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Title: First report of Erysiphe (Uncinuliella) flexuosa in western North America

Author
item GLAWE, D - WASHINGTON STATE UNIV.
item Dugan, Frank

Submitted to: Pacific Northwest Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2006
Publication Date: 10/31/2006
Citation: Glawe, D.A., Dugan, F.M. 2006. First report of Erysiphe (Uncinuliella) flexuosa in western North America. Pacific Northwest Fungi. 1(11):1-11. DOI 10.2509/pnwf.2006.001.011

Interpretive Summary: The powdery mildew Erysiphe flexuosa (also known as Uncinula flexuosa or Uncinuliella flexuosa) is an obligate parasite of horse chestnut trees. This fungus, presumably originally evolved in eastern North America on various species of horse chestnut, has recently been documented in Europe, where it is causing concern amongst phytopathologists in the UK and on the continent. Until now, it has not been formally documented west of the Rocky Mountains, and indeed seems to have only recently established itself in the Pacific Northwest. This manuscript describes what is known of the biogeography of E. flexuosa, and presents multiple photomicrographs useful for diagnosis.

Technical Abstract: Erysiphe flexuosa, a powdery mildew parasite of Aesculus species, is believed to have originated in North America where distribution records were confined to regions east of the Rocky Mountains. The fungus recently was found in eastern Washington State and northern Idaho. The fungus can be distinguished readily from other powdery mildews attacking Aesculus species by the presence of two distinctive kinds of chasmothecial appendages. Consistent with previous reports on similar species, observations determined that subulate appendages formed first, on dorsal sides of chasmothecia. The longer, uncinate appendages formed equatorially during later chasmothecial maturation. There are no Aesculus species native to northwest North America that could have hosted an undetected population of the fungus. It appears likely that E. flexuosa became established relatively recently in the inland Pacific Northwest, possibly being introduced on infected host material, similar to the situation in Europe where several reports documented the presence of the fungus beginning in 2000.