Host-pathogen interactions in rust disease pathosystems.

摘要

Understanding the evolution of host-pathogen interactions is a dynamic and rapidly growing area of study. In the thesis presented here, host-pathogen interactions in the white pine blister rust and Salix-Melampsora rust pathosystems were studied. Resistance mechanisms (or lack thereof) to the biotrophic exotic pathogen Cronartium ribicola were compared in resistant and susceptible genotypes of Pinus strobus. Fewer basidiospores germinated and resulting hyphae penetrated stomata infrequently on needles of the resistant genotype, P327. Differences in the chemical composition of wax and frequency of wax occlusion of stomata were observed between the genotypes and may be responsible for the development of fewer infections. Removal of epicuticular wax from resistant genotypes increased infection frequency to near levels observed for the susceptible genotype. GC/MS analyses indicated that at least 3 different compounds in the wax were present in resistant but not susceptible needles. After infections were established, proteomic comparisons from needle tissues elucidated important up-regulation of proteins homologous to known classes of resistance proteins in the resistant genotype, but not the susceptible genotype. In the Salix-Melampsora rust pathosystem, molecular and morphological comparisons of Arctic and temperate isolates of Melampsora epitea sensu lato were done to examine the extent of host specialization in this species complex. Results indicate that isolates diverged according to host species as evidenced by phylogenetic analyses of internal transcribed spacer region (ITS) rDNA. Environmental scanning electron microscopy studies of morphological characteristics of M. epitea urediniospores also provided evidence for evolution of distinct host-specific characteristics. This research provides important new information on host-pathogen interactions and provides insight into resistance mechanisms against the exotic blister rust pathogen in eastern white pine genotypes and Salix host specialization of Melampsora in Arctic and temperate North America.