A massive study that sequenced the DNA of more than 3,525 grape cultivars from around the world, published this month in the journal Science, has upended the history of how humans first domesticated grapes for winemaking and may reveal important information about how a few shriveled ancient Israeli grape seeds could save the future of winemaking from global warming.
Dr. Wei Chen of the Yunnan Agricultural Institution in southern China first started sequencing the DNA of grape cultivars in 2017 for a study of Chinese grape varieties. He and his lab sequenced almost 500 grapevines and found that through the DNA they could track the way different grape varieties migrated across the country, and how cultivars split off from one another to form distinct varieties.
He and his colleagues realized that if they could get their hands on enough varieties’ DNA, they would be able to map the migration of different varieties throughout the world, and throughout time, pinpointing when humans domesticated grapes for the first time.
The concept of creating a global study started off as a spitball idea among friends. But in 2019, Chen and his lab decided to take the plunge and launched an international research project focusing on grape cultivars.
“We started to reach out to our friends and colleagues in Europe, and we got the first batch from Germany, France, and Spain,” said Chen.
Colleagues sent dried young leaves from various local grape varieties, so Chen’s lab could extract and sequence the DNA, or they sequenced the DNA of local varieties themselves and sent Chen the results.
“Then colleagues from Europe started to call up their friends and colleagues, and we just got more and more people into this international collaboration,” said Chen.
Within a few months, Chen’s lab got to work sequencing the DNA and looking for patterns after they received samples from 90 scientists in 70 countries of both wild and domesticated grapes — with the Israeli contingent being the largest.
Grapes that share more DNA are more closely related, while those that have little DNA in common are less related. Tracking unique bits of DNA allows Chen and his lab to trace when different varieties split off from each other, and when domesticated grapes split from wild grapes.
The results were completely different from what Chen or anyone else had expected. Previously, it was widely believed that grapes were domesticated around 8,000 years ago during the Neolithic Agricultural Revolution, likely somewhere in the Fertile Crescent.
The key result from our study is that the original belief that there was only one domestication event was completely wrong
But by tracking the DNA from the thousands of samples, Chen pinpointed that there were actually two simultaneous domestication events, each around 11,000 years ago. One happened in Western Asia, and the other happened 1,500 kilometers away in the Caucasus.
“The key result from our study is that the original belief that there was only one domestication event was completely wrong,” said Chen. He said the belief that there was a single domestication event of grapes had seeped into history books so deeply that scientists no longer questioned it, and this was a good reminder that much of what is “known” about ancient history is really just conjecture.
One thing that the DNA sequencing did confirm is that the movement of grape varieties throughout the world correlates closely with human migration routes.
“Grapevines are really a wonderful crop that has so much to do with human history,” said Chen. “There were way more varieties [of grapes] than any other crop, and we actually care about this crop. We give each cultivar a name, and you can find these names in historical records. Naming of varieties started very late in history for other crops.”
A white grape in the wild
Prof. Elyashiv Drori, a senior lecturer at Ariel University and head of the Samson Wine and Research Center, has been swashbuckling through Israel’s last untamed wilderness for the past 12 years in search of the country’s last surviving wild grapes.
For Chen’s study, Israel’s submissions, collected by Drori and archaeobotanist Dr. Ehud Weiss of Bar Ilan University, constituted the largest contingent of wild grapes from a single country, or about 10 percent of the total wild grapes sequenced for the study.
Using this rich data set, the study determined that around 8,000 years ago, domesticated table grapes from Israel crossed with wild grapes in Turkey and then migrated throughout Europe. Today, every European wine grape – from the German Reisling to the French Chardonnay – can be traced back to this interaction.
“Spanish, French, German – every country had its own regional development of specific varieties, that all started from table grapes from Israel bred with wild grapes from Turkey,” said Drori.
Israel is the only country involved in the study to have wild white grapes, which Drori located. He is constantly astounded by the variety of wild grapes found in the country, which he calls “the wild grapevine mother collection.”
