Phytotoxic Effect of Aqueous Extracts of Acalypha wilkesiana Mull. Arg., Centrosema pubescens Benth and Phyllanthus amarus Schum. & Thonn on Germination and Growth of Amaranthus cruentus L. and Corchorus olitorius L.

Allelopathy is a concept that is applied in weed management to minimize extensively the reliance on herbicide in agriculture. The allelopathic potential of Acalypha wilkesiana, Centrosema pubescens and Phyllanthus amarus on Amaranthus cruentus and Corchorus olitorius were investigated. Different concentrations of the leaf aqueous extracts of A. wilkesiana, C. pubescens and P. amarus were applied to determine their effect on A. cruentus and C. olitorius under laboratory conditions. The profiling of phytochemicals in the extracts showed that glycosides, phenols, terpenoids, saponins and steroid were present in the extracts. The seed germination, radicle length, plumule length of test crops were significantly decreased by leaf extracts compared with control treatments. The results revealed that the inhibitory effect was proportional to the concentrations of the extracts, higher concentrations had the stronger inhibitory effect. The result suggested that the inhibitory or stimulatory effect may be due to the presence of allelochemicals like glycosides, phenols, terpenoids and steroids etc. in the aqueous leaf extracts of A. wilkesiana, C. pubescens and P. amarus which may cause allelopathic effects under field conditions. Therefore, these plants should be controlled were they grow with cultivated crops.