Pierce’s Disease-Resistant Grapes Coming Soon

Researchers trial Pierce's disease-resistant grapes. Photo: Dan Ng

Researchers trial Pierce’s disease-resistant grapes.
Photo: Dan Ng

The University of California estimates Pierce’s disease (PD) costs the state $104 million per year. But, the disease could soon meet its match with the release of new, PD-resistant grape varieties.

About 20 years ago, researchers began looking at different species to see which were most resistant to the Xylella fastidiosa bacteria that cause the disease, according to Andy Walker, Professor in the Department of Viticulture and Enology at the University of California, Davis.  They found some forms of Vitis arizonica offered good resistance, which was controlled by a single gene.

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“When we crossed vinifera – cultivated wine grapes and table grapes – to that source, they were fully resistant,” Walker says.

In the 20 years since then, researchers have been working to perfect these varieties. Walker says they’ve whittled it down from about 4,000 to 5,000 seedlings to just a handful of highly resistant plants. He adds that all the work has been done through classical breeding, so there’s no GMO component involved.

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So far, the wines have shown promise, rating highly in student, faculty, and industry tastings.

“We’re getting very close to release now,” Walker says. “We’ve got about five selections to start with, and then maybe another five that come over time.”

These new varieties don’t have catchy names just yet, and commercialization is still a ways off. The varieties have to go through two campus committees, then Foundation Plant Services, which releases them to the nurseries. Those nurseries then have to decide if they want to grow them.

Some nurseries have already been actively supplying plant material to Texas and other areas in the south, where they anticipate a high demand.

“We’re considering a pre-release program where we get them into the nurseries before they’re fully ready to be commercialized, and then out from there,” Walker says. “We’re trying to optimize things as much as possible.”

Still, he estimates it will be at least two years and could be as many as five years before the varieties will be readily available to growers. “It will be a slow process,” he says.

Ultimately, though, these new varieties will give growers one more tool to address PD. Walker says there are some large trials currently underway at wineries along the Napa River, which will help determine how well the grapes will work on a commercial scale.

And although the current resistant varieties are showing great promise, Walker and his colleagues are already working to stay one step ahead of PD.

“There’s the worry that a single gene is not enough in terms of longevity and durability over a decade, so we have other forms of resistance that we’re working on,” he says.

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