Comparative analyses of nuclear ribosomal RNA gene sequences and morphological characters of selected taxa of Loculoascomycetes: Phylogenetic implications

Abstract

The loculoascomycetes comprise a large number of fungi with fissitunicate asci and ascostromatic ascomata. Various classification schemes have been proposed based on different taxonomic criteria. Phylogenetic relationships of many organisms in the Loculoascomycetes are vague because of the complex array of these organisms. The research in this dissertation was conducted at different taxonomic levels using both molecular and morphological approaches.

The first goal was carried out at a supraordinal level using nuclear small subunit rRNA gene sequences (consensus length of 1924 bp). The phylogenetic analysis suggested that the Loculoascomycetes could have been derived from the apothecial Discomycetes. The phylogenetic results demonstrated that the Meliola spp. were closely related to the Pyrenomycetes, and the members of the Erysiphales were affiliated with the Discomycetes but not the Pyrenomycetes or the Loculoascomycetes.

The second goal of this dissertation concerned phylogenetic relationships between the Melanommatales and Pleosporales at an ordinal level. Phylogenetic analysis of molecular data demonstrated that selected members of the Melanommatales did not form any monophyletic combinations. The molecular data suggested that Barr's separation of these two orders, based mainly on morphology of pseudoparaphyses, was not supported. However, the results appeared to confirm Barr's combination of the families Lophiostomaceae and Massarinaceae and the separation of Lojkania striatispora from the genus Herpotrichia. The molecular data showed that the new genus Quintaria was related to the Melanommataceae. Meanwhile, the morphology and systematics of 17 species of Loculoascomycetes was studied. These taxa were described and illustrated. The descriptions provided information on the characters and character states used in phylogenetic analysis. Phylogenetic results based on morphological characters indicated that: (1) the morphological data generally supports monophyly of the Pleosporaceae; (2) members of the Melanommatales did not form a monophyletic group. Phylogenetic trees generated from the separate morphological and molecular data sets were incongruent. Three strategies to reconcile incongruence were used, and their advantages and disadvantages were evaluated.

The third goal of this research was centered at the familial level using partial small and large subunit rRNA gene sequences. Phylogenetic results generally supported Barr's separation of the Leptosphaeriaceae from Pleosporaceae. The analyses demonstrated that Pyrenophora trichostoma and Clathrospora diplospora were closely related to the Pleosporaceae.