Genetic variation taro (Colocasia esculenta) in South East Asia and Oceania

A study of the genetic variation existing within and between 7 countries of South East Asia and Oceania was conducted. Overall, 2298 cultivars presently held in germplasm collections, have been characterised using 23 standardised morphological descriptors. 2081 cultivara were characterised using six enzyme systems (MDH, PGI, ICD, PGD, ME, SKDH) and 319 distinct zymotypes were identified in the region. Surprisingly, only 6 zymotypes represent more than 51% of the total number of accessions electrophoresed and only 21 zymotypes represent more than the two thirds (70%) of total accessions. Furthermore, the genetic variation existing between the major 6 zymotypes is rather limited. This indicates that the genetic base of most of the cultivara existing in this vast geographical region is narrow. At the isozyme level, there is limited variation in Vanuatu, Papua New Guinea and the Philippines and significant genetic variation in Indonesia, Thailand and Malaysia. South East Asia and Melanesia seem to assemble two distinct gene pools as demonstrated by multivariate analysis of zymotypes. No correlation exists between zymotypes and morphotypes. It is not possible to clearly distinguish dasheen from eddoe types and wild types from cultivars. A hierarchical approach, using a branching method based on five characters, is used to develop a classification system. A core sample is developed that takes into consideration the existing genetic variation. The strategy adopted and the results obtained are discussed. (Résumé d'auteur