Effects of recombination on races of a barley powdery mildew population

Analyses of virulence were performed with isolates from ascospore populations and their possible parental populations in order to measure the potential effect of recombination on the pathogenic variation in populations of Erysiphe graminis f. sp. hordei. The conidial isolates and cleistothecia were sampled from a field of spring barley cv. Golden Promise. Compared to the summer conidial populations, higher frequencies of rare races and rare virulence factors together with greater diversity were observed among progeny from ascospores, and the most frequent race was less abundant. The contribution of ascospores to primary infection of barley in autumn could not be measured directly, but analyses of the conidial populations on volunteer seedlings of Golden Promise suggested that sexual recombination was one of the mechanisms that had caused the change in population structure.