An invasive tree fungus that has been killing stands of Port Orford cedar trees for decades may have finally been thwarted.

An invasive tree fungus that has been killing stands of Port Orford cedar trees for decades may have finally been thwarted.

U.S. Forest Service and Oregon State University scientists have succeeded in producing Port Orford cedars that are highly resistant to the fungus called Phytophthora lateralis.

"We now have trees that stand up to the disease in its current form," said Don Goheen, plant pathologist for the U.S. Forest Service's Southwest Oregon Forest Insect and Disease Service Center at the J. Herbert Stone Nursery in Central Point.

"This is real good news," he added. "This project to find Port Orford cedars that are disease resistant has been very successful."

The disease-resistant seedlings now being produced are the result of years of work by agency and OSU researchers identifying the few trees surviving in a stand hit by the disease, then gathering seeds from those trees, growing the seedlings and testing them for their resistance to the disease.

"This is probably the best success story we've ever had in overcoming a pathogen of forest trees, which is a very difficult thing to do," said Everett Hansen, a professor of botany and plant pathology who led OSU's research on the project, in a prepared statement.

"At least some of our trees now have complete immunity to this pathogen," he said. "Never before have we been able to come this far, this fast. The results are fairly dramatic."

Most of the disease-resistant seedlings are being grown at the agency's seed orchards near Dorena. Agency geneticist Richard Sniezko was the principal collaborator with the OSU scientists.

Commonly known as the Port Orford cedar root disease, the waterborne pathogen kills from the roots up.

Unlike the more widespread incense cedar, Port Orford cedar, which has both ecological and commercial value, grows native only in southwestern Oregon and the northwest tip of California.

It can be identified by its feathery boughs, which made it a popular ornamental plant European travelers collected when they first arrived off the coast aboard sailing ships.

It may have been the human practice of importing plants that began causing the death of the stately trees. The disease, which scientists believe originated in Asia, was first discovered in the Pacific Northwest in a Seattle nursery in the early 1920s. It began to show up in Port Orford cedar stands in the early 1950s.

The breakthrough has already resulted in disease-resistant seedlings being planted in some portions of the Rogue River-Siskiyou National Forest, Goheen said.

"We're very hopeful this provides a way to bring Port Orford cedar back in some of the places that were worst hit," Hansen said in a telephone interview. "There are enough seedlings to match the opportunities for planting at this point."

Because the disease is waterborne, the areas hit by the disease are largely in watersheds where the organism has been introduced, Goheen said.

"Looking at overall range of Port Orford cedar, we figure the wet areas only represent about 10 percent of the areas where the cedar is found," he said. "However, that's also where the cedar did the best. The disease has impacted a lot of the best places where you can find Port Orford cedars."

While both scientists are optimistic the disease-resistant trees will stand up to the current strain of the disease, they caution there is the continued risk of fungus mutation.

"That's why we continue to collect large numbers of trees that may be resistant — we want trees that represent slightly different genetic makeups in case the disease organism does mutate," said Goheen, who is also an entomologist. "With any kind of fungus organism, the possibility of mutation is great."

Disease-resistant Port Orford cedar seeds and seedlings for forest use are available through the Oregon Department of Forestry.

Reach reporter Paul Fattig at 776-4496 or e-mail him at pfattig@mailtribune.com.