ARS scientists have found that the strain of Phytopthora ramorum, the pathogen that causes sudden oak disease, found in California has a different genetic fingerprint than fungal strains found in Oregon and Washington. Photo courtesy of Joseph O'Brien, USDA Forest Service, Bugwood.org

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New ARS Study Shows Pathways of Movement of Sudden Oak Death Pathogen

By Alfredo Flores
September 18, 2009

The pathogen that causes sudden oak death disease in California has a different genetic fingerprint than fungal strains found in nurseries in Oregon and Washington, according to Agricultural Research Service (ARS) scientists. This discovery, published today in the journal PLoS Pathogens, will allow scientists to distinguish infections in other states as likely having originated from either California or the Pacific Northwest.

Sudden oak death is responsible for the rapid death of live oak and tanoak trees in coastal California forests and in urban and suburban landscapes in the San Francisco Bay area. It is feared that it could spread to other vulnerable forests in the Eastern United States.

The pathogen Phytophthora ramorum affects not only oak and tanoak trees, but also popular ornamental plants such as rhododendrons, viburnums and camellias. Movement of infected plants from one location to another can contribute to the spread of the disease.

Plant pathologist Nik Grunwald, at the ARS Horticultural Crops Research Unit in Corvallis, Ore., has been working on this project for the past four years. He and his research team examined samples of the pathogen collected from nurseries on the West Coast of the United States and across the country.

The researchers were able to show that the pathogen from California is different from isolates found in the Northwest. Grunwald and colleagues compared his results to records compiled by the U.S. Department of Agriculture (USDA) Animal and Plant Health Inspection Service on known shipments of infected plants, and these two sources of data were consistent with each other. The results could help scientists and the nursery industry in tracking the movement of this pathogen around the country and the world.

ARS is the principal intramural scientific research agency of USDA.