First report of Phytophthora ramorum lineage EU1 infecting douglas fir and grand fir in Oregon.
Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum. This fungus-like organism 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 USA. In contrast, EU1, NA1, and NA2 have all been found in USA nurseries. In the winter of 2015, a symptomatic Notholithocarpus densiflorus (tanoak) was identified during a SOD helicopter survey in Curry County, Oregon. P. 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; n=3) and Pseudotsuga menziesii (Douglas fir; n=2) saplings growing near infected tanoak trees in the mixed conifer forest of Curry County. Symptoms with shoot blight for these species were similar to those described in the literature, including wilting and dieback of new shoots, brown discoloration of needles, and needle loss on young shoots. Results of morphological observations, DNA sequence analysis and pathogenicity tests confirmed the presence of the EU1 lineage of P. ramorum.