Mating type distribution and the absence of cleistothecia of Podosphaera macularis in the Pacific Northwest
S. WOLFENBARGER (1), D. Gadoury (2), M. Twomey (1), M. J. Welser (2), D. Gent (3). (1) Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR, U.S.A.; (2) Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Geneva, NY, U.S.A.; (3) USDA-ARS, Forage Seed and Cereal Research Unit, and Depa
The hop powdery mildew pathogen is known to produce cleistothecia in the eastern North America and Europe, but ascocarps have not been reported from the Pacific Northwestern region of the U.S. (PNW). Sexual reproduction is regulated by the mating-type locus MAT1 in the Erysiphales and other Ascomycetes. For sexual reproduction to occur both mating type idiomorphs, MAT1-1 and MAT1-2 need to be present. The absence of the ascigerous stage of the fungus in the PNW may be due to only one mating type being present. To characterize the frequency of the mating type idiomorphs in populations of <i>P. macularis</i>, PCR assays were developed with primers designed from conserved domains specific to each mating type idiomorph. A survey in 2012 of <i>P. macularis</i> isolates from the PNW found only the MAT1-1 idiomorph among the 183 isolates collected: MAT1-2 was not detected. In contrast, among 43 isolates from the eastern United States and Europe, mating type idiomorphs were detected at a frequency consistent with a 1:1 ratio (Chi square <i>P=</i>0.879). Although our findings do not exclude other environmental, host, or epidemiological impediments to ascocarp formation, their current absence can be explained by the absence of the MAT1-2 mating type idiomorph. Present difficulties in managing this disease in the PNW could be exacerbated unless quarantine measures can prevent introduction of the MAT1-2 mating type.
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