BIOCHEMICALS ASSOCIATED WITH CALLOSOBRUCHUS CHINENSIS RESISTANCE IN SOYBEAN

Soybean is a very important crop worldwide because of its 40% protein and 20% oil content. However, soybean suffers damage from bruchid (Callosobruchus chinensis) during storage. Understanding of factor(s) contributing to bruchid resistance is useful for development of soybean cultivars with genetic resistance to bruchid damage. Biochemicals associated with resistance to Callosobruchus chinensis were investigated on eight soybean genotypes with varying levels of resistance. Significant differences (P<0.05) were observed amongst genotypes with regards to antinutritional factors particularly total antioxidants (TAOX), tannins, peroxidase (POD), and flavonoids. There were no significant differences among genotypes with regards to nutritional factors particularly proteins, starch, lipid peroxidation, and reducing sugars. A resistant genotype AVRDC G8527 had the highest concentration of total antioxidants (1.98 AU min-1 mg-1) and tannins (1.85mg TAE 100g-1) followed by Maksoy 3N while the least was in a very susceptible genotype AGS 292 (TAOX=0.39 AU min-1 mg-1, Tannin=0.296 mg TAE 100g-1). AGS 292 had the highest concentration of flavonoids (31.22 mg QE 100g-1) while AVRDC G8527 had the least (5.13 mg QE 100g-1). Peroxidase activity was highest in AVRDC G89 (0.27AU min-1 mg-1) while AGS 292 had the least (0.07AU min-1 mg-1). From the correlation analysis, a significant strong negative relationship between flavonoids and tannin (r=-0.73**) and TAOX (r=-0.71**) but a positive non significant relationship with phenolic (r=0.22) and alkaloids (r=0.37) was recorded. Peroxidase activity had a significant relationships with median development period (r=0.69*) indicating that increased peroxidase activity resulted into increased seed resistance through prolonged insect development period. There was a strong relationship between tannins and total antioxidants (r=0.99**). These results indicate that secondary metabolites; peroxidase, tannin, and TAOX were biochemicals associated with higher resistance to C. chinensis in soybean while flavonoids were associated with higher susceptibility.