Ochse et al. 1961*). A pistillate flower may, therefore, receive pollen from staminate flowers of the same spadix or from a later spadix on the same plant. However, if there is no overlapping of spadices, the pollen must come from another plant (Chapman 1964*). Free (1970*) stated that staminate flowers of tall plants begin opening about a month earlier than the pistillate flowers, but pistillate flowers of dwarfs begin opening about a week after the staminate flowers.
The flowers are visited by honey bees and many other insects attracted by the nectar and pollen (Sholdt 1966). Nectar production, in terms of honey stored by a colony of honey bees, is not great (Pellett 1947*, Sholdt and Mitchell 1967), and the amount stored by a colony varies with the time of the year (Wolfenbarger 1970). Whitehead (1965) stated that nectar is produced in considerable quantity from the three nectaries in the female flower. During one 30-minute period, he recorded 103 visits by bees collecting nectar from one flower, and after each visit the nectar was rapidly replaced. Ochse et al. (1961 *) also referred to the large quantity of nectar that exudes from the flower.
Pollination Requirements:
Pollen must move from staminate to the pistillate flowers if coconuts are produced. Sholdt and Mitchell (1967) showed that the source of the pollen was not important from the standpoint of fruit set for they obtained good set whether the pollen came from the same plant or from another plant.
The pollen can come from the same inflorescence, another inflorescence on the same plant, or another plant. The pollen is most effective the first day the stigma is exposed, and, theoretically, only one pollen grain per pistillate flower is sufficient to fertilize the one ovule. Aldaba (1921) calculated that one inflorescence produced 272 million pollen grains.
Whitehead (1965) studied the flowering of coconuts in Jamaica and reported all variations in the pollination requirements. He believed that to conclude that the plants are either selfed or crossed was unsafe, but the extent of crossing depended upon the relative importance of wind, insects, proximity of other trees, efficiency of selfing, presence of nectaries on male and female flowers, and the frequency of insect visitation, particularly bee visits. Copeland (1931) stated that the succession of clusters is normally so timed that pollen must come from another plant, which insures cross-pollination. However, Tammes and Whitehead (1969) stated that this applies only to tall palms. In the dwarf palms, with the exception of 'Niu Leka', the female flowers are receptive before the male flowers cease; therefore, pollen may come from the same inflorescence. Wrigley (1969) stated that self-fertilization between flower heads on a dwarf coconut plant is normal.
Pollinators:
There has been considerable question about what agents are involved in transferring the pollen from the staminate to the pistillate flowers, a transfer that is required regardless of the flowering habits of the plant. Self-pollination is frequently mentioned, but this only refers to the source of the pollen, whether from the same inflorescence on which the stigma is located or another inflorescence. The flower cannot fertilize itself. Wind, birds, mites, and insects, including ants, bees, earwigs, flies, and wasps have been mentioned as cross-pollinating agents of the coconut (Davis 1954, Kidavu and Nambiyar 1925). The effectiveness of each doubtless is associated with local situations.
Furtado (1924) considered birds of doubtful value. Sampson (1923), Tammes (1937), and Whitehead (1965) stated that pollination was by insects. Huggins (1928) considered honey bees and various other hymenoptera important but ants unimportant. Hunger (1920), Patel (1938), and Ochse et al. (1961*) considered both insects and wind important. Sholdt (1966) collected 51 species of insects on the coconut inflorescences in Hawaii, but those found most often were ants, bees, earwigs, flies, and wasps. Sholdt and Mitchell (1967) considered both wind and insects important, with the honey bees the most important insects of all.
The recognition of the value of honey bees on coconuts is not recent. An anonymous (1916) author indicated that bees played an important part in the pollination of coconuts in Fiji. The inflorescences freely visited by bees when in flower gave a high yield of nuts, and the placement of colonies into coconut plantations was suggested. Sampson (1923) stated that on estates where bees were kept in large numbers for other reasons the yield of nuts was remarkably high. Huggins (1928) felt that the lack of adequate cross-pollination frequently depressed the yield of nuts. Haldane (1958) suggested that honey bees might be used to increase yields, but Tammes and Whitehead (1969) differed with this opinion. They stated: "There is, however, sufficient natural pollination by wild bees, as appears from trials, so the keeping of honey bees has no influence on the fertility of palms." They did not indicate what population of wild bees was adequate.
Pollination Recommendations and Practices:
Except for the above references, the use of bees has not been recommended in the pollination of coconuts. Sholdt and Mitchell (1967) suggested that, "it would appear advantageous to bring in colonies of bees in an effort to increase yields." They gave no indication of the number of colonies per acre or bees per inflorescence that might be adequate.
The evidence indicates that the presence of honey bees in adequate numbers could increase production. There is no indication as to what might constitute an adequate population on the flowers. One might ponder over the well-known relatively low production of coconuts per acre in the Philippines, where the bee population is quite low (Morse and Laigo 1969) as compared to the other areas of the world where coconuts are produced. The concentration of honey bees, even if it meant the development of a strong apicultural industry in the Philippines, might considerably improve the coconut industry.
LITERATURE CITED:
ANONYMOUS.
1916. BEES AND POLLINATION. Planters' Chron., Bangalore 9(46): 572.
ALDABA, V. C.
1921. THE POLLINATION OF COCONUT. Philippine Agr. 10(5): 195 - 208.
APACIBLE, A. R.
1968. THE PHILIPPINE COCONUT. Sugar News [Manila] 44(10): 599 - 606.
COPELAND, E. B.
1931. THE COCONUT. Ed. 3, 225 pp. Macmillan, London.
DAVIS. J. A.
1954. MYSTERIES OF CROSS-POLLINATION. Indian Cent. Coconut Com. Ernakulam,
Bul. 7: 226-227.
FURTADO, C.X.
1924. A STUDY OF THE COCONUT FLOWER AND ITS RELATION TO FRUIT PRODUCTION.
Gard. Bul. [Singapore] 3(7-8): 261-273.
HALDANE, J. B. S.
1958. SOME SUGGESTIONS FOR COCONUT RESEARCH. Indian Coconut Jour. 12: 1-9.
HUGGINS. H. D.
1928. POLLINATION AND CROP PRODUCTION (CONCLUDED). Agr. Jour. Br. Guiana
1: 90-94, 164-169.
HUNGER, F. W. T.
1920. COCOS NUCIFERA 518 pp. Scheltema and Holkema's Boekhandel, Amsterdam.
JULIANO, J B., and QUISUMBING, E.
1931. MORPHOLOGY OF THE MALE FLOWER OF COCOS NUCIFERA LINN. Philippine
Jour. Sci. 45: 449 - 458.
KIDAVU, M. G., and NAMBIYAR, E. K.
1925. POLLINATION IN COCONUT. Madras Dept. Agr. Yearbook 1925: 43 - 49.
LEVER, R. J. A. W.
1961. IMMATURE NUTFALL OF COCONUTS; THE WAR OF THE ANTS. World Crops 13(2):
60 - 62.
MENON, K. P. V., and PANDALAI, K. M.
1958. THE COCONUT PALM - A MONOGRAPH. Indian Cent. Coconut Com., Ernakulam,
384 pp.
MORSE, R. A., and LAIGO, E. M.
1969. THE POTENTIAL AND PROBLEMS OF BEEKEEPING IN THE PHILIPPINES. Bee
World 50(1): 9 - 14.
PATEL, J.S.
1938. THE COCONUT - A MONOGRAPH. Madras: Government Press. 262 pp.
SAMPSON, H. C.
1923. THE COCONUT PALM. 262 pp. J. Bale, Sons, and Danielson, Ltd., London.
SCHOLDT, L. L.
1966. INSECTS ASSOCIATED WITH THE FLOWERS OF THE COCONUT PALM, COCOS NUCIFERA
L. IN HAWAII. Hawaii. Ent. Soc. Proc. 19(2): 293 - 296.
______and MTTCHELL, W. A.
1967. THE POLLINATION OF COCOS NUCIFERA L. IN HAWAII. Trop. Agr. [Trinidad]
44(2): 133 - 142.
TAMMES, P. M. L.
1937. ON THE INFLORESCENCE AND POLLINATION OF THE COCONUT. Landbouw, Buitenz.
13: 74-89.
______and WHITEHEAD, R. A.
1969. COCONUT. In Ferwerda, E. P., and Wit, F., eds., Outlines of Perennial
Crop Breeding in the Tropics, pp. 175-188. H. Veenman and Zonen, N. V.
Wageningen, The Netherlands.
WHITEHEAD, R. A.
1963. THE PROCESSING OF COCONUT POLLEN. Euphytica 12: 167-177.
______ 1965. THE FLOWERING OF COCOS NUCIFERA L. IN JAMAICA. Trop. Agr. [Trinidad] 42(1): 19-29.
WOLFENBARGER, D. O.
1970. NOTES ON POLLEN DISPERSERS AND POLLINATION OF TROPICAL PLANTS AND
ON ATTRACTANCY OF ALUMINUM MULCHED PLANTS FOR HONEY BEES. In The Indispensable
Pollinators, Ark. Agr. Ext. Serv. Misc. Pub. 127, pp. 150 - 156.
WOODRUFF, J. G.
1970. COCONUTS: PRODUCTION, PROCESSING, PRODUCTS. 241 pp. A.V.I. Publishing
Co., Inc., Westport, Conn.
WRIGLEY, G.
1969. TROPICAL AGRICULTURE. 376 pp. Frederick A. Praeger, N. Y. and Washington.
CRABAPPLE
Malus spp., family Rosaceae
A crabapple is basically a small apple. Hedrick (1938*) concluded that the most common crabapples are hybrids of the common apple and the Siberian crabapple (Malus sylvestris Mill. x M. baccata (L.) Borkh. He listed and described 23 cultivars, and Bailey (1949*) listed eight species. Jefferson (1966) stated that there were more than 200 species and cultivars in the National Arboretum. Wyman (1965) stated that there were 250 cultivars in the Arnold Arboretum. The USDA (1967) listed 19 popular cultivars including six hybrids. Van Dersal (1938) listed 10 species of crabapples of value in erosion control and of value to wildlife.
The crabapple fruit is not an important crop. The plants are grown primarily as ornamentals, although a few growers produce the fruit commercially. The fruit is preserved or pickled or it is used in making jellies. No production data are available on the quantity of fruit that is used commercially.
Plant:
Most crabapples are grown for their ornamental value, and cultivars are chosen because of their beautiful flowers, foliage, or fruit. The general appearance is similar to a small bearing apple tree. Culture is also similar to the culture of apple trees.
Inflorescence:
The flower is similar to that of the apple. Nectar secretion and pollen production has not been studied in detail. Bees freely visit the flowers, for both nectar and pollen (fig. 98).
Pollination Requirements:
Like the apple, the crabapple appears to require cross-pollination between cultivars by insects. Bradford and Bradford (1949) and Crandall (1928) concluded that all native crabapples are self-sterile. Pammell (1920) stated that self-pollination is impossible and that pollinating insects are absolutely needed. Cook (1891) covered 200 blossoms, which set no fruit, the same number not covered set three fruits. Jefferson (1968) discussed a new crabapple cultivar called "Fugi" whose anthers are generally sterile.
Pollinators:
Little is known about which insect pollinators are of most value to crabapples. Pammel and King (p. 239, 1930*) noted that the often cultivated Iowa wild crabapple was freely visited by honey bees. Considering that the only difference between the crabapple and the apple is fruit size, the deduction would appear reasonable that the most effective pollinator of apples, the honey bee, should be equally effective on the crabapple. Although the evidence is meager, it indicates that pollinating insects are essential for crabapple fruit production.
Pollination Recommendations and Practices:
Individual or dooryard plantings usually are likely to receive ample insect pollination. If commercial fruit production is anticipated, and crabapple trees are grown along with other fruit trees in commercial orchards, there is a likelihood that additional pollinating insects will be required. If the grower is providing bees for his other fruits, then he should provide enough for crabapples also.
[gfx]
FIGURE 98. - Longitudinal section of 'Transcendent' crabapple flower, x
6.
LITERATURE CITED:
BRADFORD, E. C., and BRADFORD, R. H.
1949. POLLINATION OF NATIVE CRAB APPLES OF THE NORTHEASTERN UNITED STATES.
Amer. Soc. Hort. Sci. Proc. 54: 133-136.
COOK. A. J.
1891. BEES AS FERTILIZERS. Mich. State Bd. Agr. Ann. Rpt., p. 147.
CRANDALL, C. S.
1928. NATIVE CRABS: THEIR BEHAVIOR IN BREEDING. Ill. Agr. Expt. Sta. Bul.
275, pp. 535 - 560.
DERSAL, W. R. VAN.
1938. NATIVE WOODY PLANTS OF THE U.S., THEIR EROSION-CONTROL AND WILDLIFE
VALUES. U.S. Dept. Agr. Misc. Pub. 303, 362 pp.
JEFFERSON, R. M.
1966. CRABAPPLES AT THE NATIONAL ARBORETUM. Amer. Hort. Mag. 45: 231-236.
____ 1968. FUJI - A NEW CRABAPPLE - AND OTHER DOUBLES. Amer. Hort. Mag. 47: 22 - 25.
PAMMEL, L. H.
1919. A FEW HONEY PLANTS OF THE ROSE FAMILY. In lowa State Apiarist Rpt.
1919, pp. 56-69.
UNITED STATES DEPARTMENT OF AGRICULTURE.
1967. GROWING FLOWERING CRABAPPLES. U.S. Dept. Agr. Home and Gard. Bul.
135, 8 pp. WYMAN, D. 1965. TREES FOR AMERICAN GARDENS. 502 pp. The Macmillan
Co., New York.
DATE
Phoenix dactylifera L., family Palmaceae
Dates are grown on about 4,600 acres in southern California and about 300 acres in southwestern Arizona. The value of the crop is about $4 million (Henderson and Swedberg 1970, Nixon 1959). The plants prosper in hot, arid climate with ample subsurface moisture.
Plant:
The date palm may reach 50 feet in height but has only a single bud or growing point, the leaf-crowned tip. The leaf may be 10 to 20 feet long, and it has a normal lifespan of 3 to 7 years. Leaves do not shed but are removed under cultivation after drooping in death. Palms are grown entirely under cultivation and irrigation. The trees are usually spaced 60 feet apart in the grove.
Inflorescence:
The date is normally dioecious, although occasional trees may be bisexual at times. The 2- to 4-foot staminate inflo rescence is a branching ax illary sp ad ix with numerous racemes and hundreds of flowers, each flower having three petals and usually six stamens, all in a protecting sheath or spathe (Nixon 1959). The less numerous pistillate flowers have three petals and also three ovaries but only one ovary develops into a seed. They occur on a slightly smaller branching spadix in a protecting spathe, that opens upon maturity of the flowers.
Pollen is produced in abundance on the staminate trees and is eagerly sought after by bees. If nectar is produced by date flowers it is not mentioned in the literature.
Pollination Requirements:
Pollen must be transferred from staminate trees to pistillate ones if fruit is produced. Leding (1928) showed that delay in placement of pollen on pistillate flowers reduced production to 89 percent by the second day, to 70 percent by the fourth day, to 54 percent by the sixth day, to 46 percent by the eighth day, and to 23 percent by the eleventh day. Nixon (1928) showed that the source of pollen affected the date of ripening (as much as 10 days), the shape of seed, and the size of the seed. Later, he (1935a, b, 1956) showed that pollen not only affects the seed but also the fruit pulp, which he termed "metaxenia." Nixon (1959) stated that pollination of 50 to 80 percent of the pistillate flowers is sufficient for a full crop.
Pollinators:
If sufficient staminate or "male" trees are near the pistillate or "female" ones, wind and sometimes insects will transfer sufficient pollen for adequate fruit set (Knuth 1908*, p. 487). However, the grower keeps male trees to a minimum inasmuch as they yield no fruit and he distributes the pollen manually. Meeuse ( 1961 *) stated that man was hand-pollinating dates before 800 B.C.; it is the oldest known means of controlled pollination of crops.
Pollination Recommendations and Practices:
For best set of fruit, the most common method of pollination is to cut strands of the staminate flowers from a freshly opened inflorescence and invert two or three pieces, 3 to 6 inches long, between the strands of pistillate flowers during the first three days after opening. Twine should be tied around the cluster to hold the flowers in place during the pollination process. Also the dried pollen taken from mature anthers may be dusted onto a 1- to 2-inch ball of cotton, which is then tied into the pistillate strands, or the pollen may be placed into a clean insecticide dust gun and dusted into the flowers. Aircraft have also been tried for distributing pollen (Brown 1966), but such use is economically questionable.
LITERATURE CITED:
BROWN, G. K.
1966. POLLINATION RESEARCH DISCUSSIONS. Date Growers Inst. Rpt. 43: 29.
HENDERSON, W. W., and SWEDBERG, J. H.
1970. CALIFORNIA FRUIT AND NUT STATISTICS 1968-69. Calif. Crop and Livestock
Rptg. Serv., 11 pp.
LEDING, A. R.
1928. DETERMINATION OF LENGTH OF TIME DURING WHICH THE FLOWERS OF THE DATE
PALM REMAIN RECEPTIVE TO FERTILIZATION. Jour. Agr. Res. 36: 129-134.
____ 1928. THE DIRECT EFFECT OF POLLEN ON THE FRUIT OF THE DATE PALM. Jour. Agr. Res. 36: 97 - 128.
____ 1935a. METAXENIA IN DATES. Amer. Soc. Hort. Sci. Proc. 32: 221 - 226.
____ 1935b. METAXENIA AND INTERSPECIFIC POLLINATIONS IN PHOENIX. Amer. Soc. Hort. Sci. Proc. 33: 21 - 26.
____ 1956. EFFECT OF METAXENIA AND FRUIT THINNING ON SIZE AND CHECKING OF DEGLET NOOR DATES. Amer. Soc. Hort. Sci. Proc. 67: 258-264.
____ 1959. GROWING DATES IN THE UNITED STATES. U.S. Dept. Agr., Agr. Inform. Bul. 207, 50 pp.
FIG
Ficus carica L., family Moraceae
The common or commercial fig is grown primarily in California, although dooryard and small commercial plantings occur in many other States. About 54,000 tons of the fruit, valued at almost $5 million, were produced on about 18,000 acres in 1969. About one-fourth of this fruit was canned and three-fourths dried, with a small amount consumed fresh.
Plant:
The cultivated fig is a small, barely deciduous, soft-wooded, many branched shrub or tree 6 to 20 feet high, with long-stemmed, thick, three- to five-lobed rough leaves 4 to 8 inches long. The fruit, technically referred to as a syconium, is a sweet, round or pear-shaped, infolded fleshy collection of hundreds of tiny inflorescences, each only a few millimeters long. The whole fruit is 1 to 2 l/2 inches long, with a tiny opening or "eye" on the outer end. The primary cultivars grown in California include: 'Calimyrna', 8,523 acres; 'White Adriatic', 3,645 acres; 'Kadota', 2,410 acres; 'Million', 1,753 acres, and 'Conadria', 636 acres.
Inflorescence:
Hundreds of tiny florets line the inner wall of the fleshy hollow receptacle. There are four different types of flowers; pistillate, staminate, gall flowers, and mule flowers (Eisen 1897, 1901). The influence of these different types of flowers on the development of the fruit depends on the general type of fig plant. The mule flowers produce no pollen, nor do they have receptive pistils, yet the fruit develops into an edible fig. The Smyrna type fig has receptive pistils that must be pollinated, but it has no staminate flowers; therefore, pollen must come from a donor flower - in this case, the inedible caprifig (goat fig), which has pollen-producing staminate flowers near its opening and pistillate gall flowers toward its base.
Each Smyrna fig flower has a single ovary with one ovule, which, if pollinated, develops into a nutlet embedded in the fleshy wall. The flower has four microscopic petals. The style of this pistillate flower is much longer than that of a gall flower. If pollination does not occur, the fleshy part does not develop and the fruit wilts and sheds. If pollination occurs at the time the fruit develops, two or three crops per year are produced. The first crop is referred to as breba figs, the second as profichi figs, and the third as mammoni (Condit 1926, 1941).
Pollination Requirements:
From the pollination standpoint, the figs grown commercially are basically of three types. The common type (for example, 'Mission' cv.) develops its fruit parthenocarpically. The Smyrna type (for example, 'Calimyrna' cv.) must be pollinated with pollen from the inedible caprifig. The San Pedro type produces its first crop of the season parthenocarpically, but its second crop develops only if its flowers are pollinated (Eisen 1897, Condit 1932, 1938). The 'Kadota' cv. is a common type that will produce fruit parthenocarpically, but if pollinated its seeds will develop, a feature that is desired if the figs are to be dried, but undesired if they are to be preserved (Condit 1927).
