Efficacy of different bioassays for the assessment of toxicity of plant extracts

The toxicity of eight weed species was assessed by four bioassays using different organism's viz., wheat (Triticum aestivum L), rice (Oryza sativa L.), lettuce (Lactuca sativa L.) in terrestrial, and duckweed (Spirodela polyrhiza L.) in aquatic medium. Among all, wheat bioassay gave the best results. The growth of wheat seedlings in different concentrations (1 to 3% w/v) of aqueous leachate of 5 species, C. album, E. ciliaris, A. mexicana, T. grandis and V hastata reduced significantly, whereas, A. ramosa, P. virgatum and V. cineraria were found to be least affected. Lettuce and rice bioassay were not found suitable for ascertaining allelopathy. Duckweed bioassay gave doubtful results in some species. The study suggested the use of wheat bioassay for assessment of allelopathy of plant extracts in India.