Expression of traits in cowpea as revealed by cluster analysis

In plant improvement programs, knowledge of germplasm diversity and genetic relationships among breeding materials cannot be over emphasized. Cluster analysis has been an important multivariate statistical tool used by many researchers for diversity studies; it has been found effective, irrespective of the data set involved in the study. The genetic variability among 10 genotypes of cowpea was assessed based on the expression of the quantitative and qualitative traits. Quantitative traits revealed a dendrogram which grouped genotypes into two major clusters, A and B, with cluster A having two (2) sub clusters (1 and 2). Cluster B had no sub-cluster. Sub-cluster 1 of A had one (1) genotype while sub-cluster 2 of A had only five (5) genotypes. Cluster B had four (4) genotypes. Qualitative traits revealed a dendrogram which also grouped genotypes into two major clusters (A and B). Cluster A had two sub-clusters (1 and 2); with sub-cluster 1 having two (2) genotypes, sub-cluster 2 having five (5) genotypes. Cluster B had only three (3) genotypes. All quantitative traits had very high level of contribution to the total variability observed among the genotypes, making these characters important for discriminating among genotypes of cowpea. Moreover, for any breeding work to be successful in cowpea, these characters must be considered. The level of variations showed by qualitative traits was very high, as ten traits out of thirteen studied were able to discriminate effectively among the genotypes studied, while the level of similarity for phenotypic expressions among the rest of the traits was very high. This study identified genotypes TVu3, TVu5, TVu4 and TVu7 for further genetic studies based on high number of seeds per plant. Furthermore, the choice of cluster analysis as a tool for this work proved to be a wise decision, as dendrograms were able to reveal similarities and differences among the tested genotypes.