Even the best grape breeders face a tough challenge: the skepticism toward new varieties among many winemakers and consumers who share a centuries-old preference for Vitis viniferia grapes. 

But cross-breeding for new varieties offers genetic solutions to pest and disease management, extreme cold and climate changes — potentially reducing spray bills, replanting costs and other losses. That’s why the University of California, Davis sees strong market potential for its five new disease-resistant cultivars released late last year.

Five new varieties released by the University of California, Davis offer resistance to Pierce’s disease and high wine quality with characteristics of popular cultivars. Top row, left to right, are Camminare Noir, Errante Noir and Paseante Noir. Bottom row, left to right, are Ambulo Blanc and Caminante Blanc. (Photos Courtesy of  University of California, Davis)
Five new varieties released by the University of California, Davis offer resistance to Pierce’s disease and high wine quality with characteristics of popular cultivars. Top row, left to right, are Camminare Noir, Errante Noir and Paseante Noir. Bottom row, left to right, are Ambulo Blanc and Caminante Blanc. (Photos Courtesy of University of California, Davis)

“We took the easy way out, which is to work on one of the worst diseases out there,” grape breeder Andy Walker said. “Pierce’s disease is intense. It’s one of the few diseases that kills grapevines quickly.”

Caused by the bacterium Xylella fastidiosa and spread by insects called sharpshooters, which are commonly found along rivers and creeks, Pierce’s disease infects xylem vessels in plants, disrupting the flow of water and minerals.

Management of the disease costs California growers $100 million a year, according to UC Davis economists. In the Southern U.S., it limits the wine industry to only disease-tolerant hybrids that carry more character of the native North American grapes that evolved with the pathogen, rather than the particularly susceptible European wine grape varieties.

Walker, also a professor of genetics, started his breeding program looking for the best resistance genes in the Vitis genus. He found it in Vitis arizonica,from Northern Mexico. Initially, he intended to use it to cross-breed with table grapes when that industry was hit hard by Pierce’s disease in the San Joaquin Valley in the early ’90s. But then the wine industry funded his work, so he turned his attention to wine grapes. Twenty years later, the final cultivars still have some fruity notes from those early table grape parents, Walker said. 

“We knew two things right off the bat: We knew resistance was the most important thing, extreme resistance so these things didn’t act as a host, and we knew the wine quality would be poor until we got very far along into the process,” Walker said. “The reason people were not successful (in past breeding programs) is that they were making wine every generation.” 

Instead, after four or five generations of crossing with V. vinifera parents and simply selecting for the offspring that still carried the resistance gene, Walker steered the direction of the wine style with the final parents. The final varieties released for commercial use are genetically 97 percent V. vinifera.

“The obnoxious American species’ characters, those start going away at 88 percent, and by 97 percent they are clean of all those,” Walker said. “We want high quality and high resistance at the same time.”

The final couple of crosses were designed to give each new selection wine characters similar to popular cultivars: Camminare Noir carries the character of Cabernet Sauvignon and Petite Sirah; Paseante Noir has a Zinfandel parent; Errante Noir blends well with Cabernet Sauvignon; Ambulo Blanc is reminiscent of Sauvignon Blanc; and Caminante Blanc offers characteristics of Sauvignon Blanc and Chardonnay. 

“We selected them in that way to fit needs,” Walker said. “If you tasted Ambulo Blanc in a panel, you’d call it Sauvignon Blanc.”

He expects California winemakers will predominantly use the cultivars in blends, and due to the federal 75/25 regulation that requires a wine be at least 75 percent of the listed varietal, there’s a lot of room for these new grapes to come into play. 

Doug Fletcher, a wine and vineyard consultant and former vice president of winemaking for the Terlato Wine Group, planted two of the new cultivars, Caminante Blanc and Errante Noir. He said the future for marketing the grapes is probably in blends or wineries’ proprietary branding.

“We didn’t really have Pierce’s disease issues, I just loved the varieties,” Fletcher said. “The first time I went to taste the fruit, probably five or six years ago, I remember being surprised that it tasted so good.”

Adam Tolmach, the owner of The Ojai Vineyard in Southern California, made wine for the first time this year from four of the new cultivars. 

“It’s been a thrill” starting to get to know them, he said, but he’s still thinking about how he might market them, perhaps under a whimsical brand name, rather than as an unknown new varietal.

“These taste like European grape varieties. That’s the great step forward,” Tolmach said. “We make red and white blends, so they can always go there. But I think they have more promise than that.” 

The lack of cold winter weather in Southern California means more sharpshooter pressure, Tolmach said, a risk that could be more common elsewhere in California, as the climate warms.

“In the last five or 10 years, when there are major problems with Pierce’s disease there (in northern Santa Barbara County) it appears to be associated with really mild winters,” he said. “It’s amazing to be able to grow grapes here and not spray a lot.”

In the Southern U.S., where Pierce’s disease pressure has limited vineyard production, the new varieties could also create new opportunities for wineries and wine tourism, Walker said.

A limited amount of planting material should be available for propagation this year, but it remains to be seen how much the industry will embrace the new varieties and plant them, Walker said. More cultivars from the program are in the final stages of evaluation, as well.

Like the five recent releases, all the selections in the program carry PDR1 – the powerful Pierce’s disease resistance from V. arizonica. Researchers don’t know exactly how it works, but it’s consistent across many wild accessions. Genetic markers can help select for this trait, Walker said, and help the breeding program weed out seedlings faster, but ultimately, he’s selecting based on the phenotype — all the traits the plants express.

Genetic markers matter the most for breeders who want to layer resistance genes, Walker said — one of the next goals for his program. Layering in Pierce’s disease resistance traits from other grape species will provide extra insurance against pathogen evolution.

Another target: powdery mildew. Walker hopes the breeding program eventually will incorporate resistance to both diseases into the same varieties. 

That will be up to the next breeder, Walker said, as he is nearing retirement. But he’s optimistic that the wine industry is nearing a turning point where it will be ready to accept more new cultivars bred to reduce disease pressure, reduce pesticide use and make great wine.

“The only good thing about climate change is that it’s going to force a radical re-evaluation of viticulture,” he said, breaking down the varietal traditions by region for more experimentation and greater use of genetic diversity to solve viticulture challenges. “The floodgates need to open so they realize we need to be looking at a wider variety of wine varieties. … We have all the tools we need to solve virtually all the grape disease problems through classical breeding and hard work.” •

by Kate Prengaman