In 2015 I blogged about Oregon’s first-ever detection of the EU1 strain of the sudden oak death pathogen – Phytophthora ramorum – in the forest. We know that P. ramorum has four genetic strains. Until this discovery, all P. ramorum infections in North American forests belonged to the NA1 strain.
In response to the 2015 detection, the Oregon Department of Forestry immediately began efforts to eradicate the EU1 infestation. This program was funded in part by the USDA Forest Service Forest Health Protection program and APHIS.
Unfortunately, the EU1 strain persists – and has spread. In 2017, six of ten streams in the state found to harbor P. ramorum contained the EU1 lineage. A total of 119 trees infected by the EU1 strain grow in five separate sites. Infections on 43 additional trees are still being tested to determine their lineages. Under the Oregon eradication protocols, 371 acres of private and state-owned properties will be affected by management targetting the EU1 lineage.
This news is alarming for two reasons.
First, the EU1 lineage is more aggressive than the more common NA1 strain. For example, the EU1 lineage in Europe kills several types of conifers, including western hemlock (Tsuga heterophylla). In Oregon, the EU1 strain has been found to infect both Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) (LeBoldus et al. 2017). Douglas-fir is, of course, the foundation of the wood products industry in the West.
Second, the EU1 lineage is of the opposite mating type as NA1, creating the potential for sexual reproduction and increased variability in the pathogen population. (Sexual reproduction in P. ramorum can occur only when opposite mating types meet; in the absence if opposite mating types, all reproduction is clonal.)
The Oregon Department of Forestry continues eradication efforts. The program has been completed at one site; efforts at the other four known sites are a priority this year. Funding and resource constraints mean that sites infected by the more widespread NA1 strain are not likely to be treated this year. (ODF has approximately $1,375,000 available for eradication efforts in FY 2017-18.) No mention has been made of whether the USDA Forest Service or APHIS will provide assistance.
COMTF Newsletter March 2018 
The EU1 pathogen probably spread to the original infected tree from a small private nursery nearby. That nursery had been reported to be infected with the EU1 lineage of P. ramorum in 2012. As I noted in my earlier blog, this infection confirms fears that contaminated nurseries can spread the pathogen into the forest.
SOURCES
California Oak Mortality Task Force newsletter [http://www.suddenoakdeath.org/news-and-events/newsletter-archive/ ] April 2015 and March 2018.
LeBoldus, J.M.; Sondreli, K.L.; Sutton, W.; Reeser, P.; Navarro, S.; Kanaskie, A.; and Grünwald, N.J. 2018. First Report of P ram Lineage EU1 Infecting Douglas-Fir and Grand Fir in OR. Plant Disease. 102(2): 455. [summarized in the California Oak Mortality Task Force Newsletter, March 2018, available here. [link]
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Posted by Faith Campbell