18S RIBOSOMAL-RNA GENE-SEQUENCES AND SUPRAORDINAL CLASSIFICATION OF THE ERYSIPHALES

The Erysiphales (powdery mildews) exhibit conflicting morphologies and have been classified as either Pyrenomycetes or Plectomycetes. The nuclear small subunit ribosomal RNA gene was sequenced for two isolates of Blumeria graminis forma speciales hordei in order to help resolve this classification controversy. A single most parsimonious tree was obtained grouping the Erysiphales with neither the Plectomycetes nor the Pyrenomycetes, but rather placing the powdery mildews in amongst a basal assemblage of apothecial and pseudothecial fungi. Maximum likelihood tests were conducted on constraint trees exhibiting three possible morphological classifications. The results rejected the placement of the Erysiphales amongst both the Plectomycetes and Pyrenomycetes but could not reject placement amongst the Discomycetes; therefore, the powdery mildews are not Pyrenomycetes nor Plectomycetes. However, higher order classification of the Erysiphales remains unresolved, since there is no strong bootstrap support for the Erysiphales amongst the basal assemblage of apothecial and pseudothecial fungi.