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Grape Researcher Breeds Vines Resistant to Pierce's Disease

Vinifera vines crossbred with resistant American species may someday yield good-tasting wines, but are better for blending for now

Lynn Alley

Posted: Friday, April 06, 2007

A live, adult glassy-winged sharpshooter, an insect that carries the grapevine-killing Pierce's disease, was discovered in Napa for the first time ever this spring. Thus far, the only protection for grapegrowers and agriculture officials has been a strict inspection program, but grape breeders at the University of California Davis hope they're close to offering an alternative: grapevines resistant to Pierce's disease.

UC Davis professor Andrew Walker, a grape breeder, focused primarily on breeding disease-resistant rootstocks in the past. But in his recent work, with the help of funding from the California Department of Food and Agriculture, Walker used wild American grape varieties--all of which are resistant to Pierce's disease in varying degrees--to breed a group of eight new vines (four red, four white), with high resistance to Pierce's disease.

"The goal is to make a high quality vinifera wine grape that's highly resistant to Pierce's disease and that you could blend into vinifera [juice]," explained Walker. "These grapes will be high quality blending grapes. In fact, they would make good wine in themselves, but marketing would be a problem."

The reason is that the new resistant vines don't have names anyone would recognize. The new vines are true hybrid varieties, meaning they carry the genetic code of the many grape varieties that were used in their breeding. Walker stressed that the new vines are not so-called "genetically modified," but are vines bred by painstakingly hand-pollinating one vine variety with pollen from another. Although both Chardonnay and Syrah were used in the breeding of the new vines, there is no resistant Chardonnay, Cabernet Sauvignon or Syrah. But it's a step in the right direction.

Although attempts to breed vines resistant to Pierce's disease are nothing new, this is the first hint of some success. In the 1930s, Harold Olmo, Walker's predecessor, maintained an experimental vineyard in what is now Hollywood, Calif., devoted to developing resistant vines. While Olmo, Walker and others have managed to breed vines resistant to the disease over the years, they've failed to do so without affecting the flavors and aromas of the resulting wines. Few native American vine species produce good-tasting grapes, but they are the ones that are resistant to Pierce's disease.

Walker envisions growers planting the new vines in areas that have been plagued by Pierce's disease in the past, such as along stream banks and around the periphery of their vineyards, then blending their fruit into the wines made from traditional grape varieties.

Walker's new vines are 87.5 percent vinifera, which Walker believes will yield a "good batch of wine." Come September, he'll find out just how good. Walker and his team will make wine from the small quantities of fruit yielded by the new vines, and put them to a taste test. If all goes well, the new vines could conceivably be released to growers within the next couple of years.

"If there is something good in there, I'm going to release it simply because we need something right now," said Walker.

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