2199

8: Vegetables

Sechium edule (Jacq.) Swartz

Fl. Ind. Occ. 2: 1150 (1800).

CUCURBITACEAE

2n = 24, 26 or 28

Sicyos edulis Jacq. (1760), Chayota edulis Jacq. (1780), Sechium americanum Poiret (1806).

Chayote, vegetable pear (En). Christophine, chouchou, chouchoutte (Fr). Indonesia: labu siam, waluh jepang. Papua New Guinea: choko, sako. Philippines: chayote (Tagalog), sayote (Tagalog, Bicol), hayuti (Ifugao). Cambodia: su-suu. Laos: savëëx, nooy th'ai. Thailand: ma-kheua-kreua, taeng-kariang. Vietnam: su su.

Putative wild populations of Sechium edule and related wild species are found in Central America, and therefore this region is most likely the centre of origin of chayote. Chayote was already a common cultivated vegetable among the Aztecs in pre-Columbian times. It has now spread throughout the tropics and subtropics, including South-East Asia, but is most important in tropical America. It can hardly be found in South Asia (India) and is not very popular in Africa.

Every part of chayote is useful, but it is mainly grown as a fruit vegetable. Its immature fruits, young leaves and shoots, and tuberous roots are all consumed. The fruits vary in flavour, according to cultivar, from bland to sweetish or starchy. Those of the bland cultivars are also used industrially as a food filler for pastes and sauces and as a substitute for apple in pies and tarts. The starchy tuberous roots are used sometimes in soups and stews and are also candied. The tender young shoots and leaves are a valuable pot herb, especially rich in vitamins A and C, the B vitamins, calcium and iron. It is one of the most important greens in Papua New Guinea. Fruits, shoots and tubers are also used as fodder and forage for pigs, poultry and cattle. Fibres of the stem are used locally to make hats and baskets. In Java the plant is used to shade fish ponds, and in the Philippines it has undergone trials for use in erosion control. The seed is nutlike in flavour and a source of protein.

Chayote is the fifth most important commercial vegetable in Brazil where 170 000 t were produced in 1978. Mexico produced ca. 12 000 t in 1978. Costa Rica produced less but is the leading exporter: ca. 4600 t in 1982, mainly to the United States, valued at US$ 1.5 million. It is important in all South-East Asian countries as a cheap, easy-to-produce vegetable both for home consumption and for city markets. No statistics are available for South-East Asia; chayote data are usually combined with all other gourds and pumpkins. In the Indonesian highlands it is, in quantity, the most important vegetable produced.

The edible portion of immature fruits of chayote is about 86%. Per 100 g edible portion, they contain: water 93 g, protein 0.9 g, fat 0.3 g, carbohydrates 5.3 g, vitamin A 50 IU, vitamin B₁ 0.03 mg, vitamin B₂ 0.04 mg, niacin 0.5 mg, vitamin C 11 mg, Ca 19 mg, Fe 0.4 mg, Mg 14 mg, P 20 mg. The energy value is about 109 kJ/100 g. The roots contain per 100 g edible portion: water 80 g, carbohydrates 18 g.

A monoecious, vigorous, perennial herbaceous vine with a large tuberous root. Stem climbing or sprawling, longitudinally grooved, growing 10—15 m in a single season. Tendrils large, 2—5-branched. Leaves simple, spirally arranged; petiole 3—25 cm long; leaf-blade broadly ovate-circular in outline, 7—25 cm in diameter, base deeply cordate, 3—7-angular or lobed, acute, margins obtusely dentate, scabrid hairy. Inflorescences axillary racemes with small, greenish or cream, 5-merous flowers; hypanthium saucer-shaped, with 10 pouch-like nectaries on the bottom; male racemes with peduncle 6—30 cm long, 10—30-flowered; stamens 5, filaments united; female flowers usually solitary on short pedicels, in same axil as male; corolla ca. 2 mm in diameter; connate style and stigmas, forming a small head. Fruit a one-seeded fleshy berry, variable, commonly pear-shaped, 7—20 cm long, somewhat ribbed, smooth or shortly spiny, dark green to almost white; fruit stalk 2—3 cm long, pendent; pulp white or greenish-white. Seed solitary, ovoid to ellipsoid, 2.5—5 cm long, compressed, white, germinating within the fruit, usually while the fruit is still attached to the plant; in some genotypes seed-coat with fibres radiating into the flesh, in others obsolescent and the flesh fibreless.

