Cross-Species Transferability of Cowpea SSR Markers to Vigna radiata (L.) (Mung Bean) and Phaseolus lunatus (L.) (Lima Bean)

Abstract

Simple Sequence Repeats (SSRs) are tandemly repeated sequences of 1-6 nucleotide motifs found in all genomes. They constitute a considerable portion of the noncoding region of eukaryotic genome. The transferability of SSR markers across related species can be leveraged to assess genetic diversity, particularly in crops lacking species-specific DNA markers. Considering the close evolutionary relationships within the legume family, 10 cowpea (Vigna unguiculata) SSR markers were screened for their transferability across genomic DNA from 10 accessions each of Mung bean (Vigna radiata) and Lima bean (Phaseolus lunatus) using polymerase chain reaction (PCR). The results indicated that 70% of the markers were successfully amplified in Mung bean and 90% in Lima bean, while one specific marker (SSR- 7061) failed to amplify in any of the accessions. DNA markers, SSR-7079, VM-40, VM-54, and VM-74 had an amplification success rate ranging from 70% to 100% across the accessions. On the other hand, SSR-7000 and SSR-7053-2 had 55% and 50% amplification rates, respectively, while SSR-6313, SSR-37, and VM-71 exhibited less than 50% amplification across the accessions. The study generated 21 alleles from these markers, with allele counts per marker ranging from 1 to 3 and an average of 2.10 alleles per locus. The polymorphic information content values varied between 0.00 to 0.57 with an average value of 0.32, indicating moderate variability, while gene diversity measurements ranged from 0.16 to 0.64 with an average diversity value of 0.39. Regarding genetic relationships among the accessions, cluster analysis using the unweighted pair group method (UPGMA) revealed two main groups. Factorial analysis divided the accessions into four groups, with TPI-2428, TPI-2432, TVr-46 and TVr-6 forming distinct outliers. This cross-species applicability not only reinforces the conservation of genetic markers among legumes but also underscores the potential for these markers to assist in the breeding and genetic improvement of Mung bean and Lima bean.