Abstract
Isozyme analysis was used to search for variation in barley powdery mildew ( Erysiphe graminis f.sp hordei ). Sixteen different enzymes were examined in 2·0% Triton extracts of conidia, using several different electrophoretic techniques coupled with standard enzyme-specific staining methods. Two enzymes were monomorphic; all other enzymes had at least two isozymes. No significant isozyme polymorphism was found in seventy-five barley mildew isolates collected from geographically well-separated regions of the world including Europe, Japan, the Middle East, N. America, N. Africa and New Zealand. Detailed analysis of mildew populations from two U.K. sites about 100 km apart, and where considerable variation existed in both fungicide sensitivity and virulence, also revealed no variation for isozyme markers. Isozyme variation was observed between different formae speciales of E. graminis and also between other powdery mildew genera. Although isozyme variation might provide useful taxonomic criteria for distinguishing mildew species infecting one host, so far the technique has provided no useful markers for genetic work.
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