Editors' Note: For digital images of Chardonnay, Pinot noir and Gouais blanc wine grapes, contact Patricia Bailey, firstname.lastname@example.org.
While sleuthing out the parentage of some of France's finest wine-grape varieties, researchers at the University of California, Davis, discovered that somewhere in the distant viticultural past, royalty mingled with a commoner.
It came as little surprise when DNA fingerprinting techniques revealed that 16 venerable wine-grape varieties, including Chardonnay, Aligote and Gamay noir, are the direct offspring of the classic Pinot variety. But even the researchers were surprised to find that the obscure Gouais (goo-WAY) blanc, a variety considered so mediocre that it is no longer planted in France, is the other half of the parental pair.
UC Davis professor Carole Meredith, an authority on genetic manipulation and analysis of grapevines, and John Bowers, a genetics doctoral candidate at the time the research was conducted, report their findings in the September 3 issue of the journal Science.
"Not only is this finding historically intriguing, but it also has very practical significance both for preserving old and for developing new grapevine varieties," Meredith said.
"We now know that you can conserve the entire gene pool of these 16 classic varieties just by keeping the Pinot and Gouais blanc varieties," she explained. "And we're reminded of the importance of crossing genetically diverse varieties to produce hardy offspring."
Meredith and her research group have been working for several years on genetically characterizing grape varieties so that California grape growers and vintners can be certain of which varieties they have. Two years ago, in the course of studying major wine-grape varieties maintained in the UC Davis vineyards, they discovered that the highly esteemed Cabernet Sauvignon wine grape is the offspring of the Cabernet franc and Sauvignon blanc varieties.
Expanding on that work, the researchers enlisted the collaboration of French colleagues Jean-Michel Boursiquot and Patrice This. After reviewing the historical French literature on wine grapes and taking into account previous speculation on variety origins, they chose 300 varieties from among the more than 2,000 maintained in a collection near Montpellier, France, by the Institut National de la Recherche Agronomique.
In France, Bowers took leaf samples from the 300 varieties, extracted DNA from them, and then returned to UC Davis where he used the DNA fingerprinting technique to generate a DNA profile for each variety.
For years, grapevine varieties have been identified by physical features of their leaves and fruit. But those traits can vary according to environmental conditions. In recent years, DNA fingerprinting, which compares characteristic patterns in the genetic material of a plant, animal or human, has proven to be a highly accurate way to identify grapevine varieties no matter where they are growing.
Bowers and Meredith first compared all the varieties at 17 distinct DNA sites known as "microsatellite" markers and looked for genetic evidence of close family relationships. Then they chose 60 varieties for more detailed comparisons.
Their analysis of these 60 varieties at 17 additional DNA marker sites revealed that 16 of them were probably the offspring of the same pair of parent varieties -- Pinot and Gouais blanc. A further statistical test, similar to that used to validate human DNA fingerprinting results, confirmed the very high probability that these two varieties were indeed the parents.
"We are more than 99.99 percent sure that Pinot and Gouais blanc are the original parents for these 16 varieties," Meredith said. "In other words, there is less than one chance in a trillion that we're wrong."
Some wine experts had suspected that there might be a genetic link between Pinot and Chardonnay, Meredith noted. Grown for centuries in northeastern France, Pinot is the noble red grape of the Burgundy and Champagne wine regions, and Chardonnay is its white counterpart, she said.
But Gouais blanc is quite another story. It was considered so mediocre as a wine grape that several unsuccessful attempts were made to ban it in the Middle Ages, and it is no longer planted in France. Because vineyard owners in the United States adopted only Europe's finest wine-grape varieties, Gouais blanc also is not grown in this country.
Even Gouais blanc's name, derived from the old French adjective "gou" -- a term of derision -- reveals its position of low esteem.
"It is surprising enough that Chardonnay has such a lowly parent, but that all 16 of these varieties, which include most all of the wine-grape varieties grown in northeastern France today, should have come from the same two parents is quite remarkable," Meredith said.
In addition to their disparate status, Pinot and gouais blanc are physically diverse. The highly productive Gouais blanc vine yields white grapes while the less productive Pinot bears bluish-purple grapes. (In the world of wine-grapes, high quality wines are thought to come from vines that produce relatively light crops of grapes.)
Interestingly, it may be the genetic differences between the two varieties that produced the strength and quality in their 16 offspring varieties.
"Gouais blanc and Pinot have been successful parents, perhaps because of their genetic diversity," Meredith said.
Identification of the two parent grapevine varieties provides useful information to grape breeders, she added.
"We now know that you'd never want to cross Chardonnay and Pinot, because you would be more likely to get genetically weak progeny, similar to the inbreeding problems that occur when closely related people marry," she explained, "And, it's very instructive to know that Gouais blanc can produce wine-grape varieties as fine as Chardonnay."
This study was funded by the American Vineyard Foundation and the California Department of Agriculture's Fruit Tree, Nut Tree and Grapevine Improvement Advisory Board.