Causes and consequences of fungal disease in cottonwoods

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Plant pathogens are microorganisms that cause disease and are therefore of great economic and ecological importance. Tremendous effort has been devoted to understanding plant genetic resistance to individual pathogens. Yet we know less about how natural genotypic variation in host plants affects the structure of pathogen communities. Here I test how both plant genotype and the environment influence the structure of fungal leaf pathogen communities, and how pathogens in turn affect plant herbivores. First, I test how the evolutionary history of plants affects their pathogen communities. I show that the pathogens of Populus angustifolia, the narrow leaf cottonwood of the Rocky Mountains, are consistent with a hypothesis of Beringian migration into North America by the ancestor of P. angustifolia. Second, in common garden studies and in the wild, I test how inter- and intraspecific genetic variation in Populus affects the structure of pathogen communities. I found that pathogen communities varied both among Populus species and genotypes within species, mostly in the severities of damage inflicted by constituent pathogens rather than in composition. These results suggest that quantitative genetic resistance, which is neither complete nor pathogen-specific, is affecting these communities. Third, I test how environmental variation affects both pathogen communities, and genetic resistance to pathogens. I found that the influence of plant genotype on pathogen communities attenuates as spatial scale and environmental heterogeneity increase, and that plant genetic resistance to pathogens is correlated to the level of disease risk within the environment where the plant occurs. Finally, I test how plant genotypic variation in pathogen severity influences pathogens' indirect effects on herbivores. I found that pathogens reduce the richness and abundance of herbivores most strongly on severely infected Populus species. Pathogens also reduced herbivory, but this effect was modulated by genotypic variation in herbivore resistance. Pathogens most strongly deterred herbivores on herbivore-susceptible genotypes, suggesting that they induce defenses. Overall, this thesis demonstrates that the genetic-based interactions of relatively few species (e.g., a plant and a pathogen) can be fundamental to understanding community structure.


Type of resource text
Form electronic; electronic resource; remote
Extent 1 online resource.
Publication date 2012
Issuance monographic
Language English


Associated with Busby, Posy E
Associated with Stanford University, Department of Biology.
Primary advisor Dirzo, Rodolfo
Thesis advisor Dirzo, Rodolfo
Thesis advisor Field, Christopher
Thesis advisor Newcombe, George M
Thesis advisor Whitham, Thomas, 1947-
Thesis advisor Vitousek, Peter Morrison
Advisor Field, Christopher
Advisor Newcombe, George M
Advisor Whitham, Thomas, 1947-
Advisor Vitousek, Peter Morrison


Genre Theses

Bibliographic information

Statement of responsibility Posy E. Busby.
Note Submitted to the Department of Biology.
Thesis Ph.D. Stanford University 2012
Location electronic resource

Access conditions

© 2012 by Posy E Busby
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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