The Allelopathic Effects of Platycarpha glomerata (Thunb.) Less. on Germination and Growth of Bidens pilosa L. Weed

Bidens pilosa L. is a widespread weed that invades grasslands, agricultural fields, and roadsides, and outcompetes indigenous plant species for resources, posing significant challenges to sustainable agricultural management. The study investigated the allelopathic potential of different P. glomerata plant parts on the germination and growth of B. Pilosa and identified secondary metabolites potentially responsible for the herbicidal activity. Rhizome and leaf aqueous extracts were prepared in 0, 1, 2, 3, 4 and 5% (w/v) concentrations, where the control was distilled water. Bidens pilosa seeds were subjected to a germination assay, and seedlings were foliar sprayed with the extracts in a completely randomized design. The phytochemical composition was analyzed by Gas Chromatography–Mass Spectrometry. The results demonstrated that P. glomerata extracts at ≥2% concentrations retarded seed germination and seedling growth of B. pilosa, whereas concentrations of ≥4% inhibited germination. Aqueous foliar application reduced plant height and chlorophyll content and caused leaf morphological deformities including chlorosis, necrosis, leaf folding, and purple and black spots. The phytochemical analysis revealed the presence of alkanes, cyclic alkanes, aromatic hydrocarbons, alkaloids, fatty acids ester, fluorinated esters, and thiols phytochemical groups. These findings highlight the allelopathic potential of P. glomerata aqueous extracts. However, more studies are required to determine their effects in field application as potential candidates for bioherbicide development.