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Tracking Down a Killer of Coastal Oaks

Environment: A forest pathologist battles a disease plaguing Northern California woodlands.


BERKELEY — Plant scientist Matteo Garbelotto has at times envied those who study human diseases. Their work seemed more immediate than his research on mushrooms and root rot.

But now, major developments in his cramped basement lab at UC Berkeley are the subject of headlines. Researchers abroad follow his findings. He has received emergency funding from the federal government.

That's because he is one of the lead researchers on the trail of an epidemic killing a cherished symbol of California, oak trees.

Called sudden oak death, the disease has sucked the life out of tens of thousands of oaks on the Northern and Central California coast, studding hillsides with brown pockets of death.

It has recently been found in nursery rhododendrons, wild huckleberries, madrone and California bay laurel trees. In some woodland spots in Northern California, every major tree type has been infected.

Researchers expect the list of susceptible species to keep growing. And though Garbelotto has discovered a treatment that could save individual oaks in people's yards, he doesn't think he'll find a real cure.

All that has brought a sense of urgency to the UC labs where Garbelotto and his Davis colleague David Rizzo are searching for answers.

A forest pathologist appointed to his Berkeley post less than a year ago, Garbelotto no longer envies medical researchers.

"Every finding we make is interesting because it's new," he said. "It's very exciting."

The object of their attention is an organism identified by Rizzo only last year.

Its victims were first found in 1995 in the form of a Marin County dieback of tanoaks. The problem was thought to be the result of years of drought followed by wet winters, which had stressed the trees and made them vulnerable to beetle infestations.

The disease turned up in other counties and other oak types, including the majestic coast live oak. Alarm mounted, but the cause remained uncertain.

Then last summer Rizzo took live tissue samples from dying trees in the field and analyzed them. He found a fungus-like organism belonging to the genus Phytophtora--ominously related to the cause of the Irish potato famine of the 1800s.

The pathogen appeared to be brand new. It didn't match any known Phytophtora species. The UC teams have since learned it is the same one discovered on European rhododendrons in 1993, though it has so far not been detected in European oaks.

Researchers don't know whether it originated in America or Europe or a third place where local plants were resistant. They're not sure how it is transmitted, although it has been isolated in rainwater splashes and soil.

They also don't think they're going to find a cure.

"How are we going to stop something that is so pervasive in the environment and can be found in so many different plants?" Garbelotto asked. Rather, he said, "We want to try to contain and reduce it."

So far, sudden oak death has been confirmed in seven coastal counties in Central and Northern California: Marin, Sonoma, Napa, Santa Clara, Santa Cruz, San Mateo and Monterey.

The organism likes moist, cool conditions, suggesting it may just be a matter of time before it pops up north of there.

It has been identified in tanoaks, coast live oak, black oak and, more recently, in Shreve's oak, rhododendron nursery stock in Santa Cruz County, wild huckleberries, madrone and California bay trees.

"We're testing every species that makes sense," Garbelotto said, holding a plastic baggie of sickly looking leaves collected from the field.

Chasing down the pathogen requires patience and sophisticated lab techniques.

Plant samples are placed in small tubes containing ball bearings and are ground into a fine powder. An organic solvent is added to eliminate everything but DNA, the genetic code material.

The sample is then placed in a sterile isolation hood, along with DNA from the oak-death organism. An enzyme reaction is set up, and computer imaging is used to determine if there are any matches between the two sets of DNA.

The research mission is threefold: to find out which plant types sudden oak death has infected, to determine the pathogen's origin and to devise ways of controlling it.

Garbelotto has successfully experimented with phosphonate, which breaks down into compounds that hinder the growth of the oak-death organism. But, he said, though phosphonate, customarily used as a fertilizer, will be useful in combating the disease in individual trees in people's yards, it is not something that would be broadly applied in the wild.

In a reflection of the passion a grand oak can stir, the public has suggested remedies in e-mail messages and letters. One woman swore by a water she gargled with. A man was sure the Tuscan oil that soothed him would save the trees.

Among the species that have been infected, there may be varying degrees of resistance. Bay-area tanoaks seem quite susceptible, but Garbelotto said he and Rizzo suspect coastal live oaks are less so.

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