Phytotoxicity Evaluation of Leaf Extracts and Isolation of Phytotoxic Compounds from Trewia nudiflora Linn. for Natural Weed Control

This research focuses on examining the phytotoxic effect of leaf extracts of T. nudiflora on the growth of one dicot, Lepidium sativum L. (cress), and one monocot, Lolium multiflorum Lam. (Italian ryegrass), plant. Significant shoot and root growth suppression occurred in both plants treated with different concentrations of T. nudiflora leaf extracts (p ≤ 0.05). An increase in T. nudiflora leaf extracts was associated with a progressive decline in the root and shoot development of both plants. The half maximum inhibitory doses (I50 values) for cress and Italian ryegrass root growth were 0.00037 and 0.00071 g dry weight (DW), while concentrations of 0.00129 and 0.006 g DW equivalent T. nudiflora leaf extract in mL–1 were needed for a similar reduction in shoot growth. According to these values, root development exhibited a greater sensitivity than shoot development to the applied extract, and dicot plants were more susceptible to T. nudiflora extracts than monocot plants. Chromatographic fractionation of the extracts led to the successful isolation of two phenolic acids; protocatechuic acid and gallic acid. Bioassays of T. nudiflora leaf extract-derived two phenolic acids against treated plants demonstrated significant toxic action that correlated with the concentrations of the compounds, which varied between the two plants. These results suggest that these two phenolic acids are key contributors to the phytotoxic activity observed in extracts from T. nudiflora leaves and might contribute to the development of sustainable agricultural practices, including the design of allelopathy-based weed management strategies.