Virulence Spectrum of the Erysiphe graminis f. sp. tritici Population in New York. L. O. Namuco, Former Graduate Student, Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY 14853. W. R. Coffman, G. C. Bergstrom, and M. E. Sorrells. Professor, Department of Plant Breeding and Biometry, Assistant Professor, Department of Plant Pathology, and Associate Professor, Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY 14853. Plant Dis. 71:539-541. Accepted for publication 22 January 1987. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0539.

Isolates of Erysiphe graminis f. sp. tritici collected from mildewed wheat leaves in central and western New York in 1984 were tested for virulence against differential lines and cultivars of wheat with major genes for powdery mildew resistance (Pm genes). A high percentage of the 116 isolates tested had virulence to Pm2, Pm3c, Pm4, Pm6, and Pm8. A few isolates had virulence to Pm1 and Pm3a. Isolates were found that could overcome one or more of all but two, Pm3b and Pm9, of the known Pm genes in wheat. About 40 and 46% of the isolates from commercial fields and from breeding plots had zero and one virulence gene, respectively. The most complex isolates detected in commercial fields and breeding plots had three and five virulence genes, respectively. Virulence gene pairs corresponding to wheat genes Pm4 and Pm8 occurred in close association.