Molecular genetic diversity in cowpea {Vigna unguiculata (L.) Walp.} genotypes

Cowpea {Vigna unguiculata (L.) Walp.} is one of the most important food legumes in the semi arid tropics which encompass Asia and Africa. Thirty genotypes of cowpea were used to study molecular genetic diversity using nineteen cowpea specific SSR markers. Among 19 SSR markers, 13 markers exhibited polymorphism and two markers showed monomorphic banding pattern. Four markers produced multiple alleles. A total of 33 alleles were generated. The number of alleles produced by different markers ranged from one to three with an average of 2.2 alleles per marker. Cowpea specific markers viz., VM25,VM35,VM 36,VM5 and CP 1 produced the highest number of alleles (3).The Polymorphism Information Content (PIC) ranged from 0.585 (VM 5) to 0.064 (VM 19) with an average of 0.368. SSR marker data analysis showed high dissimilarity among the 30 cowpea genotypes. The genotypes VCP 9-009 with CP 2-1, KB CP 39 and K 13 CP 25 had the highest dissimilarity index value and showed the extent of genetic diversity existed among the genotypes. A dendrogram constructed using unweighted pair group method using arithmetic average (UPGMA) analysis distinguished 30 genotypes into six clusters. Among the six clusters, cluster II was the largest with ten genotypes followed by cluster I with seven genotypes. The neighbour-joining tree developed based on weighted average for dissimilarity matrix grouped 30 genotypes into five groups. Among the five groups, group II comprised of ten genotypes followed by group I with eight genotypes. In both UPGMA analysis and neighbourhood joining tree, the results showed the potentiality of SSR markers in assessing the genetic diversity among the cowpea genotypes.