Assessment of Genetic Diversity Using Morphological Traits in Sixty Cowpea Accessions Obtained from Three Diverse Sources

Cowpea (Vigna unguiculata (L.) Walp.) is among important legumes in Kenya, although its production is partly limited by lack of improved varieties, hence the need for increased breeding efforts. Characterisation and evaluation of germplasm is a first step in breeding efforts. Consequently, 60 cowpea genotypes obtained from the International Institute of Tropical Agriculture-Nigeria, the National Gene Bank of Kenya-Muguga, and Kenyan farmers’ preferred varieties were grown in the Chuka University Kairini Farm for characterisation and evaluation. A randomized complete block design with three replications was used in two trials. Characterisation followed the International Board for Plant Genetic Resources descriptors for cowpea. Quantitative data for number of days to 50% flowering, number of main branches, number of seeds per pod, pod length, and 100-seed weight were subjected to analysis of variance, using SAS version 9.4. Significant means were separated using the least significant difference test at α=0.05. Quantitative and qualitative data were also subjected to hierarchical cluster analysis using SAS version 9.4. Results from analyses revealed significant differences (P<0.05) among the 60 accessions, suggesting that the germplasm collection had adequate variation that could be used in cowpea improvement. Qualitative traits revealed significant genetic variation based on the high Shannon-Wiener diversity indices. Seed colour showed the highest variation, indicating its importance in cowpea breeding. There was a positive association between days to 50% flowering, pod length and number of seeds per pod and grain yield. Plant breeders should consider these associations in breeding programmes. Pod length and number of seeds per pod are the most important characters closely linked to yield and hence key selection features in breeding programmes. The present study revealed that substantial genetic variation is available in the cowpea accessions assessed. Thus, crossing among the most divergent accessions could help recover desirable transgressive segregants. Moreover, they should be used to maintain genetic divergence among cultivated accessions to overcome the adverse effects of monoculture.