CASHEW
Anacardium occidentale L., family AnacardiaceaeThe 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.]