It's been more than a decade since the last major outbreak of Pierce's disease devastated grapevines in California, but visions of glassy-winged sharpshooters, the insects that carry the bacteria that cause the disease, still dance like nightmares in every grapegrower's head. Xylella fastidiosa bacteria damage a vine's vascular systems, preventing water intake and killing a vine within a few years.
Nine years ago, the industry began taxing itself to pay for research to fight the scourge, and in February those efforts produced some promising results: By using genes from humans and insects, scientists created a hybrid gene that can identify the bacteria and kill it, ridding the vine of Pierce's disease before infection. The team inserted the hybrid gene into grapevines, and sap from those vines killed the bacteria in a lab test.
“Due to the synergy of the two functions, you can recognize a pathogen and clear it instantly,” said Goutam Gupta of the Los Alamos National Laboratory, which worked on the program with researchers from the University of California at Davis and the U.S. Department of Agriculture. “This approach is altogether new. We are merely tinkering with the plant's defense system to empower the plant to clear the bacteria.” The work will hopefully become a “platform technology,” said Gupta, which means it could be used in other industries where the bacteria is a problem, including citrus, almonds, oleander, and peaches.
Steve McIntyre, who owns Monterey County's McIntyre Vineyards and sits on the Pierce's disease board that helped pay for the study, was excited by this latest round of news. “If this stuff pans out in the field as we hope it will, it will become platform technologies for other diseases," said McIntyre. But he was also hesitant. “It's a little early to declare victory unfortunately,” he said.
The biggest hurdle may not be in the science, however, but in wine customers' perception of genetically modified organisms (GMO). “If consumers have the choice, they're not gonna buy Frankenwine,” said Adam Tolmach of Ojai Vineyard, who lost his 5.5-acre Syrah vineyard to Pierce's disease in the mid-1990s. “They're just going to prefer to buy something that's not a GMO project.”
Luckily for Tolmach, who would like to replant grapes on the property that his grandfather bought in 1933, there are other possible solutions in the works. “People have been breeding P.D.-resistant grapes in Florida, Georgia and Louisiana for 300 years,” said U.C. Davis professor Andy Walker. “They're just not very good.” So Walker has been blending those resistant species, such as Muscadine, with classical Vitis vinifera grape varieties, and expects that growers will one day plant the successful offspring in vineyards that are closest to areas where glassy-winged sharpshooters congregate.
But his work presents a different sort of customer relations problem. “People will have to accept the fact that these are new varieties,” said Walker, as the mixed breeds won't be true Cabernet Sauvignons or Chardonnays, but new hybrids. “What do you name them? Can they be Chardonnay Nouvelle? It's probably best to ask the marketing department what to do about that.” Walker was proud to say that he'd been able to make quality wine from vines that were 94 percent vinifera, and is now waiting for grapes to come in from a 97 percent vinifera hybrid.
And there's a few other cures being worked on too, including a spray that could be applied to grapevines that would scramble communication between the bacterium and suppress the disease. “There's a tremendous amount of really cool stuff on the horizon,” said McIntyre, who, like every other grapegrower in California, contributes 75 cents per $1,000 of grapes sold to Pierce's disease research. “But we've got to be careful that we sort out all of the pitfalls.”