Pollinators:
Smyrna (and second crop San Pedro) figs are pollinated exclusively by the hymenopterous fig wasp (Blastophaga psenes (L.)), which overwinters in the caprifig fruit (fig. 111). The use of this wasp is the oldest form of man-manipulated insect pollination, a system referred to as caprification. With the exception of date pollination (see "Dates"), this is the oldest form of controlled pollination in plants (Condit and Enderud 1956). According to Betts (1940) the part these insects play in fertilizing the fig was known in 1782, just 11 years before the noted Sprengel published his treatise on insect pollination. This relationship was later challenged and "proved a myth" by the Italian government (Reasoner 1891). In 1887, when the astute Gustav Eisen announced in Fresno, Calif., the necessity of importing these wasps, he was "hooted down and some of the mob whistled" (Condit and Swingle 1947), but the need for these insects is now an undisputed fact.
It was common knowledge that Turkish fig growers since time immemorial had tied a few caprifigs on a string at a certain time of the year and hung them in their fig groves to assure a crop (Condit 1920). When Smyrna figs were brought to California, however, they failed to produce; and when the wasps were brought over and released, they failed to winter over. After 20 years of research, sometimes including intrigue, astute observation, patience, and diplomacy, caprifig plants infested with these wasps were successfully established in California and satisfactory pollination and fruit set was achieved (Eisen 1891, Howard 1900). Then, however, a second problem arose. Growers had difficulty in obtaining Caprifig fruit infested with wasps at the desired time, and in disgust many began the destruction of their orchards. To assist them, the USDA began a program of releasing such figs to growers by the box for pollination purposes (Rixford 1918).
The systematic distribution of the infested caprifigs tended to stabilize the fig-growing industry, but after a time the growers found that the wasps were the cause of a rot condition in the figs, called endosepsis. To prevent the damage by this contamination, the rearing of the wasps in the laboratory was developed, and wasps could be induced with proper heat control to emerge at desired times into sterile containers where they could live for a couple of weeks (Smith and Hansen 1927, Metcalf and Flint 1962). Now, when the endosepsis problem arises, the adult wasps are laboratory reared and delivered to growers at specified times in sterile containers (Bishop 1952). Most growers, however, continue to maintain their own source of caprifigs and two or three times during the pollination period suspend, a perforated bag or wire basket in the orchard, a few of the caprifigs with wasps ready to emerge.
The wasps overwinter in the immature stage in the gall flowers of the caprifig. The wingless and practically blind male wasp is the first to emerge as an adult. He crawls about within the caprifig, finds a gall flower containing a female still in her cocoon, gnaws a hole through the top of the cocoon then another hole through the side, inserts his abdomen, and fertilizes the female (Sisson 1970). The males lives only about a day, does not leave the fruit in which it emerged and consumes no food. The female emerges from her cocoon shortly after copulation and immediately leaves the fruit.
As she passes the pollen-laden male flowers near the fig opening, her moist body becomes coated with pollen. She also has the ability to carry 2,000 to 3,000 pollen grains in her corbiculae (Ramirez 1970). She then begins a search for other figs in which she can oviposit. If she finds a caprifig, she enters the small opening, inserts her ovipositor into the short style of a gall flower, and deposits an egg near the ovary.
If she enters a Smyrna fig, she searches about for short-styled gall flowers, but finds only the long-styled ones in which she is unable to oviposit. In her search, she accidentally leaves pollen on the stigmas and fertilization results by the "mess and soil" principle (Faegri and van der Pijl 1966*) rather than the more precise method of pollination caused by bees. In the caprifig, she finds gall flowers and deposits 200 to 300 eggs, then she dies. If she emerges in a Smyrna fig grove, she searches about unsuccessfully for gall flowers, cross-pollinating the flowers in her attempts until she dies of exhaustion.
The symbiotic relationship of the fig and the wasp, each dependent on the other (Ramirez 1969) similar to the yucca moth and the yucca plant (Riley 1878) is a strange and difficult to explain phenomenon in the plant- insect relationship.
[gfx] FIGURE 111. - Fig wasp greatly enlarged. A, adult female; B, female still in gall; C, and D, males.
Pollination Recommendations and Practices:
The number of wasps released in Smyrna fig groves depends upon the size of the tree. Simmons and Fisher (1947) recommended one caprifig (yielding 200 to 3001900 wasps) per 18 ft2 of fig-bearing tree surface, (about five figs for a tree 10 feet in diameter) for highest yield of 'Calimyrna' figs. Because the wasps tend to remain mostly in the tree where they emerge, the infested fruit is placed in about every other tree. An estimated three to five wasps are needed for each fig harvested. The female usually looses her wings struggling to enter the fig opening, and they remain stuck among the opening scales. A good indication that pollination is adequate in the orchard is the presence of these tiny wings, protruding like a ring of feathers from this hole in the fig.
LITERATURE CITED:
[ BETTS, A. D.]
1940. [F. CAVOLINI, IN 1782, DISCOVERED THE PART INSECTS PLAY IN FERTILIZING
THE FIG]. Bee World 21: 12.
BISHOPP, F. C.
1952. INSECT FRIENDS OF MAN. U.S. Dept. Agr. Yearbook 1952: 79-87.
CONDIT, 1. J.
1920. CAPRIFIGS AND CAPRIFICATION. Calif. Agr. Expt. Sta. Bul. 319, pp.341
- 375.
______ 1926. FRUIT-BUD AND FLOWER DEVELOPMENT IN FICUS CARICA. Amer. Soc. Hort. Sci. Proc. 259-263.
______ 1927. THE KADOTA FIG. Calif. Agr. Expt. Sta. Bul. 436,42 pp.
______ 1932. THE STRUCTURE AND DEVELOPMENT OF FLOWERS IN FICUS CARICA L. Hilgardia 6(14): 443-481.
______ 1938. PARTHENOCARPY IN THE FIG. Amer. Soc. Hort. Sci. Proc. 36: 401-404.
______ 1941. FIG CHARACTERISTICS USEFUL IN THE IDENTIFICATION OF VARIETIES. Hilgardia 14(1): 1 - 68.
______and ENDERUD, J.
1956. A BIBLIOGRAPHY OF THE FIG. Hilgardia 25: 1-663.
______and SWINGLE, W. T.
1947. THE FIG. 222 pp. Chronica Botanica Co., Waltham, Mass.
EISEN, G.
1891. THE FIRST INTRODUCTION OF BLASTOPHAGA PSENES INTO CALIFORNIA. Insect
Life 4: 128 - 129.
_______ 1897. FIG CULTURE: EDIBLE FIGS, THEIR CULTURE AND CURING. U.S. Dept. Agr. Div. Pomol. Bu1.5,31 pp.
_______ 1901. THE FIG; ITS HISTORY, CULTURE AND CURING. U.S. Dept. Agr. Div. Pomol. Bul. 9, 317 pp.
HOWARD, L. O.
1900. SMYRNA FIG CULTURE IN THE U.S. U.S. Dept. Agr. Yearbook 1900: 79
- 106.
METCALF, C. L., and FLINT, W. P.
1962. DESTRUCTIVE AND USEFUL INSECTS, THEIR HABITS AND CONTROL. Ed. 4,1087
pp. McGraw-Hill Book Co., Inc. New York and London.
RAMIREZ, B. W.
1969. FIG WASPS: MECHANISM OF POLLEN TRANSFER. Science 163(3867): 580 -
581.
______ 1970. HOST SPECIFICITY OF FIG WASPS (AGAONIDAE). Evolution 24: 680 - 691.
REASONER, P. W.
1891. THE CONDITION OF TROPICAL AND SEMI-TROPICAL FRUITS. U.S. Dept. Agr.
Div. Pomol. Bul. 1,149 pp.
RILEY, C. V.
1878. ON A NEW GENUS IN THE LEPIDOPTEROUS FAMILY TINEIDAE, WITH REMARKS
ON THE FERTILIZATION OF YUCCA. Acad. Sci. St. Louis, Trans. 3: 55 - 69.
RIXFORD, G. P.
1918. SMYRNA FIG CULTURE. U.S. Dept. Agr. Bul. 732,43 pp.
SIMMONS, P. and FISHER, C. K.
1947. CAPRIFICATION OF CALIMYRNA FIGS. SUMMARY OF THREE YEARÕS RESEARCH.
Calif. Dept. Agr. Bul. 36: 115-121.
SISSON, R. F.
1970. THE WASP THAT PLAYS CUPID TO A FIG. Natl. Geog. 138(5): 690-697.
SMITH R. E., and HANSEN, H. N.
1927. THE IMPROVEMENT OF QUALITY IN FIGS. Calif. Agr. Expt. Sta. Cir. 311,23
pp.
LITCHI OR LYCHEE
Litchi chinensis Sonn., family Sapindaceae
The litchi, or lychee, is grown for its agreeable sweet-acid tasting, white fleshy, juicy, translucent aril, or pulpy covering of its seed, which may be eaten fresh, canned in sirup, or dried to produce "litchi nuts."
The litchi was introduced into Florida in the 1880's but remained only a novelty until 1940 when an association of litchi growers was formed and some 250 to 300 acres were cultivated (Palmer 1956). Less than half that acreage exists now, due to urbanization and the occasional freezing weather that kills the plants. A few trees are grown in California.
Plant:
The plant is a dense, polygamous, oval evergreen tree, which grows to 30 feet high. It is widely scattered throughout the tropics but does well only at higher altitudes. It is propagated vegetatively, 20 to 50 trees per acre. It will grow about anywhere citrus will grow, but young plants are extremely sensitive to cold and require cold protection. The plants will produce as much as 10,000 pounds of fruit per acre. The fruit must ripen on the tree, then is harvested over a 6-week period. The shelf life of the fresh fruit is only 10 to 14 days (Palmer 19S6).
The round fruit, about the size of a large strawberry, is pendant in a loose cluster or panicle of several dozen fruits (Cobin 1952) (fig. 126). The leathery skin is covered with sharp-tipped tubercles and is usually red when ripe. The seeds are dark brown (Groff 1921).
The self-compatible 'Brewster' cv. comprises the bulk of the trees in Florida, but it is noted for being a light and irregular bearer. 'Mauritius' is a new and promising cultivar (Young 1966, Knight et al. 1968, Campbell and Malo 1968) but is not resistant to anthracnose.
The lychee tree lives for centuries. Banta (1952) reported that two trees in China are said to be 1,200 years old, the largest being 10.5 feet in diameter. Lychee thrives in the Florida citrus belt, but California's climate is generally too dry. Banta (1952) stated that a 4-year-old tree will produce 2 to 3 pounds of fruit, and a 12-year-old tree yielded 308 pounds.
[gfx] FIGURE 126. - Litchi tree with mature fruit.
Inflorescence:
The small (2 to 3 mm), greenish-yellow flowers are in terminal clusters, sometimes a foot long. They are present from mid-February through March. They have no petals, about eight stamens, a two-lobed stigma, an ovary on a short stalk, and one ovule in each of its two or three sections (Bailey 1949*). Grove (1951) stated that there are staminate and pistillate flowers. Butcher (1957a), however distinguished three types of flowers: Male or staminate flowers with no functional ovary, which appear first; female or functionally pistillate flowers with anthers that do not dehisce; and imperfect hermaphrodite flowers. Pollen produced on the last type is most viable (Mustard et al. 1953). In some years, certain cultivars produce only male flowers, and as a result no fruit sets. The reason for this is unknown but should be explored.
A nectary occurs on every flower as a large fleshy crenulate gland within a cup-shaped calyx and to which the stamens and pistils are inserted. Nectar is secreted only in the morning. The nectar is highly attractive to honey bees and flies. Lychee pollen seemed unattractive to wild bees in Florida (Butcher 1957a, Nakato 1956). When lychee' trees are plentiful, honey bees gather immense stores of high-quality honey (Groff 1943).
Khan (1929) cited two examples to show the floral variation on an individual panicle. On one plant, the panicle began flowering and for 10 days bore only male flowers. The next 11 days, the flowers were mixed (male or female). The remaining 6 days, only male flowers opened. Another panicle had male flowers for 13 days, mixed flowers for 2 days, all female for 2 days, mixed again for 3 days, and all male for the last 7 days. From 20 to 50 percent of all the flowers were functionally female.
The flowers open throughout the day but mostly before 6 a.m. Anther dehiscence also occurs more or less throughout the day and night, but it reaches its maximum around 10 a.m. Ultimate fruit set ranges from 2.8 to 8.2 fruits per panicle.
Pollination Requirements:
Mustard et al. ( 1953) concluded that shedding of fruit may be due to fertilization failure and embryo abortion. Chaturvedi (1965) reported 43 percent fertilized flowers on open pollinated branches, zero percent on branches bagged with muslin, and 15.5 percent on branches bagged under mosquito cloth. Das and Choudhury (1958) also reported no set of fruit on bagged panicles.
Pandey and Yadava (1970) reported that only 0.03 to 0.10 percent of flowers caged to exclude insects set fruit, whereas 0.7 to 11.2 percent (100 times as many) flowers exposed to insect pollination set fruit. Butcher (1957a, b) also reported that no fruit set on a tree caged to exclude insect pollination, proving that lychee plants require insect pollination. These tests supported Campbell and Malo (1968) by showing that the lychee is self-fruitful and that interplanting of compatible cultivars is unnecessary, but the pollen must be transported from anthers to stigmas for fruit set.
Pollinators:
Butcher (1957a, 1958) reported that in Florida the insect visitors to lychee flowers in order of numbers were: Calliphorid and screw-worm (Callitroga [=Cochliomyia] macellaria (Fab.)) flies and honey bees. No wild bees were seen on the plant although they were present on other flora. Pandey and Yadava (1970) reported that in India Apis spp. and Melipona spp. comprised 98 to 99 percent of the total visitors. Chaturvedi (1966) mentioned honey bees, flies, ants, and wasps as floral visitors. Groff ( 1943) considered bees the most outstanding beneficial insects on lychee. Butcher (1957a) concluded that the value of the honey bee was obvious in the setting of lychee fruit. Das and Choudhury (1958) stated that the chief pollinators were bees, other Hymenoptera, and flies.
Pollination Recommendations and Practices:
Although no specific number of colonies per unit of lychee has been recommended, Butcher (1957a, 1958) stated that supplying honey bees to lychee plantings is an important and practical recommendation for assuring adequate pollination and fruit-setting. He further felt that the bees should be present continuously throughout bloom. The degree to which growers go to in the use of bees has not been recorded.
LITERATURE CITED:
BANTA E. S.
1952. BEHOLD! THE LYCHEE. Amer. Fruit Grower 72(10): 10-11, 20-21.
BUTCHER, F. G.
1957a. POLLINATING INSECTS ON LYCHEE BLOSSOMS. Fla. State Hort. Soc. Proc.
70: 326-328.
____ 1957b. BEES POLLINATE LYCHEE BLOOMS. Fla. Lychee Growers Assoc. 1956 Yearbook and Proc. 3: 59-60.
____ 1958. POLLINATING INSECTS ON LYCHEE BLOSSOMS. Fla. Lychee Growers Assoc. 1957 Yearbook and Proc. 4: 39-41.
CAMPBELL C. W., and MALO, S. E.
1968 THE LYCHEE. Fla. Agr. Ext. Serv. Fruit Crops Fact Sheet 6. 2 pp.
CHATURVEDI, R. B.
1965. PRELIMINARY STUDIES IN THE SEX DISTRIBUTION, POLLINATION AND FRUIT
DEVELOPMENT IN LITCHI (LITCHI CHINENSIS SONN.). Allahabad Farmer 39(2):
49-5L
COBIN, M.
1952. THE LYCHEE IN FLORIDA. Fruit Varieties and Hort. Digest 6: 52-53.
DAS, C. S., and CHOUDHURY, R.
1958. FLORAL BIOLOGY OF LITCHI (LITCHI CHINENSIS SONN.). So. Indian Hort.
6(1): 17-22.
GROFF, G. W.
1921. THE LYCHEE AND LONGAN. 188 pp. Orange-Judd Publishing Co., New York.
____ 1943. SOME ECOLOGICAL FACTORS INVOLVED IN SUCCESSFUL LYCHEE CULTURE. Fla. State Hort. Soc. Proc. 56: i34-155.
GROVE, W. R.
1951. THE LYCHEE IN FLORIDA. Fla Dept. Agr. Bul. (n.s.) 134, 15 pp.
KHAN KHAN SAHEB ABDUR RAHMAN.
1929. POLLINATION AND FRUIT FORMATION IN LITCHI. Agr. Jour. lndia 24: 183-187.
KNIGHT, R. J., JR., MANIS, W. E., KOSEL, G. W., and WHITE, C. A.
1968. EVALUATION OF LONGAN AND LYCHEE INTRODUCTIONS. Fla. State Hort. Soc.
Proc. 81: 314-318.
MUSTARD, M. J., SU-YING, LIU, and NELSON, R. O.
1953. OBSERVATIONS OF FLORAL BIOLOGY AND FRUIT-SETTING IN LYCHEE VARIETIES.
Fla. State Hort. Soc. Proc. 66: 212 - 220.
NAKATA, S.
1956. LYCHEE FLOWERING AND GIRDLING. Hawaii Farm Sci. 4(3): 4-5.
PALMER, G.
1956. SOME ASPECTS OF THE LYCHEE AS A COMMERCIAL CROP. Fla. State Hort.
Soc. Proc. 69: 308.
PANDEY, R. S., and YADAVA, R. P. S.
1970. POLLINATION OF LITCHI (LITCHI CHINENSIS) BY INSECTS WITH SPECIAL
REFERENCE TO HONEYBEES. Jour. Apic. Res. 9(2): 103-105.
YOUNG, T. W.
1966. A REWEW OF THE FLORIDA LYCHEE INDUSTRY. Fla. State Hort. Soc. Proc.
79: 395-398.
MACADAMIA
Macadamia integrifolia Maiden & Betche and M. tetraphylla L. A. S. Johnson, family Proteaceae
About 4,000 acres of macadamia trees were in production in Hawaii in 1970 with another 4,700 acres of new but not yet producing trees (Wallrabenstein 1971). About 140 acres were in California, mostly in San Diego County (Swedberg and Nelson 1970), and a few acres on trial in Arizona. Coit and Miller (1951) stated that new cultivars were producing 1.5 tons of nuts (825 pounds of meat) per acre. Hamilton and Storey (1956) reported 500 tons of nuts harvested from 2,721 acres (1,395 of which were nonbearing acres) in HawaiiÑabout 700 pounds per productive acre. Production of as much as 7,000 lb/acre have been obtained (W.C. Mitchell, personal commun., 1971). The grove must be about 15 years old before the income from it pays the investment and expenses (Keeler and Fukunaga 1968).
The specific name of macadamia was formerly considered to be M. ternifolia Maiden & Betche (Hamilton and Fukunaga 1959), but now there are considered to be two species involved (Krause and Hamilton 1970), although only M. integrifolia nuts are processed commercially.
Plant:
The macadamia is an evergreen tree, native to Australia, where it may grow to a height of 50 to 60 feet. Elsewhere, however, it rarely exceeds 30 feet. The leathery leaves of M. integrifolia are narrow and long, up to 20 inches, serrate, with many spines along the edges. Those of M. tetraphylla are shorter, with few or no spines. The fruit is a fleshy exocarp or husk, enclosing a spherical l/2 to 1-inch hard brown shell or nut, a true seed, which contains the oval kernel or sometimes two hemispherical kernels (Hartung and Storey 1939). On maturity, the exocarp splits and the nut falls to the ground (Mowry et al. 1967*). The shell is tough and difficult to crack. The kernel is delicious with high energy value (9.3 percent protein, 78.2 percent fat, and 8 percent carbohydrate) (Kennard and Winters 1960*). The plants are grown about 20 feet by 35 feet apart (62 trees per acre) (Hamilton and Fukunaga 1959). They come into bearing in 5 to 7 years. The macadamia is also an excellent dooryard ornamental.
Inflorescence:
The l/4 to l/2-inch tubular flowers are borne in groups of three to four, with 100 to 500 of them on a whiplike terminal or axillary pendulous raceme about as long as the leaf (fig. 128). Urata (1954) stated that one short stamen is attached to each of four petals, but Storey (1957) stated that the flowers were without petals, the stamens being attached to the petallike sepals. Kennard and Winters (1960*) also referred to them as petalless flowers. The flowers on M. integrifolia are ivory white, on M. tetraphylla they are pink. The ovary with two ovules, bears a long straight style with a small terminal stigma. The style forms a sharp loop in its midsection just before the flower opens. The pollen is shed within the flower 1 to 2 days before it opens, then 1 to 2 hours before opening, which is about 7 to 8 a.m., the sepals curl back exposing the anthes closed over the tip of the style. Then, the anthers separate, and 5 to 10 minutes later the style breaks free and straightens, extending beyond the now empty anthers, but its stigma does not become receptive until some time later. The stigma comprises only the very apex of the style, approximately 1 mm across. It is capable of receiving only 10 to 12 grains of pollen (Schroeder 1959). The pollen of a specific flower, however, is generally removed by insects before the stigma is receptive (Knuth 1909*, p. 356 ), so pollen must come from another flower. The main flowering months in Hawaii are January and February.
