Scientific name – Pachyrhizus erosus
English common name – Yam bean, Jicama
Asian common names – Burmese: pre myit Chinese: sha ge (Cantonese sha got or sha kot), dou shu Hindi: mishrikand Japanese: mame imoKhmer: pe'kuëk Lao: man ph'au Malay: bengkuang (Indonesia), kacang sengkuang Photo: ECHO Asia staff Thai: มันแกว mankaeo (man kaeo), huapaekua, man lao Vietnamese: cur dau, san, cu san
Variety – Lao
General description and special characteristics – A leguminous, tuber-producing, annual vine. Tubers are eaten raw and remain crunchy when cooked. Yam bean can be used as a cover crop or trellised. The tuber is high in carbohydrates but is otherwise low in nutritional value. Leaves and seeds contain the toxin rotenone and may be used as an insecticide or fish poison.
Crop uses (culinary) – Yam bean tubers are low in calories and contain less than 10% carbohydrates and slightly more than 1% protein (fresh weight), but are sweet and crunchy when eaten raw. The young seed pods are sometimes cooked and eaten as a vegetable. The tubers are also a good source of vitamin C. The leaves and beans contain rotenone, a natural insecticide, and therefore should not be consumed.
Seasons of production – Yam bean does well when planted at the beginning of the rainy season. It requires short days for tuber production.
Length of production and harvest period – Depending on growth conditions, it will take 4-8 months to produce a market- sized tuber. The best tubers are approximately 10-15 cm (4-6 in) in diameter and weigh 2-3 kg (4.5-6.5 lb); overly large tubers tend to be fibrous and starchy. The preferred root shape is a flattened sphere, similar to a turnip.
Production methods – Staked or trellised plants will be more productive than those that are unsupported. If grown primarily for tuber production, flowers should be removed early to prevent pod and seed formation. Roots are harvested by hand digging or plowing. Tubers should be harvested with care, as the skin of the tubers is thin and can be damaged easily. Harvested tubers gradually lose their sweet taste. Therefore, it is recommended that tubers be eaten soon after harvest as needed, and weather permitting, tubers for subsequent harvesting periods remain in the ground until needed. The tubers will keep for a month or more in a cool shaded spot if not damaged during harvest.
Plant spacing – Plants should be spaced 15-30 cm (6-12 in) apart in rows 60-100 cm (2-3 ft) apart; use lower densities for hill planting and intercropping.
Pollination – Mostly self-pollinating, but 2-4% cross-pollination may occur.
Environmental conditions for production – Yam bean grows well in hot, humid environments and prefers full sun.
Soil requirements – Yam bean prefers well-drained, sandy soil. Such conditions discourage fungal root rot and help prevent the tuberous roots from becoming restricted during maturation. Optimum soil pH is 4.8 - 7.3.
Pests and diseases – Most insects will not bother this plant, although the ECHO Global Farm in Florida has had some problems with caterpillars attacking the stems and leaves.
Seed saving – Seeds are somewhat flattened, mostly rounded, and 5-10 mm (1/4 in) wide; unlike other Pachyrhizus species, they are never kidney shaped. Under normal conditions, it takes 10 months to produce mature seed. For seed production, allow pods to dry on the plant, and then thresh pods similarly to other beans.
References
Ashworth, Suzanne. 1991. Seed to Seed. Decorah, Iowa: Seed Savers Exchange, Inc.
Herklots, G. A. C. 1972. Vegetables in South-East Asia. London: George, Allen, & Unwin, LTD.
National Academy of Sciences. 1979. Tropical Legumes: Resources for the Future. Washington, D.C.: NAS.
Purseglove, J. W. 1968. Tropical Crops: Dicotyledons. Essex, U.K.: Longman Group Ltd.