Allelopathic screening of 260 medicinal plant species and metabolite profiling of Tribulus terrestris for natural herbicide discovery

A large-scale screening of 260 medicinal plant species from the Showa Pharmaceutical University Garden (Japan) was conducted to evaluate their allelopathic potential using the sandwich method, a standardized bioassay for plant leachates. Effects on lettuce ( Lactuca sativa ) seed germination and seedling growth were assessed. Based on standard deviation variance under normal distribution, 72 out of 260 species exhibited significant inhibitory effects on radicle elongation. Five species demonstrated particularly strong inhibition, reducing radicle growth to <22% of the control: Tamarindus indica L. (7.3%), Liriope platyphylla Wang et Tang (8.1%), Taxodium distichum Rich. (11.7%), Acacia catechu Willd. (21.4%), and Tribulus terrestris L. (21.9%). Further phytochemical profiling of T. terrestris via UPLC-Q-TOF-MS identified 47 bioactive compounds, with flavonoids and coumarins—specifically scopoletin (putatively identified) and quercetin-3-O-glucoside—showing the strongest correlation with allelopathic activity. This study provides a benchmark for the isolation of allelochemicals and highlights promising candidates for the development of natural, plant-based herbicides.