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Isozyme Variation of Physiologic Races of Ustilago hordei. R. Hellmann, Graduate student, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; B. J. Christ, Associate professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 81:1536-1540. Accepted for publication 30 July 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1536.

Sixty-three haploid isolates of the barley covered smut fungus, Ustilago hordei, were examined for isozyme variation by starch gel electrophoresis. Fifty-five isolates from North Dakota, representing different virulence genotypes, and eight isolates from Ethiopia of unknown genotype were tested. Activity was detected for nine enzymes. A single allele common to all isolates was detected for aconitase, adenylate kinase, glucose-6-phosphate dehydrogenase, phosphoglucose isomerase, 6-phosphogluconate dehydrogenase, and peptidase. Two alleles were detected for each of the enzymes isocitrate dehydrogenase and malate dehydrogenase, and three alleles, including a null, for phosphoglucomutase (PGM) were detected. In these latter three enzyme systems, greater than 70% of all isolates had the most common allele. Isolates from Ethiopia could not be differentiated from isolates from North Dakota by isozymes. Five electrophoretic types and two clusters based on the isozyme data were identified using genetic diversity and cluster analysis. Clusters from isozyme data in no way coincided with those based on virulence data. Mean allelic diversity was 0.189 based on isozyme data and 0.401 based on virulence data. Haploid sporidia from F1 progeny also were obtained from a cross of race 7 race 11 isolates, which carried two of the three alleles for PGM, and were analyzed. Isozyme patterns revealed that the enzyme PGM is coded for by at least two different alleles at a single locus.