Coevolution of the Ipomoea - Coleosporium Natural

Coevolution of the Ipomoea-Coleosporium Natural Plant-Fungus Pathosystem by Thomas Mackey Chappell Department of Biology Duke University Date:_______________________ Approved: ___________________________ Mark D. Rausher, Supervisor ___________________________ Xinnian Dong ___________________________ William G. Wilson ___________________________ Rytas Vilgalys ___________________________ John H. Willis An abstract of a dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biology in the Graduate School of Duke University 2010 Copyright by Thomas Mackey Chappell 2010 iv Abstract Plants and their pathogens coevolve, with pathogen infection and host resistance acting in evolutionary antagonism of each other. Plant-pathogen coevolution has been shown to effect genetic divergence between populations and species, resulting in localized or specialized interactions between hosts and pathogens. Because most of the studies to date investigating plant-pathogen coevolution have been carried out in managed systems and have focused on pairwise interactions, we know little about three aspects of plant pathosystems in natural settings: 1) the role in nature of the gene-forgene paradigm for genetic determination of resistance; 2) the relationship of host community diversity and structure, and host-pathogen interaction structure, to the antagonistic coevolutionary process; and 3) the factors which underlie and drive local adaptation and specialization of interactions. This dissertation constitutes the results of research in which I have begun addressing these aspects in a natural plant-fungus pathosystem comprising multiple host species and a single rust pathogen. I have expanded previous characterization of the genetics of plant resistance in one constituent host species in the system by genetic crosses to characterize the basis of resistance in two additional species, finding support for the expectation that the gene-for-gene paradigm of interaction is important in natural