Mystery on the Sammamish: What are the sources of Phytophthora ramorum infesting this Washington State waterway?
G. Chastagner (1), K. COATS (1), D. Omdal (2), A. Ramsey-Kroll (2), M. Elliott (3)
(1) Washington State University, Puyallup, WA, U.S.A.; (2) Washington State Department of Natural Resources, Olympia, WA, U.S.A.; (3) Washington State University, Puyallup Research and Extension Center, Puyallup, WA, U.S.A.
Phytophthora ramorum was first detected in Washington in 2003 and has been detected since in 48 nurseries, four streams and three drainage ditches. Genotype analysis indicates that contamination of waterways has typically resulted from spread of inoculum from nearby positive nurseries. However, the source of inoculum associated with the detection of this pathogen in a four-mile-long section of the Sammamish River is a complex situation that remains unresolved. There have been at least nine P. ramorum-positive nursery sites in the Sammamish watershed since 2004. The initial detection of P. ramorum in the river in 2007 was an NA1 genotype that was consistent with the genotype detected in a holding pond four miles upstream that drains from a positive nursery into the Sammamish. Baiting in 2008, 2009, and 2010 detected additional NA1, NA2, and EU1 genotypes of the pathogen in the river. Positive baits at the mouths of two streams and a drainage ditch that runs through an industrial site into the river in 2009 and upstream in these waterways in 2010, indicate that there are multiple sources of inoculum that have contaminated the river. The NA2 in the river appears to be coming from one of the streams, which drains an area with a NA2 positive nursery approximately three miles upstream from the river. Efforts are underway to identify the sources of inoculum that have contaminated the other stream and the industrial ditch.
© 2011 by The American
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