Interaction between Acremonium byssoides and Plasmopara viticola in Vitis vinifera

The endophytic fungus Acremonium byssoides was isolated from the leaves of grapevine cv. Regina Bianca to determine whether it could act as an antagonistic endophyte of the downy mildew agent Plasmopara viticola. The occurrence of this fungus was ascertained in 34 grapevines (cultivars Regina Bianca, Catarratto and Insolia) representing all the grapevine plants in an experimental vineyard located in Sicily and which had never been treated with any fungicides. The isolation frequency of the endophytic Acremonium strains was assessed in several plant organs by means of monthly samplings over a 2-year period. The endophyte was found in all the grapevines, with higher frequencies in the cv. Regina Bianca in the buds, and in the cooler months of the year. All the strains collected from the leaves, and most of the strains from the buds of cv. Insolia were identifi ed as A. byssoides by conventional means. The presence and spatial distribution of A. byssoides was determined in asymptomatic or P. viticola-infected leaves of the grapevine cv. Insolia using an optimised staining technique and differential interferential contrast light microscopy, as well as laser scanning microscopy. A. byssoides was a natural colonizer of grapevines and actively parasitized P. viticola. Culture fi ltrates and the crude extract of A. byssoides obtained from a cv. Insolia foliar strain, completely inhibited P. viticola sporangia.