Allelopathic effects of Eucalyptus camaldulensis Dehn on Mimosa pigra Linn. seedlings

The allelopathic effects of Eucalyptus camaldulensis Dehn.on Mimosa pigra Linn. Seedlings were studied. The results indicated that the methanolic extracts of green and fallen leaves of E. cammaldulensis were inhibitory to both germination and growth of M. pigra seedlings. While germination was not inhibited, M. pigra seedling growth bioassay with methanolic extract frm bark of E. camaldulensis demonstrated the presence of inhibitors at this state. Germination of Oryza sativa cv. RD 23 seeds was much less sensitive to the methanolic extract of green leaves than that of M. pigra seeds Two chromatographic methods, i.e. column chromatography and thin-layer chromatography were used for isolating the inhibitors from the methanolic extract of green leaves. Two inhibitors were detected on the thin-layer chromatogram one of which was identified as chlorogenic acid which is readily soluble in water. Although the author was unable to identify the other inhibitor through comparisons of thin-layer chromatography with authentic chemicals, gallic, ferulic, p-coumaric and caffeic acids were eliminated as possibilities. The effects of thirteen compounds, i.e., benzoic acid, salicylic acid, gentisic acid, protocatechuicacid, gallic acid, vanillin, thymol, t-cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, methyl cinnamate and chlorogenic acid on seedling growth of M. pigra and O. sativa were determined. It appeared that the growth inhibitory activity of these compounds varied with the position and number of –OH and –OCH3 substituents attaching to their aromatic rings. Moreover, the compounds were more inhibitory to seedling of M. pigra than that of O. sativa.