Honey bees collect pollen freely from macadamia (Urata 1954 and Gary et al. 1972). Nectar is secreted at the base of the blossom. Schroeder (1959) commented that secretion of nectar is not in any quantity to attract insects. One report (Anonymous 1958) stated that macadamia flowers produce a gas that is highly toxic to bees, with the suggestion that this gas might have a somewhat repelling effect on bees. Apparently, the bees are not repelled.
[gfx] FIGURE 128.- Flower of macadamia (macadamia integrifolia), x 20. A, Complete flower with reflexed style just before petal-like sepals seperate to release stamens; B, longitudinal section of the open flower; C, style straightened after pollination has occured.
Pollination Requirements:
Urata (1954) and Schroeder (1959) stated that most trees are at least partly self-sterile but are cross-compatible; therefore, pollen must be moved from tree to tree for good fruit set. Knuth (1909*, p. 356) concluded that self-pollination was unlikely in the Proteaceae. Hamilton and Storey (1956) stated that usually only 1 to 20 flowers on a raceme set fruit, but no reason was given for this small percentage of set. Later, Storey (1957) stated that only 1 to 2 percent set fruit. The minuteness of the stigma indicates that wind is not a factor in pollen transfer.
Pollinators:
Urata (1954) stated that honey bees are the most common pollinating insects on macadamia flowers, primarily collecting pollen. He gave no indication of the relative number of bees per flower or tree, or the relative bee population in the area. Shigeura (1967) and Shigeura et al. (1970), working with 100, 75, and 20 trees of three cultivars of M. integrifolia concluded that moving commercial apiaries beside the plantings caused 59 percent increase in production over previous years without bees, although one cultivar showed no increase. Nothing was said about the activity of the bees on the flowers, and no suggestions were made as to how the bees might be used to increase production.
Pollination Recommendations and Practices:
There are no recommendations on the use of bees or other pollinating insects on macadamia flowers. The evidence strongly indicates that for highest production the use of honey bees as pollinators should be encouragedÑsufficient bees to provide ample cross-visitation between trees throughout the flowering period. There is no evidence as to the number of bees needed nor of the relative competition between flowers of macadamia and of other plants in the vicinity. Two to three colonies per acre are recommended for the pollination of the highly attractive almond trees and probably as many are needed on macadamia. A study of this phase of macadamia production is badly needed.
LITERATURE CITED:
ANONYMOUS
1958. MACADAMIA POLLINATION. In Hawaii Agr. Expt. Sta. Bien. Rpt. [or 1956-58,
p. 40.
COTT, J. E., and MTLLER, W. W.
1951. WHAT ABOUT THE MACADAMIA? Calif. Citrog. 36: 300 - 302.
HAMILTON, R. A., and FUKUNAGA, E. T.
1959. GROWING MACADAMIA NUTS. Hawaii Agr. Expt. Sta. Bul. 121, 51 pp.
HAMILTON, R. A., and STOREY, W. B.
1956. MACADAMIA NUT PRODUCTION IN THE HAWAIIAN ISLANDS. Econ. Bot. 10:
92 - 100.
GARY, N. E., MAU, R. F. L., and MITCHELL, W. C.
1972. A PRELIMINARY STUDY OF HONEY BEE FORAGING RANGE IN MACADAMIA (MACADAMIA
INTEGRIFOLIA MAIDEN AND BETCHE). Hawaii Ent. Soc. Proc. 21: 205-212.
HARTUNG, M. E., and STOREY, W. B.
1939. THE DEVELOPMENT OF THE FRUIT OF MACADAMIA TERNIFOLIA. Jour. Agr.
Res. 59: 397 - 406.
KEELER, J. T., and FUKUNAGA, E. T.
1968. THE ECONOMIC AND HORTICULTURAL ASPECTS OF GROWING MACADAMIA NUTS
COMMERCIALLY IN HAWAII. Hawaii Agr. Expt. Sta., Agr. Econ. Bul. 27, 47
pp.
KRAUSS, B. H., and HAMILTON, R. A.
1970. BIBLIOGRAPHY OF MACADAMIA. PT. 1. AUTHOR INDEX. Hawaii Agr. Expt.
Sta. Res. Rpt. 176, 112 pp.
SCHROEDER, C. A.
1959. SOME OBSERVATIONS ON THE POLLINATION OF MACADAMIA IN CALIFORNIA.
Calif. Macadamia Soc. Yearbook 5: 49 - 53.
SHIGEURA, G. T.
1967. VARIETAL NUT SET AND SUGGESTION OF POLLINATION REQUIREMENT IN MACADAMIA.
Hawaii Macadamia Prod. Assoc. 7th Ann. Mtg. Proc: 28-32.
____ LEE, J., and SILVA, J. A.
1970. THE ROLE OF HONEY BEES IN MACADAMIA NUT (MACADAMIA INTEGRIFOLIA MAIDEN
AND BETCHE) PRODUCTION IN HAWAII. Amer. Soc. Hort. Sci. Proc. 95: 544 -
546.
STOREY, W. B.
1957. THE MACADAMIA IN CALIFORNIA. Fla. State Hort. Soc. Proc. 70: 333
- 338.
SWEDBERG, J. H., and NELSON, G. A.
1970. CALIFORNIA FRUIT AND NUT ACREAGE, BEARING AND NON- BEARING AS OF
1969. Calif. Crop and Livestock Rptg. Serv. and U.S. Dept. Agr. Statis.
Rptg. Serv. 23 pp.
URATA, U.
1954. POLLINATION REQUIREMENTS OF MACADAMIA. Hawaii Agr. Expt. Sta. Tech.
Bul. 22, 40 pp.
WALLRABENSTEIN, P. P.
1971. STATISTICS OF HAWAIIAN AGRICULTURE, 1970. U.S. Dept. Agr., Statis.
Rptg. Serv., and Hawaii. Crop and Livestock Rptg. Serv., 77 pp.
MANGO
Mangifera indica L., family Anacardiaceae
Several hundred acres of mango are grown commercially in Hawaii in addition to numerous dooryard plantings (Yee 1958). Singh (1960) reported that mangos cover about 7,000 acres in Florida but D. O. Wolfenbarger (personal commun., 1970) estimated that there were only about 2,000 acres.
Mango is grown for the egg-shaped, 2- to 6-inch long, greenish or yellowish to reddish fruit, which has a skin slightly thicker than that of a peach. The juicy, sweet to acid flesh around the hard mono- or polyembryonic stone is a popular fruit for millions of people in the tropical and subtropical areas around the world.
Plant:
The mango is an erect, multibranched evergreen tree characterized by its dome-shaped canopy. It may reach 100 feet although most trees are less than half that height, and it may live 100 years or more. The tree grows in frost-free areas of the world from sea level to 4,000 feet. Heavy rains during flowering will drastically reduce fruit production. Mangoes have a decided tendency to biennial bearing, and many cultivars produce only one good crop in 3 to 4 years (Purseglove 1968*). On the other hand, some double or even triple cropping (the setting of fruit at two or three different times during the year) also occurs (Naik and Rao 1943).
Inflorescence:
The mango inflorescence is a branched terminal panicle, 4 to 24 inches long, with from a few hundred to several thousand individual flowers, requiring up to a month for all to open. The number of panicles may range from 200 to 3,000 per tree with 500 to 10,000 flowers per panicle - 100,000 to 30 million per tree. The proportion of perfect to staminate flowers may vary from 1:4 to 2:1 (Ochse et al. 1961*). Sometimes, the entire tree comes into bloom at one time, covering itself with sweet-scented flowers.
There are perfect and staminate flowers on the same panicle. The perfect flower, 5 to 8 mm long, has a globular ovary (rarely two or three) and a lateral style, which is absent in the staminate flower. Both generally have one, but sometimes two or even three, functional stamens and several sterile staminodes. There are usually five greenish-yellow sepals and three to nine, but usually five, cream-colored petals that take on a pinkish tinge before falling (Naik and Rao 1943). In the perfect or hermaphrodite flower, a nectar-secreting fleshy disk surrounds the ovary. The stamen is on the outer margin of this disk. The pistil and stamen are the same length; therefore, pollinating insects that feed on either nectar or pollen are likely to transfer pollen from the anther to the stigma (Juliano and Cuevas 1932, Sturrock 1966).
The flower opens early in the morning, and the stigma is immediately receptive. Maximum pollen shedding is from about 8 a.m. to noon. This delayed pollen shedding can result in inadequate stigma fertilization (Spencer and Kinnard 1956). When the flowers open, they secrete nectar in considerable quantity, which attracts a large number of insects (Mukherjee 1953); however, relatively little pollen is produced on the anther (Popenoe 1917).
Pollination Requirements:
There has been some lack of agreement on the pollination of mangos. Young (1942) made pollination studies on the 'Haden' mango in Florida, which he said made up 90 percent of the commercial plantings in that State (the 'Tommy Atkins' is the current popular cultivar), and found no significant difference between percentages of set in selfed and cross- pollinated flowers. Sturrock (1944) also considered the flowers self- fertile. This self-fertility was supported by the earlier work of Popenoe (1917), who stated that the mango is selffertile but cross-pollination increases fruit set. However, Singh et al. (1962) reported that crossed flowers set fruit whereas selfed ones did not, indicating a degree of self- sterility. The actual degree of self-fertility and sterility in individual cultivars has not been determined, but there is apparently some variation. Self-sterility is not, however, a major problem in fruit set.
Within the cultivar there is a definite need for transfer of pollen from anther to stigma by an outside agent. Popenoe (1917) stated that some of the embryos are capable of developement without fertilization; however, Naik and Rao (1943) obtained no parthenocarpic fruit set of more than 100,000 flowers studied. Fraser (1927) stated that friuit bud formation and pollination were the two big problems in growing mangos. He pointed out that in some cases only 2 to 3 percent of the flowers on a panicle are perfect - in others 60 to 70 percent. Wolfe (1962) concluded that getting flowers to set fruit was more of a problem than getting the trees to produce flowers.
The effect of cool weather adversly affects pollen tube growth, but this was not considered to be a factor of major importance by Young (1955). Chapman (1964*) and Ruehle and Ledin (1955) considered that the lack of efficient pollination might be responsible in part for the low yields of some Florida cultivars.
The studies indicate that the need for cross-pollination between mango cultivars is not critical, at least for most cultivars, but there is need for pollinating insects to transfer the pollen from anthers to stigma within the cultivar to obtain satisfactory crops of fruit.
Pollinators:
Several agents have been given credit as pollinators of mango. Wagle (1929) showed that there was some selfing and some wind pollination, but insects (bees, ants, and flies) played an important part.
Popenoe (1920) disagreed with other writers that the mango is wind pollinated. He pointed out that the flowers have none of the characteristics of a wind-pollinated flower, and he considdered the mango to be an insect-pollinated plant. Galang and Lazo (1937) and Singh (1969) agreed with him.
Recent studies in India29 showed that plants caged to exclude all insects set no fruit and gall-midges were ineffective as pollinators, but a plant caged with a colony of honey bees where harmful insects were excluded set a heavy crop.
Singh (1961) reported that over 65 percent of the perfect flowers were never pollinated- a strong indication that wind is not an efective pollinating agent. Complaints about lack of adequate fruit set in larger plantings particularly of monoclonal cultivars are frequent (Singh 1969). Fraser (1927) concluded that the important problem was finding out which insets were important as pollinators.
The statement was made by Singh (L.B.) (1960) that honey bees do not
visit mango flowers, but Singh (S.) (1954) listed this plant as a source
of pollen and nectar for bees. Popenoe (1917) reported that honey bees
were the most important hymenopterous insect visitor to the mango flowers,
but the number present was variable, possible because of the location of
apiaries or other relatively more attractive flora. This probably explained
the low population of honey bees reported by Simao and Maranhao (1959).
__________
29 UNIVERSITY OF ALLAHABAD, INDIA. P. L. (PUBLIC
LAW) 480 RESEARCH REPORT OF PROGRESS, PROJECT A-7-ENT-26, PERIOD 1-10-64
TO 31-3-65. From Dept. Zoology, Allahabad Univ., to U.S. Dept. Agr., Agr.
Res. Serv., Foreign Res. and Tech. Rpts. Div., 1 p.
Pollination Recommendations and Practices:
There is no indication that the recommendation by Young (1942) to place colonies of honey bees in mango groves has become an accepted practice; however, the chances are likely that such bee usage is needed today much more so than when his studies were made. The evidence is quite strong that concentration of colonies of honey bees within the mango grove would result in increased floral visitation and possibly more stabilized set of fruit, particularly in some years. The mango flowers do not appear to be overly attractive to honey bees, and they tend to open in large numbers at a time of year when many other flowers are also available, so visitation in commercial groves is likely to be far below that necessary for maximum floral visitation. If such is the case, a heavy concentration of colonies in the grove, possibly three to six per acre, may be necessary to obtain maximum fruit set.
LITERATURE CITED:
FRASER, S.
1927. AMERICAN FRUITS, THEIR PROPAGATION, CULTIVATION, HARVESTING AND DISTRIBUTION.
829 pp. Orange- Judd Publishing Co., Inc., New York.
GALANG, F. G., and LAZO, F. D.
1937. THE SETTING OF CARABO MANGO FRUITS AS AFFECTED BY CERTAIN SPRAYS.
Phillipine Jour. Agr. 8(2): 187-210.
JULIANO, J. B. and CUEVAS, N. L.
1932. FLORAL MORPHOLOGY OF THE MANGO (MANGIFERA INDICA L. ) WITH SPECIAL
REFERENCE TO THE PICO VARIETY. Phillipine Agr. 21: 449-472.
MUKHERJEE, S.K.
1953. THE MANGO, ITS BOTANY, CULTIVATION, USES AND FUTURE IMPROVEMENT.
Econ. Bot. 7(2): 130-162.
NAIK, K.C., and RAO, M.M.
1943. STUDIES ON THE BLOSSOM BIOLOGY AND POLLINATION IN MANGOES (MANGIFERA
INDICA L. ). Indian Jour. Hort. 1(2): 107-119.
POPENOE, W.
1917. THE POLLINATION OF THE MANGO. U.S. Dept. Agr. Bul. 542, 20 pp.
_____1920. MANUAL OF TROPICAL AND SUBTROPICAL FRUITS. 474 pp. The Macmillan Co., New York.
RUEHLE, G. D., and LEDIN, R. B.
1955. MANGO GROWING IN FLORIDA. Fla. Agr. Expt. Sta. Bul. 574, 90 pp.
SIMAO, S., and MARANHAO, Z. C.
1959. [INSECTS POLLINATING MANGO.] Anais Esc. sup. Agr. 'Luiz Queiroz'
16: 299-304. [In Portuguese, English Summary.]
SINGH, L. B.
1960. POLLINATION. His the Mango: Botany, Cultivation, and Utilization,
chap 3, pp. 42-43. Interscience Publishers, New York.
SINGH L. B. STURROCK, D.
1969. MANGO. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial
Crop Breeding in the Tropics, pp. 309-327. H. Veenman and Zonen, N. V.
Wageningen, The Netherlands.
SINGH, S.
1954. HORTICULTURAL CROPS AS BEE PASTURE. Indian Jour. Hort. 11(2): [49]-52.
SINGH, S. N.
1961. STUDIES ON THE MORPHOLOGY AND VIABILITY OF THE POLLEN GRAINS OF MANGO.
Hort. Adv. 5: 121-144.
SINGH, R. N., MAJUMDAR, P. K., and SHARMA, D. K.
1962. SELF-INCOMPATIBILITY IN MANGO (MANGIFERA INDICA L.) VAR. DASHEHARI.
Cur. Sci. 31(5): 209.
SPENCER, J. L., and KENNARD W. C.
1956. LIMITED STIGMATIC RECEPTIVITY MAY CONTRIBUTE TO LOW FRUIT SET IN
THE MANGO (MANGIFERA INDICA L.). Amer. Soc. Hort. Sci. Proc. 67: 287-289.
STURROCK, T. T.
1944. NOTES ON THE MANGO. Sturart Daily News, Inc., Sturart, Fla. 122 pp.
STURROCK, T. T.
1966; THE MANGO INFLORESCENCE. Fla. State Hort. Soc. Proc. 79:- 366-369.
WAGLE, P. V.
1929. A PRELIMINARY STUDY OF THE POLLINATION OF THE ALPHONSO MANGO. Agr.
Jour. India 24(14): 259-263.
WOLFE. H. S.
1962. THE MANGO IN FLORIDA 1887-1962. Fla. State Hort. Soc. Proc. 75: 387-391.
YEE, W.
1958. THE MANGO IN HAWAII. Hawaii Agr. Ext. Sen. Cir. 388, 26 pp.
YOUNG, T. W.
1942. INVESTIGATIONS OF THE UNFRUITFULNESS OF THE HADEN MANGO IN FLORIDA.
Fla. State Hort. Soc. Proc. 55: 106-110.
______ 1955. INFLUENCE OF TEMPERATURE ON GROWTH OF MANGO POLLEN. Fla. State Hort. Soc. Proc. 68: 308-313.
OIL PALM
Elaeis guineensis Jacq., family Palmaceae
The oil palm or African oil palm is one of the leading oil palms of industrial importance as a source of vegetable oil and fat. Under favorable conditions, it yields 2 tons of oil per acre. It grows naturally in tropical Africa from Senegal to Angola, especially in the coastal belt 100 to 150 miles in depth from Sierra Leone to the Cameroons. In 1951, 200,000 tons of the oil was produced in the Belgian Congo (Johnson and Raymond 1955). Plantations of this palm are being expanded in West Africa and Southeast Asia, especially in Malaysia.
This production would indicate that there are at least 100,000 acres. Recent development of new cultivars is expected to increase the yield of oil by 20 percent. Oil production per acre in Asia is much higher than in Africa (Sparnaaij 1969).
To obtain the oil, the pulpfruit is boiled. The nuts are then removed from the fibrous material, cracked, the kernels removed, and the oil pressed from them (Johnson and Raymond 1955).
Plant:
The oil palm is erect, monoecious, and may reach 30 feet in height with a trunk or bole 12 inches or more in diameter. It produces clusters of nuts, each of which has two locules and is about 1 1/2 inches long, the aggregate weighing as much as 100 pounds. The nuts are classified into three types according to the shell thickness; namely dura (3 to 8 mm thick), tenera (up to 3 mm thick), and pisefera (with no shell). The plant itself has a dense head of pinnate leaves, 10 to 15 feet long, and in the leaf axil is the separate dense staminate or pistillate inflorescence.
Inflorescence:
The staminate inflorescence may consist of 200 spikelets, with each spikelet bearing 700 to 1,200 florets (fig. 131). It may produce 3 ounces of pollen. The pollen is released over a 5-day period, and most of it on the third day after flowering starts; the pistillate inflorescence may have as many spikelets but only five to 30 florets on each. The pistillate floret is larger than the staminate one and bears an ovoid or nearly cylindrical three-celled ovary. The florets take about a week to open, the individual floret being receptive 36 to 48 hours (Sparnaaij 1969).
[gfx] FIGURE 131. - Fruit and inflorescence of African oil palm.
Pollination Requirements:
Pollen must be transferred from the staminate clusters to the pistillate ones. There is no indication of parthenogenetic development; furthermore, Sparnaaij (1969) stated that the pisefera nuts are often partially sterile. The oil palm male and female inflorescences open at different times on the plant; thus, rarely is the plant self-fertilized (Wrigley 1969).
Pollinators:
There is lack of agreement on the pollinating agents involved on oil palms. Ochse et al. (1961*) considered the flowers to be largely, if not exclusively, wind pollinated. Hardon and Turner (1967) considered them wind pollinated, pointed out the large amount of pollen produced, and noted that the pollen is distributed at least 55 feet from the original source.
However, Sparnaaij (1969) stated that both insects and wind contribute to pollen transfer. He noted that specialists in Africa generally assign the principal pollinating role to insects, whereas in Asia wind pollination is considered most important.
If insects are of significance, they must be attracted to the pistillate flowers by the nectar and to the staminate flowers by pollen and/or nectar.
Pollination Recommendations and Practices:
None. Because of the economic importance of this crop, its pollinating agents should be studied.
