Agro-Morphological, Nutritional, and Preliminary Molecular Diversity of Northern Thai Cowpea (Vigna unguiculata) Landraces from Three Geo-Ecological Zones

Cowpea (Vigna unguiculata [L.] Walp.) is an important food legume whose cultivated germplasm is generally characterized by limited genetic diversity resulting from domestication and predominant self-pollination. This study evaluated the agro-morphological and nutritional diversity of 21 farmer-maintained cowpea accessions collected from three geo-ecological zones of northern Thailand; western, eastern, and southwestern. A representative subset comprising nine landrace accessions and one commercial check was further analysed using start codon targeted (SCoT) markers to provide a preliminary assessment of molecular diversity. Considerable variation was observed among accessions for qualitative and quantitative traits. The cumulative Shannon diversity index for qualitative traits was highest in the southwestern collection (H'=3.80), followed by the eastern (H'=3.34) and western (H'=2.42) collections. Seed protein content was highest in accession SW5 (36.00 g/100 g), seed iron content was highest in accession W4 (78.19 mg/kg), and crude fibre content was highest in accession W6 (5.97 g/100 g), with different accessions exhibiting superior values for individual nutritional traits. Molecular analysis of the selected subset showed that 68% of the SCoT marker variation occurred within accessions, whereas 19% and 13% occurred among accessions within zones and among zones, respectively. The selected accessions exhibited moderate genetic differentiation (GST=0.41), and principal coordinate analysis indicated partial grouping according to their collection zones. Overall, this study provides baseline information on the agro-morphological, nutritional, and preliminary molecular diversity of northern Thai cowpea germplasm and identifies accessions that warrant further evaluation for germplasm conservation and future cowpea improvement.