ABSTRACT
Yam (Dioscorea spp.) is a tuber-producing plant and is popular in the humid and sub-humid tropics, particularly in Africa, West Indies, parts of Asia and South and Central America. Knuth (1924) estimated that there are about 600 species in the genus Dioscorea. Yam species are annual or perennial vines and climbers with annual or perennial underground tubers. The Guinea yam (Dioscorea rotundata Poir. and D. cayenensis Lam.), are most preferred in Africa but in the Caribbean and Pacifi c, D. alata L. and D. esculenta (Lour.) Burk. are preferred. D. bulbifera L. also forms small aerial tubers or bulbils in the leaf axils. D. hispida Dennst. (Asia), D. Dumetorum (Knuth.) Pax. (Africa) and D. trifi da L. (Central America and the Caribbean), D. opposite Thunb. and D. japonica Thunb. (China and Japan) are other edible species. Yam is a primary source of income in West Africa, from where 94% of global yam production emanates. The edible portion is the underground tuber which is a major source of carbohydrate. Nigeria produces 71% (FAO 2006) of global yam production, equivalent to 37 million tonne. The consumption of yam on a per capita basis on the West African coast is highest in Togo, followed by Cote d’Ivoire, Ghana, Benin Republic and Nigeria (Onwueme 1978, Kalu and Erhabor 1992). The most preferred form of eating yam is the boiled and pounded form. It is also fried in palm oil or roasted and eaten with oil, while yam fl akes and chips are taken as snack (Orkwor 1998).
