Seed storage proteins and seed coat compounds additively influence Callosobruchus maculatus Fab. tolerance in selected cowpea (Vigna unguiculata L. Walp.) varieties

Abstract

The cowpea weevil, Callosobruchus maculatus, is a major threat to stable cowpea production, especially in storage, and has been reported to facilitate postharvest losses in cowpea grains. Host resistance has been suggested as the best control method but with conflicting knowledge on the source of resistance. Hence, the study seeks to evaluate seed storage proteins (SSPs) and seed coat compounds (SCCs) associated with tolerance to C. maculatus. SSPs and SCCs were assayed and associated with C. maculatus tolerance in 19 cowpea varieties with varied tolerance levels using a stepwise multiple regression analysis. Top C. maculatus tolerants were TVu-2027, TVu-11952, TVu-11953, and TVu-145. The protein fraction with a mass of 51 kDa was a significant predictor associated with percentage adult insect emergence (PAE) and host suitability index (H.S.I.), and 57 and 71 kDa were associated with mean development period (MDP) whereas 59 and 131 kDa were associated with seed damage tolerance (TolSD). Several SCCs identified were associated with the C. maculatus tolerant measures used in the study. However, Thiazole, tetrahydro- and Undecane were consistently identified with C. maculatus tolerance. Higher phenotypic variability was accounted for by SCC than SSP fractions associated with C. maculatus tolerance in the study indicating that SCCs contributed more to the C. maculatus tolerance than the SSPs identified. These compounds can be incorporated into breeding for C. maculatus tolerant in cowpea and biopesticide formulations whereas cowpea varieties with the high or significant amount of these compounds can also be recommended to the farmers or to the cowpea producers.