Genetic Diversity of Cowpea Parental Lines Assembled for Breeding in Uganda

Cowpea is a grain legume that is commonly grown in Sub-Saharan Africa (SSA) for a variety of uses including food, feed, and soil fertility enhancement through nitrogen fixation. Genetic improvement in cowpea can be accomplished by creating breeding populations from high-performing but genetically diverse parental lines. The goal of this study was to use single nucleotide polymorphic markers (SNPs) to estimate genetic diversity and population stratification among cowpea parental genotypes from five countries. A total of 2,746 SNP markers were used to analyze 62 cowpea genotypes that differed in key characteristics. Only 55% of the SNP markers were polymorphic across the 62 genotypes and met the selection requirement. The gene diversity varied from 0.52 to 0.57 with an average of 0.55, while the polymorphic information content ranged from 0.46 to 0.51 with an average of 0.49, showing that the cowpea parental lines are genetically diverse. The analysis of molecular variance (AMOVA) found high significant (p < 0.001) variation among genotypes and non-significant variation across genotypes depending on country of origin. The cluster analysis for the 62 genotypes using the unweighted pair group procedure with arithmetic mean approach divided the genotypes into two distinct groups. Genotypes from the same geographical regions tended to cluster together and there was a significant level of genetic variation among genotypes from Uganda and Nigeria. The SNP markers utilized in this study were effective at distinguishing genotypes and may be used to estimate the diversity in the cowpea core collection. The genetic diversity in this collection is important for future development of improved varieties of cowpea in Uganda.