Ingadosides A-C, acacic acid-type saponins from Inga sapindoides with potent inhibitory activity against grapevine downy mildew as potential alternatives to copper fungicides

Summary

The reduction of copper-based fungicides has a high priority in European policy as well as in organic agriculture. To successfully reduce copper use, preventive strategies have to be fully implemented, and several substitution products need to be brought to the market. Plantderived plant protection products could provide sustainable and environmentally friendly alternatives. As part of a project aiming at the discovery of such new products, we screened a library of more than 3000 plant extracts against important plant pathogens. One of the extracts with promising activity against grapevine downy mildew (Plasmopara viticola) was an 96% ethanolic extract from the leaves of Inga sapindoides (in vitro MIC100 25 μg/mL). On grapevine plantlets under controlled conditions, compared to non-treated plants, the I.sapindoides ethanolic extract reduced grapevine downy mildew by 96%-97% at 0.5 mg/mL, and its efficacy was comparable to a standard copper treatment (two independent experiments). Targeted isolation of the active constituents resulted in the characterization of three acacic acid-type bidesmosidic saponins with high antifungal activity (in vitro MIC100 values of 3 - 6 μg/mL). I. sapindoides, a tree which is often cultivated for shading coffee plantations in Central America, may represent a sustainable source of fungicidal products to be used in the replacement of copper.