J. Lohr Vineyards & Wines grows most of their white grapes in California’s Monterey County, which has a cooler, moister environment than their vineyards in Paso Robles, where they grow their reds. Because powdery mildew is more active in humid areas with lower temperatures, they spray the vines in Monterey County 10 to 11 times every season, according to Anji Perry, the viticulturist and vineyard research director at J. Lohr. The Paso Robles vines, in contrast, are only sprayed 3 to 4 times. “In many years, powdery mildew is the only thing we spray for,” says Perry. “It’s our biggest pest for sure.”
Powdery mildew comes from a fungus called Erysiphe necator that’s native to eastern North America. While America’s native grape species have developed some resistance, Vitis vinifera have not. Particularly vulnerable are some of the world’s most popular varieties, including Chardonnay, Riesling, Cabernet Sauvignon, and Sauvignon Blanc.
The disease’s impact on the grape industry, both financially and environmentally, is significant; it’s the reason for the majority of its pesticide use. As a result, the industry has invested considerable resources into finding more effective ways to combat it. Now, new research is offering a ray of hope for mildew-fighters everywhere. The VitisGen research collaboration, a grape breeding project now in its third iteration, is working on a disease-resistant ‘SuperGrape.’
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“If they could take a Chardonnay plant and breed it so that it’s still Chardonnay but has powdery mildew resistance, then that’s a game changer for our industry,” says Perry. “They’re not there yet, but that would be the hope.”
Editing Grape Genomes
After creating genetic maps for more than 20 Vitis families during the VitisGen2 project, researchers working on VitisGen3 are now using the data to choose and test candidate genes that are responsible for mildew resistance. Using gene-editing technologies like CRISPR, the researchers will remove those candidate genes and insert them into other grapevines, and then test them against powdery mildew to see how they respond. The goal is to better understand the genes’ functions, similarities, and differences, which will allow them to isolate favorable characteristics—and possibly lead to a super-resistant SuperGrape.
This SuperGrape research could then be used to help breeders develop a grapevine that’s disease resistant, and not only to powdery mildew. Then, those susceptible-but-popular grapes could possibly be tweaked to be more resistant to a variety of things.
The goal isn’t to create new grape varieties through gene-editing—although that technically could be done through this process, says Matthew Clark, an associate professor in horticultural science at the University of Minnesota, and the project director of VitisGen3. The idea is to see if there are common regulatory mechanisms, he says. “We really want to understand the fundamental biology of how these genes work, because that’ll give us better clues of which ones to stack in the future and how to find more of them and understand their function,” says Clark.
Donnell Brown, the president of the National Grape Research Alliance, is impressed by the speed with which the VitisGen program has completed the gene research; it’s the only project of this scale that’s achieved this much in the United States, she says. But she’s particularly excited about the potential of the SuperGrape. If there’s a genetic defense mechanism that flips on when menaced with a threat like powdery mildew, that would be a remarkable tool, she says. “If there’s a common regulator for the way that those genes turn off and on, could you develop a grapevine that was resistant to almost anything?”
The SuperGrape research is based on the previous two iterations of VitisGen, where researchers were able to “stack” the plant material with several mildew-resistant genes—in some cases, up to six—that can fight off the fungus. That’s because a single form of resistance isn’t enough; diseases like Erysiphe necator can evolve and outpace treatments faster than they can be developed. Budwood cuttings from those vines were sent to the University of California, Davis’ Foundation Plant Services, where they’re being propagated. They should be ready as soon as this winter, says director Maher Al Rwahnih, and they’ll be available for breeders who want to incorporate resistance into their breeding programs, or develop completely new mildew-resistant hybrid varieties.
Maintaining Varietal Character
The SuperGrape research, however, wouldn’t create hybrids; any gene-edited variety remains the same grape, although it may be labeled to reflect that it’s been edited, explains Clark, since policy makers and consumers seem to have a preference for that delineation.
Kevin Corliss, the vice president of vineyards at Ste. Michelle Wine Estates in Woodinville, Washington, agrees. “Through the CRISPR process, if you’re only making small changes that protect the flavor and the growth habit, then a Chardonnay would still be a Chardonnay,” he says.
Like J. Lohr, Ste. Michelle Wine Estates spends significant resources spraying for powdery mildew. Corliss says they spray susceptible varieties like Chardonnay every two to three weeks, from six to nine inches of shoot growth until berry softening. “For all the grapes that we touch in Washington, Oregon, and California, powdery mildew is the number one disease in terms of lost fruiting, and the number one that we spend time and money protecting against,” says Corliss.
Bigger gene edits would impact what ends up in the glass, however. “Things will really change if you alter the color, the size of the berries, or the size of the canopy. In that case you’re likely to change the character of the resulting wine,” he says.
Labeled or not, the results of this research will be important to the future of wine, says Brown. She thinks consumers will have to accept gene-edited vinifera varieties eventually simply because of climate change. “That’s the only way they’re going to have Cabernet Sauvignon in 50 years,” she says.
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Danielle Beurteaux is a writer whose work has appeared in many outlets, including The New York Times, Eos, Scientific American, and Wine Enthusiast. She also has a Level 2 WSET Award in Wines.