Isolation and characterization of allelopathic compounds from the indigenous rice variety ‘Boterswar’ and their biological activity against Echinochloa crus-galli L

Aqueous methanol extracts of the Bangladesh indigenous rice (Oryza sativa L.ssp. indica) variety „Boterswar? inhibited the germination and seedling growth of Lepidium sativum L. and Echinochloa crus-galli L. Beauv which suggested that this variety may contain phytotoxic substance(s). Four biologically active compounds, syringaldehyde (4-hydroxy-3,5dimethoxybenzaldehyde), (-) loliolide, 3ß-hydroxy-5a,6a-epoxy-7-megastigmen-9-one and 3hydroxy-ß –ionone, were isolated from the ethyl acetate phase using several chromatographic steps. The chemical structures of the compounds were determined through electrospray ionization and spectroscopic analyses. The biological activity of these compounds showed that concentration > 10 µM significantly inhibited the root and shoot growth of E. crus-galli seedlings, and the I50 (50% growth inhibition) values ranged from 16.03 to 27.23 µM and 23.94 to 75.49 µM for root and shoot growth, respectively. The four compounds synergistically suppressed the growth of E. crus-galli more strongly than the individual compounds. Thus, the indigenous rice „Boterswar? has potential use for weed management and this indigenous variety could be used to develop a new commercial rice variety that may suppress weeds.