Date of Award


Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Joyce E. Longcore

Second Committee Member

Seanna L. Annis

Third Committee Member

Christopher S. Campbell


The genus Powellomyces was described to accommodate two monocentric chytrid species from soil that develop exogenously and possess zoosporic ultrastructure similar to members of the order Spizellomycetales. Despite Powellomyces-like chytrids being commonly observed in gross culture, the genus contained only two species. To determine diversity in this group I amassed 49 isolates of Powellomyces-like chytrids, including the cultures upon which species types were based and new isolates from pollen-baited, water cultures of soils, plant detritus and manure. I sequenced portions of nucSSU and nucLSU rDNA regions and the EF-1α-like gene from each isolate to produce a molecular phylogeny. This phylogeny supports monophyly of spizellomycetalean chytrids with exogenous development and suggests that multiple distinct lineages exist within this group. An evaluation of ultrastructural features of new and described lineages and a linear discriminant function analysis of thallus characters to determine features most useful for separating species grown in pure culture on identical media support recognition of the new family Powellomycetaceae, which contains three new genera, Geranomyces, Thoreauomyces, and Fimicolochytrium, and eight species, six of which I describe here. Several isolates representing new lineages of Spizellomycetales were cultured from manure or manure-inoculated substrates, and I compared nucLSU and EF-1α-like sequences of cultured isolates to environmental DNA sequences produced from horse manure, lawn soils, and horse paddock soils to determine if species were specific to manure substrates and if the same species could be identified by culturing and eDNA methods. The eDNA analyses did not indicate a significant substrate preference, though the majority of isolates were cultured from manure substrates. In only one instance was the same species detected by an eDNA analysis and represented by a cultured isolate from the same substrate, though not the same sample. Both eDNA sequences and culture methods detected unidentified lineages of Spizellomycetales.