By Sharon Omahen
University of Georgia

Bobby Scott Jr. had two choices. He could yank up his grape
vines
or watch as Pierce’s disease ate through his earnings.

He chose option three.

When the Aiken, S.C., wine grape grower called University of
Georgia professor C.J. Chang, he needed hope, help and answers.
“Pierce’s disease is the major limiting factor for the success of
the wine industry in the southern United States,” Chang said.

Replace or import

Within two to four years of contracting the disease, most
grape
vines originating from Europe die, he said. To fight the disease,
wine grape growers must either replant vines periodically to
replace the diseased vines or import grapes from other regions to
keep their businesses going.

Since the early 1980s, Chang has been searching for a way to
control Xylella fastidiosa. The bacterium is associated
with
three major crop diseases in Georgia: Pierce’s disease of grapes,
phony peach disease and plum leaf scald.

When Scott contacted Chang, he was running out of options. No
plant pathologists in South Carolina were studying Pierce’s
disease. He turned to Chang in desperation.

Since that first phone call, the two have developed a
partnership
in the fight against Xylella fastidiosa. Scott has been
crossbreeding European grape varieties with bunch grape-muscadine
hybrids resistant to Xylella fastidiosa. To date, he’s
bred
thousands of young seedlings. Oddly enough, he needed Chang to
inoculate the fledgling vines with the bacterium.

Breeding for resistance

“I start in the greenhouse with the new crosses,” Scott said.
“Then they have to be inoculated so we can see how many
survive.”

Scott then plants the new potentially-tolerant vines in the
field. Many of his crosses don’t survive to live outside the
greenhouse and many die in the field.

“We lose a lot of crosses along the way, but I know eventually
we’re gonna be successful,” he said. “I feel good about the
progress we’re making. But it’s taking a little longer than I
had hoped.”

Scott now has 3,000 Pierce’s disease-tolerant vines in his
family’s Montmorenci Vineyard. Vineifier grapes are used to
introduce good quality wine genes.

“We both acknowledge that as long as we work hard, the fruit
of
our labor will be tolerant wine grapes for the Southern region,”
Chang said.

Besides breeding disease-tolerant grape varieties, UGA
researchers have been searching for other ways to control the
bacterium. In 1979, scientists found it can be slowed down by
tetracycline treatments. The find turned out to be a breakthrough
in controlling diseases caused by Xylella
fastidiosa.

Tetracycline successfully suppressed the symptoms of plum leaf
scald disease and oak leaf scorch. But researchers hit a snag
when it came to using it on food-bearing crops.

“Unfortunately, EPA frowned on the use of tetracycline as a
control method,” Chang said. “They were concerned over the
environmental hazards, and they think it could produce a bug
that’s resistant to tetracycline. So we can use it on trees like
oaks and sycamores, but not on food crops.”

Plant-derived control

Undeterred, Chang set out to find a plant-derived compound for
control. His answer came in a product called terpene, developed
by the Eden Research of Oxfordshire, U.K.

Scott is allowing Chang to test these potential control
methods
in his vineyard. More than 500 test-plot wine grapes are now part
of Scott’s 20 acres of wine grapes.

The terpene solution is being fed to the grapevines through
the
vineyard’s drip irrigation system. Comparing the treatment to
untreated control vines, the grower is seeing dramatic results.
The treated vines are thriving while the untreated are suffering
the effects of the disease.

Chang is now working to develop a strategy to put in place in
case wine-grape growers in north Georgia begin to see disease
symptoms. Time is on the side of Georgia growers as the disease
spreads slowly at higher elevations.

“The disease spreads slowly in vineyards that are 1,600 to
1,800
feet or more above sea level,” Chang said. “There are some
resistant muscadine and American wild grape hybrids available,
but relying on these flavors alone limits marketability for
Southern growers.”

As Chang and Scott work to develop ways to fight Pierce’s
disease
in grapes, growers wait.

“Until we can control it, our county agents are recommending
that
growers yank out the diseased vines,” Chang said. “It sounds
harsh, but right now it’s the most effective control around.”