Preliminary study on character associations, phenotypic and genotypic divergence for yield and related quantitative traits among cowpea landraces (Vigna unguiculata) from the Western Highland Region of Cameroon

Cowpea (Vigna unguiculata) is an important tropical legume crop contributing significantly to food security in tropical regions. The present study was carried out to determine the extent of genetic variation, to estimate character associations, heritability and genetic advance of 25 quantitative traits in 30 genotypes of cultivated Vigna unguiculata from the western highland region of Cameroon. These quantitative traits were selected among cowpea descriptor lists. For all these traits, the analysis of variance showed significant difference among genotypes, highlighting the existence of important genetic divergence among the studied accessions. The highest phenotypic and genotypic coefficient of variation was observed in grain yield, pod yield and 100 seed weight. Genetic advance of these three characters was also the highest. Broad sense heritability was high in general, with 20 traits out of 25 having heritability values greater than 70%. This high heritability indicates little influence of the environment on these characters in cowpea. The highest heritability was recorded for 100 seed weight (98.15%) and the lowest for shoot weight (41.38%). At 0.05 probability level, grain yield correlated significantly with 21 out of the 24 other quantitative traits. Among others, grain yield correlated positively and significantly with 100 seed weight, number of pods per plant, number of branches per plant, number of nodes per plant, plant height, plant width, pod length, pod width, seed length, seed width and number of seeds per pod. These positive correlations between grain yield and many other traits indicate that a selection program based on any of these traits will result in increasing yield. Cluster analysis using UPGMA method revealed five distinct clusters. Genotypes named KEBCP025, KEB-CP006, KEB-CP098, KEB-CP070, and more importantly KEB-CP054 and KEB-CP004, were grouped in a single cluster and were characterized by a significantly higher grain yield, pod yield, number of pods per plant, number of seed per pod, plant height, pod length and pod width compared to other clusters. Accessions KEB-CP036 and KEB-CP031 produced significantly more important fresh biomass. These genotypes could be used as parents in genetic improvement programs aiming to increase yield and fresh biomass in cowpea.