LITERATURE CITED:
HARDON, J. J., and TURNER. P. D.
1967. OSERVATIONS ON NATURAL POLLINATION IN COMMERCIAL PLANTINGS OF OIL
PALM (ELAEIS GUINEENSIS) IN MALAYA. Expt. Agr. 3(2): 105 - 116.
JOHNSON, R. M., and RAYMOND, W. D.
1955. AFRICAN OIL PALM. Econ. Bot. 9(1): 77.
SPARNAAIJ, L. D.
1969. OIL PALM. In Ferwerda, F. P., and Wit, F., eds., Outlines of Perennial
Crop Breeding in the Tropics, pp. 339-387. H. Veenman and Zonen, N. V.
Wageningen, The Netherlands.
WRIGLEY, G.
1969. TROPICAL AGRICULTURE. 376 pp. Frederick A. Praeger, N.Y. and
Washington.
OLIVE
Olea europaea L., family Oleaceae
The olive is grown commercially in California on about 27,000 acres where 52,000 tons, valued at $12.8 million, were produced in 1970. In addition, in 1970, we imported 16.3 million gallons of olives in brine and 64 million pounds of edible olive oil.
Plant:
The olive tree is usually 15 to 20 feet tall, but sometimes reaches 30 to 35 feet when fully developed and properly nurtured, with oval 1- to 3-inch gray-green leaves and gray branches. Its beauty, sturdiness, and symmetrical growth make it a prized ornamental as well as a commercial fruit tree. It will live hundreds of years in mild, arid climates. It blossoms profusely in the spring, producing the well-known oval, one- seeded, green to blue-black fruit about an inch long. It is cultivated somewhat like other warm-weather fruit or nut trees. In the grove, the trees are spaced well apart (35 to 40 feet) so the sunlight can reach the tree on all sides.
Inflorescence:
The cluster of one to two dozen, 4 mm, cream-colored to white fragrant flowers that develops in the axil of the leaf is usually shorter than the leaf itself. The individual flower has four valvate corolla lobes, a short four-toothed calyx, and two stamens that produce pollen copiously and little, if any, nectar (fig. 134). The flower opens before pollen is released from the anthers so cross-pollination can occur before selfing with the flower is possible. The flower may be either perfect and potentially fruitful with a plump green pistil, short style, and green ovary; or only staminate with a yellow abortive pistil (Condit 1947). No purely pistillate flowers occur. Most cultivars are self-fertile, but some are self-sterile, and others are intermediate (Crider 1922, Morettini 1957, Mort 1952, Pierce 1896). Occasionally, a poor fruit crop results from a flowering of almost entirely staminate flowers (Hartmann and Opitz 1966).
Honey bees collect pollen rather sparingly from the olive even though it is present in great abundance at flowering time. Sometimes, an olive honey flow is reported by beekeepers, but Silvestri et al. (1947) and Pellett (1949*) believed that the food source was honey dew from aphids on the olive and not nectar from the blossoms.
[gfx] FIGURE 134. - Longitudinal section of olive flower, x 20.
Pollination Requirements:
The pollination requirements of different cultivars of olives vary considerably. Crider (1922) listed two self-sterile, one partly self- sterile, and five self-fertile cultivars. Bradley et al. (1961) showed in greenhouse studies that even in self-pollinating cultivars, the pollen tubes of other cultivars grew down the style faster than self pollen tubes under the same temperature conditions. They found that if pollen tube growth was too slow, the embryo sac began to degenerate before the tube reached it; therefore, no fertilization would result. They concluded that "the chances of fertilization were greater in cross- than in self- pollinations, as indicated by the higher percentages of pistils in which a pollen tube reached the embryo sac."
Hartmann and Opitz (1966) stated that most varieties examined in Italy were self-sterile, a few were self-fertile, and some were partially self-fertile. They also stated that both in Portugal and in California satisfactory crops are obtained when some cultivars are planted in solid blocks although highest and most consistent yields are obtained in orchards where two cultivars are interplanted. This, they said, reaffirmed former studies at Davis and Winters, Calif., that cross-pollination of some varieties will increase fruit set in some years.
Pollinators:
Wind is considered the primary agent in the transfer of olive pollen. Honey bees visit the trees for pollen, and the general knowledge of bee activity on other plants would indicate that if they moved freely from plant to plant they would effectively transfer some pollen between varieties. Should insignificant wind movement - in the proper direction - occur during flowering so that it would fail to transfer the pollen adequately then the activity of honey bees could supplement wind activity.
Honey bees do not collect olive pollen as avidly as they do that of other plants. To create heavy olive flower visitation, might require a relatively heavy concentration of honey bee colonies in or near the grove. There is no information on the concentration that might be desired. Studies in this area would be productive.
Pollination Recommendations and Practices:
None.
LITERATURE CITED:
BRADLEY, M. V., GRIGGS, W. H., and HARTMANN, H. T.
1961. STUDIES ON SELF- AND CROSS-POLLINATION OF OLIVES UNDER VARYING
TEMPERATURE
CONDITIONS. Calif. Agr. 15(3): 4-5.
CONDIT. I. J.
1947. OLIVE CULTURE IN CALIFORNIA. Calif. Agr. Ext. Serv. Cir. 135,36 PP.
CRIDER, F. J.
1922. THE OLIVE IN ARIZONA. Ariz. Agr. Expt. Sta. Bul. 94: 491-528.
HARTMANN, H. T., and OPITZ, K. W.
1966. OLIVE PRODUCTION IN CALIFORNIA. Calif. Agr. Expt. Sta. and Ext. Serv.
Cir. 540,63 PP.
MORETTINI, A.
1958. [THE BIOLOGY OF FERTILIZATION IN OLIVE CULTIVARS AND ITS PRACTICAL
IMPORTANCE.] Italian. Agr. 94: 1103-1116. [In Italian. ] Plant Breed. Abstracts
28(3): 586587.
MORT, C. H.
1952. FRUITFULNESS IN OLIVES. Agr. Gaz. N.S. Wales 63: 371-372.
PIERCE, N. B.
1896. OLIVE CULTURE IN THE UNITED STATES. U.S. Dept. Agr. Yearbook 1896:
371-390.
SILVESTRI, F., MORETTINI, A., and ZAPPI-RECORDATI, A.
1947. [THE BEE AS A POLLINATOR OF THE OLIVE.] Olivicoltura 2(9): 12-15.
[In Italian.]
PAPAW OR PAWPAW
Asimina triloba (L.) Dunal, family Annonaceae
The papaw, not to be confused with the papaya, is native from New York to the Gulf of Mexico and west to Wisconsin and Texas (Gould 1939). It is rarely cultivated other than as a dooryard planting, but it (Anonymous 1969) is just awaiting final development. Its fruit is most prized of the native species of Annonaceae. It belongs to the same family as the cherimoya and related custard apples and produces a similar, delicious, many-seeded fruit.
Plant:
The papaw is a small, shrubby, deciduous tree, 15 to 20 feet tall, with straight upright branches forming a rounded crown. The oblong, glossy leaves are 6 to 12 inches long. The plants usually occur in thickets of many specimens in a small area. The greenish to yellow, banana-shaped fruit is 3 to 7 inches thick and turns brown when ripe (fig. 139). It ripens in the fall. The seeds are about an inch long, flat, blackish brown, and imbedded in the soft, edible pulp (Walden 1963). From l/2 to 1 bushel of fruit may be harvested from one tree.
[gfx] FIGURE 139. - Papaw branch with leaves and fruit
Inflorescence:
The chocolate, dark-purple, or maroon-colored flowers are about 2 inches across. They occur on last year's growth, solitary or in small clusters. They are protogynous, the three to 15 stigmas becoming receptive about 24 hours before the pollen is shed from the surrounding anthers borne on short fleshy filaments. The short styles lead to the numerous ovules to produce the large compressed seed (Ochse et al. 1961*). There are six petals, the three inner ones small and erect, the larger ones forming a corolla similar to a tulip blossom.
Pollination Requirements:
The stigma, being receptive before the anthers dehisce their pollen, requires pollen from another flower. Selfing is impossible (Ochse et al. 1961*).
Pollinators:
Evidence has shown that pollination is accomplished by insects especially honey bees bringing pollen from older flowers. Knuth (1908*, p. 54) stated that "In the first (female) stage of anthesis the three inner petals lie so close to the stamens that insect visitors (flies) cannot suck the nectar secreted at the bases of the former without touching the already mature stigmas. In the second (male) stage the stigmas have dried up and the inner petals have raised themselves so that the anthers - now covered with pollen - are touched by insects on their way to the nectar. Cross-pollination of the younger flowers is therefore effected by transference from the older ones."
Pollination Recommendations and Practices:
None.
LITERATURE CITED:
ANONYMOUS.
1969. CALIFORNIA RARE FRUIT GROWERS NEWSLETTER. 1(1): 1-4.
GOULD H. P.
1939. THE NATIVE PAPAW. U.S. Dept. Agr. Leaflet 179, 6 pp.
WALDEN F.
1963. A DICTIONARY OF TREES. 80 pp. Great Outdoor Publishing Co., St. Petersburg,
Fla.
PAPAYA
Carica papaya L., family Caricaceae
The papaya is sometimes called papaw or pawpaw, but in the United States these names are generally restricted to Asimina triloba (L.) Dunal (see "Papaw"). Papayas are grown to a limited extent in continental United States. They have been tried in Texas and in California, have never exceeded a few hundred acres even in Florida (Harkness 1967), but are more common in Hawaii and Puerto Rico. The 1964 United States Census of Agriculture showed that 32 farms in Florida produced almost 1.5 million pounds of fruit, while 266 farms in Hawaii produced almost 22 million pounds.
Papayas grow from about 32 deg N. to 32 deg S. latitude, from sea level to 5,000 feet altitude. They are killed by frost but do well in full sun or under irrigation. They do not occur in the wild, probably originated in Mexico or Costa Rica, and now consist of many cultivars (Purseglove 1968*).
The ripe fresh fruit (90 percent water, 4 to 10 percent sugar) (Wolfe and Lynch 1940) is eaten throughout the tropics for breakfast, dessert, in salads, jams, ice creams, and soft drinks. The dried latex or "milk" of immature fruit yields papain, a proteolytic enzyme similar in action to pepsin, which is used as a meat tenderizer (Becker 1958). It also creates shrink-resistance in wool.
Plant:
The papaya is a dioecious or hermaphrodite herbaceous plant, rather than a tree, that grows to 30 feet tall, but more frequently 10 to 20 feet. It is grown for its melonlike fruit, on a rarely branched trunk, having a terminal crown of palmately lobed leaves to 2 feet across. The fruit weighs 1 to 20 pounds, may be 3 to 20 inches long, oblong to round, with a five-angled cavity that may contain more than 1,000 blackish, round seed 1/8 to 1/4 inch in diameter. Pistillate flowers produce ovoid-oblong to nearly round fruits, but hermaphrodite flowers usually produce pear- shaped, cylindrical or grooved fruits (fig. 140). The skin is thin, smooth, and green, turning yellowish or orange when ripe. The flesh is orange or reddish orange and soft, with a mild pleasant flavor. The fruit matures 6 to 8 months after pollination (Bailey 1949*). Purseglove (1968*) stated there were many cultivars but that they were difficult to maintain in dioecious plants. He considered the hermaphrodite cv. 'Solo' to be one of the best, producing pear-shaped fruit about 4 inches by 6 inches and weighing about a pound. When 'Solo' is grown, the female plants are removed so that fruits of uniform shape and size are produced on the hermaphrodite plants.
The usual spacing of these plants is 8 to 12 feet apart (Purseglove 1968*), but when male and female plants are used one male is used for each 10 to 25 female trees (Greenway and Wallace 1953, Harkness 1967). Yields in a season may vary from 30 to 150 fruits per tree, usually 20 to 40, and may amount to as much as 150 tons per acre. For papain production in East Africa, one male for every 25 to 100 female plants is recommended (Purseglove 1968*).
[gfx] FIGURE 140. - Papaya fruit on a section of the plant.
Inflorescence:
The fragrant but complex flowers of the more or less dioecious papaya are described and illustrated by Lassoudiere (1969). In general, the five-petal staminate flowers occur in pendant panicles, 25 to 75 cm long, the corolla is trumpet shaped, 2.5 cm long, narrow, and creamy-white or yellow, with 10 short stamens inserted at the throat of the corolla in two whorls. The 3.5 to 5 cm pistillate flowers are solitary or in small cluster, 3 inches or more long, on a short stalk in axils along the trunk (Popenoe 1920, Pope 1930). The corolla of five fleshy yellow petals is almost completely free of the large, 2 to 3 cm, pale-green ovary, which is terminated by five sessile deeply cleft, fan-shaped stigmas. Some selections produce a higher percentage of female flowers than others (Sfemanthani 1965). Pistillate plants can be recognized easily by the long (3 to 4 feet) hanging panicle on which no fruit or only inedible fruit is produced (Harkness 1967). The nectar is relatively thin (24 to 34 percent), and bees usually prefer to visit the staminate flowers only for pollen (Allen 1963).
In addition, there are three types of hermaphrodite flowers (Higgins and Holt 1914; Storey 1937, 1941, 1958, 1969), namely:
Hermaphrodite, elongata, has an elongate pistil that develops
into an elongate fruit, and 10 stamens borne at the throat of the corolla.
Hermaphrodite, pentandria, has a more or less globose ovary that
develops into a five-furrowed fruit, and five stamens attached by long
filaments near the base of the ovary and lying in furrows between the lobes
of the ovary.
Hermaphrodite, intermedia, has some or all (2 to 10) of its stamens
distorted, and its pistil distorted and developing into a ridged or irregular-shaped
fruit.
Furthermore, staminate and hermaphrodite plants may undergo sex reversal and become pistillate (Free 1970*). Such sex reversal does not occur in pistillate plants; however, pistillate plants may be sterile in warm weather then become fertile during cool weather. Honey bees collect pollen from the staminate and hermaphrodite flowers and nectar from the pistillate and hermaphrodite flowers. The corolla tube of the staminate flower is too narrow to permit entrance by the bees and too deep to permit their proboscis to reach the nectar secreted at the base of the corolla (Bayless 1931). Hummingbirds (Brooks 1936) and sphinx moths (Stambaugh 1960, Traub et al. 1942) can apparently reach this nectar. Malan (1964) reported that honey bees were the most active insects around papaya flowers.
Pollination Requirements:
Pollen must be transferred from the staminate flowers to the pistillate ones if seeded fruit develops. Some commercial varieties are known to be parthenocarpic; therefore, pollinating agents are not necessary. Harkness (1967) stated that hermaphrodite flowers will self if bagged but did not indicate how the pollen would be moved from the anthers to the stigmas. Cheema and Dani (1929) and Traub et al. (1942) showed that flowers bagged to exclude pollen set fruit, but it was seedless with both size and quality reduced. The pollen should come from staminate plants, because pollen from hermaphrodite ones is inferior (Wolfe and Lynch 1940). The length of time individual flowers are open, and releasing pollen or receptive to pollen, has not been determined. Since 1,000 or more seeds may be produced in a single fruit, well over 1,000 viable pollen grains must be deposited on the stigma while it is receptive. Fruits with fewer than 300 seeds are usually not marketable (Allen 1963), and the more seeds, the larger the fruit. The Hawaiian types are generally known to be able to set fruit without the need of any staminate plants.
Pollinators:
Purseglove (1968*) stated that the method of natural pollination is not known with certainty. Stambaugh (1960) stated that sphinx moths are the sole pollinating agents of the papaya. Prest (1957) and Agnew (1941) considered wind as the primary agent. Agnew also stated that bees are occasionally seen gathering pollen although they are not particularly attracted by the flowers on the pistillate plants. Storey (1941) considered papaya to be pollinated by wind and insects. Brooks (1936) gave honey bees some credit, but he and Traub et al. (1942) also gave credit to the hummingbird moth for the transfer. Marin Acosta (1969) recorded 17 species of insect pollinators, including Trigona spp. and Xylocopa spp.
Allan (1963) showed that the papaya in South Africa is pollinated by insects, especially honey bees. When he covered plants with a 16-mesh- per-inch screen, only two fruits per plant developed, and they had an average of only six seeds. This showed that not wind but larger insects pollinated the flowers. Malan (1964) showed that neither wind, nor gravity-dispersed pollen, nor insects that could pass through 16 mesh- per-inch wire gauze were effective. He believed that honey bees were the most effective pollinating agents of papaya and recommended their use by growers.
Pollination Recommendations and Practices:
There seems to be no recommendation for the use of pollinating agents on this crop, other than the recommendation by Malan (1964) that growers of papaya use bees, and by Allan (1963) that growers keep bees in their orchards. The data, however, indicate a need for pollen transfer from stamens to pistils, and, since the honey bee is an easily managed pollinating agent, its value and use should be more thoroughly explored. In the meantime, the placement of beehives around papaya groves would appear to be good assurance that sufficient pollen is likely to be transferred to result in maximum quality fruit.
LITERATURE CITED:
AGNEW, G. W. J.
1941. NOTES ON THE PAPAW AND ITS IMPROVEMENT IN QUEENSLAND. Queensland
Agr. Jour. 56(5): 358-373.
ALLAN, P.
1963. POLLINATION OF PAPAWS. Farming in So. Africa 38(11): 13-15.
BAYLESS, B.
1931. PAPAYAS. Fla. State Hort. Soc. Proc. 44: 86-89.
BECKER, S.
1958. THE PRODUCTION OF PAPAINÑAN AGRICULTURAL INDUSTRY FOR TROPICAL
AMERICA. Econ. Bot. 12: 62-79.
BROOKS. J. R.
1936. THE PAPAYA. Fla. State Hort. Soc. Proc. 49: 134-136.
CHEEMA, G. S., and DANI, P. G.
1929. SEEDLESSNESS IN PAPAYAS. Agr. Jour. India 26(3): 206-207.
GREENWAY. P. J., and WABBACE, M. M.
1953. THE PAPAW, ITS BOTANY, CULTIVATION, DISEASES, AND CHEMISTRY. Tanganyika
Dept. Agr. Pam. 52, 32 pp.
HARKNESS, R. W.
1967. PAPAYA GROWING IN FLORIDA. Fla. Agr. Expt. Sta. Cir. S-180, 15 pp.
HIGGINS J. E., and HOBT, V. S.
1914. THE PAPAYA IN HAWAII. Hawaii Agr. Expt. Sta. Bul. 32, 44 pp.
LASSOUDIERE, A.
1969. [THE PAPAYA IV. DESCRIPTION OF INFLORESCENCES AND FLOWERS OF 'SOLO'
PAPAYA.] Fruits 24(3): 143-151. [In French.]
MABAN, E. E.
1964. PAPAWS IN SOUTH AFRICA. So. Africa Dept. Agr. Tech. Serv. Bul. 375,
12 pp.
MARIN ACOSTA, J. C.
1969. [INSECTS IN RELATION TO THE PAPAYA IN VENEZUELA. ] Trop. Agron. 19(4):
251-267. [In Spanish.]
POPE, W. T.
1930. PAPAYA CULTURE IN HAWAII. Hawaii Agr. Expt. Sta. Bul. 61, 40 pp.
POPENOE, W.
1920. MANUAL OF TROPICAL AND SUB-TROPICAL FRUITS. 474 pp. The Macmillan
CO., New York.
PREST, R L.
1957. UNFRUITFULNES IN PAWPAWS. Queensland Agr. Jour. 81(3): 144-148.
SFEMANTHANI, B.
1965. SEX EXPRESSION IN CERTAIN INBRED SELECTIONS OF PAPAYA (CARICA PAPAYA
LINN.). So. Indian Hort. 13(1/2): 15-19.
STAMBAUGH, S. V.
1960. FORTY YEARS OF PAPAYA DEVELOPMENT. Fla. State Hort. Soc. Proc. 73:
311-314.
STOREY, W. B.
1937. THE PRIMARY FLOWER TYPES OF PAPAYA AND THE FRUIT TYPES THAT DEVELOP
FROM THEM. Amer. Soc. Hort. Sci. Proc. 35: 80-82.
______ 1941. THE BOTANY AND SEX RELATIONSHIPS OF THE PAPAYA. PART 1. In Papaya Production in the Hawaiian Islands, Hawaii Agr. Expt. Sta. Bul. 87, 64 pp.
______ 1958. MODIFICATION OF SEX EXPRESSION IN PAPAYA. Hort. Adv. 2: 49-60.
STOREY, W. B.
1969. PAPAYA. In Ferwerda, F. P., and Wit, F., eds., pp. 389-408. Outlines
of Perennial Crop Breeding in the Tropics. H. Veenman and Zonen, N. V.
