Abstract

Characterization of cowpea (Vigna unguiculata [L.] Walp.) accessions is an important exercise in improvement of the crop. A total of 432 cowpea germplasm accessions collected from five agricultural districts of Botswana during 1972 to 1987 were evaluated under field conditions at the Department of Agricultural Research Station, Gaborone. The germplasm were assessed using 37 agro-morphological characters to determine the diversity of Botswana cowpea germplasm. DIVA-GIS were used to conduct a gap analysis to estimate the degree of coverage of the germplasm accessions across the country. Areas not yet explored and those that need additional sampling were identified. The study demonstrated a significant amount of diversity among the germplasm based on the analysis of variance (ANOVA) and Shannon Weaver Diversity Index (H’). The majority of accessions had their first flowering more than 50 days after sowing and 100 days for 95% of maturity which shows that they are more inclined towards late maturing cowpeas. Early maturing accessions with less than 110 days to maturity are found in Ngamiland, Southeast and unknown origin. The accessions from Central districts had the largest variation for most characters (11) followed by Southeast with 10 among the 22 quantitative characters evaluated. Principal components analysis (PCA), revealed characters which discriminated more efficiently between accessions than others such as peduncle length, 10 seeds weight, seed width, seed thickness, pods per peduncle,  and 100 seed weight. Cluster analysis delineates germplasm into three clusters, based on the origin of the germplasm according to different agro-ecological zones. Germplasm accessions originating from Ngamiland formed a separate cluster from the rest and had several peculiar materials, which could be a potential source for new germplasm for cowpea improvement. Further molecular studies are required to complement and validate the current agro-morphological variation observed in the Botswana cowpea germplasm.

Key words: Accessions, agro-morphology, cowpea, diversity, germplasm.