MOLECULAR MARKER BASED TAXONOMY AND PHYLOGENY OF GUINEA YAM (DIOSCOREA-ROTUNDATA D-CAYENENSIS)

Four different molecular techniques were used to assess relationships among 21 accessions of Guinea yam (Dioscorea rotundata and Dioscorea c ayenensis) and 21 accessions belonging to seven putative progenitor sp ecies. Random amplified polymorphic DNA (RAPD) and microsatellite-prim ed PCR (MP-PCR) analysis yielded 246 informative characters that were transformed into a matrix of pairwise distances and analyzed by neighb or joining or split decomposition. Both methods gave congruent results . Well-separated groups were formed that corresponded to their species designation. Dioscorea rotundata and D. cayenensis accessions were cl early separated from each other, supporting the concept that both are distinct species. Two morphological intermediates grouped together wit h D. rotundata. All investigated species fell into two main clusters, one comprising D. rotundata, D. cayenensis, Dioscorea abyssinica, Dios corea liebrechtsiana, and Dioscorea praehensilis, the other comprising Dioscorea smilacifolia, Dioscorea minutiflora, Dioscorea burkilliana, and Dioscorea togoensis. The same grouping was also obtained by compa rative sequence analysis of chloroplast DNA, which supports earlier st udies of nuclear rDNA variation and chloroplast restriction fragment l ength polymorphisms. We also analyzed the same set of Dioscorea sample s with the recently developed random amplified microsatellite polymorp hism (RAMPO) technique. A series of diagnostic RAMPO bands was identif ied that clearly distinguished between D. rotundata and D. cayenensis. Some of these bands could also be traced back to the putative progeni tors of both species. The evolutionary origin of Guinea yam is discuss ed in light of the present results.