WATER SOLUBLE PHENOLICS IN FIVE WINTER SEASON LEGUMINOUS WEEDS AND THEIR PHYTOTOXICITY AGAINST WHEAT

Weeds cause losses to crops by exerting their allelopathic effect through the release of leachates and decomposition of their residues in field. The present study was conducted to assess the allelopathic effect of aqueous extracts at different concentrations [2.5% (w/v) and 5% (w/v)] and residues with different decomposition durations (0, 15 and 30 days) at 2% (w/w) concentration of five winter season leguminous weeds viz. Medicago polymorpha, Lathyrus aphaca, Melilotus indica, Trigonella polycerata and Vicia sativa against germination and seedling growth of wheat. Aqueous extracts and residues of weeds suppressed wheat germination/emergence and seedling growth in differential pattern. Compared with control, maximum reduction in germination percentage (78.4%), germination index (86.2%), root length (88.6%) and seedling vigor index (SVI) (97.4%) of wheat was shown by 5% aqueous extracts of M. indica. However, 5% aqueous extracts of L. aphaca, M. polymorpha and V. sativa produced significantly lower shoot length (9.53 cm), seedling dry weight (14.72 mg) and higher mean germination time (3.98 d), respectively. Among weed residues, T. polycerata, V. sativa and M. polymorpha showed lowest emergence percentage (35%), emergence index (0.73), SVI (398.5); root (15.72 cm) and shoot length (7.25 cm); and seedling dry weight (16.2 mg) of wheat, respectively. The differential suppressive phytotoxic ability of weeds tested seem to be due to presence of phenolic compounds namely 4-hydroxy-3-methoxy benzoic, chlorogenic, caffeic, gallic, ferulic, p-coumaric, m-coumaric, syringic and vanillic acids in different concentrations as detected by HPLC analysis of their aqueous extracts.