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 nu clear small subunit ribosomal RNA gene was sequenced for two isolates of Blumeria graminis forma speciales hordei in order to help resolve t his classification controversy. A single most parsimonious tree was ob tained grouping the Erysiphales with neither the Plectomycetes nor the Pyrenomycetes, but rather placing the powdery mildews in amongst a ba sal assemblage of apothecial and pseudothecial fungi. Maximum likeliho od tests were conducted on constraint trees exhibiting three possible morphological classifications. The results rejected the placement of t he Erysiphales amongst both the Plectomycetes and Pyrenomycetes but co uld not reject placement amongst the Discomycetes; therefore, the powd ery mildews are not Pyrenomycetes nor Plectomycetes. However, higher o rder 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.