Wageningen. The Netherlands.
TRAUB, H. P., ROBINSON, T. R., and STEVENS, H. E.
1942. PAPAYA PRODUCTION IN THE UNITED STATES. U.S. Dept. Agr. Cir. 633,
36 PP.
WOLFE, H. S., and LYNCH, S. J.
1940. PAPAYA CULTURE IN FLORIDA. Fla. Agr. Expt. Sta. Bul. 350, 35 pp.
PASSIONFRUIT AND GIANT GRANADILLA
Passiflora spp., family Passifloraceae
The passionfruit is a perennial, vigorous, climbing, woody vine that produces an edible round or ovoid fruit with many small seeds. The fruit is eaten alone or in fruit salads, sherbets, ice cream, jams, and in cool drinks.
Commercial production of passionfruit in the United States is limited to Hawaii. A few plants are grown in dooryards in southern Florida and commercial planting in that area is recommended (Morton 1967). No production figures are available, although Morton (1967) stated that in 1958, 1,200 acres was devoted to production of yellow passionfruit in Hawaii (see below), and the industry was firmly established on a satisfactory economic level. The volume of production of this crop is small compared to most other fruit crops. Worldwide, the greatest volume of production is in Brazil, but the fruit is also produced in Colombia, Venezuela, Australia, New Zealand, Kenya, South Africa, India, and Indonesia.
Passionfruit is known in Hawaii as lilikoi, in Australia as golden passionfruit, in Brazil as maracuja peroba, and in South Africa as yellow granadilla.
There are about 300 species of Passiflora, most of which are native to the warmer moist regions of the Americas, and many produce edible fruit, but only two species are cultivated - P. edulis Sims and P. quadrangularis L.
There are two recognized forms of P. edulis. The purple passionfruit, f. edulis, is the normal form. Its fruit is egg shaped or round, 1 1/2 to 2 1/2 inches in diameter, and purple when ripe. It has the best flavor but does not grow well in the wet lowlands. The yellow passionfruit, P. edulis f. flavicarpa Degener, presumably originated as a mutation from the purple passionfruit (Akamine and Girolami 1959). Its fruit is slightly larger, 2 to 2 l/2 inches in diameter, and deep yellow when ripe. The crop is suited to the lowlands of the tropics, but the fruit is more acid than that of the purple passionfruit. There are various cultivars of the yellow passionfruit.
Passiflora quadrangularis L., the giant granadilla, is also cultivated to a limited extent in Brazil for local consumption. It grows best in a hot moist climate, and produces a round or oblong, pale-yellow to yellowish- green fruit when ripe, which may reach 6 by 12 inches in size.
Plant:
Cultivation and pollination requirements of both species are similar and will be combined in subsequent remarks. The plants are usually set in rows 10 feet apart with the plants 6 to 10 feet apart in the row. The vines are trained onto a trellis about 7 feet high. They are cut back to the ground each year but send up new runners to produce the next crop. A plant may be productive 4 to 6 years. The crop is usually grown from seeds in the nursery and transplanted to the field 3 to 4 months later when about 12 inches high. No information is available on seed quality in relation to cross-pollination between cultivars, which could influence productivity. Propagation by cuttings is possible, but is usually not practiced. Plants that are started in the fall produce a light crop the next year. If they are started in the spring, they produce a light crop the same year and a good crop the next year (Meurant 1959).
Average yields in Kenya are 15,000 pounds of fruit per acre per year (Purseglove 1968*); however, 40,000 lb/acre of fruit with 35 percent juice content has been produced from choice strains of yellow passionfruit in Hawaii (Morton 1967). Willis (1954) stated that in Australia a yield of 100 bu/acre may be expected the first summer, 12 to 15 months after planting. The relation of pollination to these drastic differences is not given but likely plays an important part.
Inflorescence:
The attractive and fragrant complete flower is 2 to 3 inches in diameter. It is solitary on the vine amongst the large 4- to 6-inch by 5- to 10-inch, three-lobed leaves. It has three bracts, a five-lobed calyx tube, five white spreading petals, a colorful filamentous corona, five strong stamens with large anthers, a triple-branched prominent style, each branch with an enlarged stigma, and a single ovary with several hundred ovules that, when fertilized, form the small seed within the fruit (fig. 141 ).
The passionfruit was named by early missionaries in South America who saw in it the implements of crucifixion, that is, the crown of thorns (corona), the five wounds (five anthers), the nails of the cross (divisions of the pistil), the whips and cords (the tendrils on the vine), and the spear (leaf).
Flowers of the purple passionfruit open at dawn and close about noon. Flowers of the yellow passionfruit open about noon and close at the end of the day. Flowering extends from early spring to late fall. Peak flowering occurs in late spring when one flower can be found per 2 to 5 feet of row (Nishida 1963). Nectar is secreted at the base of the pistil stalk (Akamine et al. 1954). The nectar is relatively rich (50 percent soluble solids).
The style is upright when the flower opens but recurves downward shortly afterwards until each branch is about on a level with the anthers. Shortly before the flower closes, the style returns to its upright position. About an hour is required for each change to occur. In some flowers, the style may remain erect, but such flowers are female-sterile, although their pollen is functional. The most effective time for pollination is after the style has recurved. At this time, the stigma is in the position where it is most likely to be brushed by pollinating insects, and the stigmatic fluid is present to insure adhesion by the pollen grains so the pollen tube growth can start. The stigma is receptive from the time of flower opening to closing (Cox 1957). Pollen is released before the flower opens and before the stigma is receptive. The pollen is not windblown.
[gfx] FIGURE 141.- Longitudinal section of passion fruit flower, x 2.
Pollination Requirements:
The flowers of passionfruit are self-sterile, and some plants are even self-incompatible (Akamine and Girolami 1957). Care must be taken, therefore, in the selection and distribution of compatible clones or cultivars in the field to insure maximum fruit production (Gilmartin 1958). The amount of pollen deposited on the stigma determines the number of seeds set and size of the fruit. The ovule must be pollinated and the seeds developed if juice is to form in the aril (pulp sac) (Knight and Winters 1962, 1963). A fruit can develop as many as 350 seeds. Unless about 100 ovules develop into seeds, the fruit is likely to be "hollow" (light in weight and with little juice). Few fruit develop with fewer than 50 seeds. There is no parthenocarpic set of fruit.
Akamine and Girolami (1959) found that fruit set, numbers of seed, fruit weight, and juice yield correlated with numbers of pollen grains deposited upon the stigma. They concluded that the maximum effect of pollination was not attained with their largest number (1,776) of pollen grains deposited on a stigma. This shows the importance of adequate bee visitation and pollen transfer between flowers within the brief span of time of stigma receptivity for maximum set of fruit.
Pollinators:
Honey bees and carpenter bees (Xylocopa sonorina Smith but known in Hawaii as X. varipuncta Patton) (Nishida 1954, 1958, 1963) are the primary pollinators of passionfruit. Where they are abundant, carpenter bees are doubtless the best pollinating agents because of their larger size. Unfortunately, they are scarce or nonexistent in some areas. Honey bees can be established wherever desired, but they sometimes show preference for more attractive plants than passionfruit. Various species of diptera are sometimes frequent visitors to the flowers, but they are of little value in transferring the pollen between plants. They tend to feed, then rest, without going immediately to the next flower, as the nectar and pollen collecting bees normally do. Other insects in Hawaii never more than occasionally visit the flowers and are of no consideration as pollinators of passionfruit. In Brazil, Trigona spp., and Epicharis spp., are frequent visitors and are unlikely to sting, a factor of concern to some growers. In India, Apis cerana is the primary pollinator (Sriram and Raman 1961).
Honey bees may visit the flowers for nectar or pollen or both. The nectar-collector crawls to the base of the style to the nectary, whereas the pollen-collector crawls busily over the anthers and is soon recognizable by the pellets of pollen in the corbiculae or pollen baskets on its hind legs. The type of food gathered depends upon competing food sources. Satisfactory crops are usually obtained with adequate pollinating agents.
Sriram and Raman (1961) reported that hand pollination of the flowers increased the set of yellow passionfruit by 21 percent over open pollination, whereas it increased set of granadilla by 84 percent.
Nishida (1963) noted that, because pollen is released shortly before the stigma is receptive, some growers feared that complete removal of pollen from the anthers by honey bees might be detrimental to fruit set (Bowers 1953), but experimental results have not confirmed this. If all the pollen is removed from the flowers by honeybees, which is highly unlikely, at least the flower is pollinated first.
Nishida (1 963) also noted that when flowering reached its peak (120 flowers per 200 feet of row), the honey bee population was 35 per 200 feet, or one bee for each four flowers. The number of carpenter bees varied according to their local population.
Pollination Recommendations and Practices:
One of the major problems in passionfruit production is in obtaining a satisfactory set of fruit. This set can only occur when an abundance of pollinators are the flowers and transferring pollen between compatible cultivars. One carpenter bee per 50 feet of row or one honey bee per four blossoms may be sufficient. The optimum number for maximum pollination of passion fruit is unknown. Pope (1935) mentioned large moths and hummingbirds, but in general, moths are not daytime feeders and hummingbirds are never sufficiently prevalent to pollinate crops grown commercially.
Honey bee colonies can be transported and increased wherever and whenever desired. Placement of redwood boards, poplar, or sisal logs can serve as carpenter bee nesting sites and may aid in increasing their number. Logs with carpenter bee nests in them may be transported to a field to establish this insect in a new area.
The yucca plant produces a flower stalk that eventually dries and becomes a choice nesting site for the carpenter bee; therefore, this plant might be grown near passionfruit fields. The larger the planting of passionfruit, the more efficient becomes the activity of the two primary pollinating agents - the carpenter bee and the honey bee - because competing plants are relatively reduced.
On most insect-pollinated crops, and this would appear to include passionfruit, the most satisfactory and surest way to supply ample pollination is by stocking the area with sufficient honey bee colonies. The number per acre of passionfruit might vary enormously with the (generally small) size of the crop and with competing plants.
A fact worth considering would be the interplanting of the purple passionfruit that has flowers open and attractive to bees from dawn to noon, and yellow passionfruit with flowers open from about noon to dusk. This might tend to lure and hold the activity of the bees within the field throughout the day and increase their pollinating effectiveness.
LITERATURE CITED:
AKAMINE, E. K., HAMILTON, R. A., NISHIDA, T., and others.
1954. PASSION FRUIT CULTURE IN HAWAII. Hawaii Agr. Ext. Serv. Cir. 345,
23 pp., rev.
______and GIROLAMI, G.
1957. PROBLEMS IN FRUIT SET IN YELLOW PASSION FRUIT. Hawaii Farm Sci. 5:
3-5.
______and GIROLAMI, G.
1959. POLLINATION AND FRUIT SET IN THE YELLOW PASSION FRUIT. Hawaii Agr.
Expt. Sta. Tech. Bul. 59, 44 pp.
BOWERS, F. A. I., JR.
1953. PASSION FRUIT TESTS SHOW PROMISE. Hawaii Farm Sci 2(2): 3, 6, 8.
COX, J. E.
1957. FLOWERING AND POLLINATION OF PASSION FRUIT Agr.. GAZ. N.S. Wales,
68: 573-576.
GILMARTIN, A. J.
1958. POST-FERTILIZATION SEED AND OVARY DEVELOPMENT IN PASSIFLORA EDULIS
SIMS. Trop. Agr. [Trinidad.] 35: 41-58.
KNIGHT, R. J., JR., and WINTERS, H. F.
1962. POLLINATION AND FRUIT SET OF YELLOW PASSIONFRUIT IN SOUTHERN FLORIDA.
Fla. State Hort. Soc. proc. 75: 412-418.
______and WINTERS, H. F.
1963. EFFECTS OF SELFING AND CROSSING IN THE YELLOW PASSIONFRUIT. Fla.
State Hort. Soc. Proc. 76: 345347.
MEURANT, N.
1959. FAULTY FRUIT-SETTING IN THE PASSION VINE. Queensland Fruit and Vegetable
News [ Brisbane] 15: 202.
MORTON, J. F.
1967. YELLOW PASSIONFRUIT IDEAL FOR FLORIDA WILLIS, J. M. HOME GARDENS.
Fla. State Hort.. Soc. Proc. 80: 320-330.
NISHIDA, T.
1954. ENTOMOLOGICAL PROBLEMS OF THE PASSIONFRUIT. Hawaii Farm Sci. 3(1):
1,3,7.
______ 1958. POLLINATION OF THE PASSION FRUIT IN HAWAII. Jour. Econ. Ent.. 51: 146-148.
______ 1963. ECOLOGY OF THE POLLINATORS OF PASSION FRUIT. Hawaii Agr. Expt. sta. Tech. Bul. 55,38 pp.
POPE, W. T.
1935. THE EDIBLE PASSIONFRUIT IN HAWAII. Hawaii Agr. Expt. Sta. Bul. 74,22
pp.
SRIRAM, T. A., and RAMAN, K. R.
1961. SOME ASPECTS OF FLOWERING AND FRUITING IN YELLOW PASSIONFRUIT AND
GRANADILLA. So. Indian Hort.. 9(1-4): 30-37.
WILLIS, J. M.
1954. PASSION FRUITS AND GRANADILLAS. Queensland Agr. Jour. 79(4): 205-217.
PEACH AND NECTARINE
Prunus persica (L.) Batsch, family Rosaceae
The peach and the nectarine (P. persica var. nectarina (Ait.) Maxim.) differ primarily in that the nectarine has a smooth skin, but the peach is covered with needlelike hairs or fuzz. Nectarines are known as a single factor mutation of the peach. Nectarine-like fruit has been obtained from peach trees and peaches have been found on nectarine trees (Philp and Davis 1936).
The farm value of the 1970 peach crop was $176.3 million compared to $10 million for nectarines. Peaches are grown on about 200,000 acres, 81,810 acres of which are in California. Nectarines are produced almost exclusively in California on 7,790 acres (Kitterman and Nelson 1971).
Plant:
The deciduous trees, set in the orchard about 20 feet apart, are usually
trimmed to 8 to 16 feet in height (fig. 142). There are scores of cultivars
only recognizable by the type of fruit they produce. Flowering occurs at
about the same time each spring on all cultivars except for a few early
and late blooming cultivars. The plant usually requires some winter chilling
to promote normal growth and flower development in the spring. Freestone
cultivars, those with fruits that break away easily from the stone or seed,
are much more popular for the fresh market than the clingstone type in
which the flesh of the fruit is firmly attached to the stone. The freestone
'Elberta' cv. has been the most popular of all cultivars, but it is being
replaced by firmer, more attractive cultivars. The highly perishable fruit
must be harvested at a precise stage of ripening.
[gfx] FIGURE 142.- Peach orchard in bloom.
Inflorescence:
The many attractive pink or reddish blossoms of the peach and nectarine appear in the spring at about the time leaf development begins (fig. 143). The structure of the flower is ordinary in that sepals are present but small; there are usually five rather oval petals, 25 to 40 mm across, and 15 to 30 pollen-laden anthers surrounding the single erect pistil through which the pollen tube reaches a single ovary, which contains two ovules. Following fertilization, only one ovule normally develops at the expense of the other, leading to the development of a one- seeded stone. As a result, the fruit develops asymmetrically (Stewart et al. 1967). The peach ovary is covered with a dense coat of hairs. The nectarine ovary is usually bare, similar to that of the plum (figs. 144, 145).
Most cultivars produce pollen at the time the stigma is receptive. Nectar is secreted at the base of the corolla. The flowers are highly attractive to honey bees and other pollen- and nectar-collecting insects. The fact that only one ovule must be fertilized for a peach fruit to set as compared to hundreds of ovules in other fruit such as melons or papayas, enormously simplifies the pollination of the peach.
Normally, the flowers are fully closed at 6 a.m., but most of them are open by 10 a.m., and all are open by noon. They do not close at night; they may stay open and the stigma may be receptive for 3 days (Randhawa et al. 1963).
[gfx] FIGURE 143.- Peach blossoms.
FIGURE 144.- Longitudinal section of 'Babcock' peach flower, x 4.
FIGURE 145. - Longitudinal section of 'Perfection' nectarine flower, x
4.
Pollination Requirements:
Considering the economic importance of the peach crop, surprisingly little has been done about its pollination requirements. There are many references to fruit production (for example, Cullinan 1937, Hedrick 1917, USDA 1967), which usually state that most cultivars are self-fertile and a few are self-sterile (Kanato et al. 1967, Lagasse 1926). Many self- sterile cultivars have been largely or completely eliminated from the market, regardless of their other good qualities, because interplanting of cultivars and insect pollination are necessary in their production. These include 'Alamar', 'Candoka', 'Chinese Cling', 'Hal-berta', 'J. H. Hale', 'June Elberta', 'Mikado', and a few others. Unfortunately, the references to the self-sterility of such cultivars has tended to draw attention away from the "self-fertile" cultivars and the possibility that they might not be capable of fertilizing themselves without the aid of an outside agency.
GLASSHOUSE POLLINATION STUDIES:
Grieve (1879) discounted the need for or value of bees in a glasshouse.
Conners (1922b, 1926) reported that peaches in a glasshouse failed to set
unless pollinated by hand or bees because of a lack of air currents to
sway the blossoms and cause the stamens to come in contact with the stigma.
Coote (1895) also showed that when trees were grown in the greenhouse with
bees to visit the flowers a heavy set resulted. Vermeulen and Pelerents
(1965) obtained 84 fruits per tree in a glasshouse with bees but only five
per tree with bees absent. Thompson (1940) reported on the value of bees
to peaches in greenhouses in England.
BAGGING AND WIND POLLINATION STUDIES:
Conners (1917) reported that trees of 'Belle', 'Early Crawford', 'Elberta',
and 'Greensboro' cvs. caged to exclude insects set fruit readily. Later,
he (1922a )mentioned the 'Susquehanna' as being self-sterile and that he
discarded three other selections for that reason. Crandall (1920) found
that more than twice as man: bagged flowers set fruit if they were hand
pollinated than if bagged only. Detjen (1945) performed a similar experiment
with similar results, that is, flowers bagged and hand pollinated set more
fruit than did open flowers, but flowers bagged only, without additional
pollination, set fewer flowers. He felt that buffeting of the flowers by
wind was sufficient to dislodge the pollen and transfer it to the stigma.
Sharma (1961) reported that while bagged peach flowers "gave a commercial
set without pollination insects," the set was higher on unbagged branches.
Kerr (1927) bagged branches of 27 cultivars and found that 19 were "sufficiently
self fruitful, 5 did not set enough and 2 were unfruitful".Both Chandler
(1951*) and Langridge (1969) reported that there is little airborne peach
pollen.
INSECT POLLINATION STUDIES:
Factual tests on the relation of insects to pollination of peaches are
woefully inadequate although numerous tests have given indications, and
conclusions have been drawn, on the relation of insects to set of fruit
of peaches. For example, MacDaniels and Heinecke (1929) stated: "Most
peach varieties are self-fertile and present no pollination difficulties
except that attributable to lack of sufficient insects at blooming time
to accomplish self-pollination. "
Bulatovic and Konstantinovic (1962) obtained better set on various species with exposed flowers than with selfed flowers, and they concluded that there was slightly more fruit set on all cultivars when visited by bees.
Rather thorough studies were conducted by Marsha et al. (1929) who summarized their findings with the statement, "Enough has been written to show the satisfactory crops from either self-sterile or self-fertile varieties of orchard fruits cannot be obtained unless there are plenty of honey bees or other pollen-carrying insects working in the orchard at the time the trees are in bloom." Murneek (1937) also stated that "Whether variety is self-sterile or self-fertile insects are equally necessary for proper pollination and setting of fruit. Chandler (1951*) stated that the pollen must be applied to the stigma by insects that visit the flowers. Jorgense and Drage (1953) listed peaches as "largely self-fruitful, but "bees are necessary" in their pollination. Khan (1930) also concluded that cross-pollination is necessary to obtain good yields and that bees are the chief agent for cross-pollination.
Boller (1953) stated that "Some pollination occurs' without the help of bees, probably by shaking of the flowers by the wind. Whether we get enough self-pollination by this means is unknown. We do know that a small number of bees can do a lot of self-pollinating since almost every visit to a flower results in self- pollination."
H. W. Fogle (personal commun., 1971) stated that the flowers are receptive to pollination 4 to 7 days, depending upon the weather, but the set is unlikely "unless a bee or similar insect enters the flower and spreads the pollen around."
These references indicate that, although the actual data are sparse, pollinating insects are of value even for the self-fertile cultivars of peaches.
Some growers consider thinning of a heavy set of fruit to be a greater problem than pollination (Snyder et al. 1952); however, thinning the fruit after flowering is easier than getting fruit to set if the flowers are gone and the set is inadequate.
