Polymorphic Rate of SSR Markers in Cowpea Genotyping

Microsatellites or Simple Sequence Repeats (SSRs) are co-dominant markers that are routinely used for a wide range of applications in genetic mapping and genome analysis, genetic diversity, paternity determination, and marker-assisted breeding. It consist of tandemly repeated 2-7 base pair units arranged in repeats of mono-, di-, tri-, tetra and penta-nucleotides with different lengths of repeat motifs.

A total of seventy seven SSR primers were screened using two wild (TVNU 1473 and 270) and two cultivated (TVu 8510 and 14901) cowpea accessions obtained from International Institute of Tropical Agriculture (IITA). The PCR was carried out with touchdown annealing temperature ranging from 64⁰C to 54⁰C. Twenty one primers were found to be polymorphic with the four cowpea accessions while others were monomorphic. The polymorphic ones were later used to assess forty eight accessions each from wild, cultivated and vegetable cowpea populations. The polymorphic primers were run on Polyacrylamide gel electrophoresis, stained with silver staining kits and gel analyzed. The results revealed that 14 (Vm 9, 22, 24, 27, 28, 34, 35, 36, 37, 39, 71, 74, 78 and 98) primers were polymorphic across all the three populations while seven primers (Vm 2, 3, 11, 15, 23, 26, and 29) showed multiple bands with the populations. The number of alleles per locus ranged from 3 to 13 in wild, 2 to 3 in vegetables and 2 to 5 in cultivated cowpeas with different primers detecting varying number of alleles in each case (Vm 36 in wild, Vm 39 in vegetables and Vm 35 in cultivated cowpeas. It was established that SSR markers were highly information and an efficient means of detecting genetic variations in cowpea.