Patterns of qualitative traits-based diversity and among traits dependencies in cowpea germplasm from the Sahelian and Western highlands agroecological zones of Cameroon: Opportunities for crop conservation and improvement

<p xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" dir="auto" id="P000001">Cowpea is a tropical grain legume with significant contribution to the livelihood of millions of people in developing countries. One hundred cowpea landraces from seven populations in two distinct agroecological zones of Cameroon were screened by means of 20 qualitative traits using a randomised complete block design with three replications. For each qualitative trait, frequencies of identified phenotypic classes were estimated. The number of observed phenotypic class per trait (Na) and Shannon-Weaver diversity (H’) were used to estimate morphological diversity. Considering all landraces, Na varied from 2 (Growth pattern, Plant hairiness, Leaf hairiness and Leaf V marking) to 5 (Growth habits and seed colour) with the overall mean at 3.45. Diversity index (H’) ranged from 0.27 (Leaf hairiness) to 0.83 (Growth habit) with the mean at 0.57. Student t-test showed significant higher diversity for Western compared to Sahelian agroecological origin of accessions. One-way ANOVA showed significant differences of these indices between populations. Partitioning revealed most of the diversity was distributed within agroecological sites (78%) and populations (66%). Cluster analysis assembled the landraces into four clusters with high proportion of landrace sharing similar ecosite grouped together. The genetic distance was affected by geography as Mantel test was significant (R ² = 0.795; p < 0.010). Multiple correspondence analysis (MCA) showed 72.46% and 50.72% of phenotypic variants associated respectively with axis 1 and axis 2, both axes explaining 64.05% of the total variation. Chi-square test revealed that seed colour is dependent on 18 of the 19 remaining traits excluding plant pigmentation. Flower colour, twinning tendency and growth pattern all showed dependence on 16 other qualitative traits. Any pair of traits related to colour, pubescence and shape showed dependence. The genotype named C14 was the only one with no crowded black seed and pendant pod attachment to peduncle. Only KEB-CP008 had pale green leaf colour, KEB-CP013 was unique with splashes of pigments and C9 was the single germplasm with pigmented sutures on immature pods. The outcome of this study confirmed a vast qualitative variation in cowpea from Cameroon across agroecological sites and villages of origin, highlighting a huge potential required for cowpea improvement. </p>