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SNP Study Squeezes French Wine Clues From Ancient Grape Seeds

SAN DIEGO (GenomeWeb) – A genetic study encompassing more than two dozen archeological seeds from grapevine (Vitis vinifera) hints that a domesticated wine cultivar currently grown in France has been propagated in the region for a millennium or more.

At the annual Plant and Animal Genome meeting here this weekend, Jazmin Ramos Madrigal, an evolutionary genomics researcher and research assistant with the University of Copenhagen's Natural History Museum of Denmark, presented preliminary findings for a study of grape seeds at sites in France that were dated to the Iron Age, Roman Period, or Medieval Period at sites in France.

As Madrigal reported during a session on Degraded DNA and Paleogenomics, the team targeted 10,000 SNPs in the ancient grape seed samples, focusing on selected variants expected to provide informative information about the grape cultivars.

From these genetic data, the researchers determined that the ancient seeds came from plants in the cultivated V. vinifera sub-species vinifera, for example, rather than the wild sub-species sylvestris. Moreover, these domesticated grape plants were genetically closer to the wine-making grapes of today than to so-called table grapes for munching. 

When the team compared SNPs in the ancient seed set to variants found in hundreds of wild grapes or modern domesticated varieties contained in the GrapeReSeq reference panel, for example, it saw that they all clustered more closely to domestic wine grapes, particularly those in West or Central Europe.

With identity-by-descent patterns gleaned from the variant data, meanwhile, the researchers narrowed in on a variety of different cultivars in the seed set, Madrigal noted. Though the relatively small number of seeds at hand made it tricky to trace the precise distribution of each, at least one cultivar turned up at more than one site, hinting at historical transport of grapes used to make wine.

Although the team's network analysis of ancient and modern grape varieties pointed to waning genetic connections between modern grapes and the oldest (Iron Age) seeds, many of the Roman Period samples and most Medieval grape seeds did appear to fall in a genetic network with modern grapes based on the SNPs considered.

Moreover, a seed sample dated at around 900 years old appeared to be a genetic match to the Savagnin cultivar, Madrigal noted, raising the possibility that the wine grape variety — and perhaps others like it — have been continuously cultivated by clonal propagation for a very long stretches of time. 

"[W]e show genetic evidence of clonal propagation over at least one thousand years, which gave rise to the Savagnin cultivar as well as some of the most important cultivars found in the region today" Madrigal wrote in the abstract accompanying her PAG presentation.