Phytotoxic effects of Piper betle L. extracts on germination of Eclipta prostrata L. and Chloris barbata Sw. weeds

Abstract

Weeds are the major problem in agricultural crop fields. To control weeds nowadays, tremendous hazardous herbicides have been applied into fields, causing harm to farmers, consumers and environment. Alternatively, nature products have been evaluating for allelopathic property and using as clean weed management. In this work, the effect of betel extracts on weed germination was investigated and their potential allelochemicals were identified. Betel oil, hexane, dichloromethane (DCM), ethanol (EtOH) and ethyl acetate (EtOAc) crude extracts were derived from Piper betle leaf. The chemical constituents of the extracts were determined using Gas chromatography/Mass spectrometry (GC/MS). Then, the extracts were applied to 2 species of weeds, a broadleaf (Eclipta prostrata L.) and a narrowleaf (Chloris barbata Sw.), and 3 crop species (Oryza sativa L., Lactuca sativa L. and Brassica alboglabra L.H. Bailey) on filter paper. The results demonstrated that yields of oil, hexane, DCM, EtOAc and EtOH extracts were 0.25%, 1.86%, 8.14%, 11.21% and 9.57% respectively. All extracts contained mainly phenylpropanoids approximately 65% and sesquiterpenoids approximately 13% including ??-caryophyllene. All betel extracts had allelopathic effect with different activities. Betel oil at 1 mg/mL was suitable for weed control, since it had a slight effect on crops, but completely inhibited germination of weeds. Hexane extract at 0.5 mg/mL significantly inhibited weeds germination with a little effect on crops germination. EtOH extract and EtOAc extract at 1 mg/mL unaffected crop germination, but totally inhibited weed germination. Taken together, EtOH and EtOAc were the choice of solvents for betel extraction for weed control. These extracts had high recovery yields and had selective action only to weeds without crops interference. Interestingly, the extracts affected more to the narrowleaf weed, the main problem in paddy, than to the broadleaf. The finding suggested P. betle as a potential source of natural herbicide.