Phylogeny of the Erysiphales (powdery mildews), Meliola (black mildews), and Meliolina inferred from ribosomal DNA

This dissertation is composed of three separate studies that relate to the phylogeny of ascomycetous fungi inferred from ribosomal DNA sequences.;Chapter I addresses the problem of classifying fungi exhibiting conflicting morphologies. The class Plectomycetes develop closed ascomata, and passively release their ascospores. The class Pyrenomycetes develop flask-shaped ascomata and forcibly discharge their ascospores. The Erysiphales have closed ascomata, yet forcibly discharge their ascospores. Depending on which of these two major morphological characters are emphasized, the Erysiphales are classified either as Plectomycetes or as Pyrenomycetes. 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 with the Erysiphales grouping neither with the Plectomycetes nor the Pyrenomycetes. Rather, the powdery mildews lay amongst a basal assemblage of apothecial and pseudothecial fungi. The likelihood-based Kishino-Hasegawa test was used to evaluate constraint trees reflecting 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.;Chapter II addresses the phylogenetic relationships for 45 powdery mildew isolates in 10 genera of the Erysiphales inferred from internal transcribed spacer (ITS) rDNA sequence. Phylogenetic analyses revealed that the powdery mildews were split into six evolutionary lineages which correspond to different mitosporic types. Fifteen morphological characters were analyzed and found not to be in conflict with the molecular data, so the morphological and molecular data were combined. The combined data increased the overall support for the six clades.;Two Meliola species (Meliolaceae) and one Meliolina species, fungi with phenotypic similarities to the Erysiphales, were compared to 33 other ascomycetes, and their phylogenetic relationships were inferred from nuclear small subunit ribosomal RNA gene sequences. Phylogenetic analyses revealed that the Meliolaceae are members of the Pyrenomycetes, and not closely related to the bitunicate ascomycetes. The Meliolaceae are not closely related to the Erysiphales as had been hypothesized. The phylogenetic position of Meliolina is found amongst the bitunicate ascomycetes and is unrelated to the Meliolaceae or the Erysiphales.