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|Title:||Systematics of some Leptosphaeria and Phaeosphaeria species (Loculoascomycetes) based on morphological and molecular evidence|
|Doctoral Committee Chair(s):||Shearer, Carol Anne|
|Department / Program:||Plant Biology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Leptosphaeria is one of the largest genera in the order Pleosporales, which itself includes the most complex array of organisms in the Loculoascomycetes. The initial description of Leptosphaeria was superficial and based on only a few characters. Due to this rudimentary circumscription many, often remotely related, taxa have been placed in this genus. In recent years, more thorough reexamination and taxonomic reassessment of many species of Leptosphaeria have resulted in their disposition in other allied genera, especially Phaeosphaeria. Currently, relatively few morphological characters, such as location of ascomata in relation to the substrate, thickness of peridium, type of peridial cells, and host are used to delimit these two genera. In each genus there are some species which do not show all the attributes typical for that genus. For instance, the placement of a fungus showing some states typical of Leptosphaeria, and some other states typical of Phaeosphaeria, would depend on the intuition of the individual mycologist. Compared to many plants and animals, this group of fungi is morphologically simple and doesn't offer many traits for classification or cladistic purposes. Moreover, many of these traits show considerable plasticity, and it is not known with any degree of certainty whether the observed variation has genetic or environmental underpinnings. As such, these fungi are prime candidates for analysis using an independent, non-morphological, data set.
Thus far, the separation of Phaeosphaeria from Leptosphaeria has not been tested by cladistic analysis. The current study investigates whether the two genera represent independent lineages in the context of the species examined, and evaluates the taxonomic usefulness of various morphological characters in delineating the two taxa. Within Phaeosphaeria the hypothesis that the subgenera of Phaeosphaeria sensu Shoemaker and Babcock (1989) reflect independent clades is tested, along with the other competing hypotheses of relationships put forth by various authors.
In this study, the phylogenetic relationships of three species of Leptosphaeria and six species of Phaeosphaeria (from four of six subgenera) were evaluated using both morphological characters and molecular data from two regions of the nuclear ribosomal DNA. Melanomma radicans and Passeriniella obiones were used to root the trees. Morphological data were analyzed cladistically, and molecular data were analyzed using both cladistic and phenetic methods. Evaluation of morphological characters of all 11 taxa was based on type or other authentic materials; these taxa are redescribed and illustrated. In an expanded cladistic study based solely on morphology, six more species of both Phaeosphaeria and Leptosphaeria were added to the 11 taxa mentioned previously. The aim of this cladistic analysis was to investigate which morphological characters hold together particular clades, and assess their relative merit from a phylogenetic point of view.
|Rights Information:||Copyright 1995 Khashnobish, Aruna|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9543626|
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