Forty eight accessions of cultivated cowpea were assessed using 12 simple sequence repeat (SSR) markers. The unweighted pair group method with arithmetic mean (UPGMA) dendrogram constructed revealed three main clusters when truncated at 65% similarity coefficient. All accessions showed high genetic variation except four which are genetically similar at 100% similarity coefficient. A two dimensional principal coordinate analysis (PCA) also revealed high genetic relationships among the accessions used. The polymorphism information content (PIC) revealed that the number of alleles per locus ranged from 2 to 5 with a total of 37 alleles generated from the SSR primers. The PIC value ranged from 0.075 to 0.603 with a mean value of 0.344 from a total of 4.467. There was no significant correlation between the repeat number and the allele numbers (r=0.21) so also between repeat numbers and PIC (r=0.11). The PIC also revealed the comparative genetic diversity from three sub-regions in Africa; West Africa, North East and Central Africa and Southern Africa with thirteen accessions each. West African accessions were the most diverse with a PIC value of 4.4310, showing the greatest genetic diversity and most likely the center of origin of cultivated cowpea.
Key words: Cowpea, dendrogram, genetic diversity, polymorphism, simple sequence repeat (SSR) markers.
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