Publication Type:
Journal ArticleSource:
Plant Disease, Volume 102, Issue 2, p.455 - 455 (2018)URL:
https://apsjournals.apsnet.org/doi/10.1094/PDIS-05-17-0681-PDNhttps://apsjournals.apsnet.org/doi/full/10.1094/PDIS-05-17-0681-PDNAbstract:
Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum S. Werres, A. W. A. M. de Cock & W. A. Man in’t Veld. This fungus-like organism has four clonal lineages: NA1, NA2, EU1, and EU2 (Grünwald et al. 2016; Prospero et al. 2007). 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 (Grünwald et al. 2012). In the winter of 2015, a symptomatic Notholithocarpus densiflorus Manos, Cannon & S.H.Oh (tanoak) was identified during a SOD helicopter survey in Curry County, OR. P. ramorum was isolated from symptomatic bark tissue. Subsequently, the isolate was determined to be of the EU1 lineage based on 14 microsatellite loci (Grünwald et al. 2016). Continued monitoring of the area in 2016 and 2017 has identified symptomatic Abies grandis (Douglas ex D. Don) Lindl. (grand fir; n = 3) and Pseudotsuga menziesii (Mirb.) Franco (Douglas fir; n = 2) saplings growing near infected tanoak trees in the mixed conifer forest of Curry County, OR. 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. Isolations were made by plating surface-sterilized tip dieback tissue from A. grandis and P. menziesii on a Phytophthora-selective medium. Based on the presence of chlamydospores, characteristic hyphae, and sporangial morphology, the isolates were identified as P. ramorum. DNA was extracted from hyphae, and a portion of the cellulose binding elicitor lectin (CBEL) gene was amplified and sequenced using the CBEL5U and CBEL6L primers (Gagnon et al. 2014). The sequences of the unknown lineage were aligned to sequences of CBEL for NA1, NA2, EU1, and EU2 using the Staden package in GAP version 4.11.2. The lineage of the isolates from A. grandis and P. menziesii (GenBank accession nos. MF918374 and MF918375, respectively) had 100% identity to the EU1 reference sequences (GenBank nos. EU688952 and EF117945). To satisfy Koch’s postulates, three branches of A. grandis and P. menziessii were inoculated with the original EU1 isolates of P. ramorum from those hosts. Ten days after inoculation, the same pathogen was reisolated from symptomatic stem tissue of both tree species. The EU1 lineage is considered more aggressive than the NA1 lineage and is of opposite mating type to NA1, thus potentially resulting in establishment of sexual populations.
Sudden oak death (SOD) is caused by the introduced oomycete pathogen Phytophthora ramorum S. Werres, A. W. A. M. de Cock & W. A. Man in’t Veld. This fungus-like organism has four clonal lineages: NA1, NA2, EU1, and EU2 (Grünwald et al. 2016; Prospero et al. 2007). 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 (Grünwald et al. 2012). In the winter of 2015, a symptomatic Notholithocarpus densiflorus Manos, Cannon & S.H.Oh (tanoak) was identified during a SOD helicopter survey in Curry County, OR. P. ramorum was isolated from symptomatic bark tissue. Subsequently, the isolate was determined to be of the EU1 lineage based on 14 microsatellite loci (Grünwald et al. 2016). Continued monitoring of the area in 2016 and 2017 has identified symptomatic Abies grandis (Douglas ex D. Don) Lindl. (grand fir; n = 3) and Pseudotsuga menziesii (Mirb.) Franco (Douglas fir; n = 2) saplings growing near infected tanoak trees in the mixed conifer forest of Curry County, OR. 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. Isolations were made by plating surface-sterilized tip dieback tissue from A. grandis and P. menziesii on a Phytophthora-selective medium. Based on the presence of chlamydospores, characteristic hyphae, and sporangial morphology, the isolates were identified as P. ramorum. DNA was extracted from hyphae, and a portion of the cellulose binding elicitor lectin (CBEL) gene was amplified and sequenced using the CBEL5U and CBEL6L primers (Gagnon et al. 2014). The sequences of the unknown lineage were aligned to sequences of CBEL for NA1, NA2, EU1, and EU2 using the Staden package in GAP version 4.11.2. The lineage of the isolates from A. grandis and P. menziesii (GenBank accession nos. MF918374 and MF918375, respectively) had 100% identity to the EU1 reference sequences (GenBank nos. EU688952 and EF117945). To satisfy Koch’s postulates, three branches of A. grandis and P. menziessii were inoculated with the original EU1 isolates of P. ramorum from those hosts. Ten days after inoculation, the same pathogen was reisolated from symptomatic stem tissue of both tree species. The EU1 lineage is considered more aggressive than the NA1 lineage and is of opposite mating type to NA1, thus potentially resulting in establishment of sexual populations.