First report of Phytophthora ramorum lineage EU1 infecting douglas-fir and grand fir in Oregon

Authors: LEBOLDUS, JARED - Oregon State University; SONDRELI, KELSEY - Oregon State University; SUTTON, WENDY - Oregon State University; REESER, PAUL - Oregon State University; NAVARRO, SARAH - Oregon Department Of Forestry; KANASKIE, ALAN - Oregon Department Of Forestry; Grunwald, Niklaus - Nik

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2017
Publication Date: 11/21/2017
Citation: Leboldus, J.M., Sondreli, K.L., Sutton, W., Reeser, P., Navarro, S., Kanaskie, A., Grunwald, N.J. 2017. First report of Phytophthora ramorum lineage EU1 infecting douglas-fir and grand fir in Oregon. Plant Disease. 102(2):455. https://doi.org/10.1094/pdis-05-17-0681-pdn.
DOI: https://doi.org/10.1094/pdis-05-17-0681-pdn

Interpretive Summary: Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum. This pathogen has four clonal lineages: NA1, NA2, EU1, and EU2. Until recently, the NA1 lineage was the only clonal lineage of P. ramorum reported in wildland forests in the western United States. In the winter of 2015, a symptomatic tanoak was identified during a SOD helicopter survey in Curry County, OR. Continued monitoring of the area in 2016 and 2017 has identified symptomatic grand fir and and Douglas-fir saplings growing near infected tanoak trees. The lineage of the isolates from A. grandis and P. menziesii was confirmed to be EU1. The EU1 lineage is considered more aggressive than the NA1 lineage and is of opposite mating to NA1 thus potentially resulting in establishment of sexual populations. These results provide further evidence of a distinct new introduction of P. ramorum into OR forests and the potential threat to economically important conifer species.

Technical Abstract: Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum. This pathogen has four clonal lineages: NA1, NA2, EU1, and EU2. Until recently, the NA1 lineage was the only clonal lineage of P. ramorum reported in wildland forests in the western United States. In contrast, EU1, NA1, and NA2 have all been found in U.S. nurseries. In the winter of 2015, a symptomatic Notholithocarpus densiflorus (tanoak) was identified during a SOD helicopter survey in Curry County, OR. Phytophthora ramorum was isolated from symptomatic bark tissue. Subsequently, the isolate was determined to be of the EU1 lineage based on 14 microsatellite loci. Continued monitoring of the area in 2016 and 2017 has identified symptomatic Abies grandis (grand fir) and Pseudotsuga menziessii (Douglas-fir) saplings growing near infected tanoak trees. Symptoms were consistent with shoot blight of these two species described in the literature. Isolations were made by plating tip dieback from A. grandis and P. menziesii on selective medium. Based on the presence of chlamydospores, characteristic hyphae, and sporangial morphology, the isolates were identified as P. ramorum. DNA was extracted from P. ramorum hyphae and a portion of the CBEL gene was amplified and sequenced using the CBEL5U and CBEL6L primers. The sequences of the unknown lineage were aligned to sequences of CBEL for NA1, NA2, EU1, and EU2 using the Staden package. The lineage of the isolates from A. grandis and P. menziesii was confirmed to be EU1. The EU1 lineage is considered more aggressive than the NA1 lineage and is of opposite mating to NA1 thus potentially resulting in establishment of sexual populations. These results provide further evidence of a distinct third introduction of P. ramorum into OR forests and the potential threat to economically important conifer species.