Origin and Proportions of the Components of Composite Populations of Erysiphe graminis f. sp. hordei

Comparisons of the pathotype composition in random samples of barley mildew populations collected in 1985 and 1986 in several European regions were made in an attempt to quantify the influence of migration on population structures. In each of the situations studied (northern France 1986 and eastern Lower Austria 1985 and 1986), evidence was obtained from influx of spores from at least two remote areas. Depending on year and location, 48 to 87 % of the resulting composite samples consisted of ‘foreign‐type’ isolates. Implication of long‐distance dispersal for studies on population dynamics and for control strategies relative to mildews and other wind‐spread pathogens are discussed.