Genetic relationships between Discorea alata L. cultivars

Isozyme variation was studied to determine genetic relationships among 269 cultivars of #Dioscorea alata# originating from the South Pacific, Asia, Alrica and the Caribbean. Four polymorphic enzyme systems (MDH, PGI, SkDH' 6PGD) revealed 66 isozyme phenotypes, or zymotypes, each uniquely characterized by the presence or absence of 27 electromorphs. Identical zymotypes were found to be distributed in different geographical areas and vice versa, different zymotypes exist within the same geographic zone. Subsequently, distinct local cultivars from the New Caledonia germplasm collection were rated and 131 morphotypes were identified by 25 morpho-agronomic descriptors. Four major groups of morphotypes were identified and compared with the zymotypes of the described accessions. Each of the 131 cultivars was also analysed for the physico-chemical characteristics of the tubers (percent dry matter, percent starch, total minerals, proteins content, polyphenolic compounds, P, K and Ca contents) and three major chemotypic groups were identified. No correlations were found between morphotypes, zymotypes and chemotypes of accessions grown in a common garden. Many cultivars exhibited variation in qualitative traits, such as anthocyan pigmentation, probably as a result of human selection of somatic mutations. The most widespread #D. alta# cultivars exhibit a narrow genetic base. However, the existing genetic variation is also due to ancient sexuel recombinations as demonstrated by the isozyme patterns. #Dioscorea alata# might be a true species and not a putative cultigen as previously reported. (Résumé d'auteur