Phytotoxicity and weed management potential of leaf extracts of Callistemon viminalis against the weeds of rice

Abstract

We explored the phytotoxicity of Callistemon viminalis leaf extracts (LE; 0.5, 1, 2 and 4%) towards germination and early growth of rice (Oryza sativa L.) and its associated weeds [Echinochloa crus-galli (L.) Beauv., Cyperus rotundus L., Leptochloa chinensis (L.) Nees. and Commelina benghalensis L.], under laboratory and greenhouse conditions. In a laboratory assay, leaf extracts (4%) inhibited germination (40–52%), root length (36–85%), shoot length (37–64%), dry weight (27–67%) and chlorophyll content (20–42%) in all the weeds. Under greenhouse conditions, 2% leaf extracts (LE) + Butachlor (well-known herbicide; H; 50% E.C.; 2:1, v/v) severely affected the emergence and biomass of all the weeds. However, there was no effect on the growth and yield attributes of rice. Moreover, upon 2% LE + H treatment, the plant height and number of grains per plant increased significantly and the effect was comparable to the recommended dose of Butachlor. The results suggested the presence of water-soluble allelochemicals (mainly phenolics) in the leaf extracts that could be responsible for the observed inhibitory effect. Based on the study, it could be concluded that C. viminalis leaf extracts hold good potential for possible weed management, and further research could be done to develop it as an alternative to synthetic herbicides in sustainable agriculture under field conditions.