Phytotoxic effects of stem aqueous extract of Lepidium didymum L. against Lens culinaris and Melilotus albus

Allelopathy involves plants releasing allelochemicals, inhibiting the growth of nearby plants, and influencing their physiological and morphological characteristics. Donor plants with allelopathic capabilities dominate, which affects the survival of other plant species. The effect of Lepidium didymum stem aqueous extract (SAE) on Lens culinaris and Melilotus albus was investigated in this study. The experiment involved extracting compounds from the stems of L. didymum and applying varying concentrations (0.5, 1, 2, and 4%) of these stem extracts to test plant seeds and seedlings. Multiple parameters, including germination percentage, growth parameters, and biochemical activities, were measured and compared to those of the control group. Germination percentage, seedling growth, seedling length, fresh and dry biomass, chlorophyll, and carotenoid content decreased notably, especially at higher concentrations (4%), whereas proline content increased in a concentration-dependent manner. Scanning electron microscopy revealed ultrastructural abnormalities in the roots of treated plants compared to those in the control. GC–MS analysis revealed the presence of 31 volatile chemicals in the methanolic stem extract. The compounds found in the major amounts are benzyl nitrile (29.19%), lauric acid (7.86%), benzene acetic acid (6.44%), 11-bromoundecanoic acid (7.36%), palmitic acid (4.85%), dodecanoic acid (4.80%), menthol, trans-1,3, cis-1,4 (3.28%), 11-bromoundecanoic acid (7.36%), and linolenic acid (8.64%). These compounds may be responsible for imparting allelopathic effects on the test species L. culinaris and M. albus. Our study revealed that the stem of L. didymum possesses a high concentration of water-soluble allelochemicals, which are thought to reduce test plant growth and can be used as potential weedicides.