CHERIMOYA
Annona cherimola Mill., family Annonaceae 20The cherimoya occurs naturally in the Andean valleys of Ecuador and Peru (Purseglove 1968*), but it has been carried to various other subtropical areas of the world where it has become very popular. It is grown to a limited extent in Hawaii and Florida, with an estimated 50 to 60 acres in California (Schroeder 1948, 1956). Sarasola (1960) stated that about 300 acres are grown in the area of Almunecar, Spain. There are numerous cultivars (Anonymous 1956, Brooks and Olmo 1952). The hybrid of A. cherimola X A. squamosa L., termed "atemoya," has also been cultivated (Ahmed 1936, Thakur and Singh 1965).
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20 Other species of Annona that are cultivated or sometimes cultivated include: A. diversifolia Saff., the Ilana; A. montana Macfad., mountain soursop; A. muricata L., soursop or guanababa; A. squamosa L., sugarapple or sweetsop; and A. reticulata L., custard-apple or bullocks-heart. Unlike A. cherimola, none have floral fragrance, but otherwise their pollination requirements may be similar. They are mentioned here because of their popularity in Asia and the tropics and their potential value in ou subtropical areas (R. J. Kinght, Jr., personal commun., 1971).Plant:
The cherimoya tree may reach 30 feet tall but is usually much smaller, somewhat spreading or scraggly, and semideciduous. It sheds its leaves in the spring just before the flowers appear (Schroeder 1941). It will grow anywhere the avocado will grow. The 'Bays' cv. is the most satisfactory in California (Schroeder 1956). The plants are usually set about 12 feet apart each way in the field (Ahmed 1936).
Cherimoyas are grown for the fruit, 3 to 6 inches in diameter and l/2 to 2 l/2 pounds in weight, which ripens 5 to 8 months after pollination. The thick brown, green, or gray-green skin has the appearance of rough leather. The fruit can be broken apart easily and the delicious white, sweet (18 percent sugar) pulp eaten out of hand with a spoon. It tastes somewhat like banana or pineapple custard. There may be 20 to 80 black or mahogany-colored oval seed l/2 to 3/4-inch in diameter that separate quite easily from among the delicious pulp. The fruit is seldom good more than 7 or 8 days after harvest (Sarasola 1960).
Inflorescence:
The rather primitive but scented cherimoya flower may be solitary, or there may be two or three in a cluster on a short peduncle (fig. 70). There are three light-green, fleshy petals about an inch long. Almost hidden at the base of the petals are the numerous but practically filamentless stamens, surrounding but just below the stigma, the whole androecium resembling the immature strawberry fruit. There is no nectary.
When the petals open, towards midday, the stigma is covered with a viscid material and is receptive to fertilization. Receptivity may last 2 to 6 hours depending upon temperature and humidity (Schroeder 1971). When receptivity ceases, the stigma dries and turns brown. Later in the day, or more frequently the following morning, the stamens shed their pollen (Brooks and Hesse 1953, Schroeder 1941, Watts 1942). If fertilization occurs, the petals drop within about 24 hours and fruit development proceeds. If fertilization is prevented, the entire inflorescence dries and drops within 4 days.
[gfx] FIGURE.- Longitudinal section of cherimoya flower, x 5, with detail showing an additional stamen and pistil, greatly enlarged.
Pollination Requirements:
The maturation of the pistil before pollen is available creates a pollination problem and prevents ample fruit set on at least some cherimoya cultivars (Watts 1942). Schroeder (1941) established that the flowers are self-fertile but usually not capable of self-pollination. When he hand- pollinated flowers, 70 percent set perfect fruit, 17 percent were misshapen, and 13 percent were "runts." In open-pollinated flowers, only 10 percent produced perfect fruit, 39 percent were misshapen, and 51 percent were runts. The hand-pollinated fruits weighed an average of 461 g, whereas the open-pollinated fruits weighed an average of only 261 g. Thakur and Singh ( 1965) also reported 44 to 60 percent set of hand- pollinated flowers as compared to less than 6 percent of open-pollinated flowers. No explanation was given for the fruit set that occurred in the open-pollinated flowers, but Brooks and Olmo (1952) stated that at least the 'Carter' and 'McPherson' cvs. set well without hand pollination.
Thomson (1970) stated that near the ocean the stigma stays receptive longer and selfing is normal. Clark (1925) also reported that heavy crops result without hand pollination although he admitted that he had never seen pollen-bearing insects visit the flowers, and he thought that self-pollination occurred. Krishnamurthi and Madhava Rao (1963) stated that comprehensive studies on pollination of the annonas are needed, with which there seems to be no disagreement.
