Stilbenes from common spruce (Picea abies) bark as natural antifungal agent against downy mildew (Plasmopara viticola)

The antifungal activity of spruce bark (Picea abies (L.) Kars. Pinaceae) extract against downy mildew (Plasmopara viticola) was investigated. The analysis of the extract using UHPLC MS allowed stilbenes to be targeted as the main components. The structure of stilbenes isolated from the hydro-alcoholic extract by preparative HPLC was determined by mass and NMR analysis. In addition to aglycone and glycosylated monomeric forms such as piceatannol, astringin, resveratrol, piceid, isorhapontigenin and isorhapontin, several stilbene glycoside dimers were also identified. Six new compounds (piceasides I-N) are reported for the first time in the literature and the plant kingdom. The extract as well as pure compounds showed significant antifungal activity with an inhibition of the zoospore mobility and mycelium growth of P. viticola. Our results show that spruce bark extract, which is considered as a wood industry co-product, could potentially be used as a natural fungicide against downy mildew.