Evaluation of cowpea MAGIC recombinant inbred lines for seedling-stage drought tolerance

Drought stress causes yield losses of 35-65% in cowpea (Vigna unguiculata (L.) Walp.) in sub-Saharan Africa (SSA), under moderate to severe water deficits. Hence, drought tolerance is vital even in crops with inherent tolerance characteristics. This study evaluated F9 lines of the Multi-parent Advanced Generation Inter-cross (MAGIC) recombinant inbred lines (RILs) and their eight founder parents, for seedling-stage drought tolerance for the Sudan Savanna Zone of Ghana. A screenhouse experiment was conducted using an augmented design, with three replications and a wooden box screening technique. Plants were watered daily with 8.2 L of borehole water for 10 days after planting. Drought stress was then imposed for 21 days, after which watering was resumed to assess the recovery of each genotype. The moisture content within the box decreased from 37.39% at the imposition of drought to 2.45% at the time of stress removal. Significant (P < 0.05) genotypic differences were observed for leaf wilting index (0.77 - 1.00), delayed leaf senescence (3.50 - 5), stem greenness (1 to 5), regrowth (0 - 5) and survival rate (0 to 100%), indicating substantial genetic variation. Drought symptoms increased progressively from 7 to 21 days after stress imposition. Strong positive correlations were detected among traits, with survival rate having the highest correlation coefficient with all drought traits, making it the most reliable indicator of drought tolerance at the seedling stage. Based on post-drought survival, 57 genotypes were classified as highly tolerant (>50% survival), 74 as tolerant (20-49%), 37 as susceptible, and 140 as highly susceptible. The high level of susceptible genotypes identified was partly attributed to the stringent conditions of the wooden box techniques that leave little room for escape. The wooden box method proved effective for discriminating seedling-stage drought responses. The phenotypic data obtained would be useful for QTL mapping to identify markers for marker-assisted selection. This also calls for further field validation of the findings of this study. The identified tolerant genotypes provide valuable genetic resources for improving drought resilience in cowpea breeding programmes.