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Some Redwoods Show Evidence of Disease That Is Killing Coastal Oaks

Botany: Traces of organism show up on saplings, but scientists not sure it is harmful to the stately tree.


Evidence of a disease that has wiped out thousands of California coastal oaks has shown up on redwoods, although scientists are not yet certain whether the towering trees are susceptible to it.

University of California researchers found genetic material from the fungus-like organism that causes sudden oak death on samples of sickly redwood sprouts in Berkeley and Big Sur, heightening the potential threat of the epidemic. There is no known cure.

Until lab tests are completed, it is not known if, or to what extent, one of California's best known symbols could fall victim to the infection.

"I can tell you we have reason to believe they are a potential host and we are doing experiments to see if they are," said UC Berkeley plant scientist Matteo Garbelotto, one of the lead researchers on the disease.

First detected on Marin County tanoaks in 1995, sudden oak death has been found on a growing list of plant species and in 10 counties along California's central and north coasts.

It has been most devastating to tanoaks, which are important to wildlife. It has also killed some coast live oaks, beloved for their stately elegance and one of the state's signature trees.

If the disease proves to be fatal to redwoods, it would raise the stakes of the epidemic, striking an important commercial timber source and a symbol of California's natural grandeur.

Scientists noticed signs of the disease on redwoods while on a September field trip to observe other infected trees in Big Sur. They collected wilted sprouts and, later, samples from redwoods on the UC Berkeley campus.

Genetic testing confirmed that the material contained the DNA of Phytophthora ramorum, the pathogen that causes sudden oak death.

Lab tests were run to see if healthy redwood shoots inoculated with the Phytophthora became infected.

Because of contamination, the experiment had to be scrapped and restarted, Garbelotto said. He expects results by the end of this month.

Even if redwoods are a host of sudden oak death, they may have some resistance to it. It could take years of research to ascertain whether redwoods are vulnerable, and to what degree.

"If we started to see mortality similar to tanoaks, then we start to worry. So far we haven't," said Garbelotto. "In my mind, I'm not picturing a scene of total destruction [of redwoods] at all."

Researchers have confirmed the Phytophthora in California black oak, coast live oak, Shreve's oak, tanoak, rhododendron, California bay laurel, big leaf maple, madrone, manzanita, huckleberry, California honeysuckle, toyon--a type of tree--California buckeye and California coffeeberry.

It has also been found on arrow wood plants growing in Germany and The Netherlands.

Thus far confined to within 50 miles of the coast, the disease's reach extends from Mendocino to Monterey counties and has been found in southern Oregon.

Researchers are experimenting with treatments but have said that in the wild, their best hope is to find ways of containing the epidemic rather than eliminating it.

The disease continues to progress, killing trees in infected areas and infecting new areas. "The number of dead trees has increased," Garbelotto said.

Scientists are unsure of the origins of the pathogen, which is related to the organism that caused the Irish potato famine of the 1800s.

They are also uncertain of how the disease is spread. California and Oregon have imposed restrictions on the movement of infected wood and hikers in infected areas are advised to wash off their shoes to avoid the possibility of carrying the disease with them.

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