Preliminary phytochemical analysis and assessment of herbicidal activity of Parthenium hysterophorus L. extract on germination and initial development of two selected rice weeds in Malaysia.
The excessive use of synthetic herbicides for weed control has resulted in adverse environmental problems such as pollution, herbicide resistance and diseases. Therefore, the search for alternative sources of herbicide by using natural sources that are ecofriendly, effective and safe, becomes imperative. The present study was undertaken to investigate the presence of phytochemicals in Parthenium hysterophorus L. leaf, stem and root extracts using the different polarity of solvents (methanol, hexane, ethyl acetate and water) and to evaluate the phytotoxic effect of the extracts on germination and seedling growth of two rice weed species: Echinochloa colona (L.) Link. and Ludwigia decurrens Walt. under laboratory conditions. The standard procedure for qualitative phytochemical analysis was adopted for the analysis. For the germination test, the extracts were reconstituted at 2.5, 5.0, 7.5 and 10% concentration levels with distilled water as a control. Phytochemical analysis showed both the presence as well as the absence of alkaloids, flavonoids, anthraquinones, steroids, phenols, saponins, tannins, resins and terpenoids from the different solvents and plant parts. The study revealed that ethyl acetate leaf extract had the highest number of phytochemicals followed by the methanol leaf extract. Extracts in different solvents and plant parts demonstrated distinctly varying herbicidal actions towards the bioassay weed species. It was also found that both ethyl acetate and methanol leaf extracts significantly reduced (P <0.05) seed germination, plumule, and radicle lengths by 100% inhibition at a concentration as low as 2.5%. Conversely, less inhibition was provided by hexane and water extracts across all plant tissue concentrations. The results of this study suggested that ethyl acetate and methanol leaf extracts of P. hysterophorus L. can be utilized as an organic herbicide for the management of rice weeds.