Spatial and temporal analysis of populations of the Sudden Oak Death pathogen in Oregon forests

Authors: KAMVAR, Z - Oregon State University; Larsen, Meredith; KANASKIE, A - State Of Oregon; HANSEN, E - Oregon State University; Grunwald, Niklaus - Nik

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2015
Publication Date: 7/23/2015
Citation: Kamvar, Z.N., Larsen, M.M., Kanaskie, A.M., Hansen, E.M., Grunwald, N.J. 2015. Spatial and temporal analysis of populations of the Sudden Oak Death pathogen in Oregon forests. Phytopathology. 105:982-989.

Interpretive Summary: Sudden oak death is caused by the plant pathogen Phytophthora ramorum which first discovered in California towards the end of the 20th century. Subsequently sudden oak death emerged in tanoak forests in Oregon as detected by aerial surveys in 2001. The Oregon Department of Forestry has since monitored the epidemic and sampled symptomatic tanoaks from 2001 to the present. We sampled populations of the pathogen over this period and used genetic markers to determine changes in the populations over space in time. Interestingly, although three clonal lineages of the pathogen exist worldwide, only the NA1 clone was found in Oregon forests. Clustering of populations by genetic distance indicates that two introduction occurred into Oregon forests. Comparing the genetic makeup of population to nursery populations from Oregon and Washington indicates that these two introductions might have come for nurseries most likely in California, but maybe also Oregon. Continued vigilance and eradication of nursery populations of P. ramorum are important to avoid further emergence and potential introduction of other clonal lineages.

Technical Abstract: Sudden oak death caused by the oomycete Phytophthora ramorum was first discovered in California towards the end of the 20th century and subsequently emerged on tanoak forests in Oregon before its first detection in 2001 by aerial surveys. The Oregon Department of Forestry has since monitored the epidemic and sampled symptomatic tanoaks from 2001 to the present. Populations sampled over this period were genotyped using microsatellites and studied to infer the population genetic history. To date, only the NA1 clonal lineage is established in this region, although 3 lineages exist on the North American West coast. The original introduction into the Joe Hall area eventually spread to several regions mostly North, but also East and Southwest. A new introduction into Hunter Creek appears to correspond to a second introduction not clustering with the early introduction. Our data are best explained by both introductions originating from nursery populations in California or Oregon and resulting from two distinct introduction events. Continued vigilance and eradication of nursery populations of P. ramorum are important to avoid further emergence and potential introduction of other clonal lineages.