Pollinators:
The degree of pollination actually accomplished by wind as compared to insects is unknown. Also, if, as some references indicate, wind alone is insufficient and insects are needed, the number of visitors is unknown. If the weather is clear and mild, the bees will visit the flowers throughout much of the day; however, if the weather is cold or wet, bees may be absent. In visiting the nectaries in the base of the flower, the bee either pushes one or more anthers against the stigma or rubs against it. In either case, pollen is transferred to the stigma. If the cultivar is self-fertile, a high population of bees would not be needed to set an adequate crop (Boiler 1963). Should the population of bees in the area be inadequate, honey bees can be transported and placed in the orchard. The evidence indicates that their presence in the orchard is important. Randhawa et al. (1963) considered the honey bee most important as a pollinator of peaches. Yokozawa and Yasui (1957) reported that when the weather was generally cloudy and rainy the Diptera were the most common floral visitors, but during clear weather the Hymenoptera were more frequently observed on the flowers.
Pollination Recommendations and Practices:
Numerous horticulturists have indicated that bees are beneficial to peaches, and most State bulletins recommend to growers that action be taken to increase the number of insect pollinators in the orchard. The growers are fortunate in that the peach flowers are attractive and ample pollination is obtained free when conditions are favorable, with bees coming long distances.
Newell (1903) urged the keeping of honey bees near peach orchards. Jorgensen and Drage (1953) considered bees necessary. Kelly (1964) made a study relating to cost of peach growing in Pennsylvania and found that an average of only one hive per 16 acres was used.
Benner (1963) recommended one strong colony of honey bees for each three to five acres of orchard just coming into bearing but stated that in older orchards one good colony of bees for each acre might be needed.
Several hundred colonies of honey bees are rented annually for pollination of peaches in New Jersey (J. C. Matthenius, Jr., personal commun., (1970). Most growers, however, take no action in relation to pollination of the crop.
LITERATURE CITED:
BENNER, B.
1963. FRUIT AND VEGETABLE FACTS AND POINTERS: PEACHES. United Fresh Fruit
and Vegetable Assoc., Washington, D.C., 3d rev. and expanded ea., p. 11
(total pagination not known).
BOILER, C. A.
1953. POLLINATION OF STONE FRUITS. Oreg. State Hort. Soc. Proc. 45: 122-125.
BULATOVIC, S., and KONSTANTINOVIC, B.
1962. THE ROLE OF BEES IN THE POLLINATION OF THE MORE IMPORTANT KINDS OF
FRUIT IN SERBIA. In 1st Internatl. Symposium on Pollination Proc., Copenhagen,
Aug. 1960. Commun. 7, Swedish Seed Growers' Assn., pp. 167 - 172.
CONNERS, C. H.
1917. METHODS IN BREEDING PEACHES. Amer. Soc. Hort. Sci. 14th Ann. Mtg.
Proc.: 126-127.
______ 1922a. PEACH BREEDING A SUMMARY OF RESULTS. Amer. Soc. Hort.. Sci. I9th Ann. Mtg. Proc: 108-115.
______ 1922b. FRUIT SETTING OF THE J. H. HALE PEACH. Amer. Soc. Hort.. Sci. 19th Ann. Mtg. Proc.: 147-151.
______ 1926. STERILITY IN PEACHES. Hort. Soc. N.Y. Mem. 3: 215-221.
COOTE, G.
1895. FRUITS AND VEGETABLES. Oreg Agr. Expt. Sta. Bul. 34: 17-32.
CRANDALL, C. S.
1920. AN EXPERIENCE IN SELF-FERTILIZATION OF THE PEACH. Amer. Soc. Hort..
Sci. Proc. 17: 33-37.
CULLINAN, E. P.
1937. IMPROVEMENT OF STONE FRUITS. U.S. Dept. Agr. Yearbook 1937: 665-748.
DETJEN, L. R.
1945. FRUITFULNESS IN PEACHES AND ITS RELATIONSHIP TO MORPHOLOGY AND PHYSIOLOGY
OF POLLEN GRAINS. Del. Agr. Expt. Sta. Bul. 257 (Tech. Bul. 34), 24 pp.
GRIEVE, P.
1879. BEES AS FERTILIZING AGENTS. Gard. Chron. 11: 204.
HEDRICK, U. P.
1917. THE PEACHES OF NEW YORK. PART 2. N.Y. (Geneva) Agr. Expt. Sta. 541
pp.
JORGENSEN, C., and DRAGE, C. M.
1953. POLLINATION OF COLORADO FRUITS. Colo. Agr. Expt. Sta. and Ext. Serv.
Bul. 427A, 13 pp.
KANATO, K., YOSHIDA, M., KURIHARA, A., and MAKINO, Y.
1967. [STUDIES ON POLLEN STERILITY OF PEACH.] Hiratsuka Hort. Res. Sta.
Bul. Ser. A, 6: 91 - 104. [In Japanese, English tables and summary.]
KELLY, B. W.
1964. FACTORS RELATING TO THE COST OF PRODUCING PEACHES IN PENSYLVANIA,
1959-63. Pa. Agr. Ext. Serv. Farm Mangt. Pub. 19, 20 pp.
KERR W. L.
1927. CROSS AND SELF-POLLINATION STUDIES WITH THE PEACH IN MARYLAND. Amer.
Soc. Hort. Sci. 24th Ann. Mtg Proc.: 97-101.
KHAN, KHAN SAHEB ABDUR RAHMAN.
1930. SOME OBSERVATIONS ON THE POLLINATION OF PEACHES (PRUNUS PERSICA BENTH.
AND HOOK.). Agr. Jour. India 25(6): 492-494.
KITTERMAN, J M., and NELSON, G.
1971. 1970 CALIFORNIA FRUIT AND NUT ACREAGE. Calif. Crop and Livestock
Rptg. Serv., 19 pp.
LAGASSE, F. S.
1926. THE STERILITY AND CROSS-POLLINATION OF THE J. H. HALE PEACH. Del.
Agr. Expt. Sta. Bul. 147: 29.
LANGRIDGE, D. E.
1969. EFFECTS OF TEMPERATURE, HUMIDITY, AND CAGING ON THE CONCENTRATION
OF FRUIT POLLEN IN THE AIR. Austral. Jour. Expt. Agr. Anim. Husb. 9:549-552.
MACDANIELS L. H., and HEINICKE, A. J.
1929. POLLINATION AND OTHER FACTORS AFFECTING THE SET OF FRUIT WITH SPECIAL
REFERENCE TO THE APPLE. N.Y. (Cornell) Agr. Expt. Sta. Bul. 497, 47 pp.
MARSHALL, R. E., JOHNSTON, S., HOOTMAN, H. D., and WELLS, H. M.
1929. POLLINATION OF ORCHARD FRUITS IN MICHIGAN. Mich. Agr. Expt. Sta.
Spec. Bul. 188, 38 pp.
MURNEEK, A. E.
1931. POLLINATION AND FRUIT SETTING. Mo. Agr. Expt. Sta. Bul. 379, 28 pp.
NEWELL, W.
1903. THE RELATION OF BEES TO FRUIT GROWING. Ga. State Hort. SOc. Proc.
27: 58-66.
PHILP G. L., and DAVIS L. D.
1936. PEACH AND NECTARINE GROWING IN CALIFORNIA. Calif. Agr. Ext. Sen.
Cir. 98, 62 pp.
RANDHAWA, G. S., YADAV, I. S., and NATH, N.
1963. STUDIES ON FLOWERING, POLLINATION AND FRUIT DEVELOPMENT IN PEACH
GROWN UNDER SUBTROPICAL CONDITIONS. Indian Jour. Agr. Sci. 33(2): 129-138.
SHARMA, P. L.
1961. THE HONEYBEE [APIS INDICA] POPULATION AMONG INSECTS VISITING TEMPERATE-ZONE
FRUIT FLOWERS AND THEIR ROLE IN SETTING FRUIT. Bee World 42: 6-7.
SNYDER, J. C., BRANNON, D. H., and HARRIS, M. R.
1952. GROWING PEACHES. Wash. Agr. Ext. Serv. Bul. 462, 29 pp.
STEWART, N., LUCKWILL, L. C., MEALY, A. G., and others.
1967. THE POLLINATION OF FRUIT CROPS. Sci. Hort. 14 and 15: 1-68.
THOMPSON, F.
1940. THE IMPORTANCE OF BEES IN AGRICULTURE. Bee Craft 22(250): 6-7.
UNITED STATES DEPARTMENT OF AGRICULTURE.
1967. GROWING PEACHES EAST OF THE ROCKY MOUNTAINS. U.S. Dept. Agr. Farmers'
Bul. 2205, 24 pp.
VERMEULEN, L., and PELERENTS, C.
1965. [EFFECT OF THE HONEYBEE ON FRUIT SETTING.] Fruitrev. [Belgium]: 1-4.
[In Dutch.] AA-792/71.
YOKOZAWA, Y., and YASUI, A.
1957. [STUDIES ON THE POLLINATION OF PEACH.] 1. INSECT VISITORS TO THE
FLOWERS OF PEACH.] Hort. Assoc. Jap. Jour. 26(3): 185-191. [In Japanese,
English title and summary.]
PEAR
Pyrus spp., family Rosaceae
All of the important pears growing in the United States, referred to as the French or European types, belong to P. communis L., except a few hybrids such as the 'Kieffer' and 'Le Conte', which are crosses between P. communis and the fire blight resistant Chinese sand pear (P. pyrifolia (Burm. f.) Nakai) (Davis and Tufts 1941).
The estimated production of pears in 1971, was 701,120 tons, almost half of which (309,000 tons) were produced in California. Production in Washington was 165,400 tons and in Oregon, 174,000 tons. Production in other States was relatively insignificant. The total value of the crop was $63 million.
Plant:
The pear tree may live 100 years or more and if unpruned may reach a height of 50 feet. When grown in orchards, however, the trees are usually pruned to 10 to 20 feet. Its general appearance is similar to the apple although its limbs are usually somewhat less gnarled and more upright. It flowers in the springtime about the same time that apples flower or slightly earlier. The fruit is consumed fresh, canned, preserved, or pickled. The trees are usually spaced 20 feet apart in the orchard, except for dwarf trees, which are sometimes as close as 12 feet (Davis and Tufts 1941).
Although Hedrick (1921) stated that thousands of cultivars of pears are grown in Europe and the United States, the 'Bartlett', 'Williams', or 'Williams Bon Chretien', a European cultivar, is probably the most widely grown pear in the world (Griggs and Iwakiri 1954). Other important European cultivars are: 'Anjou', 'Bosc', 'Comice', 'Hardy', and 'Winter Nelis' (Magness 1937). According to Hedrick (1938*), the Europeans have listed more than 5,000 pear cultivars, the Americans, more than 1,000 cultivars. Hedrick considered the 'Kieffer' next in importance to the 'Bartlett', the 'Le Conte' about like the 'Kieffer' in quality but not quite as good. Today, 'Kieffer' is important only in the Eastern and Southern States where better quality pears cannot be grown because of fire blight (Batjer et al. 1967). The 'Winter Nelis', which was the standard winter pear in the United States, has been replaced in many places by the 'Anjou'. The relatively unimportant 'Pound' is grown primarily for its monstrous fruit (3 to 4 pounds each). Auchter and Knapp (1937*) showed a production of 210 bu/acre for 'Kieffer' pears versus 140 to 160 for 'Bartletts'.
Inflorescence:
Pear flowers are at least 1 inch in diameter, pure white, and in simple clusters (fig. 148). The flower is protogynous (the stigma of an individual flower is receptive to pollen before its anthers release pollen). The flowering on a tree usually lasts about a week. The flowers produce abundant pollen, which is highly attractive to bees (Tufts and Philp 1923), but the nectar is low in sugar content (Vansell 1946) and frequently fails to attract bees. When the flower opens, the style stands erect, the stigma is receptive, and the stamens are so bent inward that the unripe anthers are crowded together around the style but below the stigma (fig. 149). Later, they extend to the full height of the style and release their pollen. Unlike the plum and nectarine, the pear does not have a deep cup lined with nectar tissue, but only five small, slitlike openings in the flat top surface or disk area between the petals and stamens (Vansell 1942*). Vansell showed that the percentage of sugar concentration of pear nectar was quite low, for example, apple, 46.2 percent; peach, 28.9; plum, 25.8; sour cherry, 23.5; 'Winter Nelis' pear, 9.9; and 'Bartlett' pear, 7.9. He observed that bees frequently visited other blossoms for nectar but visited pear blossoms only for pollen.
Brown and Childs (1929) stated that a full-bearing need for 'Anjou' tree at 15 years of age may have as many as 8,000 fruit buds, each of which contains a cluster of at least seven perfect flowers. A single tree may therefore produce as many as 56,000 flowers, all of which are potential fruit producers. They estimated that 1.96 percent of the flowers could set and produce a satisfactory crop. Powell (1902) stated that if 6 percent of a moderately blooming tree set fruit, a heavy crop would result. Brown and Childs (1929) showed that a 7.1 percent set resulted in production of 12,851 lb/acre over a number of years.
[gfx] FIGURE 148.- Branch of pear tree in full flower.
FIGURE 149. - Longitudinal section of 'Bartlett' pear flower, x 9.
Pollination Requirements:
The classic research by Waite (1895, 1899) established the principles of fruit pollination and clarified the need for pollination insects on fruit. In particular, he showed that the 'Bartlett' pear was self-sterile in Virginia and only set good crops when other cultivars were grown nearby so that bees could bring compatible pollen to its flowers. This basic pollination principle for pears was shown by Swayne (1824) (see also, Chittenden 1914), but it was largely forgotten until Waite's research. Close (1903) also showed that neither 'Kieffer' nor 'Angouleme' set fruit on bagged flowers. Fletcher (1907,1911) showed that both 'Kieffer' and 'Bartlett', if planted in solid blocks in West Virginia and Michigan, yield poorly if not properly pollinated. Florin (1925) found that 'Bartlett' were self-sterile in Sweden. Powell (1902) recommended the interplanting of pollinizer cultivars with the 'Kieffer'. Kraus (1912) advised growers in Ohio to plant 'Anjou', 'Clairgeau', 'Howell', or 'Kieffer' with 'Bartletts' for cross-pollination.
Luce and Morris (1928) reported that the 'Bartlett', 'Bosc', 'Anjou', and 'Winter Nelis' were partly or entirely self-sterile in the Wenatchee, Wash., area. However, rumors began to develop that 'Bartletts' might not require cross-pollination and considerable controversy developed on the subject. Weldon (1918) reported that large solid plantings of 'Bartletts' in California produced satisfactory crops. Tufts (1919), after a study of fruit production from hand-crossed flowers and from commercial orchards, concluded that all 'Bartlett' orchards should be provided with facilities for cross-pollination, that is, supplied with other varieties and bees. Westwood and Grim (1962) showed that 'Bartlett' yields were inversely related to distance from the pollenizer.
Kinman and Magness (1935) stated that the setting of fruit by all important pear varieties is aided by cross-pollination under some if not all conditions in the Pacific States. Magness also admitted that in some areas in some years 'Bartlett' sets good crops where no provision was made for pollination but that in other years heavier crops might be expected if pollination were provided. Davis and Tufts (1941) also considered the 'Bartlett' varying from almost completely self-sterile in the Sierra Nevada foothills of California to only partially self-sterile under interior valley and coastal conditions. Under these latter conditions, orchards planted solidly usually produce satisfactory crops. Griggs and Iwakiri (1954) finally showed that it was not the area where 'Bartletts' grew but the conditions under which they grew that determined their fruitfulness. They showed that the inclination of 'Bartletts' to produce parthenocarpic fruit determines its need for cross-pollination. This was supported by Bulatovic and Konstantinovic (1962); Wellington (1930); Reinecke (1930); Griggs and Vansell (1949); Konstantinovic and Milutinovic (1968); and Griggs et al. (1951).
If the orchard is well cared for, it will set a commercial crop of parthenocarpic fruit in many of the main pear-growing areas. If conditions are not good for parthenocarpic set, cross-pollination by bees will insure set of the crop. Parthenocarpic fruit, being seedless, is more desired by the consumer, although Reinecke (1930) showed that such fruit does not keep as well as pollinated fruit.
Stephen (1958) showed that when 'Bartlett' trees were caged for several seasons, the amount of fruit that set declined rapidly in succeeding years whether the tree was caged without bees or with bees alone without a bouquet of blooms from other varieties. The first year, there was no apparent difference. The second year, production in the cage containing only bees declined 58 percent. The following year, production was down by 92 percent. Stephen believed that the ability to produce fruit-set parthenocarpically decreased as time increased after the tree was cross-pollinated. These studies indicate that parthenocarpic fruit may be produced satisfactorily in some parts of Western United States, although, as Griggs (1970*) indicated, fruit set could be increased by interplanting pollinizers and using an ample supply of bees.
In other parts of the United States, 'Bartlett' should be interplanted with other cultivars and provided with bees. Evidently insect cross- pollination is essential for some cultivars in all areas (Hutson 1925, van Laere 1957) and for all cultivars in some areas. Where 'Bartletts' produce fruit parthenocarpically, the presence of other cultivars and bees can be an insurance in marginal seasons, and, during favorable seasons, tend to increase the number of seeded fruit. Lewis (1942) showed that parthenocarpy can be induced in some cultivars by frost. Steche (1959) showed that cross-pollination by honey bees trebled the crop when compared to the weight of fruit from self- or non-pollination.
Pollinators:
Waite (1895, 1899); Johnston (1927); Overholser et al. (1944); and Vansell (1942*, 1946) mentioned numerous species of insect visitors to the pear flowers, including hymenoptera, diptera, coleoptera, and other major groups. Like the other observers, Vansell (1942*) found that the honey bee was the most important visitor of all. In an orchard adjacent to uncultivated brush and timberland, which should have provided an abundant supply of insect visitors, honey bees accounted for more than 62 percent of the visitors to the flowers over two seasons even though there were few colonies of honey bees in the area. Vansell pointed out that although blowflies accounted for 23 percent of the visitors, they were of little value as pollinators, and concluded that honey bees were "practically the only distributors of pear pollen." He noted also, as did Scullen and Vansell (1942) Smith and Bradt (1967*), Stephen (1958), and Tufts and Philp (1923), that the bees showed a strong preference for pear pollen but weak interest in the nectar, which had a concentration of only 4 to 25 percent sugar and which influences the bee foraging behavior (Free and Smith 1961).
Pollination Recommendations and Practices:
Most growers of 'Bartlett' pears in California make no attempt to interplant pollenizer cultivars or to increase the local pollinating insects although the evidence indicates that they would benefit at times by doing so. Growers in other areas, and of most other cultivars should provide for cross-cultivar pollination and arrange to some degree for placement of honey bee colonies in or near their orchards. The colonies should be strong, sheltered from cold wind, exposed to the warm sun, provided with clean water, and protected from pesticides - a standard operation in the pollination of most fruit crops.
The number of visits by insect pollinators to pear flowers for optimum cross-pollination has not been determined. The pollinator population should be sufficiently heavy on cultivars that require cross-pollination that the bees are forced to forage on many blossoms to obtain a load of food. Waite (1895, 1899) recommended that there be honey bees in the neighborhood or at least within 2 or 3 miles, and that each large orchardist should keep bees. Root (1899) recommended that hives should be within one-half mile of the orchard. Fletcher (1900) stated that the keeping of bees by the grower might become necessary. Hooper (1935) advised growers to have one or more hives of bees in the vicinity of the orchard. Tufts (1919), Davis and Tufts (1941), Stephen (1968), Brown and Childs (1929), Vansell and DeOng (1925), and various others recommended that one colony of honey bees per acre be scattered throughout the orchard. Batjer et al. (1967) and Luce and Morris (1928) recommended one strong colony per two acres. Corner et al. (1964) recommended two colonies per acre of pears.
LITERATURE CITED:
BATJER, L. P., SCHOMER, H. A., NEWCOMER, E. J., and COYIER D. L.
1967. COMMERCIAL PEAR GROWING. U.S. Dept. Agr., Agr. Handb. 330, 47 pp.
BROWN, G. G., and CHI1DS, L.
1929. POLLINATION STUDIES OF THE ANJOU PEAR IN THE HOOD RIVER VALLEY. Oreg.
Agr. Expt. Sta. Bul. 239, 15 pp.
BULATOVIC, S., and KONSTANTINOVIC, B.
1962. THE ROLE OF BEES IN THE POLLINATION OF THE MORE IMPORTANT KINDS OF
FRUIT IN SERBIA. In 1st Internatl. Symposium on Pollination Proc., Copenhagen,
Aug. 1960. Commun. 7, Swedish Seed Growers' Assn., pp. 167-172.
