Research at OSU helps contain the threat of sudden oak death

September 30, 2003

CORVALLIS - A team of plant pathologists at Oregon State University is helping officials battle a pathogen that threatens sudden death. The disease, sudden oak death, is not always sudden and does not always cause death.

But because it affects far more than just oaks, it could inflict a multi-million dollar wound upon Oregon's nursery industry.

Everett Hansen, an OSU plant pathologist, is a world expert on forest Phytophthora, a family of notorious pathogens linked to the Irish potato famine and the die-off of Port Orford cedars. These are cousins of Phytophthora ramorum, the pathogen that causes sudden oak death.

Hansen has been part of the investigation of sudden oak death from the moment it was first diagnosed in 2000. Since then, the OSU team has expanded to include Jennifer Parke, a plant pathologist in OSU's College of Agricultural Sciences, and Bob Linderman, research plant pathologist for the U.S.D.A. Agriculture Research Service in Corvallis.

Working with researchers from the University of California, USDA, the Oregon Department of Agriculture and the Oregon Department of Forestry, the scientists have found that sudden oak death infects more than just oaks and tanoaks. Less severe signs of the disease have been observed in Douglas fir and redwoods - discoloring needles and small branches.

Dozens of plants that define Oregon landscapes can harbor the pathogen, including rhododendron, big leaf maple, madrone, camellia, viburnum, and huckleberry. The OSU team has found hundreds of other plants that are susceptible, native as well as ornamentals. It is the threat to horticultural plants that has prompted new rules for reporting and inspecting nursery stock imported into Oregon.

In 2003, sudden oak death was reported for the first time in nurseries in California, Oregon, Washington, and British Columbia.

Oregon's nursery industry is one of the state's largest grossing agricultural industries, and second in the nation in the production of woody plants. When Canada briefly closed its doors to Oregon nursery products, the state faced losses of $20 million, according to Dan Hilburn, an Oregon Department of Agriculture spokesman. Trade resumed after survey and eradication procedures were set in place to contain sudden oak death.

"The ultimate potential impact for the nursery industry is tied to consumer perceptions," Linderman said. "If consumers are led - or misled - to believe that horticultural plants may harbor the pathogen, they may simply quit buying. Even after a few years of research effort on sudden oak death, the unknowns still outweigh the knowns."

In California, where the disease first surfaced in 1995, the pathogen was too widespread to contain or eradicate by the time it was identified. By contrast, in Oregon rapid identification has made it possible to contain the disease and limit new cases, according to Parke.

"Oregon has responded with an eradication effort that so far, is keeping the disease in check," said Hansen. "We support the eradication program by providing diagnostic and survey methods including molecular probes for the pathogen."

Almost immediately upon discovery of the pathogen in Oregon, the OSU team has focused on methods of diagnosis in order to understand more about this pathogen, how it spreads and how it infects plants.

The detective work continues. With the Oregon Department of Forestry monitoring the forests and the Oregon Department of Agriculture scouring nurseries, new infestations can be identified and quickly contained. When something suspicious is uncovered, Hansen's lab extracts a sample for DNA analysis to determine if the sudden oak death pathogen is the culprit.

This summer, the OSU team uncovered a new type of the disease in infected nursery plants. Their analysis revealed a second source of infection, not from the forest but from imported nursery stock, probably from Europe.

"This European type is more aggressive, causing disease more rapidly than the forest type," said Hansen. In addition, having both types makes genetic mixing possible, which could result in new forms of the pathogen.

"Following the diagnosis, the ODA response was rapid and aggressive," said Hansen. "All known infected nursery material has been destroyed."

"These investigations are expensive," said ODA's Hilburn, "and they are being conducted with no additional funds from the state."

However, the Pacific Northwest congressional delegations, led by the support of U.S. Rep. Darlene Hooley, have helped secure federal funding for continued research and diagnostics at OSU that will help protect Oregon's nursery industry.

Author: Peg Herring
Source: Jennifer Parke, Bob Linderman, Everett Hansen