Tracking the history of grapevine cultivation in Georgia by combining geometric morphometrics and ancient DNA

The Near East and the Caucasus are commonly regarded as the original domestication centres of Vitis vinifera (grapevine), and the region continues to be home to a high diversity of wild and cultivated grapevines, particularly within Georgia. The earliest chemical evidence for wine making was recorded in Georgian Neolithic sites (6000-5800 bc) and grape pips, possibly of the domesticated morphotype, have been reported from several sites of about the same period. We performed geometric morphometric and palaeogenomic investigations of grape pip samples in order to identify the appearance of domesticated grapevine and explore the changes in cultivated diversity in relation to modern varieties. We systematically investigated charred and uncharred grape pip samples from Georgian archaeological sites. Their chronology was thoroughly assessed by direct radiocarbon dating. More than 500 grape pips from 14 sites from the Middle Bronze Age to modern times were selected for geometric morphometric studies. The shapes of the ancient pips were compared to hundreds of modern wild individuals and cultivated varieties. Degraded DNA was isolated from three pips from two sites, converted to Illumina libraries, sequenced at approximately 10,000 single nucleotide polymorphism (SNP) sites, and compared to a large public database of grapevine diversity. The most ancient pip dates from the Middle Bronze Age (1900-1500 cal bc) and the domesticated morphotype is identified from ca. 1000 bc onwards. A great diversity of domesticated shapes was regularly seen in the samples. Most are close to modern cultivars from the Caucasian, southwest Asian and Balkan areas, which suggests that the modern local vine diversity is deeply rooted in early viticulture. DNA was successfully recovered from historic pips and genome-wide analyses found close parental relationships to modern Georgian cultivars.