Wheat powdery mildew in the USA: status of pathogen virulence and host resistance
1991
Leath, S.
The presence and relative frequency of virulence genes in the Blumeria graminis f.sp. tritici population in the eastern United States was determined in nurseries at numerous sites in 1987-1988 and 1988-1989. Genes Pml, Pm2, Pm3a, Pm3b, Pm4a, Pm5, and a gene from Michigan Amber were in a Chancellor background. Genes Pm6, Pm7, Pm8, and Pm17 also were evaluated. Relative disease severity was higher on Pm3b and Pm3c in the north, and Pm3a was less effective there than had been observed in recent years. Pm3a virulence remains high in the South. Gene Pm8 continues to be unmatched with virulence except in very low frequencies at all but one location. No virulence corresponding to gene Pm17 from Amigo has been observed. Greenhouse testing of twenty-one soft red winter wheat cultivars at the three to four-leaf stage with isolates of previously characterized virulence was completed. Only Pm3a, Pm5, and Pm6 wcre identified in the cultivars studied. The genes Pm5 and Pm6 were identified in three cultivars each, and three additional cultivars contained both genes. The incorporation of Pm3a into four cultivars adapted to the southeastern US could explain why Pm3a virulence has been higher in the South as compared to thc North in recent years
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