Genetic diversity and conservation of common bean (Phaseolus vulgaris L., Fabaceae) landraces in Nilgiris

Genetic diversity was studied among 20 common bean (Phaseolus vulgaris L.) landraces collected from different traditional farming villages of Nilgiris District, Tamil Nadu, India, with Random Amplified Polymorphic DNA (RAPD) markers. Evaluation of genetic diversity is essential for conservation, management and to trace the hybrids. Thirteen RAPD primers were selected from an initial screening with 72 primers. The PCR product revealed 102 bands, out of which 63 were found to be polymorphic (63.5%). Jaccard's pair-wise similarity coefficient (0.50 to 0.95) indicating an intra-specific genetic variation prevails in landraces of common bean in the Nilgiris biosphere reserve. No two accessions had a similarity of one or a distance of zero, showing that there were no duplicate entries. A dendrogram of the relationship of accessions constructed based on Jaccard's coefficients of 102 RAPD markers using the average distance method (UPGMA), separated the accessions into two major clusters, A and B, with Mesoamerican and Andean gene pools respectively. Principal coordinate analysis of the same dataset revealed similar results as those of the dendrogram, with the first two components accounting for 61.8% of the total variation. Among the 20 landraces, seven were Mesoamerican origin, 11 Andean origin, and two were possible recombinants between the two gene pools. A correlation was observed between RAPD dendrogram clustering and seed weight. The common bean population of the Nilgiris is highly diverse and the Nilgiris can be considered as a secondary centre of genetic diversity of common bean. A better knowledge of genetic aspects of common bean will help in genetic improvement and conservation programmes for its endangered landraces in the Nilgiris.