ISOZYME DIVERSITY WITHIN AFRICAN MANIHOT GERMPLASM

Isozyme diversity is described among a collection of 365 Manihot esculenta cultivars plus 109 accessions from wild relatives (M. glaziovii and spontaneous hybrids) from Africa. The study is based on 17 polymorphic loci. A natural hybrid swarm is detected between the two species. Although they were recently introduced, M. esculenta and M. glaziovii show high levels of polymorphism: heterozygosity estimates are 0.225 and 0.252 respectively. For the wild species, diversity is structured at the unilocus level, and the multilocus approach reveals a geographical pattern. The organization of the diversity is not so clear for the cultivated cassava, but a multilocus approach, based on both common and rare alleles, led us to identify different groups of clones with many intermediate genotypes between them. Elements of the secondary diversification process of Manihot in Ivory Coast are discussed.