Isozyme variation was studied to determine genetic relationships among 269
cultivars of Dioscorea alata originating from the South Pacific, Asia, Afri
ca 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 f
ound to be distributed in different geographical areas and vice versa, diff
erent zymotypes exist within the same geographic zone. Subsequently, distin
ct local cultivars from the New Caledonia germplasm collection were rated a
nd 131 morphotypes were identified by 25 morphoagronomic 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 f
or 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 ac
cessions grown in a common garden. Many cultivars exhibited variation in qu
alitative traits, such as anthocyan pigmentation, probably as a result of h
uman selection of somatic mutations. The most widespread D. alata cultivars
exhibit a narrow genetic base. However, the existing genetic variation is
also due to ancient sexual recombinations as demonstrated by the isozyme pa
tterns. Dioscorea alata might be a true species and not a putative cultigen
as previously reported.