In the course of finding new antifungal natural compounds against plant pathogens, the methanol extract of Desmodium triflorum was investigated phytochemically. From n-butanol-soluble fraction, seven compounds (1-7) were isolated and structurally elucidated. Of which, six compounds belong to flavone 6- or 8-C-glycoside class (1-6). Three major compounds (1-3) exhibited moderate in vitro antifungal activity against Sclerotium rolfsii, Fusarium oxysporum f. sp. cubense, and Phytophthora palmivora. Compound 1 (IC50 = 162.1 μg/mL) was most active against S. rolfsii in a dose-dependent manner. At 300 μg/mL, compounds 1 and 2 significantly inhibited P. palmivora, whereas compound 3 lacked effectiveness. In addition, the nanoemulsion of the methanol extract with a droplet size of 12.2 nm displayed an excellent inhibition against S. rolfsii and P. palmivora compared with the normal extract. The presence of 1 (0.846%) and 2 (0.759%) in the methanol extract may attribute to the antifungal activity of D. triflorum. These results proved the potential of D. triflorum and its C-glycoside flavonoids against phytopathogenic fungi for the first time. Besides, an enhancement in the effectiveness of nanoemulsion containing D. triflorum extract against the fungi was confirmed. The structural characteristics of 1 and 2 could be considered to develop new fungicidal substances in the future.
Keywords: Desmodium triflorum; Phytophthora palmivora; Sclerotium rolfsii; antifungal activity; flavone C-glycoside.
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