Grape Vine Researchers Works Magic with Vaccines

Researcher Caroline Roper turned a potted grape vine onto its side and treated the stem with a clear liquid intended to protect it from the ravages of Pierce's disease.

Her work is part of promising vaccine trials being funded by growers through millions of dollars in self-imposed fees targeting the disease that nearly wiped out a major California wine region and has stifled wine industries in several other states.

Growers in Florida and Texas are eagerly watching the results of the trials and other experiments with the hope that they might soon be able to grow their own cabernets, pinots and other European varietals.

"We're finally getting to the point where we're seeing some results," said Ben Drake, a grower in the Temecula Valley area of Southern California, where Pierce's disease destroyed more than 2,000 acres of grapes a decade ago.

The region is making a comeback but about 1,000 acres have yet to be returned to production.

Since the outbreak, the state and federal governments have been spending a combined $21 million a year to control its spread.

Among other things, the money pays for spraying insecticides in the Central Valley to keep the glassy-winged sharpshooter -- the insect that spreads the disease -- from moving farther north and wreaking havoc on wine country in Napa and Sonoma counties.

Many growers, however, say research, not pesticide, is the best solution.

"You can eliminate 95 percent of the insect vector, but that 5 percent that's still left is enough to efficiently spread the disease," said Roper, a professor at the University of California, Riverside. "You can never get rid of all the sharpshooters."

Drake said he would prefer a vaccine to more widespread use of pesticides.

"I'd like to be an organic vineyard grower," he said "But I can't because I've got to use something to keep my vines alive until I come up with another solution."

Drake lost about half of the 400 acres he farmed himself or managed for others in the 1999-2000 outbreak in Temecula Valley.

The devastation prompted growers to levy the assessment on themselves in 2001. It has raised about $4 million a year since then, with growers paying as much as $3 for every $1,000 in grapes they produce.

Other research bankrolled by the funding involves crossbreeding classic European varietals with disease-resistant native grapes and an attempt to keep the bacteria that causes Pierce's disease from becoming virulent.
However, with few recent outbreaks and years of experimentation still needed to verify the results of research, some worry that growers might discontinue the fees when the issue comes up for reconsideration next year.

"I just don't want to see complacency," said Bob Wynn, head of California Department of Food and Agriculture's Pierce's Disease Control Program.
The disease was first discovered in the state in the 1880s. But it wasn't considered a real threat until the early 1990s, when the glassy-winged sharpshooter first appeared in California to spread it.

Grape vines inoculated as part of the vaccine study have resisted Pierce's disease in greenhouse tests and field trials in Florida, but it will be a few more years before its effectiveness can be proven in California vineyards.

Test plots have been planted in Temecula, Napa and Sonoma over the past year as part of the ongoing testing.

Meanwhile, researchers at the University of California, Davis are using genetic mapping to identify genes in a native grape variety that are resistant to Pierce's disease.

By crossing those native types with traditional varietals and testing for resistant genes in young seedlings, researchers have been able to establish a line of plants with 97 percent resistance to the disease.

The researchers' next step is to winnow that line of highly resistant grapes into the best-tasting strains for wine, UC Davis genetics professor Andrew Walker said.

Another group of researchers at the University of California, Berkeley, is seeking to capitalize on a characteristic of the Pierce's disease bacteria that keeps it from turning deadly if it senses the host plant has already been infected.

UC Berkeley plant pathology professor Steven Lindow's team is preparing its first field tests of the method, which has held off infection in greenhouse trials.

"Either it could work much better or much worse than in a greenhouse," he said. "Hopefully in a few months we'll have an answer."

Copyright AP - Associated Press
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