Biopesticidal potential of alfalfa extracts against tomato diseases and assessment of their nontarget effects

Abstract BACKGROUND Bioactive compounds from plant biomasses are becoming increasingly popular in plant protection because of their potential application as new eco‐friendly biopesticide alternatives to agrochemicals. In this work, three extracts from Medicago sativa were prepared, characterized, and assessed for their efficacy in controlling some pathogens of tomato. The potential nontarget effects on selected beneficial predatory mites were also evaluated. RESULTS Flavonoids, saponins and the corresponding prosapogenins were obtained from the aerial parts of alfalfa. Apigenin and chrysoeriol glycosides were the most abundant constituents of the flavonoid extract. Saponins were composed mainly of bidesmosides of medicagenic and zanhic acids, whereas prosapogenins were composed only of the corresponding monodesmosidic compounds. In biological activity assays, prosapogenins effectively inhibited both the mycelial growth and conidia germination of Alternaria alternata and Botrytis cinerea. The same mixture also showed significant in vivo control efficacy against alternariosis and grey mold in a dose‐dependent manner. The flavonoid mixture was the best performing extract against tomato spotted wilt orthotospovirus, decreasing the virus titer by 10−2 fold one month post‐inoculation. Toxic effects were not observed on two beneficial mites used as biological control agents, Phytoseiulus persimilis and Amblyseius swirskii. CONCLUSION Flavonoid and prosapogenin mixtures displayed biopesticide activity against fungi and virus in tomato; they were also evaluated as safe towards beneficial mites; these results support the application of these extracts in biopesticide development programs. © 2025 Society of Chemical Industry.