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Since the discovery five years ago that a ravenous insect was spreading
grape-killing Pierce's Disease in California, grape growers have contributed
millions of dollars to fund research projects they hope can end the scourge,
August 2004 by Daisy Nguyen.
One project at the University of California, Riverside involves
introducing genetically altered bacteria into the plant. When the bug -
known as the glassy-winged sharpshooter - eats the material, it neutralizes
the pathogen that causes the disease.
The technique, however, alarms environmentalists opposed to using
genetically modified organisms, or GMOs, in nature.
In addition, some grape growers are concerned that even a slight change to
plants would taint classic grape varieties - Merlot, Chardonnay, Pinot Noir,
for example - that are prized by wine lovers.
"Growers say it's a marketing issue," said Ray Van Rein, a spokesman for the
California Department of Food and Agriculture Pierce's Disease Control
Program. "Even if the solution becomes available in the lab, it won't make
it into the field unless consumers find it palatable."
A major outbreak of Pierce's Disease was detected in 1999 when vineyards in
Temecula in San Diego County showed yellowing leaves and shriveled young
The culprit was determined to be the sharpshooter, a half-inch flying insect
that can suck up and excrete about 30 times its body weight in fluid from a
Since then, sharpshooter infestations have decimated vineyards elsewhere in
Southern California but have been found in just a few spots in the northern
part of the state.
In June, however, alarms sounded when a colony of the insects was discovered
in Vacaville, about 30 miles from Napa Valley, the heart of California wine
If left unchecked, the sharpshooter could cause major damage to California's
880,000 acres of grape vines and paralyze the $2.3 billion grape industry -
the state's second-largest agriculture commodity behind dairy.
"It's put the fear of God in us," said Ben Drake, who grows and manages
vineyards in Temecula.
Before the infestation, the region had 2,500 acres of vines, Drake said.
That number has since been reduced to 1,800.
Pierce's Disease is caused by a bacterium known as Xylella fastidiosa, which
sharpshooters spread as they feed. The bacteria infects and kills plants by
clogging the vessels that carry water and nutrients.
At UC Riverside, a research group led by Thomas A. Miller has isolated
another bacteria found inside the sharpshooter, called Alcaligenes, and is
genetically altering it.
In the technique called "symbiotic control," scientists inject the altered
bacterium into a plant. When the sharpshooter feeds on it, the bacterium can
kill Xylella, said Miller, an entomology professor.
"The way I envision it, it gives a grower a tool with which he can protect
the plant," he said.
The Environmental Protection Agency, which regulates most microorganisms,
has granted Miller permits to experiment outdoors. So far, he said
cautiously, his team of researchers have seen promising results.
"We've been warned by our sponsors not to be too enthusiastic too soon
because agriculture industries are plagued with false hopes all the time,"
So far, the field tests have shown that altered Alcaligenes injected into
plants were not detected in grapes or soil. Still, Miller concedes a lot
more research needs to be done, and it will take time for the public to get
used to the idea.
In a review of research projects targeting Pierce's Disease, the National
Research Council of the National Academies concluded that such transgenic
approaches may be a long-term, expensive strategy.
Although scientifically appealing, the report said, regulatory and legal
hurdles along with public resistance to the release of GMOs would have to be
Meanwhile, state agriculture officials and growers are settling on a
combination of tactics to fight sharpshooters, including using pesticides
and releasing natural enemies.
Drake, the grower who also chairs the California Association of Winegrape
Growers, has donated some vineyards for Miller to conduct his field test.
"I feel the research needs to go forward, and I think that as we move
forward, at some point the industry has to address GMOs and everything else
going on," Drake said.
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