Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item DIVERSITY AND DISTRIBUTION OF FUNGAL ENDOPHYTES IN TWO AMAZONIAN HARDWOOD GENERA(2017) Skaltsas, Demetra N; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hevea brasiliensis (Euphorbiaceae) is the primary species for tapped natural rubber and an economically important crop since the 1870’s. Plantation-grown trees of H. brasiliensis are susceptible to numerous pathogens, some which are resistant to traditional chemical control. Fungal endophytes obtained from the wild are often considered ideal candidates for developing biological controls for pathogens, however little knowledge of the fungal endophytes associated with wild rubber and related hosts exists. The objectives of this study were the following: 1) determine the composition of the fungal endophyte communities associated with wild H. brasiliensis and its close relatives in Micrandra using cultures and culture-independent methods; 2) determine the species identities of endophytes in the genus Diaporthe associated with the two host genera; and 3) assess the overall utility of automated and manual methods for curating operational taxonomic unit (OTU) characterization of endophytes. To accomplish these objectives, fungal isolates and DNA from 381 seedlings and 144 adults of Hevea and Micrandra from three Amazon Peru locations were characterized using sequences from the internal transcribed spacer regions (ITS) of the ribosomal DNA repeat unit for both cultures and culture-independent samples, the latter using metagenomics methods. To determine the species identities of the Diaporthe isolates, four loci were analyzed using phylogenetic methods. A comparison of the effects of manual and automated operational taxonomic unit (OTU) classification was performed by using four different methods. Trichoderma species were most frequently identified from adult trees while Diaporthe species were the most abundant from seedlings, suggesting host developmental stage may be a key determinant of tropical endophytic community assemblage. Twenty-one distinct Diaporthe lineages were recovered with seven described as new species. Manual OTU curation methods were less error-prone suggesting that algorithm adjustments are needed for currently used automated methods. This study resulted in a greater understanding of the diversity of endophytes, particularly Diaporthe spp., associated with wild rubber. Knowledge of fungal diversity, host life stage associations, and spatial distribution of Hevea and Micrandra endophytes will provide additional tools for integrated disease management approaches and aid development of successful biocontrol methods.Item EVALUATING THE ENDOPHYTIC FUNGAL COMMUNITY IN PLANTED AND WILD RUBBER TREES (Hevea brasiliensis)(2012) Gazis, Romina O.; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The main objectives of this dissertation project were to characterize and compare the fungal endophytic communities associated with rubber trees (Hevea brasiliensis) distributed in wild habitats and under plantations. This study recovered an extensive number of isolates (more than 2,500) from a large sample size (190 individual trees) distributed in diverse regions (various locations in Peru, Cameroon, and Mexico). Molecular and classic taxonomic tools were used to identify, quantify, describe, and compare the diversity of the different assemblages. Innovative phylogenetic analyses for species delimitation were superimposed with ecological data to recognize operational taxonomic units (OTUs) or "putative species" within commonly found species complexes, helping in the detection of meaningful differences between tree populations. Sapwood and leaf fragments showed high infection frequency, but sapwood was inhabited by a significantly higher number of species. More than 700 OTUs were recovered, supporting the hypothesis that tropical fungal endophytes are highly diverse. Furthermore, this study shows that not only leaf tissue can harbor a high diversity of endophytes, but also that sapwood can contain an even more diverse assemblage. Wild and managed habitats presented high species richness of comparable complexity (phylogenetic diversity). Nevertheless, main differences were found in the assemblage's taxonomic composition and frequency of specific strains. Trees growing within their native range were dominated by strains belonging to Trichoderma and even though they were also present in managed trees, plantations trees were dominated by strains of Colletotrichum. Species of Trichoderma are known for their biocontrol properties, whereas species of Colletotrichum have been always associated with plant disease.