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Shoots affected by powdery mildew had been collected from Siberian pea bushes in July 2009 on the University of Wisconsin-Madison campus and on the campus of Université Laval, Quebec City, Quebec. This unique shrub or small tree is occasionally planted in Wisconsin and three shrubs in a bunch that had been affected are the one examples identified on the UW-Madison campus.

In Quebec City, Siberian pea tree is extra generally used as a decorative, usually in hedges (as is the case of the affected vegetation on the Université Laval campus). In each areas, <10% of foliage was visibly affected, however incidence was better on shoots nearer to the bottom than on increased shoots. White-to-grayish mycelium was current on leaves and younger stems and generally utterly lined each higher and decrease leaf surfaces. Dark brown-to-black chasmothecia had been quite a few on leaf blades, petioles, and younger stems, however had been most plentiful on decrease surfaces of leaves.

Morphology of chasmothecia, together with appendages with distinctive terminal dichotomous branching, (1) was in line with descriptions and illustrations of the fungus Erysiphe palczewskii Jacz. (synonym Microsphaera palczewskii) (1-4) considered native to Asia, however often known as an invader of Europe the place it happens on the identical host. For a pattern from Université Laval, imply diameter of chasmothecia was 113 μm, imply appendage size was 185 μm, and barrel-shaped conidia that lacked fibrosin our bodies averaged 30 × 14 μm. Asci contained oval, yellow ascospores with imply dimensions of 20 × 12 μm.

DNA was extracted from chasmothecia, and nuclear rDNA sequences (633 nucleotides) of the Wisconsin (GenBank Accession No. GQ497277) and Quebec (GenBank Accession No. GQ497276) specimens differed by just one nucleotide. The sequences that had been obtained most intently matched GenBank sequences for Oidium spp. (98%) and Erysiphe spp. (97%). Further observations indicated that the identical pathogen affected Siberian pea bushes planted as ornamentals at a number of areas separated by ≥15 km in the metropolitan Quebec space.

This report extends the japanese identified restrict of E. palczewskii in the United States, beforehand identified from collections in Alaska (2), Washington (4), Idaho (4), North Dakota (3), and Minnesota (3). To our information, that is the primary report of this illness in Canada, and it signifies that the distribution of E. palczewskii is transcontinental.

Specimens from Madison, WI and Quebec, QC have been deposited in the U.S. National Fungus Collections (BPI 879152) and the Rene Pomerleau Herbarium of the Canadian Forest Service Laurentian Forestry Centre (QFB-22601). References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. A. Glawe and G. A. Laursen. Online publication. doi:10:1094/PHP-2005-1017-01-BR. Plant Health Progress, 2005. (3) D. A. Glawe et al. Online publication. doi:10.1094/PHP-2006-0117-01-BR. Plant Health Progress, 2006. (4) C. Nischwitz and G. Newcombe. Plant Dis. 87:451, 2003.