Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Understanding the Influence of Microbial Sources and Time on the Developing Creeping Bentgrass Microbiome(2018) Doherty, Joseph Ryan; Roberts, Joseph A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microbial communities are intimately intertwined with many processes affecting the health of plants. There is increasing interest in utilizing microbial communities to increase plant health while reducing management inputs. To that end, bacterial and fungal communities associated with creeping bentgrass were evaluated using next-generation sequencing technologies. Evaluating the impact of resident seed and soil microbial communities revealed introductions of microbes from the seed despite a strong influence from the soil. Observing long-term population dynamics revealed no shifts in fungal diversity over six months, while bacterial diversity increased from emergence to two months post-emergence. Across both studies taxonomic profiling revealed that bacterial and fungal communities were consistently dominated by just a few groups. In both studies, ordination analyses revealed clustering of samples by sampling time. These results show that changes in the microbiome are driven by rare species, and that the turfgrass microbiome is resilient to change over time.Item Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation(2016) Allard, Sarah Michelle; Micallef, Shirley A; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.