Molecular variation in populations of Erysiphe graminis on barley, oats and rye

DNA isolated from the formae speciales of Erysiphe graminis that grow on barley, wheat, rye and oats was studied using restriction endonucleases and DNA/DNA hybridization procedures. DNA fragments were purified by molecular cloning and a few containing repeated sequences were used to demonstrate the many variations in restriction fragments both within and between the four formae speciales. In an analysis of six single-colony isolates of the barley mildew pathogen collected from different UK sites in different years, more than a quarter of the fragments scored varied among isolates. One isolate, with an uncommon pathogenicity character, differed from the remainder in the distribution of DNA bands. Isolates of rye mildew were also distinct from one another but isolates of oat mildew from a population of similar size appeared to belong to a single clone.
It is concluded that the chromosomes of E. graminis contain many families of dispersed repeated sequences and that there may be extensive polymorphism for restriction endonuclease cleavage sites associated with these repeats. Such unselected polymorphisms could be useful in helping to understand and discriminate among the factors affecting population structure in the pathogen as it responds to different agricultural practices.