The fight to save California's emblematic oaks from disease is gaining momentum as scientists decipher the genetic code of the microbe responsible for sudden oak death.
Sudden oak death has killed more than 1 million oak trees in 14 counties along the California and Oregon coast since it was first reported a decade ago.
The Energy Department's Joint Genome Institute in Walnut Creek and an army of other institutions have discovered that the pathogens that cause soybean root rot disease and sudden oak death are well-armed.
Nearly half of the bugs' genes are involved in infecting their victims, a much higher percentage than with other pathogens. In addition to this vast arsenal, the microbes are quick evolvers.
"It's the genetic arms race between the plant and the pathogen where they're changing their genes rapidly to find better ways to attack and better ways to defend," said evolutionary genomicist Jeffrey Boore at JGI.
The research appears in the journal Science today and is part of a four-year, $4 million project supported by the Energy Department, the Agriculture Department and the National Science Foundation.
Sudden oak death was first spotted in Contra Costa County in 2002 in Wildcat Canyon near Kensington. There have been just a dozen more reports of the disease in Contra Costa and Alameda counties.
Marin and Santa Cruz counties have not been as lucky.
"The last two years, we've had pretty wet springs, so the disease has really exploded in some areas," said David Rizzo, the University of California, Davis, plant pathologist who discovered the microbe responsible for sudden oak death.
Contra Costa County may have fewer infected trees because the area has fewer tanoaks, which are highly susceptible to the disease, Rizzo said. But that could change because the effects of the wet weather will continue for several years.
And the number of other plants that can act as hosts and spread the disease while not succumbing to it themselves has grown to about 100, said Katie Palmieri of the California Oak Mortality Task Force.
Soybean root rot disease causes more than $1 billion in losses annually, a major problem for the United States, which produces nearly half the world's soybeans. The Energy Department is particularly interested in fighting the disease because soybeans are the main source of biodiesel fuel.
Scientists hope to turn the pathogens' ability to rapidly evolve against them. Because they change so quickly, there are many small genetic differences between individual strains.
Each strain of the sudden oak death bug has a unique set of these minor genetic differences that is like a fingerprint that could be used to map how the disease spreads, and hopefully to get a few steps ahead of it.
"It helps you track where an infection came from," said Boore. "Did it come in on a rhododendron plant that was shipped from somewhere or did it blow in on the wind from some other forest? If we knew more about what that route of movement is, then maybe we could be more effective at stopping it."
Scientists are comparing the genetic blueprints of the oak death pathogen and the soybean disease pathogen to identify specific genes that enable the pathogens to infect plants. Much of the two sequences are identical, but by finding areas that differ, scientists can zero in on genes that may have evolved specifically to attack each organism's preferred victim. These genes are potential targets for fighting the diseases.
JGI is planning to sequence the genomes of two more closely related microbes, including the one responsible for potato blight. This will help narrow the list of potential target genes from thousands to hundreds and help scientists find the key to stopping the diseases.
"It's somewhere in those genes, but there are a lot of them," Boore said. "But it's not just a needle in a haystack, because now we know something about these genes."Inside Bay Area
