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CORVALLIS - New research has shown that a fungal pathogen that is causing the Swiss needle cast epidemic in forests of the Pacific Northwest is present in two forms - and one form of the fungus may be more virulent and damaging than the other.

Scientists working with the Swiss Needle Cast Cooperative at Oregon State University have just presented information in a trade journal that the fungus causing this disease exists as two distinct genetic lineages. Continuing research will determine the implications of this for needle loss, reduced growth and tree death, they say. At least one of the fungal lineages has a worldwide distribution due to its movement on Douglas-fir nursery stock. So far the second lineage, which may cause the more severe damage, has been found only in the Oregon Coast Range, and it's not yet clear whether or not it also occurs elsewhere.

Large forest areas of western Oregon and Washington are suffering from this disease, with the newest surveys showing 385,000 acres as being moderately to severely affected. It attacks only Douglas-fir trees, which form the foundation of the Pacific Northwest forest products industry. The disease and fungus that causes it, which are native to the Pacific Northwest, were first described in 1925, but were long believed to be of no particular significance. In old-growth forests - with trees of many species, sizes and ages - the fungus caused no major outbreaks in recorded history.

By the 1970s, however, Swiss needle cast had become an important problem for the region's Christmas tree industry, and just in the last decade the disease has spread rapidly. It has dramatically reduced the growth of hundreds of thousands of acres of Douglas-firs on public and private forest land.

For years scientists have tried to determine why a fungus that was native to the region had rather suddenly evolved from a minor nuisance into a serious and costly threat. Some experts point to the huge growth of plantation forestry in the area, in which many forests were harvested and converted from perhaps 20 percent Douglas-fir to 80 percent or more, in an even-aged monoculture that may encourage the growth and spread of the fungus. Climate patterns may also play a role.

These factors may still be keys to the epidemic, but the presence of two lineages of the pathogen now offers another possible explanation, experts say.

"It's now clear that we have two different genetic lineages of the fungus that are present in Oregon's coastal region," said Greg Filip, a professor of forest science and director of the Swiss Needle Cast Cooperative - a collaboration of private industry, public agencies and university researchers.

The two lineages are likely related to a common ancestor, researchers say, and may represent a mutation or divergence that occurred at some point in the past. Exactly when is uncertain.

"There is also evidence that the second lineage of the fungus may cause more damage, with more severe needle loss, retarded growth and possibly tree death," Filip said. "But more controlled research needs to be done before we can be sure how these two strains of the fungus interact and what problems they will cause, together or separately. Those studies are already under way."

The new discoveries about the fungal lineages were made by OSU research associate Lori Winton, in collaboration with professors Jeff Stone and Everett Hansen.

The work is being supported by the cooperative, and has already entailed studies, with new DNA-based techniques, of the genetic diversity and population structure of this fungus. The identification of two fungal lineages, possibly differing in virulence, poses a number of questions that scientists cannot yet fully answer, Filip said. It's not certain what the natural distribution of the two lineages is, whether the two lineages together will cause more tree damage than either one separately, whether both lineages can infect a tree at the same time, or whether the two lineages may affect disease differently.

Studies on all of these issues will be conducted by the Swiss Needle Cast Cooperative, Filip said, which was created by the OSU College of Forestry. The cooperative has already developed a number of management practices that can help reduce problems with this fungus, and an Extension publication is available that outlines some of these approaches. They can include different regeneration methods, vegetation management techniques, fertilization, thinning, pruning, clearcutting, and planting of different tree species. Development of a genetically resistant Douglas-fir species is also being explored.

Swiss needle cast is still a major problem, expanding in scope, and may be the worst forest disease epidemic in the Pacific Northwest in a century, Filip said. When conditions are favorable, Swiss needle cast can spread rapidly, with mobile spores that travel on wind-blown rain in late spring. It's more aggressive than many fungal problems. Some plantations of Douglas-fir in the Oregon Coast Range have barely grown in the past 10 years, experts say.