Wine aficionados sampling a Cabernet Sauvignon may be able to sniff out the vineyard that made it and the year it was bottled, but they can't pierce the hazy origins of one of the world's most coveted wine grapes. That was left to two geneticists, who report in next month's issue of Nature Genetics that they have solved the centuries-old mystery of Cabernet Sauvignon's pedigree.
Experts had thought that this deep red grape--which propelled Bordeaux, France, to worldwide fame in the 1800s--came from Spain, the Adriatic, or even Central Asia, and dated to the Roman Empire. But it turns out that the grape has a humble heritage: a relatively recent alliance between two common French grapes. Geneticists John Bowers and Carole Meredith of the University of California, Davis, stumbled upon Cabernet Sauvignon's motley past while building a database of genetic signatures of California's common grape cultivars. Their goal is to use DNA fingerprinting to identify grape varieties more accurately than is possible on the basis of the plants' physical characteristics. Accurate identification is very important in today's global wine markets, says Meredith.
The scientists had sequenced short strands of DNA in 30 discrete locations in the genomes of 50 grape cultivars. The more nucleic acids the sequences have in common, the more closely related two cultivars are. Bowers noticed that in Cabernet Sauvignon, the 30 sequences were the same as in two common cultivars, the white grape Sauvignon blanc and the red grape Cabernet franc. That suggests, says Meredith, that Cabernet Sauvignon arose as a cross between these two grapes in France--not some exotic locale--sometime before the 1800s.
"The genetic [data] are pretty convincing," says grape geneticist Bruce Reisch of the New York Agricultural Experiment Station in Geneva. "At last, we know there was a hybridization, possibly a chance cross" between Cabernet franc and Sauvignon blanc. That would also explain why Cabernet Sauvignon, when self-pollinated, sometimes produces white instead of red grapes.