Chayote is a long-lived perennial, but in cultivation it is recommended to renew it at least every 3 years because of disease problems. The tubers do not develop until the second year, and do not develop well in perpetually wet climates. In regions with a season of arrested growth, they can reach 10 kg in weight and they resemble yam tubers. Flowering starts 1—2 months after germination. Chayote is predominantly cross-pollinated, but is self-compatible. It is a renowned honey-producing plant, loved by beekeepers because it flowers abundantly throughout the year. Fruit development takes 1—2 months after pollination. In good conditions, chayote plants grow profusely and can form a dense foliage cover on trellis, producing hundreds of hanging fruits. The seed germinates in the ripe fruit while still on the mother plant. This phenomenon is called viviparous germination (comparable to viviparity in mangrove species).

The genus Sechium P. Browne has long been considered as monotypic with Sechium edule as the only species. Since the 1970s wider genus concepts have been proposed, including 3—9 species, all indigenous to Central America. Sechium compositum (Donn. Smith) C. Jeffrey, occurring in southern Mexico and in Guatemala, is considered the closest wild relative of Sechium edule. Its fruit is bitter and it bears spines along its 5—10 ridges.
Chayote cultivars do not breed true, although it has been observed that cultivars do not segregate significantly from one generation to the next because of the relative isolation of chayote plants from one another when planted in home gardens. When planted together, complete panmixy can be observed. Substantial efforts made at CATIE (Costa Rica) to describe cultivars on the basis of fruit characteristics proved to be of limited relevance because of the extraordinary variability, with continuous variation in almost all the characters. The variable fruit characters include size (7—20 cm long), weight (100—1000 g), colour (continuous range from white to dark green), shape, fruit-wall features (spines, lenticels, grooves and ridges), flavour and texture. Nevertheless, farmers 'classify' the genotypes by a combination of such fruit characteristics. Instead of speaking of cultivars, it seems best to consider those types as landraces or as primitive populations. At least 25 landraces exist in Central America. Commercially grown chayote consists of two types: a medium sized, light-green, smooth, pear-shaped fruit and a small, white, smooth, globular one. Several types can be distinguished in South-East Asia. For example, in West Java (Indonesia) the common type is dark green and almost glabrous, but more spiny and lighter green types can be found. A complete white type, less tender and spiny, is sometimes grown as a botanical curiosity.

Chayote requires high relative humidity (80—85%), annual rainfall of at least 1500—2000 mm (or irrigation) and average temperatures of 20—25°C (with limits of 12—28°C). It grows best at 300—2000 m altitude. In Java it is abundant in the highlands between 700—1800 m. When planted in the lowlands, it does not produce any fruits. At higher latitudes, it grows and produces well in the lowlands, but the production stops during the hottest months. A daylength of a little more than 12 hours is required to initiate flowering. It is susceptible to frost, drought and wind. Chayote does best in a rich well-drained, rather loose sandy loam. The natural habitats of wild chayote are moist steep hillsides.

Chayote is propagated by placing a whole fruit on its side in a hollow scooped out at the foot of a trellis support and covering the fruit slightly with soil and farmyard manure. Sometimes up to 4 fruits, already bearing sprouts of 10—12 cm length, are planted in the same pit. More recently, cuttings are being used in Costa Rica to propagate selected genotypes for commercial production on large acreages. The plants are usually spaced 1.5 m apart along a fence or trellis, but when they are allowed to sprawl they need much more room. They grow in trees to a height of over 10 m.

