Pathogenicity of Phytophthora species from Oregon waterways

Graduation date: 2014Described as one of the most destructive pathogens of agricultural crops and forest trees, Phytophthora is a genus of microorganisms containing over 100 known species. Phytophthora alni has caused collar and root disease in alders throughout Europe and a form of the species has recently been isolated in North America. Red alder, Alnus rubra, is native to Oregon and has been reported to be suffering from dieback, which prompted a survey of their overall health as well as determining if P. alni was present. Over 1200 individual Phytophthora isolates were recovered in the survey, which are representative of 22 species and 2 taxa, including P. alni subsp. uniformis. High levels of mortality for red alder were not observed during the WORE survey, which suggests these Phytophthora species are not aggressive pathogens of red alder. In order to test the hypothesis that red alder is not susceptible to the twelve Phytophthora species recovered from western Oregon riparian ecosystems, a variety of pathogenicity tests were conducted. Twelve\ud species of Phytophthora were selected from the Phytophthora species recovered from the western Oregon riparian ecosystem survey for pathogenicity testing. Red alder seedlings were selected for testing because they have adapted to survive in riparian ecosystems, which is where these Phytophthora species have been recovered. Pathogenicity tests conducted for this study demonstrated that the twelve Phytophthora species from the survey of riparian ecosystems were able to cause minor disease symptoms on red alder, but did not cause the same symptoms observed during the WORE survey. Phytophthora species have the potential to have global impacts on forest ecosystems, which can be mitigated by conducting research on indigenous species before they become global issues of forest health