The principal root and tuber crops of the tropics are cassava (Manihot esculenta Crantz), yam (Dioscorea spp.), sweet potato (Ipomoea batatas L.), potato (Solanum spp.) and edible aroids (Colocasia spp. and Xanthosoma sagittifolium). They are widely grown and consumed as subsistence staples in many parts of Africa, Latin America, the Pacific Islands and Asia. The potential of these crops is particularly high in the humid tropics and those sub-humid tropics, which are not suitable for cereal production.