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 EFFECT OF HABITAT FACTORS AND HOST PLANT ON NATURAL ENEMIES OF EMERALD ASH BORER (AGRILUS PLANIPENNIS) AND IMPLICATIONS FOR BIOLOGICAL CONTROL(2017) Hoban, Jacqueline Nicole; Shrewsbury, Paula; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In an effort to manage the invasive wood-boring buprestid, emerald ash borer (Agrilus planipennis), biological control efforts have resulted in the release of four classical biological control agents. Emerald ash borer is known to infest ash trees (Fraxinus spp.) in both urban and natural habitats and, recently emerald ash borer has expanded its host range to include white fringetree (Chionanthus virginicus). While these parasitoids have been studied in forested habitats, little is known about their efficacy in urban landscapes and in white fringetree. Here, I evaluated the efficacy of Tetrastichus planipennisi an introduced, larval endoparasitoid, at parasitizing emerald ash borer in white fringetree. Additionally, I released T. planipennisi at sites along an urbanization gradient in Maryland and northern Virginia and evaluated habitat factors for their effect on emerald ash borer and its natural enemies. From my results, implications for biological control and management of emerald ash borer are discussed.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.Item Assessment of select isolates of Trichoderma virens as a potential biocontrol against Meloidogyne incognita(2004-05-03) Mallozzi, Tonya Suzanne; Kratochvil, Robert J.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Three isolates of the soil-dwelling fungal organism, Trichoderma virens (Miller, Giddens and Foster) von Arx., were studied as potential biocontrols for the management of root-knot nematode (RKN) on bell pepper (Capsicum annuum L.). The study was conducted within the Moisture Replacement System (MRS), which was concurrently evaluated for its ability to serve as a culture system for Meloidogyne incognita (Kofoid and White) Chitwood and as an environment supportive of the growth and maintenance of Trichoderma isolates for biocontrol studies of this nature. Trichoderma isolates selected for study did not suppress populations of RKN on bell pepper under the conditions of this study. A review of the literature provided a multitude of complexities potentially contributing to the final results obtained. Investigation into these various complexities with the incorporation of the MRS will help to fully ascertain Trichoderma's potential as a biocontrol and perhaps reveal viable alternatives in the management of RKN.