Suppressive Activity of Glechoma hederacea Extracts against the Phytopathogenic Oomycete Plasmopara viticola, and First Screening of the Active Metabolites

Plasmopara viticola is a destructive oomycete that affects grapevines, causing significant economic losses worldwide. This study highlights how the plant Glechoma hederacea might be at the basis for the development of biofungicides to control P. viticola. The aqueous extract obtained from G. hederacea aerial parts showed strong inhibition activity against P. viticola, comparable to that of copper hydroxide. The bioguided purification of the extract by chromatographic techniques led to the isolation of six pure metabolites, identified as the aromatic compounds carvacrol, caffeic acid and methyl caffeate, the flavonoids cirsimaritin and apigenin and the polyphenolic acid rosmarinic acid by spectroscopic methods. This is the first report about the isolation of methyl caffeate and cirsimaritin from G. hederacea. Caffeic acid and methyl caffeate showed the highest disease severity reduction, while carvacrol, cirsimaritin and apigenin also showed moderate activity against P. viticola. The inhibitory activity of the aqueous extract could suggest synergetic or additive action of caffeic acid and methyl caffeate together with other compounds contained in the extract. This study provides insights into the potential of G. hederacea as an allelopathic tool for developing control methods against P. viticola, revealing the combined action of different metabolites involved in the mechanism of action of the active compounds.