Morphometric Analysis of some Species in the Genus Vigna (L.) Walp: Implication for Utilization for Genetic Improvement

Abstract

A B S T R A C TThe genus Vigna (L.) Walp is a large cosmopolitan leguminous genus comprising both cultivated and wild species. Vigna unguiculata (L.) Walp. (Cowpea) is an important food legume that is widely cultivated in the tropics, but its production and storage are hampered by insect pests. The present study evaluated the intra-and inter-specific morphological variabilities among 20 accessions of six Vigna species, comprising wild and cultivated species. The species are Vigna unguiculata (L.) Walp, V. vexillata (A. Richard), V. oblongifolia (A. Richard), V. ambacensis (Baker), V. luteola (Jacq.) (Bentham) and V. racemosa (G. Don) (Hutch and Dalziel). Thirty-one morphological characters involving qualitative and quantitative vegetative and reproductive traits were used for the evaluation. Multivariate analysis such as Pearson Correlation Coefficient (PCC), Principal Component Analysis (PCA) and Cluster Analysis (CA) were employed to evaluate the intra and inter specific variabilities. The paired-sample T test indicated significant differences among the 20 accessions (p#0.000, df = 19) in their morphometric traits. The relative significant correlation observed among some traits such as pod length, number of locules per pod and number of seeds per pod indicated their closeness and potential for genetic improvement of cowpea. The PCA showed that reproductive traits such as days to 50% flowering (0.984), days to 50% ripe pod (0.993), number of pods per peduncle (0.340) and 100-seed weight (0.132) are the major traits that accounted for the variations among the species. The UPGMA using the average (between groups) segregated the 20 accessions into two main clusters, cluster I (comprising mainly wild Vigna species) and cluster II (comprising both wild and cultivated species). The taxonomic affinities and genetic diversity among the species are of great importance in the utilization of the species for food and nutrition, fodder for ruminant animals, cover crop for rotational farming and more importantly genetic improvement of cowpea.

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