Cocoyam (Xanthosoma sagittifolium (L.) Schott) genetic resources and breeding: a review of 50 years of research efforts

Cocoyam (Xanthosoma sagittifolium (L.) Schott) cultivated throughout the wet tropics is consumed by hundreds of millions. This underexploited species plays a major role for food security but is not under the mandate of the international research system. Development activities are left to national institutions in developing countries, the conservation and characterization of its genetic resources are uncoordinated. Breeding activities are rare and isolated. Despite these major constraints, significant research efforts have been made over the last fifty years and are being discussed in the present review. The taxonomic position of many Xanthosoma spp. is suspicious and cultivated forms of unknown species are often called X. sagittifolium. In most countries, germplasm collections are small with accessions number ranging from a few to 80. They are often grouped based on different pigmentations on their vegetative parts and side-cormels flesh colors. Limited variation in quantitative traits is observed. Isozymes, random amplified polymorphic DNA (RAPD), amplified fragment length polymorphism (AFLP), inter-retrotransposon amplified polymorphism (IRAP) and simple sequence repeat (SSR) markers have been used and reveal limited allelic diversity. Significant investments have been made in the development of various tissue culture protocols to ease preservation and sanitation. Despite controversial reports regarding sterility or incompatibility, the efforts made to induce flowering, to cross-pollination and to raising hybrids were successful. It appears that there are no major technical and biological constraint to conventional cocoyam breeding. Unfortunately, most programs are based on narrow genetic bases and if cocoyam breeding is to have any future, there is an urgent need to encourage the international exchange of selected germplasm.