Response of the MAGIC population of cowpea to scab disease resistance and grain yield

Scab disease, caused by Sphaceloma spp., is a major constraint to cowpea (Vigna unguiculata L. Walp) production in sub-Saharan Africa (SSA), with yield losses of up to 100% under severe infection. Currently, no scab-resistant cowpea varieties have been developed or identified. The objective of this study was to identify novel sources of resistance by evaluating the response of the cowpea Multiparent Advanced Generation Inter-Cross (MAGIC) population to natural scab pressure. A total of 208 cowpea genotypes, including MAGIC varieties, were evaluated across two locations at Kabanyolo and Arapai, in Uganda, during the 2023 cropping seasons. Significant genotypic variation in disease response was observed, with the highest severity recorded at Kabanyolo, likely due to elevated precipitation of the 2023B rainy seasons. Pearson correlation analysis revealed negative associations between scab severity (week 10 and AUDPC) and days to 50% maturity, with a significant correlation at 10 WAP (r = -0.14, P<0.05). Scab severity at 10 WAP was also negatively correlated with yield traits (r = -0.01 to -0.14). Five lines, MAGIC 064, MAGIC 254, NAROCOWPEA 2, NAROCOWPEA 3 and MAGIC 062, were found to be resistant. Overall, NAROCOWPEA 3 combined resistance with high yield (1,562 kg ha-1), making it a strong parent for Scab resistance and grain yield breeding.