Endophytes of grapevine as potential control agents against fungal vine diseases

Abstract: Grapevine trunk diseases like esca are difficult to control and cause significanteconomic loss in vine growing areas all over the world. The causal organisms are xyleminhabiting, pathogenic fungi sharing habitat with other endophytic microorganisms. Xylem sap oftwigs of healthy and esca affected vines was plated onto nutrient media. The isolated endophyteswere identified morphologically and by DNA sequence analysis. Dominant yeast endophyteswere Aureobasidium pullulans, Cryptococcus magnus and Rhodotorula cf. glutinis. The mostabundant endophytic bacteria belonged to the genera Curtobacterium, Frigoribacterium,Pantoea, Pseudomonas and Bacillus. The antagonistic potential of selected endophytes againstgrapevine pathogenic fungi (Phomopsis viticola, Phaeomoniella chlamydospora, Cylindrocarponsp., Roesleria subterranea) was evaluated in vitro. Isolated yeasts (e.g. Aureobasidium pullulans)and bacteria (esp. Gammaproteobacteria) considerably inhibited the growth of grapevinepathogenic fungi. To test the effect on plant growth cress tests with the culture-supernatant ofendophytic yeasts cultures were conducted. Sporobolomyces roseus, Rhodotorula pinicola and anunknown Cryptococcus species promoted the root growth of cress seedlings. These results pointtowards endophytes playing a critical role as plant growth promoters and in the defense againstplant pathogens. Endophytes have the potential to play a future key role as biocontrol agents andbiofertilizers.