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Differential Strain Dynamics Under Host and Environmental Stressors: A Pathway to Better Understanding Pathogen Presence and Fitness of Xanthomonas perforans




Russell, Ivory

Type of Degree

Master's Thesis


Entomology and Plant Pathology

Restriction Status


Restriction Type

Auburn University Users

Date Available



The bacterium Xanthomonas perforans is a worldwide pathogen of tomato and pepper plants causing bacterial leaf spot (BLS) resulting in necrotic spotting with which advanced disease can lead to complete defoliation of plants and subsequent yield loss for farmers. BLS is a seedborne disease that is considered endemic to the Southeastern United States, and while management strategies focus on the creation and use of resistant (R) cultivars in pepper, no R tomato cultivars are available in tomato due to the range of genetic diversity and subsequent difficulty of breeding for single-gene resistance. To understand this pathosystem better with hopes of aiding in the development of better disease management practices, we firstly profiled X. perforans pathogen diversity and disease dynamics across the Southeastern United States. We found that the pathogen was intraspecifically heterogenous within fields and across space and time, that the pathogen population had an effect on disease outcomes, and that climatic parameters were associated with disease and pathogen dynamics. These findings were then narrowed down in a greenhouse experiment to study host:pathogen and pathogen:pathogen interactions where we found that pathogen population assemblage was determined irrespective of environment. Lastly, we conducted research in light of global changes occurring by studying X. perforans under an extreme environmental variable to understand more about pathogen evolution across a single growing season and found that when in a combination of stress with host resistance and an environmental extreme, pathogen and disease dynamics shifted and an adaptive response was observed at a genomic level. With a look into pathogen dynamics in the field and implications of how those dynamics might change with environmental extremes, this work advances plant pathological research of the diverse and adaptive Xanthomonas perforans.