Cassava (Manihot esculenta Crantz) is a major food source for more than 500 million people in Africa, Latin America and Asia. Cultivated for its starchy roots, this New World native species claims a world production of 152 million t (FAO 1995), ranking seventh in yield production among all crops and fourth as an important source of calories in the tropics (Cock 1985; Balogapalan et al. 1988). The storage roots form the basic carbohydrate component of the diet and the leaves are consumed as a preferred green vegetable in many parts of Africa, providing protein, mineral and vitamins (Hahn 1989). Two CGIAR Centres, CIAT and IITA, share the mandate for cassava. Genetic diversity of the Manihot genus is eroding in the face of expansion of agriculture in the American tropical lowlands, while in important cassava-growing regions of Africa, hundreds of traditional varieties have been abandoned during the 20th century (Nweke and Polson 1990; Nweke et al. 1994), and newer production regions in Asia tend to rely on single-cultivar plantations.

BOTANY AND DISTRIBUTION

Cassava is a member of the Euphorbiaceae, subfamily Crotonoideae and tribe Manihotae. The genus Manihot contains nearly 100 species of herbs, shrubs and trees among which the production of latex and cyanogenic glucosides is common (Rogers and Fleming 1973; Bailey 1976) and these are grouped into 19 taxonomic sections (Rogers and Appan 1973).