Wine-grape genome cracked

Scientists may have cracked the genetic code of the wine grape, but don't hold your breath for that first bottle of "Double Helix Red."

After spending decades teaching consumers to savor familiar, often centuries-old grape varieties, wineries have little motivation to add an uncertain new variable to a crowded field of products.

"Wine-grape breeding is basically dead, because there's no interest in new varieties," said Andrew Walker, a professor of oenology and viticulture who specializes in plant breeding at the University of California, Davis.

A team of French and Italian scientists reported Sunday in the online version of the journal Nature that they'd sequenced the genome of the wine grape. The announcement marked the first full accounting of a fruit's genetic material and revealed tantalizing information about the link between a grapevine's DNA and the aromas and flavors of its grapes.

Researchers have completed genome sequences for only a handful of species, including fruit flies, humans and rice. In food crops, knowing the DNA code of a species gives researchers a jumping-off point for developing new varieties with desirable traits, such as resistance to drought or disease or, potentially, flavor and aroma. It can help to guide conventional breeding programs as well as the development of genetically engineered varieties.

But in the case of the wine grape, consumer recognition of traditional varieties is so high that winemakers are leery of taking a chance on something new, even if it was developed without controversial genetic engineering techniques.

"If it's not (an established variety), it's a tough sell," said Eric Aafedt, winemaker at Bogle Vineyards in Clarksburg. "If the wine was great, it'd still be a tough sell."

Grapevines are propagated by grafting a shoot from one plant onto the rootstock of another, producing a vine that is a clone of the plant that produced the shoot.

All the vines of a particular variety can be traced to a single common ancestor, said Carole Meredith, professor emeritus of oenology and viticulture at UC Davis and now a grape grower and winemaker in the Napa Valley.

The millions of cabernet sauvignon varieties grown around the world today, for instance, are all near-copies of a single vine grown in France several hundred years ago. Only the grapes from these clones can be sold as "cabernet sauvignon."

Plant breeders have, over the years, introduced new varieties of wine grapes developed by cross-pollinating one variety of grape with another. But there are few success stories.

The late UC Davis professor Harold Olmo developed several varieties starting in the late 1940s. But those grapes, such as emerald riesling and ruby cabernet, haven't become familiar to wine lovers. Developed mainly for heat-tolerance, they're generally planted in the San Joaquin Valley and made into low-end wines that aren't marketed as being made from any particular type of grape.

By contrast, new varieties of table grapes developed by Olmo and others were widely adopted, greatly expanding the crop's harvest season and geographic range.

If the genetic map of the wine grape is unlikely to lead quickly to new varieties of wine, Meredith said, that doesn't mean the study was for naught.

"I personally think that the biggest benefit is that it will allow us to better understand how grapes work," she said.

Learning what sorts of weather conditions or farming practices can "turn on" a certain gene linked to a floral aroma or susceptibility to a disease could help growers fine-tune the way they care for their crop.

"The benefits are really in understanding how grapes respond to different environments," she said.

About the writer:

• The Bee's Jim Downing can be reached at (916) 321-1065 or jdowning@sacbee.com.