BIOCHEMICAL-MECHANISMS OF RESISTANCE TO INSECTS IN SOYBEAN - EXTRACTION AND FRACTIONATION OF ANTIFEEDANTS

Leaf extractables/fractions obtained from the leaves of soybean PI 227687 showed greater antifeedant activity towards the third-instar larvae of the cabbage looper, Trichoplusia ni (Hub.). Extraction of leaves with ethyl acetate followed by 60% methanol, and counter-current partitioning of leaf extractables between ethyl acetate, water and hexane was not convenient for isolation of antifeedants. Methanol (60%) in water extracted most of the antifeedants from leaves, and this extract when partitioned between ethyl acetate and water (the latter repeatedly extracted with the former), concentrated the antifeedants from soybean leaves for further processing on thin layer chromatography or high performance liquid chromatography. There were quantitative differences in ethyl acetate fraction of PI 227687 (6%) and Davis (3.2%), and in flavonoids resolved at Rf 0.10-0.20 in benzene: ethyl acetate: methanol (4:3:3). Most of the flavonoids with antifeedant activity resolved at Rf 0.10-0.80. The antifeedant activity of flavonoid bands from PI 227687 was greater than the corresponding bands of Davis.