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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.

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