12.29.2011  
 

Fight Against Vineyard Foe Near End?

Promising research presented at symposium on Pierce's disease and glassy-winged sharpshooter

 
by Andrew Adams
 
pierce's disease glassy-winged sharpshooter
 
Attendees at the recent Pierce's disease and glassy-winged sharpshooter research symposium held in Sacramento examined and discussed research projects into the disease and its vector.
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Sacramento, Calif.—After a decade of research, millions of dollars and the death of more than a few good vines, the battle against Pierce’s disease and its vector the glassy-winged sharpshooter carries on, but the end may be in sight.

Once dreaded as the harbinger of a California winegrape industry apocalypse, the GWSS and PD have been effectively managed; research is now close to perfecting methods to treat PD and cultivate plants resistant to the disease.

PD has been present in California since the 1800s, but when the invasive GWSS arrived in the late 1990s, it created the potential for a devastating spread of PD, decimating Temecula vineyards.

More than 100 researchers gathered in Sacramento from Dec. 13 to 15 to discuss their current research into PD and the glassy-winged sharpshooter.

Dr. Andy Walker of the University of California, Davis, presented results on his work breeding PD-resistant Vitis vinifera vines. These vines have been bred to contain the PD resistant gene PdR1.

In the spring of 2010, Walker and his team planted 2,000 seedlings that were 97% vinifera. In September 2011, Walker evaluated fruit from 1,200 of these vines and even made a small-scale wine from one. The next step will be to determine which of the vines have the best potential for field testing.

Harvest results
According to results published after the symposium, the PD-resistant vine with 97% vinifera yielded fruit harvested at 25.1º Brix, 5.0 TA and 3.67 pH. Juice had an orange hue, and its flavor was described as “fruity, red apple.” In his conclusions, Walker said “strong progress” has been made breeding PD-resistant winegrapes, and he plans to combine multiple resistant sources to broaden overall resistance to the disease.

Jay Van Rein, a spokesman with the California Department
of Food and Agriculture’s PD Control Program, said it’s exciting to hear that research is getting ever closer to finding solutions to PD. “Researchers have really gotten to the point now were they’re focused on real possibilities to finding a solution to Pierce’s disease,” he said.

Success in the lab has been complemented with efforts in the field to contain the GWSS to mainly southern California. Van Rein said the efforts to control the pest have provided a model to deal with other destructive invasive bugs such as the Asian citrus psyllid and the European grapevine moth.

The California PD control program began in 2001, when the state’s winegrape growers voted to impose an assessment on their grapes to fund the fight against the pest. The assessment provided nearly $20 million to fight PD in the past year, and growers voted in 2010 to extend it until 2016.

Fight must continue
Despite the vote, there’s a sense that some in the industry feel the problem has been nullified. “I know there are some people out there with a sense of complacency, but that is not a good thing,” said Pete Downs, a member of the board overseeing the state’s fight against PD. “I don’t want to seem like an alarmist, but this thing has not gone away.”

Downs, who is also the senior vice president of external affairs for Jackson Family Wines, said that while efforts to contain and control PD have been successful, there’s far more work to be done to find ways ultimately to beat the problem.

Downs spent a day at the symposium and said he was impressed by the level of detail and focus in the most current research. He recalled that in earlier days when the problem first emerged, the goal was just to get a handle on it.

Now, he said, it’s reached an almost esoteric level of highly focused research endeavors. Research projects at the symposium covered the Pierce’s disease pathogen, Xylella fastidiosa; the biology and ecology of the GWSS; efforts to manage the sharpshooter; fighting the disease, and efforts to breed crops resistant to PD.

Many of the researchers presenting their work at the symposium came from universities in the United States, but a team from Brazil presented an abstract of research into using the substance N-acetyl-L-cysteine, or NAC, to break up the biofilm that clogs vine xylem and leads to a plant’s ultimate demise from PD. The researchers found that doses of NAC in infected vines did lead to some reduction of symptoms and improved xylem functionality.

More progress
Other research included:

• A report on GWSS management areas in the Coachella and Temecula valleys in California found that the population of the pest has continued to decrease because of trapping and insecticide treatment on citrus groves near vineyards. In 2008, researchers trapped a high of 2,400 GWSS during a week in mid-July; this fell to fewer than 100 for the same period in 2011. The same trend held true for Coachella Valley. Temecula and Riverside counties are considered “ground zero” for the PD and GWSS problem. A 2001 economic study found the counties suffered nearly $40 million in lost winegrape production in 1988 and 1989.

• A team from the University of Texas and the United States Department of Agriculture studied propagating cell structures of the glassy-winged sharpshooter to serve as a vector for a virus that could serve as a biological control of the pest.

• Chardonnay grafted onto Dog Ridge rootstock in areas of Texas with a high level of PD vectors yielded the highest weight of dormant prunings in a study conducted by the USDA. The USDA studied five rootstocks: Florilush, Freedom, Lenoir, Tampa and Dog Ridge; the Dog Ridge yielded almost 2:1 the weight of prunings compared to the other stocks.

• UC Davis researchers presented work on engineering rootstocks with mutli-component transgenic resistance to PD. The focus of the work is on rootstocks 101-14 and 1103-P; researches hope to modify these stocks so that they can pass along proteins and help make scions more resistant to PD.

• By studying how Xylella fastidiosa is transmitted, a team of scientists from University of California, Berkeley, and the University of Florida found there is the potential to block transmission from pathogen to vector at a cellular level. This could lead to control efforts not aimed at killing the vector or pathogen.

To review the entire proceedings of the 2011 Pierce’s Disease Research Symposium visit: cdfa.ca.gov/pdcp.

(Wines & Vines columnist Cliff Ohmart attended the PD symposium and will provide an in-depth look a the research presented at the symposium in a coming edition of the magazine.)

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