Phylogenetic relationship of wild and cultivated yam species (Dioscorea spp.) of India inferred from PCR–RFLP analysis of two cpDNA loci

The genus Dioscorea comprises approximately 600 species worldwide and about 50 in India. Dioscorea is economically very useful because of its food and medicinal value. Polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis was employed to study interspecific relationship between four cultivated and thirteen wild species belonging to seven taxonomical sections found in India. Restriction digestion analysis was performed for the amplified products of chloroplast DNA (cpDNA) loci psbA–trnH and trnL-F regions. Out of 17 restriction endonucleases tested, 5 endonucleases had restriction sites in psbA–trnH region and 6 endonucleases had restriction sites in trnL-F region. Digestion of amplified products with these restriction endonucleases showed 70 fragments of which 62 fragments (88 %) were polymorphic. Dendrogram obtained from UPGMA cluster analysis of two combined loci shows D. bulbifera of section Opsophyton to be closely placed with species of sect. Enantiophyllum. High similarity values obtained in this study between D. pentaphylla (sect. Botrysicyos) and D. esculenta (sect. Combilium) support their common origin. The average of genetic similarities between the ten species of Enantiophyllum section was 82.3 % showing their closeness. The present study suggests that the less studied New World species, D. floribunda (sect. Heterostemon) could have evolved from old world section, Lasiophyton. The principal component analysis (PCA) obtained from data of the two loci shows D. deltoidea of sect. Stenophora to be an outgroup. Interspecific genetic similarities showed D. deltoidea with low similarity values ranging from 27.5 to 37.5 % compared with other species and was, therefore, the most divergent species. D. deltoidea of section Stenophora shows distinctness because of its primitive characters. This study, therefore, establishes species relationships between wild and cultivated yams of India which would help in yam crop improvement programmes.