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Title: FIRST REPORT OF POWDERY MILDEW ON DIPSACUS SYLVESTRIS CAUSED BY SPHAEROTHECA DIPSACEARUM IN NORTH AMERICA

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

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2006
Publication Date: 6/1/2006
Citation: Dugan, F.M., Glawe, D.A. 2006. First report of powdery mildew on dipsacus sylvestris caused by sphaerotheca dipsacearum in north america. Plant Health Progress. doi:10.1094/PHP-2006-0607-02-BR.

Interpretive Summary: Powdery mildews are obligate, fungal pathogens of plants. Common teasel is a noxious weed, originally from Europe but now widespread in North America. One powdery mildew, Sphaerotheca dipsacearum, recorded as occurring on teasel in Europe, has been discovered on teasel in Washington State. This is the first time that this particular powdery mildew has been reported on teasel in North America. A report of another powdery mildew, Phyllactinia sp., from Washington State in 1905, has been verified by examination of the original herbarium specimen. However, nomenclatural problems have resulted in some inaccurate reports of other powdery mildews on teasel. This report documents S. dipsacearum and Phyllactinia sp. on teasel in Washington State, states the essentials of the nomenclatural problems, and presents for the first time a detailed description and photographs of the asexual state of S. dipsacearum. Recent literature has listed some powdery mildews as potential biological control agents of teasel, but the nomenclatural errors alluded to above have introduced some inconsistencies into that literature.

Technical Abstract: Dipsacus sylvestris (syn. D. fullonum, common teasel) (Dipsacaceae) is a European species introduced into North America, and now widely established and regarded as a noxious weed. Powdery mildew fungi (Erysiphales) reported previously from this host included Phyllactinia species in Washington State and Sphaerotheca fuliginea in Europe. These reports are inconsistent with Uwe Braun’s world (1987) and European (1995) monographs of Erysiphales which list only Sphaerotheca dipsacearum, Erysiphe knautiae, and Leveillula taurica on dipsacaceous hosts. In October 2005, a powdery mildew was observed on D. sylvestris in two locations in Pullman, Washington. Examination of diseased material confirmed that the causal agent was S. dipsacearum. This report provides the first documentation of S. dipsacearum on D. sylvestris in North America. Based on host and the production of chains of conidia with fibrosin bodies the observed fungus was determined to be S. dipsacearum [also known as Podosphaera dipsacearum]. However, detailed features of the anamorph of this fungus are not contained in Braun’s monographs and this report appears to be the first characterizing the anamorph in detail. Recent tabulations of potential biological control agents on Dipsacus spp. world-wide include Sphaerotheca fuliginea on the basis of host-fungus records. However, that species is subject to varying taxonomic interpretations and now is regarded as specific to hosts in the Scrophulariaceae. However, we have confirmed presence of a Phyllactinia sp. on D. sylvestris by examination of the herbarium specimen WSP 5500, collected in Washington State in 1905 and the original source of subsequent references.