Allelopathic Potential of Root Exudates from Cosmos sulphureus at Different Phenological Stages

Species of the Asteraceae family are recognized as important sources of secondary metabolites with allelopathic activity.Among them, Cosmos sulphureus exhibits notable allelopathic potential, mainly associated with flavonoids and sesquiterpene lactones.This study aimed to evaluate the allelopathic effects of vegetative-stage root exudates of C. sulphureus on three agronomically relevant weed species: Eleusine indica, Panicum maximum and Portulaca oleracea.Root exudates were collected using an inverted-bottle system.Part of the material was purified by Amberlite XAD-4 column chromatography, vacuum filtration, and lyophilization, and subsequently diluted to concentrations of 50, 100, 200, 400 and 800 ppm.Crude exudates were used for scanning electron microscopy (SEM) analyses.In vitro cytotoxicity and phytotoxicity bioassays were conducted to assess allelopathic activity.Cytotoxicity assays using Triticum aestivum coleoptiles revealed a hormetic response, with stimulation at 50-200 ppm and strong inhibition at 400-800 ppm.Phytotoxicity assays showed pronounced inhibition of root growth, reaching 91.5% for E. indica at 50 ppm, 89.8% for P. oleracea and 80.0% for P. maximum at 200 ppm.Shoot growth was inhibited by up to 74.0% in P. oleracea.SEM analyses confirmed severe structural damage in treated roots, including necrosis, loss of root hairs, irregular cell surfaces and apical deformities.These findings demonstrate that vegetative-stage root exudates of C. sulphureus strongly inhibit early seedling development by altering physiological and structural traits, highlighting their potential application for sustainable weed management.