Evaluation of phytotoxicity of neem (Azadirachta indica. A. Juss) to crops and weeds

Xuan, T.D.; Eiji, T.; Hiroyuki, T.; Mitsuhiro, M.; Khanh, T.D.; Chung, I.M.

Evaluation of phytotoxicity of neem (Azadirachta indica. A. Juss) to crops and weeds

2004

Although the neem (Azadirachta indica. A. Juss) tree has been known to be useful in soil enrichment and for insect, pest and disease control, its allelopathic potential has not been described. This study documents that neem strongly inhibits germination and growth of several specific crops: alfalfa (Medicago sativa L.), bean (Vigna angularis), carrot (Daucus carota L.), radish (Raphanus sativus L.), rice (Oryza sativa L.), and sesame (Sesamum indicum L.) and weeds: Echinochloa crus-galli, Monochoria vaginalis, and Aeschynomene indica L. in a bioassay and in soil. The sensitivity of weeds varied between bioassay and soil. In all culture conditions, inhibition from neem bark was greater than from leaves. Six phenolic compounds including gallic acid, benzoic acid, p-coumaric acid, p-hydroxybenzoic acid, vanillic acid, and trans-cinamic acid were isolated and identified in both neem bark and leaves. Ferulic acid was found in the bark. Concentration of these phenolic compounds in bark was higher than in the leaves. We suggest that the dose and greater number of allelochemicals result in the stronger allelopathic activity of neem's bark than the leaves.

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