Frequencies of Virulence and Fungicide Resistance in the European Barley Mildew Population in 1985*

Abstract

Abstract Representative random samples of spores of Erysiphe graminis f. sp. hordei , causing powdery mildew of barley, were taken from the atmosphere by means of a Schwarzbach jet spore sampler over important barley growing areas in Europe and tested in the laboratory for their virulence on host plants with resistance Ml 41/145, Mlg, Mla6, Mla12, Mla7+Mlk, MlLa, Mla1, Mla9, Mla3, Mla13+Ml (Ru3) and mlo. Virulence frequencies mostly showed regional differentiation and efficiency of, the resistance factors generally increased in the order given. Frequency and level of resistance against triadimenol also showed significant regional differences. Against fenpropimorph similar levels of sensitivity were observed in different parts ofEurope, close to that of standard‐isolates, which had a mean position. The results are discussed with respect to current and previous conditions of cultivation, to the spread of the pathogen by wind and towards strategies for more effective use of hostresistance and of fungicides.