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Title: The systematic position of Phaeocryptopus gaeumannii

Author
item WINTON, LORETTA
item STONE, J - OREGON STATE UNIV.
item HANSEN, E - OREGON STATE UNIV.
item SHOEMAKER, R - AGRIC. & AGRI-FOOD CANADA

Submitted to: Mycologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2007
Publication Date: 3/20/2007
Citation: Winton, L.M., Stone, J.K., Hansen, E.M., Shoemaker, R.A. 2007. The systematic position of Phaeocryptopus gaeumannii. Mycologia. 99(2):240-252.

Interpretive Summary: Phaeocryptopus gaeumannii is a widespread foliar parasite of Douglas-fir. Although normally innocuous, the fungus also causes the defoliating disease 'Swiss needle cast' in heavily infected needles. The current taxonomy suggests that Phaeocryptopus' nearest relatives are in the family Venturiaceae, which includes the apple scab pathogen Venturia inaequalis. Apple scab is a well-characterized disease that might provide important clues into the behavior and control of Swiss needle cast. We used DNA sequences to test this relationship in a phylogenetic context. Phylogenetic analyses of partial nuclear ribosomal gene sequences indicated that P. gaeumannii is closely related to neither Phaeocryptopus nudus, type of the genus, Venturia inaequalis, type of the Venturiaceae, nor Rhizosphaera form-species, accepted anamorphic states of Phaeocryptopus. Instead, it is closely related to members of the sooty molds, particularly the common and morphologically similar Douglas-fir epiphyte Rasutoria pseudotsugae. Disputed classifications at nearly every level necessitated a wide sampling of fungal taxa, particularly the bitunicate ascomycetes, which includes P. gaeumannii. Many of these taxa, including P. gaeumannii, have not previously been sequenced. We therefore contributed to current concepts in ascomycete systematics for several groups of fungi. These results will be of interest to plant pathologists, mycologists, and fungal systematists by providing a better understanding of the relationships among these parasitic fungi.

Technical Abstract: Phaeocryptopus gaeumannii, causal agent of the Douglas-fir foliar disease Swiss needle cast, is the only known pathogenic species of the genus. While coelomycetous Rhizosphaera form-species have been accepted as anamorphic states of Phaeocryptopus the relationship has never been conclusively established. Current classifications place Phaeocryptopus in the Venturiaceae (Pleosporales), typified by the apple-scab pathogen Venturia inaequalis. All core members of this family have hyphomycetous anamorphs. We sought to confirm these relationships by means of phylogenetic analyses of the small (SSU) and large (LSU) subunits of nuclear ribosomal gene sequences (nrDNA). Cladistic analyses indicated that both the genus Phaeocryptopus and the family Venturiaceae are unnatural groups. Phaeocryptopus nudus, type of the genus, is aligned in the Dothioraceae (Dothideales) and P. gaeumannii in the Euantennariaceae (Capnodiales) near Rasutoria. Species of Rhizosphaera are very closely related to P. nudus but not to P. gaeumannii. Ordinal placement of the Venturiaceae was unresolved, but the family is apparently not included in the Pleosporales, Dothideales, or Capnodiales.