Allelopathic activity of some medicinal plant extracts and allelopathic activity guided fractionation of Methanolic leaf extract of Cassia Alata

Abstract

The current study investigated the allelopathic activity of twenty six medicinal plant extracts using Radish seed germination bioassay. The investigation result suggested that the methanolic leaf extract of Dregea volubilis, Cassia alata and Azadirachta indica have the highest allopathic activity against seed germination. As a continuation of our research work on allelopathic activity studies of some medicinal plant and seaweeds, methanolic leaf extract of Cassia alata was further investigated with the hope of discovering new eco-friendly natural herbicides. Methanolic leaf extract (25 g) of Cassia alata was chromatographed on a column of silica gel (50 g, Merk Kiselegel 60, 230- 400 mesh ASTM) using n-hexane, ethyl acetate, methanol and water as eluents to give fifteen major fractions F- 1 to F-15. Lettuce seed germination bioassay which is widely used in the detection of allelochemicals, throughout the world was carried out to examine the active fractions for seed germination inhibitory activity. Out of 15 fractions and crude tested, F-11 (80% -100% ethyl acetate in hexane), F-12 (0% - 10% methanol in ethyl acetate) and crude showed statistically potent seed germination inhibitory activities (0 % germination), this might be due to the allelochemicals present in the Cassia alata. F-9 (45% to 65% Ethyl acetate with hexane) has also shown significant inhibition activity with 12.5% germination.