Pollinators:
In general, cherimoya flowers have been considered incapable of self-pollination and unattractive to pollinating insects. Ahmed (1936) reported that the flowers do not attract bees but stated: "Insects of the lady-bird type such as Coccinella sp. and Scymnus sp. have been observed to visit the flowers either in search for one of the preys such as aphis, or mealy-bugs or feeding on the pollen-grains.... Ants may also be responsible to a smaller extent." He also stated, "Under normal conditions, as in the home-forests of anonas the insect agency is sufficient. But under cultivation, it has been noticed that such agents may be very scarce or absent altogether, thus inducing very low fruit-setting or none." Wester (1910) concluded that nonproductiveness of cherimoyas was due to the scarcity of pollinating insects, but Schroeder (1971) stated that insects visited the flowers upon occasions. Sarasola (1960) doubted that the good fruit set in Spain was the result of special pollinating insect activity but resulted from self-pollination, although he offered no proof for this assumption.
Usually, growers collect pollen by hand from dehiscing anthers, then pollinate stigmas the following day. Ahmed (1936) showed that a man and a little boy working full time daily throughout the 6-week flowering season could pollinate 1 acre. There seems to be no question that hand- pollinated flowers produce more and better fruit than is obtained under natural conditions, but no attempt has been made to influence the supply of pollinators available to the flowers.
Pollination Recommendations and Practices:
Cherimoya growers either collect pollen and hand-pollinate the flowers or leave the plant to chance pollination and the possibility of little or no set of high-quality fruit.
Considering the high cost of hand pollination, the fact that insects visit the flowers only occasionally, and that fruit set occurs in the natural home of cherimoya, other steps should be taken to improve the production and decrease costs. A search might be made for the particular species of insects responsible for the pollination of the plants in their native habitat. Attention might be given to selecting self-fertile cultivars. An immediate step might be to supply "saturation pollination" with honey bees. This has proven feasible on some other crops. Bee visitation should be aufficient to get an ample supply of pollen to all parts of the stigma at the earliest possible moment after it becomes receptive.
LITERATURE CITED:
ANONYMUS
1956. CHECKLIST OF VARIETIES OF CERTAIN SUBTROPICAL FRUITS. Calif. Avocado Soc. Yearbook 40:43 - 44.AHMED, M. S.
1936. POLLINATION AND SELECTION IN ANNONA SQUAMOSA AND A. CHERIMOYA. Egypt Min. Agr. Tech. and Sci. Serv., Hort. Sect., Bul. 157, 29 pp.BROOKS, R. M., and HESSE, C. O.
1953. WESTERN FRUIT GARDENING. 287 pp. University ot California Press, Berkeley and Los Angeles.____ and OLMO, H. P.
1952. REGISTER OF NEW FRUIT AND NUT VARIETIES: 1920-50. 205 pp. University of California Press, Berkeley and Los Angeles.CLARK, O. I.
1925. CHERIMOYA INVESTIGATIONS AT POINT LOMA HOMESTEAD. Calif. Avocado Assoc. Ann. Rpt. 1924-25, pp. 14-17.KRISHNAMURTHI, S., and MADHAVA RAO, V. N.
1963. CERTAIN PROBBEMS IN POBBINATION OF FRUIT CROPS. So. Indian Hort. 11(1/2): 1-17.SARASOLA, L.
1960. CHERIMOYA CULTURE IN SPAIN. Calif. Avocado Soc. Yearbook 44: 47-53.SCHROEDER, C. A.
1941. HAND POLLINATION EFFECTS IN THE CHERIMOYA (ANNONA CHERIMOBA). Calif. Avocado Soc. Yearbook 1941: 67-70.____ 1948. REPORT OF THE COMMITTEE ON SUB-TROPICAL FRUIT VARIETIES. Calif. Avocado Soc. Yearbook 1948: 17 - 19.
____ 1956. CHERIMOYAS, SAPOTES AND GUAVAS OF CABIFORNIA. Calif. Avocado Soc. Yearbook 40: 49 - 56.
____ 1971. POLLINATION OF CHERIMOYA. Calif. Avocado Soc. Yearbook 54: 119 - 122.
THAKUR, D. R., and SINGH, R. N.
1965. STUDIES ON POLLEN MORPHOLOGY, POLLINATION AND FRUIT SETIN SOME ANNONAS. Indian Jour. Hort. 22: 10-18.THOMSON, P. H. THE CHERIMOYA IN CALIFORNIA. Calif. Rare Fruit Growers Yearbook 1970 (2): 20-34. 138
WATTS, J. C.
1942. THE FRUIT OF THE GODS. Calif. Cult. 89(7): 170.WESTER, P. J.
1910. POLLINATION EXPERIMENTS WITH ANNONAS. Torrey Bot. Club Bul. 37: 529 - 539.
