BIOCHEMICAL BASIS OF COWPEA RESISTANCE TO BRUCHID, CALLOSOBRUCHUS MACULATUS (F.).

Abstract

Bruchids are the most destructive pest of stored cowpea seeds leading to losses in quantity and quality of seeds. To overcome this problem, farmers use different synthetic insecticides but these have toxic effects on the environment and non-target organisms. The use of resistant genotypes is considered a cost effective and safe alternative to synthetic insecticides. The metabolites are reported to play a major role in resistance but the basis of this role in resistance to the bruchid is not well understood. Understanding the biochemical mechanisms of pest resistance could be utilized in exploiting the trait in crop breeding. The present study investigated the roles of seed coat (condensed and free tannins, flavonoids, total phenolic content and their anti-oxidant activity) and cotyledon (carbohydrate, proteins and α-amylase inhibitory activity) biochemical compounds in conferring cowpea seed resistance to bruchid infestation. None of the seed coat biochemical traits were associated with the seed resistance parameters. With the exception of protein content which was only associated with weight loss, all the cotyledon biochemical traits were strongly associated with all of the seed resistance parameters. These results indicated that seed coat biochemical traits have no role in conferring resistance but cotyledon biochemical traits namely, α-amylase inhibitory and carbohydrate content are involved in conferring resistance to bruchid attack by reducing the growth and development of the pest. These traits can be used as biochemical markers for quick and accurate selection of cowpea genotypes resistant to bruchid.