Natural antagonists of the grapevine root rot fungus Roesleria subterranea

Abstract: Roesleria subterranea is a root-pathogenic ascomycete of grapevine causing severeeconomic loss in vineyards in Germany, Luxemburg and the US. Currently, no efficient controlmethods are available. To isolate potential fungal, antagonist soil-particles were placed onto wellestablishedR. subterranea cultures. Fungi growing out of the soil particles were isolated. Themajority of the isolated fungal strains belonged to the genus Clonostachys. These isolatestogether with Trichoderma spp. and Clonostachys spp. strains previously isolated from vineyardsoils, endophytic isolates from diseased vines, and commercialised strains were tested in dualculture for their antagonistic effect against four Roesleria strains. All Roesleria strains reactedwith an enhanced production of a green pigment in the contact zone that limited or stopped thegrowth of the antagonistic fungi. Most Trichoderma strains were able to restrict the growth ofRoesleria and to overgrow the colony. Two out of nine Clonostachys strains restricted the growthof all four Roesleria strains. In contrast to Trichoderma a bleaching of the green pigment wasobservable when Clonostachys strains were growing over the Roesleria colonies. Whether or notrapid overgrowth of Roesleria colonies or bleaching of the green pigment is the key character ofan effective antagonist cannot be decided at the moment. Promising strains of Trichoderma andClonostachys will be tested in future pot experiments and field trials.