PHYTOTOXIC EFFECT OF WATER SOLUBLE PHENOLICS FROM FIVE LEGUMINOUS WEEDS ON GERMINATION AND SEEDLING GROWTH OF RICE

Allelopathic effects of five leguminous weeds viz., Lathyrus aphaca L., Medicago polymorpha L., Melilotus indica L., Vicia sativa L. and Trigonella polycerata L. against the germination and seedling growth of rice was studied. The 2.5% and 5% (w/v) aqueous extracts and 2% (w/w) soil incorporated residues with varying decomposition durations (0, 15, 30 days) of these weeds were used. Inhibitory effects against rice were shown by water extracts and residues of these weeds. The 100% germination inhibition was caused by 5% aqueous extract of M. indica. However, among others, 5% aqueous extracts of T. polycerata showed significantly lower germination percentage (20), germination index (0.40), root length (1.01 cm) and seedling vigor index (19.0) whereas V. sativa and L. aphaca resulted in higher mean germination times (6.92 and 6.75 days) of rice, respectively. Medicago polymorpha aqueous extract with 5% concentration and residues decomposed for 30 days produced significantly lower shoot lengths (3.8 and 4.72 cm) and seedling dry weight (4.49 and 4.84 mg) while significantly lower root lengths (1.01 and 2.36 cm) and seedling vigor indices (19.0 and 53.43) of rice seedlings were noted in response to 5% aqueous extract of T. polycerata and residues of V. sativa decomposed for 30 days which also resulted in minimum emergence percentage (22.5), emergence index (0.26) and mean emergence time (9.08 days). Presence of phenolic compounds such as caffeic acid, gallic acid, chlorogenic acid, vanillic acid, 4-hydroxy-3-methoxybenzoic acid, ferulic acid, p-coumaric acid, m-coumaric acid and syringic acid seem to be the cause of phytotoxity of these allelopathic weeds.