Herbicidal activities of compounds isolated from the medicinal plant Piper sarmentosum

Abstract

The discovery of novel natural herbicides is crucial to address increased weed resistance and environmental issues. In our previous screening for naturally occurring plant-derived herbicides, the ethanol extract of Piper sarmentosum leaves and stems possessed herbicidal activity against Echinochloa crusgalli and Amaranthus retroflexus. Here, four known compounds were isolated from the extracts by bioassay-guided fractionation. They were characterized as sarmentosine, sarmentine, piperine and pellitorine based on their spectral data. Phytotoxic analyses revealed that sarmentosine and sarmentine were more phytotoxic against E. crusgalli and A. retroflexus, inhibiting the shoot and root growth process in a concentration-dependent manner. The greenhouse herbicidal activity assay showed that sarmentine and sarmentosine could effectively control E. crusgalli and A. retroflexus at 5-mg/mL concentrations, resulting in inhibition rates of more than 80%. The weed-controlling spectrum test indicated that sarmentosine could effectively control barnyard grass (E. crusgalli), feather fingergrass (Chloris virgata), morning glory (Pharbitis nil), redroot pigweed (A. retroflexus) and Chinese jute (Abutilon theophrasti). In particular, sarmentosine exhibited synergistic effects against E. crusgalli and A. retroflexus when it was applied in combination with propanil (a commercial herbicide). This is the first report of the herbicidal activity of the natural amine alkaloid sarmentosine and its synergistic effects. These findings warrant further investigations of P. sarmentosum to produce amine alkaloid-based weed control agents.