Plant Science & Landscape Architecture Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2797

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Subject: search.filters.subject.Phylogeny

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    Diversity of Phytophthora Species in Costa Rica's Tropical Forest
    (2015) Wallace, Sydney F.; Balci, Yilmaz; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The fungus-like organism Phytophthora includes more than 130 species, most of which are destructive plant pathogens. Information about the occurrence and diversity of Phytophthora species in forest and protected areas are largely unknown. The purpose of this study was to fill in the scientific gap in species biodiversity by conducting a survey in tropical forest ecosystems. The survey was conducted at 10 sites across Costa Rica. Leaves with lesions attached to live plants (LP), fallen from tree canopies (LF), submerged in forest streams (LS) and soil was sampled. Isolate identification was based on a multi-locus (4 mitochondrial and 4 nuclear) phylogeny, and examination of morphological features. In total 258 isolates were characterized into 21 species: eight known and 13 novel species. Phylogenetically, species discovered were placed in seven different clades and clade 9 included the most number of species. Species were more common in transitional forests. The number of unknown species discovered suggests that tropical forests are a “hotspot “for Phytophthora diversity.
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    MOLECULAR PHYLOGENY AND TAXONOMIC REVISION OF FUNGI IN THE GENUS Thelonectria AND RELATED SPECIES WITH Cylindrocarpon-LIKE ANAMORPHS
    (2014) Salgado-Salazar, Catalina; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The genus Thelonectria and related species with Cylindrocarpon-like anamorphs are a group of perithecial ascomycetes in the family Nectriaceae that occur as saprobes and in few cases as pathogens of hardwood trees, shrubs or other plant substrates. Despite of being a key component of forest ecosystems around the world, species relationships and distribution are largely unknown. The objectives of this study were to: 1) infer species level phylogenetic relationships of the genus Thelonectria and related species with Cylindrocarpon-like anamorphs with uncertain classification, testing monophyly of each one of the groups studied; 2) delimit taxa, establishing taxon circumscriptions and providing brief descriptions; 3) resolve nomenclatural issues by identifying redundantly used names and synonyms; 4) provide identification tools, specifically, diagnostic keys and molecular data that can be used further as molecular barcodes; 4) provide distribution data and to take the first steps into the identification of speciation patterns observed in these fungi. To achieve these goals, herbarium materials, as well as freshly collected material obtained from the field or from fungal repositories were compared using phylogenetic analyses of multiple loci, morphology and geographic distribution. This research resulted in the narrower circumscription of the genus Thelonectria, not to contain one of the most common species in the group, T. jungneri. According to the results of the phylogenetic analyses it was found T. jungneri is a segregating clade that needs to be recognized as a different genus. For the genus Thelonectria, a total of 31 new species were described, and three new genera, closely related to Thelonectria were created to accommodate the diversity of other species with Cylindrocarpon-like anamorphs: Cinnamonectria gen nov. with C. cinnamomea as type taxon, Macronectria gen. nov. with M. jungneri as type taxon, and Tumenectria gen. nov. with T. laetidisca as type taxon. Species in this group of fungi present extensive morphological conservationism, representing a challenge for species identification without the use of molecular techniques, however offering a great opportunity to explore mechanisms of speciation and evolutionary diversification.