A trellis support must be provided for optimum growth. In gardens, plants can be trained over a fence, porch or tree. They are best planted where there is some shelter from strong winds. Chayote requires large quantities of water (ca. 50 mm per week during the growing season) and should be abundantly irrigated in regions of low rainfall and during periods of drought. The incorporation of manure or compost is recommended. In India, ammonium sulphate and superphosphate at the rate of 1 kg and 0.5 kg respectively per pit are applied in two doses before flowering. In some parts of the world, the plants are pruned at the end of the season, leaving only a small portion of about 1.5 m of the stem.

Chayote is susceptible to several fungal and viral diseases, root-knot nematodes and spider mites. It has been observed in Central Java (Indonesia) that whole plantings of chayote perished through an aggressive mosaic virus infection. Downy mildew (Pseudoperonospora cubensis) has been reported to cause damage in Java (Indonesia). Powdery mildew (Erysiphe cichoracearum) and Mycosphaerella occur on chayote in Central America, but they are not very damaging. The use of pesticides may reduce yield by killing pollinating insects. Because of disease problems, chayote plants are kept in commercial production no more than 3 years.

Chayote plants start producing fruits in 3—5 months after planting and a fruit needs 4—6 weeks from pollination to market size (approximately 0.5 kg). The fruits are hand-picked and marketed directly. To harvest tubers, the plant is not necessarily killed. Individual tubers can be carefully harvested, while the plant continues to produce fruits and new tubers.

Production can be seasonal or almost continuous, depending on the climate, and annual yields may vary from 75—300 or more fruits per plant. In commercial plantations, yields of 22—28 t/ha have been reported.

When fruits are stored in a cool and dark place, sprouting will start after approximately 2 weeks. In cold storage the fruits keep well for several weeks.

Chayote cannot be stored as seed for much longer than one month since it is viviparous, the seed having no dormancy and germinating within the fruit. Long-term maintenance of germplasm collections must therefore be in the form of living plants, or as tissue cultures under slow growth conditions. Germplasm collections are at present held by CATIE (Turrialba, Costa Rica), Chapingo Regional Centre (Huatusco, Vera Cruz, Mexico), INIA (Celaya, Guanajuato, Mexico) and EMBRAPA (Brasilia, Brazil). Genetic erosion of chayote in its region of indigenous cultivation is accelerating as a result of rapidly increasing commercialization and the replacement of landraces by a few improved cultivars.

Commercial production is limited by some disease problems. A breeding programme for fruit quality and disease resistances is needed, but, logically, private seed companies are not interested in chayote because it is viviparous. A bland cultivar is required for the industrial market and a tasty one for the table vegetable market. Further collection and evaluation of landraces in Mexico and Central America is also required.

Because of its low energy value, chayote is gaining importance as a dietary food in hospitals and nursing homes. Its use as a food filler for pastes seems to be promising.

Engels, J.M.M., 1983. Variation in Sechium edule Sw. in Central America. Journal of the American Society for Horticultural Science 108: 706-710.
Engels, J.M.M., 1984. Chayote: a little known Central American crop. FAO/IBPGR Plant Genetic Resources Newsletter 63: 2-5.
Herklots, G.A.C., 1972. Vegetables in South-East Asia. George Allen & Unwin, London, United Kingdom. pp. 339-342.
Newstrom, L.E., 1985. Collection of chayote and its wild relatives. FAO/IBPGR Plant Genetic Resources Newsletter 64: 14-20.
Newstrom, L.E., 1986. Studies on the origin and evolution of chayote. Thesis, University of California, Berkeley, United States. 149 pp.
Newstrom, L.E., 1989. Reproductive biology and evolution of the cultivated chayote (Sechium edule, Cucurbitaceae). In: Bock, G.H. & Linhart, Y.B. (Editors): The evolutionary ecology of plants. Westview Press, Boulder, San Francisco/London, United States/United Kingdom. pp. 491-509.
Whitaker, T.W. & Davis, G.N., 1962. Cucurbits: botany, cultivation and utilization. Leonard Hill, London, United Kingdom. 250 pp.

J.M.M. Engels & C. Jeffrey

Engels, J.M.M. & Jeffrey, C., 1993. Sechium edule (Jacq.) Swartz. In: Siemonsma, J.S and Piluek, K (Editors): Plant Resources of South-East Asia No 8: Vegetables. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea