Date of Award

1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

Meredith Blackwell

Abstract

Maximum parsimony analysis of partial sequences from the small subunit ribosomal DNA (ssrDNA) rejects the monophyly of unitunicate, perithecial ascomycetes (pyrenomycetes). The genera Kathistes, Pyxidiophora and Subbaromyces are separated from a large clade of relatively derived pyrenomycetes. This derived pyrenomycete clade is supported by a bootstrap confidence level of 100% and a decay index of $>$10 steps, and contains two subclades, A and B. Subclade A comprises the orders Clavicipitales, Hypocreales, Microascales and the genus Ceratocystis; subclade B consists of the Diaporthales, Sordariales, Xylariales and the genus Ophiostoma. The Clavicipitales is a sister taxon to the Hypocreales, which consists of two paraphyletic lineages. The ophiostomatalean taxa sampled do not form a monophyletic group; the data support the removal of Ophiostoma H. & P. Sydow from Ceratocystis Ellis and Halst. as proposed by several investigators. The Xylaria and Ophiostoma centrum types of Luttrell (1951) are inconsistent with the monophyletic groups inferred from the ssrDNA. Hypotheses concerning the evolution of centrum development are refined in light of these data. An additional data set was derived from the B subunit of vacuolar ATPase (BvATPase) to provide an independent test of the ssrDNA gene tree and morphologically based hypotheses. Analysis of the first and second position of the codon support the separation of the genera Pyxidiophora and Subbaromyces from the larger clade of relatively derived pyrenomycetes. Inclusion of the third position of the codon does not support the separation of these genera from the larger clade of relatively derived pyrenomycetes or relationships within the derived clade that are mutually supported by the ssrDNA and morphology. Over 95% of the third codon positions sampled were variable, which constituted 76% of the synapomorphies of the BvATPase data set. Retention indices (RI) and rescaled consistency indices (RC) of the two BvATPase data sets suggest that the third codon position is too variable with respect to frequency of characters state variation and distribution of character states for use in the systematics of the taxa sampled. The nonmonophyly of unitunicate, perithecial ascomycetes is suggested to be the better of two hypotheses.

Pages

137

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