Allelopathic effects of four spontaneous plants from arid regions on the germination and growth of selected weeds and crops

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The study investigates the allelopathic potential of the aqueous extracts of four plants species; Cleome arabica L., Diplotaxis harra (Forssk.) Boiss., Nerium oleander L., and Retama raetam (Forssk.) Webb. Collected from Tunisian arid regions. The effects of these extracts were evaluated on seed germination and seedling growth of two weeds ( Setaria verticillata L. and Sisymbrium irio L.) and two crops ( Solanum lycopersicum L. and Capsicum annuum L.) at different concentrations. Aqueous extracts, prepared by cold maceration, were analyzed for their allelochemicals content, mainly polyphenols, flavonoids, and tannins and further characterized by LC-MS analysis. Antioxidant capacity was assessed using total antioxidant and antiradical capacities. Retama raetam, followed by N. oleander , exhibited the highest phenolic compounds content as well as the strongest total antioxidant capacity. Both species strongly inhibited the germination of S. verticillata and S. irio, particularly at 20 g/L. In contrast, crop species showed greater tolerance, with S. lycopersicum maintaining germination rates above 50%, even at the highest concentrations. Growth bioassays revealed that roots were more sensitive than shoots, especially in weed species, indicating both organ selectivity and dose-dependent responses. Furthermore, allelopathic activity was supported by an in silico molecular docking study. The main metabolites of the studied samples were docked into the active pocket of glutathione S-transferase (GST; PDB: 1BX9) and 4-hydroxyphenylpyruvate dioxygenase (hydroxyphenylpyruvate dioxygenase; PDB: 6J63). These findings highlight the potential of arid-land allelopathic plants as natural herbicides, with R. raetam and N. oleander emerging as promising candidates for sustainable weed management.

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