CHITTENDEN E. J.
1914. POLLINATION IN ORCHARDS. Ann. Appl. Biol. 1 (1): 37-42.
CLOSE, C. P.
1903. REPORT OF THE HORTICULTURIST. In 14th Ann. Rpt. Del. Agr. Expt. Sta.
for year ending June 1902: 89-108.
CORNER, J., LAPINS, K. O., and ARRAND, J. C.
1964. ORCHARD AND HONEY BEE MANAGEMENT IN PLANNED TREE FRUIT POLLINATION.
Brit. Columbia Dept. Agr. Apiary Cir. 14, 18 pp.
DAVIS, L. D., and TUFTS, W. P.
1941. PEAR GROWING IN CALIFORNIA. Calif. Agr. Ext. Serv. Cir. 122, 87 pp.
FLETCHER, S. W.
1900. POLLINATION IN ORCHARDS. N.Y. (Cornell) Agr. Expt. Sta. Bull 181,
pp. 361-386.
______ 1907. POLLINATION OF KIEFFER AND BARTLETT PEARS. Mich. State Hort. Soc. 37th Ann. Rpt.: 36.
______ 1911. POLLINATION OF BARTLETT AND KIEFFER PEARS. In Va. Agr. Expt. Sta. Ann. Rpt. 1909 and 1910 pp. 212-232.
FLORIN, E. H.
1925. [PEAR POLLINATION.] Meddel. Perm. Kom. Eruktodlingsforsok. Sweden.
No. 5, pp. 38. From 1925 Expt. Sta. Rec. 53(7): 641. [In Swedish.]
FREE, J. B., and SMITH, M. V.
1961. THE FORAGING BEHAVIOUR OF HONEYBEES FROM COLONIES MOVED INTO A PEAR
ORCHARD IN FULL FLOWER. Bee World 42: 11-12.
GRIGGS, W. H., and IWAKIRI, B. T.
1954. POLLINATION AND PARTHENOCARPY IN THE PRODUCTION OF BARTLETT PEARS
IN CALIFORNIA. Hilgardia 22(19): 643-678.
______and VANSELL, G. H.
1949. THE USE OF BEE-COLLECTED POLLEN IN ARTIFICIAL POLLINATION OF DECIDUOUS
FRUITS. Amer. Soc. Hort. Sci. Proc. 54: 118-124.
______ IWAKIRI. B. T.. and DETAR. J. E.
1951. THE EFFECT OF 2, 4-5 TRICHLOROPHENOXYPROPIONIC ACID APPLIED DURING
THE BLOOM PERIOD ON THE FRUIT SET OF SEVERAL PEAR VARIETIES AND ON THE
SHAPE, SIZE, STEM LENGTH, SEED CONTENT AND STORAGE OF BARTLETT PEARS. Amer.
Soc. Hort. Sci. Proc. 58: 37-45.
HEDRICK, U. P.
1921. THE PEARS OF NEW YORK. 636 pp. N.Y. State Dept. Agr. 29th Ann. Rpt.,
v. 2, part 2. J. B. Lyons CO., Albany.
HOOPER, C. H.
1935. PEARS - THEIR POLLINATION, THE RELATIVE ORDER OF FLOWERING OF VARIETIES,
THEIR CROSS-FERTILIZATION AND THE INSECT VISITORS TO THE BLOSSOMS. Jour.
Sol-East. Agr. Col. [Wye, Kent] 36: 111-118.
HUTSON, R.
1925. THE HONEYBEE AS AN AGENT IN THE POLLINATION OF PEARS, APPLES AND
CRANBERRIES. Jour. Econ. Ent. 18: 387-391.
JOHNSTON, S.
1927. POLLINATION, AN IMPORTANT FACTOR IN SUCCESSFUL PEAR PRODUCTION. Mich
State Hort. Soc. 57th Ann. Rpt., pp. 196-199.
KINMAN, C. E., and MAGNESS, J. R.
1935. PEAR GROWING IN THE PACIFIC COAST STATES. U.S. Dept. Agr. Farmers'
Bul. 1739, 40 pp.
KONSTANTINOVIC, B., and MILUTINOVIC, M.
1968. [INFLUENCE OF BEES ON YIELD INCREASE IN SOME APPLE AND PEAR VARIETIES.]
Savremena Poljoprivreda 16(2): 161-166. [In Serbo-Croation, English summary.]
KRAUS, E. J.
1912. THE POLLINATION QUESTION. Oreg. Agr. Expt. Sta. Cir. Bul. 20, 7 pp.
LAERE, O. VAN
1957. [THE EFFECT OF BEES ON THE SETTING OF TREE FRUIT.] Maandbl. van de
Vlaamse Bieenb. 42(7): 188-193. [In Dutch.] AA-274/58.
LEWIS, D.
1942. PARTHENOCARPY INDUCED BY FROST IN PEARS. Jour. Pomol. and Hort. Sci.
20(1-2): 40-41.
LUCK, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223,
22 pp.
MAGNESS, J. R.
1937. PROGRESS IN PEAR IMPROVEMENT. U.S. Dept. Agr. Yearbook 1937: 615-630.
OVERHOLSER, E. L., OVERLEY, F. L., and ALLMENDINGER, D. F.
1944. PEAR GROWING AND HANDLING IN WASHINGTON. Wash. Agr. Expt. Sta. Pop.
Bul. 174: 30-35. 292
POWELL, G. H.
1902. KIEFFER PEAR POLLINATION. REPORT OF THE HORTICULTURIST. Del Agr.
Expt. Sta. Ann. Rpt. 13: 121-124.
REINECKE, O. S. H.
1930. THE RELATION OF SEED FORMATION TO FRUIT DEVELOPMENT OF THE PEAR.
So. African Jour. Sci. 27: 303-309.
ROOT, A. I.
1899. BEES NEAR BY ALMOST A NECESSITY TO SUCCESSFUL FRUIT- GROWING. Gleanings
Bee Cult. 27: 56.
SCULLEN, H. A., and VANSELL, G. (A.) H.
1942. NECTAR AND POLLEN PLANTS OF OREGON. Oreg. Agr. Expt. Sta. Bul. 412,
63 pp.
STECHE, W.
1959. [EFFECT OF POLLINATION BY BEES ON YIELD AND FRUIT FORMATION IN THE
PEAR FONDANT DE CHARNEU.] Erwerbsobstbau 1(7): 132-134. [In German.] AA-315/60.
STEPHEN, W. P.
1958. PEAR POLLINATION STUDIES IN OREGON. Oreg. Agr. Expt. Sta. Tech. Bul.
43, 43 pp.
SWAYNE, G.
1824. ON FERTILIZING THE BLOSSOMS OF PEAR TREES. London Hort. Soc. Trans.
5: 208-212.
TUFTS, W. P.
1919. POLLINATION OF THE BARTLETT PEAR. Calif. Agr. Expt. Sta. Bul. 307:
369-390.
TUFTS W. P. and PHILP, G. L.
1923. PEAR POLLINATION. Calif. Agr. Expt. Sta. Bul. 373, 36 pp.
VANSELL, G. H.
1946. BEES AND PEAR POLLINATION. Oreg. State Hort. Soc. Proc. 37: 51-53.
______and DE ONG E. R.
1925. A SURVEY OF BEEKEEPING IN CALIFORNIA AND THE HONEYBEE AS A POLLENIZER.
Calif. Agr. Expt. Sta. Cir. 297, 22 pp.
WAITE, M. B.
1895. THE POLLINATION OF PEAR FLOWERS. U.S. Dept. Agr. Div. Veg. Path.
Bul. 5, 86 pp.
______ 1899. POLLINATION OF POMACEOUS FRUIT U.S. Dept. Agr. Yearbook 1898: 167-180.
WELDON, G. P.
1918. PEAR GROWING IN CALIFORNIA. Calif. State Commr. Hort. Monthly Bul.
7: 219-410.
WELLINGTON, R. A.
1930. POLLINATION OF PEARS AND SMALL FRUITS. N.Y. State Hort. Soc. Proc.
75th Ann. Mtg.: 216-220.
WESTWOOD, M. N., and GRIM, J.
1962. EFFECT OF POLLINIZER PLACEMENT ON LONG TERM YIELD OF ANJOU, BARTLETT
AND BOSE PEARS. Amer. Soc. Hort. Sci. Proc. 81: 103-107.
PERSIMMON (ORIENTAL OR KAKI)
Diospyros kaki L. f., family Ebenaceae
The Oriental or Kaki persimmon (fig. 153) is cultivated for its delicious, highly nutritious, pale-orange to red, 1- to 5-inch, zero- to eight-seeded fruit that may be eaten out of hand or used in culinary dishes ranging from appetizers to yogurt.
It is grown on about 500 acres in California (Swedberg and Nelson 1970) and to a lesser extent in several other Southern States. It is hardy as far north as Pennsylvania (Griffith and Preston 1961).
The Oriental should not be confused with the smaller-fruited but edible
American persimmon (D. virginiana L., and D. texana Scheele)
(fig. 154), which are common forest plants but rarely cultivated except
as dooryard ornamentals (Pape 1957). The fruits of D. virginiana also
contain up to eight large seeds. The trees are generally dioecious, with
single pistillate flowers and usually three staminate flowers in a group.
The pollen is generally carried from the staminate to the pistillate flowers
by insects, but Fletcher (1942) stated that wind may also contribute. The
flowers are a good source of nectar and are visited throughout the day
by bees for nectar and pollen (Pellett 1947*). Oertel (1939) listed D.
virginiana as a major source of nectar in five States and of some value
in 22 States, indicating that in acres it is far more common than the Oriental
one. (See also Condit 1919, and Preston and Griffith 1966.)
[gfx]FIGURE 153. - Complete and sectioned fruit of kaki persimmon.
FIGURE 154. - Fruiting branch of American persimmon.
Plant:
The Oriental persimmon is a round-topped, usually deciduous, tree to 20 feet high unless it is competing with other trees for light, when it might reach 40 feet. It has 3 to 7-inch elliptic glossy leaves and 3/4 inch long, yellowish-white flowers. The fruit is variable in shapeÑ oval, round, globular, or elongatedÑand ribbed with brownish pulp surrounding the seed, if any are present. Cultivation is similar to that of citrus or stone- fruit trees grown in warmer areas. Camp and Mowry (1945) reported 14 to 18 percent total sugars in the mature fruit.
Inflorescence:
The campanulate flowers are three-quarters of an inch long and yellowish white, with outfolded, prominent green sepals extending beyond the corolla. The staminate ones have 16 to 24 stamens, the pistillate ones have eight staminodia (Bailey 1949*) (fig. 155). Nectar secretion is probably similar to that of the American species. The blossoms hang downward, with the stigma rarely exposed beyond the petals, which offers little opportunity for wind pollination. Hume (1913) stated that no crosses between D. kaki and D. virginiana had ever resulted in production of viable seed.
[gfx] FIGURE 155. - Longitudinal section of 'Fuji' kaki persimmon blossom, x 5.
Pollination Requirements:
Ryerson (1927) stated that Oriental persimmon trees may be staminate, pistillate, or both, but that pollination is not essential for fruit setting. He believed that ample crops of seedless fruits could be obtained without pollination. Hodgson (1938) confirmed that Oriental plants produce seedy fruits if pollinated but set a few of the preferred seedless fruit if no pollen is available. Later, Hodgson (1939) stated that there was a high degree of parthenocarpy, and that various cultivars of Orientals contained the following types of plants: (1) Pistillate; (2) pistillate, sporadically monoecious; (3) monoecious; (4) monoecious, sporadically staminate or pistillate; and (5) staminate.
Gould (1940) concluded there are pollination problems with Oriental persimmons just as there are with many other fruits. Some cultivars will develop some fruit to maturity without pollination, whereas other cultivars drop their fruit prematurely or fail entirely to set without pollination. The length of time to flower opening and the actual time of pollination of individual flowers has not been determined.
Pollinators:
Honey bees and bumble bees visit persimmon blossoms freely for nectar and pollen and would appear to be dependable agents in the transfer of pollen. Fletcher (1942) stated that pollen is generally distributed by bees although wind can carry the pollen great distances. The effectiveness of wind on the downward hanging campanulate flower would appear to be minor. Abbott (1926) stated that pollen from our native species does not cause Oriental persimmon fruit set, but the pollen must come from staminate Oriental plants.
Pollination Recommendations and Practices:
None.
LITERATURE CITED:
ABBOTT, C. E.
1926. THE KAKI AND THE LOQUAT. Fla. State Hort. Soc. Proc. 39: 228-233.
CAMP A. F. and MOWRY. H.
1945. THE CULTIVATED PERSIMMON IN FLORIDA. Fla. Agr. Expt. Sta. Bul. 124,
31 pp.
CONDIT, I. J.
1919. THE KAKI OR ORIENTAL PERSIMMON. Calif. Agr. Expt. Sta. Bul. 316,
pp. 231-266.
FLETCHER, W. F.
1942 THE NATIVE PERSIMMON. U.S. Dept. Agr. Farmers' Bul. 685, 22 pp.
GOULD, H. P.
1940. ORIENTAL PERSIMMONS. U.S.. Dept. Agr. Leaflet 194, 8 pp.
GRIFFITH, E., and PRESTON, W. H., JR.
1961. THE ORIENTAL PERSIMMON IN MARYLAND, VIRGINIA AND PENNSYLVANIA. Plants
and Gard. 17(1): 32-34.
HODGSON, R. W.
1938. GIRDLING TO REDUCE FRUIT DROP IN THE HACHIYA PERSIMMON. Amer. Soc.
Hort. Sci. Proc. 36: 405-409.
______ 1939. FLORAL SITUATION, SEX CONDITION AND PARTHENOCARPY IN THE ORIENTAL PERSIMMON. Amer. Soc. Hort. Sci. Proc. 37: 250252.
HUME, H. H.
1913. THE FLOWERING OF DIOSPYROUS KAKI. St. Louis Acad. Sci. Trans. 12(5):
125-135.
OERTEL, E.
1939. HONEY AND POLLEN PLANTS OF THE UNITED STATES. U.S. Dept. Agr. Cir.
554, 64 pp.
PAPE, E. W.
1957. THE AMERICAN PERSIMMON. Organic Gard. and Farming 4(11): 28.
PRESTON, W. H., JR., and GRIFFITH, E.
1966. CURRENT STATUS OF THE ORIENTAL PERSIMMON IN TEMPERATE EASTERN UNITED
STATES. North. Nut Growers' Assoc. 57th Ann. Rpt.. pp. 112-123.
RYERSON, K. A.
1927. CULTURE OF THE ORIENTAL PERSIMMON IN CALIFORNIA. Calif. Agr. Expt.
Sta. Bul. 416, 63 pp.
SWEDBERG, J. H., and NELSON, G. A.
1970. CALIFORNIA FRUIT AND NUT ACREAGE. Calif. Crop and Livestock Rptg.
Serv., 19 pp.
PLUM AND PRUNE
Prunus spp., family Rosaceae
Prunes are basically plums that because of their high sugar content can be dried successfully without removal of the stone. More than 2,000 varieties of plums and prunes, comprising 15 species, have been grown in the United States. Some are native to America; however, all commercially grown cultivars in California, the major producer of plums and prunes, belong to the European plum (P. domestica L.), the Japanese plum (P. salicina Lindl.), or the hybrids of the latter (Allen 1929). The best known and most important are the European plums and prunes of which the Italian prune is the most widely grown in the world. Of the numerous species of native plums (P. americana Marsh.) (fig. 156), only a few are commercially less important. These include the 'Damson ' (P. insititia L.), myrobalan or cherry plum (P. cerasifera Ehrh.) and the Simon type (P. simonii Carr.) (Allen 1929).
In 1971, California produced an estimated 101,000 tons of plums and 131,000 tons of prunes, while Idaho, Michigan, Oregon, and Washington, produced a combined total of only 63,500 tons. The total value of the crop in all of these States was $62 million. The 1969 acreage in California was 21,770 acres of plums (producing 3.08 tons per acre) and 97,560 acres of prunes (producing 1.33 tons of fruit per acre) (Henderson and Swedberg 1970).
[gfx] FIGURE 156. - Flowers of the native plum.
Plant:
The deciduous trees of plums and prunes (fig. 157) are spaced in orchards 16 to 24 (average 20) feet apart, depending upon species, soil type, and other factors (Kinman 1943). The Japanese types are in general smaller than the European types, but, depending upon vigor and type, the height may vary from 10 to 20 feet. In California, the numerous white flowers appear ahead of the leaves from late February to mid-March, and the fruit is harvested from May to July.
[gfx] FIGURE 157. - Closeup of prune flowers.
Inflorescence:
The numerous white to cream-colored, 1 inch or smaller flowers occur in clusters of one to three along the new growth of the branches of the plum. The Japanese types bloom about the time almonds bloom. The European types bloom about the time peaches bloom. Buchanan (1903) stated that the anthers are about level with the two-lobed stigma, but Brown (1951) noted that the stigma of 'President' cv. was twice the length of the stamens (figs. 158 and 159).He also referred to the "long-styled low- nectared 'Jefferson' cv." Knuth (1908, p. 344) stated that the stigma of P. domestica projects beyond the inner stamens but is at the same level of the outer ones, but in P. insititia it exceeds the longest stamen in length. The style leads to one ovary with two ovules, one of which rarely develops. Considerable nectar is secreted by the fleshy lining of the receptacle at the base of the styler column (Buchanan 1903), and, although quite dilute in the early morning, it becomes more concentrated as the day advances. Vansell (1934) reported the sugar concentration of only 6.2 percent at 7 to 8 a.m. when the relative humidity (R.H.) was 100 percent and the weather was foggy; 8.1 percent at 9:40 a.m., when the R.H. was down to 85 percent; and 25.8 at 2 p.m., when the R.H. was down to 53 percent. Later, Vansell (1942*) reported that the sugar concentration in the nectar of the 'Gos' plum blossom increased from 20 percent at 8:30 a.m. to 37 percent at 4 p.m.
Brown (1951) found considerable differences in the amount of nectar produced per flower, with one cv. ('Kea') producing 1.7 ml per 100 flowersÑmore than 10 times as much as the lowest nectar-yielding cultivar. He reported a close correlation between nectar volume per flower and the number of bees present. Vansell (1942*) also observed bees that in one case shifted their activity from plums at about 10 a.m. to more attractive manzanita (Arctostaphylos sp.) but shifted back to plums in the midafternoon. Roberts and Congdon (1955) considered that plum pollen was not sufficiently attractive to pollen-gathering insects to insure effective pollination.
The flower is open for 5 days according to Knuth (1908, p. 344) with the stigma being receptive almost 2 days before the anthers dehisce. How long it is receptive is not clear. Backhouse (1911) said that if the flowers are not pollinated, they shed in 3 or 4 days.
As a source of pollen and nectar for honey bees, plums are considered of stimulative value but because of the short flowering period and low sugar content of the nectar little surplus honey is obtained.
[gfx] FIGURE 158. - Longitudinal section of French prune flower, x 7.
FIGURE 159. - Longitudinal section of 'Mariposa ' plum flower, x 8.
Pollination Requirements:
Rather thorough studies have been made to determine the pollination requirements of the different species of plums (Backhouse 1911, 1912; Hendrickson 1916, 1918, 1919a, 1919b, 1922, 1923, 1930; Luce and Morris 1928; Marshall 1920; MacDaniels 1942; Philp and Vansell 1932, 1944; Waugh 1898). These studies established that plum cultivars vary from completely self-incompatible, in which they set no fruit with their own pollen, to complete self-compatibility, where a full crop is set from the plants' own pollen. Some are also cross-incompatible - not receptive to pollen of certain other cultivars. The majority are self-incompatible (Backhouse 1911; Griggs 1970*; Griggs and Hesse 1963). Pollinating insects are necessary on all cultivars to transfer the pollen from the anthers to the stigmas (Alderman and Angelo 1933). Thompson and Liu (1972) concluded from their tests that the Italian prune is fully self- fruitful and bees are not necessary for pollen distribution. Dickson and Smith (1953) stated that except for the Italian prune and Stanley, all European cultivars in Canada are self-unfruitful and require mixed plantings, and those two benefit from cross-pollination in many orchards. They also stated that the 'Burbank' and the 'Shiro', the main Japanese cultivars are also self-unfruitful and concluded that insect pollination is necessary for all cultivars, both European and Japanese. Luce and Morris (1928) also noted that most cultivars are self-sterile. Dorsey (1919) concluded that pollen abortion was not the cause of sterility, but rather it was associated with genetic factors in embryo development.
