Abstract

Cowpea is fascinating for its diverse flowering times, which can range from 30 to over 90 days after planting, depending on genotype, photoperiod, and environmental conditions. The primary objective of this study was to conduct genome-wide association studies (GWAS) to identify genomic regions associated with earliness in flowering in cowpea (Vigna unguiculata L. Walp.). The cowpea genotypes, DArT Panel Population, were made up of four distinct groups with different genetic backgrounds. These groups included elite breeding lines, germplasm accessions from the IITA Genetic Resources Centre, and multi- and bi-parental recombinant inbred, totalling 300 genotypes. Our research involved a genome-wide scan of these 300 cowpea genotypes to identify markers linked to early flowering. We phenotypically screened the population across two locations: Wudil and Minjibir in Kano state. Notably, we observed significant differences in the days to first flowering among the various populations. We conducted the GWAS using TASSEL v.5.2.79, applying a mixed linear model (MLM) with (Q + K) models, incorporating principal components and kinship matrices to correct for population structure. The statistical models from TASSEL generated Manhattan and quantile-quantile (QQ) plots. Results from genome-wide scan revealed three major regions on chromosomes Vu09, Vu03, and Vu011, along with three minor regions on chromosomes Vu07, Vu06, and Vu05, all significantly associated with early flowering. Among these regions, the gene Vigun09g063800 was found to be closest to the peak SNP positions and plays a crucial role in regulating flowering time, which is vital for transition of the plant from vegetative to reproductive phase. It is recommended that future studies focus on establishing a marker-assisted breeding platform and developing extra- early cowpea cultivars. In addition, the SNP markers associated with early flowering should be tested for consistent associations across different genetic backgrounds.