To provide pollen within the orchard, Griggs and Hesse (1963) recommended that in every fourth tree location in every fourth row there should be planted a compatible cultivar that flowers consistently at the same time as the primary cultivar flowers. Free (1962) showed that fruit set on plum trees decreased sharply with increased distance from the pollenizer tree. Trees adjacent to pollenizer trees had a greater set on the sides facing the pollenizers than on their far sides, indicating that the pollen was not thoroughly distributed over the tree.
Pollinators:
The honey bee has been recognized as the primary pollinating agent of plums and prunes by numerous workers since Waugh (1898, 1900) stressed its importance (Buchanan 1903; Free 1962; Hendrickson 1916, 1930; Hooper 1936; Kinman 1938,1943; MacDaniels 1942), although bumble bees and other wild bees and blowflies and other flies are given some credit by Backhouse (1912) and Brown (1951). Wind is not a factor (Backhouse 1912, Waugh 1900). Hooper (1936) pointed out that the honey bee was best because of its strong tendency to continue foraging from one source. As with many other deciduous fruit trees, plums and prunes bloom early in the spring when few pollinating agents are active. Also, large plantings have more blooms than local pollinators can service. Kinman (1924, 1938, 1943) warned that crop failures can be expected if no bees are present. Honey bees are easy to transport and establish in the orchard at flowering time, and are essential in the commercial production of both plums and prunes. The blooms are usually attractive to bees all day but more so in the morning. The plums and prunes, like other stone fruits, require that only one viable pollen tube reach the ovary to produce a fruit, but this pollen grain must, in most cases, arrive from another compatible blossom and at the right time. To assure that such pollen reaches the maximum number of flowers to produce the plum or prune crop desired, a heavy population of pollinators is required.
Hendrickson (1916, 1918) indicated that although the number of blooms on a tree varies greatly from year to year, a set of 15 to 20 percent results in massive crops. This only occurs when proper pollenizers are interplanted and bees are present in large numbers.
Pollination Recommendations and Practices:
Hendrickson (1916) concluded that best pollination would result " . . . if the bees were brought in from some outside district and scattered about the orchard, about one hive to the acre, during the blossoming period, and then removed." Philp and Vansell (1932) stated that bees were rented for plum pollination during World War I at $5 to $7 per colony.
Allen (1929) recommended one colony per acre, but believed that a centrally located apiary might serve one or even more small orchards. Roberts and Congdon (1955) said that the groups of colonies should be no further than 150 yards apart. Philp and Vansell (1944) suggested one colony per acre, the colonies in groups of 10 to 20. The Great Britain Ministry of Agriculture, Fisheries, and Food (1958) also recommended strong colonies be placed in the orchard. Roberts (1956) stated that the number of colonies per acre necessary to insure good pollination will vary (in New Zealand), but in most circumstances one vigorous colony per acre will meet all requirements. Stephen (1961) also recommended one colony per acre, with the bees to be moved in at one-third bloom stage.
Griggs and Hesse (1963) recommended for each acre at least one strong colony of honey bees with four or five frames of brood and enough bees to cover eight frames, the colonies to be placed in the orchard in groups of 5 to 10.
Most growers take some steps to see that bee colonies are in or near their orchards.
LITERATURE CITED:
ALDERMAN, W. H., and ANGELO, E.
1933. SELF AND CROSS STERILITY IN PLUM HYBRIDS. Amer. Soc. Hort. Sci. Proc.
29: 118-121.
ALLEN, F. W.
1929. PLUM GROWING IN CALIFORNIA. Calif. Agr. Ext. Sen. Cir. 34, 65 pp.
BACKHOUSE, W. [O.]
1911. SELF-STERILITY IN PLUMS. Gard. Chron. 1296: 299.
______ 1912. THE POLLINATION OF FRUIT TREES. Gard. Chron. 1352: 381.
BROWN, A. G.
1951. FACTORS AFFECTING FRUIT PRODUCTION IN PLUMS. Fruit Yearbook 1950
(4): 12-18.
BUCHANAN, R. E.
1903. CONTRIBUTION TO OUR KNOWLEDGE OF THE DEVELOPMENT OF PRUNUS AMERICANA.
Iowa Acad. Sci. Proc.: 77-93.
DICKSON, G. H., and SMITH, M. V.
1953. FRUIT POLLINATION. Ontario Agr. Col. Cir. 172, 6 pp.
DORSEY M. J.
1919. A STUDY OF STERILITY IN THE PLUM. Genetics 4: 417-488.
FREE, J. B.
1962. THE EFFECT OF DISTANCE FROM POLLINIZER VARIETIES ON THE FRUIT SET
ON TREES IN PLUM AND APPLE ORCHARDS. Jour. Hort. Sci. 37(4): 262-271.
GREAT BRITAIN MINISTRY OF AGRICULTURE, FISHERIES AND FOOD.
1958. THE POLLINATION OF PLUMS AND CHERRIES. Gr. Brit. Min. Agr. Fish.
and Food Adv. Leaflet 378, rev., 6 pp. London.
GRIGGS, W. H., and HESSE, C. O.
1963. POLLINATION REQUIREMENTS OF JAPANESE PLUMS. Calif. Agr. Expt. Stat.
Ext. Serv. Leaflet 163, n.p.
HENDERSON, W. W., and SWEDBERG, J. H.
1970. CALIFORNIA FRUIT AND NUT STATISTICS. 1968-1969. Calif. Crop and Livestock
Rptg. Serv., 11 pp.
HENDRICKSON, A. H.
1916. THE COMMON HONEYBEE AS AN AGENT IN PRUNE POLLINATION. Calif. Agr.
Expt. Sta. Bul. 274: 127-132.
______ 1918. THE COMMON HONEYBEE AS AN AGENT IN PRUNE POLLINATION. Calif. Agr. Expt. Sta. Bul. 291: 215-236.
______ 1919a. PLUM POLLINATION. Calif. Agr. Expt. Sta. Bul. 310, 28 pp.
______ 1919b. FIVE YEARS RESULTS IN PLUM POLLINATION. Amer. Soc. Hort. Sci. Proc. 15: 65-66.
______ 1922. FURTHER EXPERIMENTS IN PLUM POLLINATION. Calif. Agr. Expt. Sta. Bul. 352: 247-266.
______ 1923. PRUNE GROWING IN CALIFORNIA. Calif. Agr. Expt. Sta. Bul. 328, 38 pp.
______ 1930. THE ESSENTIALS OF PLUM POLLINATION. Blue Anchor [Sacramento] 7(2): 8-9, 31-32.
HOOPER, C. H.
1936. PLUMS; NOTES ON THEIR POLLINATION, ORDER OF FLOWERING OF VARIETIES
AND INSECT VISITORS TO THE BLOSSOMS. Jour. Sol-East. Agr. Col. [Wye, Kent]
38: 131-140.
KINMAN, C. F.
1924. PLUM AND PRUNE GROWING IN THE PACIFIC STATES. U.S. Dept. Agr. Farmers'
Bul. 1372, 59 pp. ______ 1938. PLUM AND PRUNE GROWING IN THE PACIFIC STATES.
U.S. Dept. Agr. Farmers' Bul. 1372, rev., 55 pp. _
_____ 1943. PLUM AND PRUNE GROWING IN THE PACIFIC STATES. U.S. Dept. Agr. Farmers' Bul. 1372, rev., 55 pp.
LUCE, W. A., and MORRIS, O. M.
1928. POLLINATION OF DECIDUOUS FRUITS. Wash. Agr. Expt. Sta. Bul. 223,
22 pp.
ACDANIELS, L. H.
1942. NOTES ON THE POLLINATION OF THE ITALIAN PRUNE. Amer. Soc. Hort. Sci.
Proc. 40: 84-86.
MARSHALL, R. E.
1920. REPORT OF THREE YEARS, RESULTS IN PLUM POLLINATION IN OREGON. Amer.
Soc. Hort. Sci. Proc. 16: 42 - 49.
PHILP, G. L., and VANSELL G. H.
1932. POLLINATION OF DECIDUOUS FRUITS BY BEES. Calif. Agr. Ext. Serv. Cir.
62, 26 pp.
______and VANSELL, G. H.
1944. POLLINATION OF DECIDUOUS FRUITS BY BEES. Calif. Agr. Ext. Serv. Cir.
62, rev., 26 pp.
ROBERTS, D.
1956. SUGAR SPRAYS AID FERTILISATION OF PLUMS BY BEES. New Zeal. Jour.
Agr. 93(3): 206-207, 209, 211.
______and CONGDON, N. B.
1955. THE RELATIONSHIP OF NECTAR SECRETION (VOLUME) AND SUGAR CONCENTRATION
TO INSECT POLLINATION OF PLUMS (PRUNUS SPP.). New Zeal. Jour. Sci. and
Tech. Sect. A, 37(3): 196206.
STEPHEN, W. P.
1961. BEES AND POLLINATION OF STONE FRUITS. Oreg. State Hort. Soc. Ann.
Rpt 53, pp. 78-79.
THOMPSON, M. M., and LIU, L. J.
1972. POLLINATION AND ERRATIC BEARING IN 'ITALIAN PRUNES' Amer. Soc. Hort.
Sci. Proc. 97: 489-491.
VANSELL, G. H.
1934. RELATION BETWEEN THE NECTAR CONCENTRATION IN FRUIT BLOSSOMS AND THE
VISITS OF HONEY BEES. Jour. Econ. Ent. 27: 943-945.
WAUGH, F. A.
1898. POLLINATION OF PLUMS. Vt. Agr. Expt. Sta. 11th Ann. Rpt. 1897-98:
238-262.
______ 1900. PROPAGATION OF PLUMS - PRELIMINARY REPORT. Vt. Agr. Expt. Sta. 13th Ann. Rpt: 333.
POMEGRANATE
Punica granatum L., family Punicaceae
Pomegranates were grown in 1970 on 1,220 acres in California, the leading State in the production of this delicious fruit (Henderson and Kitterman 1971). The largest single planting was 120 acres (Larue 1964). The estimated value of the crop is less than one-half million dollars. Average production per acre is about 5 tons of fruit. Only one cv., 'Wonderful', is grown commercially in California. It grows best in areas of cool winters and hot dry summers (Purseglove 1968*).
Plant:
The plant usually grows as a bush or shrub 6 to 15 feet in height and is deciduous in the cooler areas of its range. Spacing in the orchard is 12 to 15 feet, or the plants are doubleset in hedgerows with more space between rows.
The fruit is a large, globose berry, red-green or violet when ripe (fig. 160). Its pulp is eaten out of hand and in salads, or its juice is used in a refreshing drink or sirup. A jet-black ink is made from the rind. Kihara (1958) stated that normal fruit contains an average of 667 seeds. Evreinoff (1963) stated that vegetative growth starts from mid-March to mid-April and flowering is primarily in May.
[gfx] FIGURE 160. - Mature pomegranate fruit on the tree.
Inflorescence:
From one to several flowers may be borne on a twig, one being terminal,
the others lateral and solitary. The odorless but colorful flowers are
large, 1 1/2 to 3 inches in length, campanulate or cylindrical, and generally
reddish but sometimes yellow to white. There are five or more petals, some
of which may be doubled. The stamens are numerous, erect to slightly curved
at the apex, and red (fig. 161). The anthers are yellow. The ovary is many
celled, each cell with numerous ovules. The style is yellowissh red and
roughly an inch long. The stigma is globose or truncate and yellowish green
(Bailey 1916*, v. 5., pp. 2750- 2751, 2861-2862; Knuth 1908*, p. 440; Ochse
et al. 1961).
The pomegranate flower has been referred to as nectarless; however, flowers of cv. 'Wonderful', grown in Tucson in 1973, contained several drops of nectar with 27 percent soluble solids (sugars).
The flowers are primarily of two types: the fruitful, large, long- styled, long-stamened, colorful flowers, in which the anthers and the stigma are at about the same height; and the smaller, barren, short- styled, short-stamened flower, in which the stigma is far below the anthers. Occasionally, "intermediate" flowers have styles that may equal the length of the long-styled flowers or be as short as the short-styled ones. Those with long styles occasionally become fertilized, but only rarely does such fruit mature and then it is malformed and defective. On the contrary, short-styled flowers are never fertilized and soon shed. The petals of these are a dull, pale rose, and the pollen is defective (Hodgson 1917).
The long-styled flowers usually develop on old wood, whereas the short-styled flowers develop on new growth. The relative proportion of each is influenced by many factors. The best fruit is obtained from the early flowers, probably because they develop during more favorable meteorological conditions (Evreinoff 1953).
[gfx] FIGURE 161. - Longitudinal section of 'Wonderful' pomegranate flower, x 2.
Pollination Requirements:
Little is known about the pollination of pomegranates. Knuth (1908*, p. 440) stated that beetles belonging to the genera Cetonia and Trichodes effect both cross- as well as self-pollination, while devouring the flowers. The ability of the plant to self-pollinate or its need for transfer of pollen either within its own flower, between flowers, or between plants is unknown.
Kihara (1958) reported the discovery of a "seedless" pomegranate in which the pollen was sterile but the fruit developed. It had only half (307) of the normal number of developed embryos. These were not viable seeds; however, the size of the fruit was normal.
Pollinators:
Where no nectar is produced, only pollen-collecting insects would be of value to the blossom. If beetles contribute to the pollination of this plant, as Knuth (p. 440, 1908*) indicated, the visitation by pollen- collecting bees would appear to be much more valuable. No information is available on the degree of benefit such flowers may derive from beetles or, if bees are beneficial, how many bee visits would be desired.
Pollination Recommendations and Practices:
There are no recommendations for the use of pollinating agents on pomegranates, but some growers in California arrange for honey bee colonies to be placed in or near their fields, believing that their presence benefits pomegranate fruit production.
LITERATURE CITED:
EVREINOFF. V. A.
1953. [POMOLOGICAL STUDIES OF THE POMEGRANATE.] Ecole Natl. Super. Agron.
Ann. 1: 141-154. [In French.]
HENDERSON, W. W., and KITTERMAN, J. M.
1971. 1970 CALIFORNIA FRUIT AND NUT ACREAGE. U.S. Dept. Agr. Statis. Rptg.
Serv., 19 pp.
HODGSON, R. W.
1917. THE POMEGRANATE. Calif. Agr. Expt. Sta. Bul. 276, pp. 163-192.
KIHARA, J. H.
1958. BREEDING OF SEEDLESS FRUIT. Seiken Ziho 9: 1-7.
LARUE, J. H.
1964. POMEGRANATES: BACKYARD FRUIT WITH COMMERCIAL IDEAS. West. Fruit Grower
18(3): 27-28.
QUINCE
Cydonia oblonga Mill., family Rosaceae
The common quince is closely related to the apple and pear but is of much less importance in the United States, where possibly 1,000 tons are produced commercially each year (Magness et al. 1971). In Europe, the fruit is more highly esteemed and more extensively grown than in the United States. This species should not be confused with the flowering quinces (Chaenomoles spp.) grown primarily as ornamentals, but whose fruit is occasionally utilized also. Chandler (1951*) stated that the Chinese quince (Chaenomoles sinensis (Thouin) Koehne) makes nearly as good jams and jellies as the common quince.
Plant:
The quince is deciduous, about as hardy as the peach, but is less tolerant to warm weather. The plant is 10 to 20 feet tall, spineless, and similar in appearance and growth habits to the apple. The trees are usually set 6 to 12 feet apart. The fruit is smaller than the average apple and has a pleasant odor but may contain more than 50 seeds.
Inflorescence:
Quince trees may bloom from February to May depending upon the species and geographical area. Blooms on a tree may last 11 to 20 days with full bloom lasting 6 to 10 days.
The quince flower is similar to the apple, but in general it is coarser and more colorful. It develops on first year growth and therefore appears later in the season than the apple blossom. It may be as much as 2 inches across, with five cup-shaped petals that vary, according to cultivar, from white to scarlet. It bears 20 or more stamens and five styles leading to a five-carpel ovary that, as a fruit, may produce the more than 50 seeds (fig. 165). The stamens and pistils are fully twice as large as and thicker than those of the apple (Waite 1899). A nectary at the base of the styles is half concealed by the closely spaced filaments, and only honey bees or larger insects can push in between the petals and stamens to reach the nectar.
Nectar secretion and pollination of the common quince was studied by Stancevic (1963) and Simidchiev (1967) who found that the amount secreted by a blossom in 24 hours varied from 0.851 to 1.634 mg on an average in the different cultivars with sugar concentration varying from 41.3 to 49.9 percent. Nectar secretion continued day and night for 5 days but was highest around noon each day. The flowers are freely visited by pollen and nectar collecting insects.
[gfx] FIGURE 165. - Longitudinal section of 'Smyrna' quince flower, x 4.
Pollination Requirements:
The stigma of the quince is receptive even before the flower opens. When it opens, the outer anthers are first to dehisce, the inner ones remaining closed and beneath the receptive stigma. Because most insects settle on the flower center, crossing is effected before selfing is possible. Later, the inner anthers dehisce in contact with the stigma, but whether it remains receptive seems to be unknown. The question then deals with the effectiveness of this self-pollination. Chandler (1951*) stated that the flowers of the quince varieties seem self-fruitful enough, but he did not indicate whether he referred to self-compatibility or self- fertilization. Waite (1899) cross-pollinated several cultivars and observed no striking benefit to be derived from pollinating insects bringing pollen from other cultivars. Gardner et al (1962) and Shoemaker and Teskey (1959) also concluded that quinces were self-fertile. Mace (1949) stated that insects cross-pollinate the flowers shortly after the, open, but if this is not accomplished the flowers self later. He did not indicate how he arrived at this conclusion.
Ershov (1966) conducted fertility studies on quince varieties from different places over a 5-year period. Of 23 varieties tested, only five were self-fertile. The other were partially to completely self-sterile. He concludec that for all practical purposes the quince is a self-sterile crop. Where mutual pollination exists, a good harves can be obtained.
There seems to be no question that pollinating insect are needed when the flower first opens. In apples and numerous other plants, pollination at the earliest possible time is highly desirable. This would appear to be the case with quince.
Pollinators:
The most thorough study of pollinating agents of quince was made by Simidchiev (1967) on five cultivar of the common quince. He showed that quince is highly attractive to honey bees throughout the day for both nectar and pollen. This activity is highly conducive to transfer of pollen from anther to stigma between cultivars as well as within the individual flower. Simidchiev (1967) noted that under favorable conditions for bee flight, when bees visited the blossoms from morning to night, 5 percent gathered only nectar, 11 percent gathered only pollen, and 84 percent gathered both. The flowers are highly attractive to honey bees, therefore where needed they should be satisfactory pollinatin agents.
Pollination Recommendations and Practices:
None.
LITERATURE CITED:
ERSHOV, L. A.
1966. [BIOLOGY OF QUINCE POLLINATION.] In Trushechkin, V. G., Tarakanov,
G. I., and Nicolaenko, N. P. Reports of the Soviet Scientists to the 17th
International Congress on Horticulture, pp. 106-111, Moscow. [In Russian,
English summary.]
GARDNER, V. R., BRADFORD, F. C., and HOOKER, H. D., JR.
1952. THE FUNDAMENTALS OF FRUIT PRODUCTION. 739 pp. McGraw-Hill Book Co.,
Inc., New York.
MACE, H.
1949. BEES, FLOWERS AND FRUIT. 184 pp. Wyman and Sons Ltd., London.
MAGNESS, J R., MARKLE, G. M., and COMPTON, C. C.
1971. FOOD AND FEED CROPS OF THE UNITED STATES - A DESCRIPTIVE LIST CLASSIFIED
ACCORDING TO POTENTIALS FOR PESTICIDES RESIDUES. N.J. Agr. Expt. Sta.,
Interregion. Res. Pro;. IR-4, IR Bul.1, 255 pp.
SHOEMAKER, J. S., and TESKEY, B. J. E.
1959. TREE FRUIT PRODUCTION. 456 pp. John Wiley & Sons, New York.
SIMIDCHEIV, T.
1967. [INVESTIGATIONS ON THE NECTAR AND HONEY PRODUCTIVITY OF THE QUINCE
(CYDONIA VULGARIS PERS.).] Nauch. Trud. Vissh. Selskostop. Inst. Vasil
Kolarov 16(2): 241- 253. [In Bulgarian, German and Russian summaries.]
STANCEVIC, A. S.
1963. [STUDY OF THE POLLEN GERMINATION AND SELF-POLLINATION OF THE MORE
IMPORTANT QUINCE VARIETIES GROWN IN YUGOSLAVIA.] Arh. za Poljaprivredne
Nauke 16(52): 106-112. [In Serbian, English summary.]
WAITE, M. B.
1899. POLLINATION OF QUINCE. U.S. Dept. Agr. Yearbook 1898: 167-180.