He started searching for the country’s wild grapes more than a decade ago with a different goal in mind.
“The idea was to try to find the ancient grapevines used for winemaking in ancient Israel,” said Drori.
Ancient Israeli winemaking was among the most developed in the world, until the 7th century, when alcohol fell out of favor following the Islamic conquest. For that reason, many of the surviving domesticated grape cultivars in Israel are for table grapes, which were selected for things such as large berry size, high sugar, long shelf life, and delicate skin. Wine grapes generally have higher acid, and attributes such as berry size, shelf life, and skin toughness do not matter.
Because of the decline in wine production during the Islamic period, the cultivation of grapes used for making wine in ancient times tapered off. This means today’s wild grape varieties are the most genetically similar to the types of grapes grown for ancient wine. Drori hopes it’s only a matter of time before he finds a wild grape with closely matching DNA to the grapes found in archaeological digs.
Each grape variety has a unique seed structure, like a thumbprint, that can be mapped, explained Drori. Any excavated grape seed that is larger than five milliliters can be scanned by high-powered microscopes to see if a match can be identified with modern counterparts. So far, Drori’s lab has scanned 20 seeds from archaeological digs.
The biggest haul of ancient material came from archaeologist Dr. Eilat Mazar, who excavated at the Ophel, between the City of David and the Temple Mount in Jerusalem.
“She called me one day and said, ‘I have three kilos of grapes,’” Drori recalled. “I said, you mean seeds? And she said, ‘No, three kilos of grapes.’ I dropped everything and ran to her lab. They found a big pot, maybe a wine jar used for fermentation. They also found a very nice inscription on it that says ‘smooth wine’ so we know what it was for.” The dried berries dated to around the 10th century BCE, said Drori.
Over the years, by scrambling up hillsides and through abandoned villages, Drori has collected about 600 wild grape plants from across the country, representing more than 90 varieties. Most wild grapevines are concentrated near areas of water, including the Jordan River, around the Sea of Galilee, and along streams running through the Golan Heights.
However, as Israel develops the last tracks of untouched land, these wild grape varieties are at risk of disappearing. Wild grape vines are not protected plants in Israel, though Drori is trying to petition the Nature and Parks Authority to give them protection like wildflowers or other endangered plants.
The future of wine is in Israeli wild grapes
Drori is a winemaker himself, and he believes that Israeli wild grapes may hold secrets to helping other varieties face climate change.
All Israeli grapes – wild and domesticated – have adapted to thrive amid heat waves and drought conditions. Wild grapes could also have new genes that scientists and vintners haven’t even considered.
“We already have the conditions here that will start other regions of the world in 20 or 30 years,” said Drori. “We might be able to find new genes, like finding stress-resistant genes, or find stronger plants.”
As the climate warms, winemakers around the world are scrambling to adapt to changing conditions.
“Grapevines that were selected and bred in the northern hemisphere, in cooler areas will not be suitable,” said Drori. “Now is the time to look into Levantine populations and understand which genes give strains unique drought resistance and heat resistance, and try to breed them into known varieties in areas where climate change will happen,” he said.
Chen from China agreed, saying, “The genetic diversity in wild grapes is beyond our imagination, and until now, we didn’t have the chance to see it, let alone analyze it.”
Currently, Drori and his lab are cultivating some of the wild vines they’ve found, while cleaning them of viruses and pathogens that occur naturally in the wild but could decimate domesticated crops.
Drori hopes that in the future, enterprising Israeli vintners will use not just ancient grape varieties but other artisanal methods, including fermentation inside ceramic vessels and other ancient tactics, the way people once made wine thousands of years ago. He envisions a boutique wine experience offering a glass of wine close to one that King David could have drunk.
For those looking to approximate that experience on Passover, Drori recommends drinking Muscat wine, which is similar to the grape varieties found in Egypt 5,000 years ago. Drori’s personal favorite wine is a pinot noir, due to its complex taste. (Chen said he doesn’t drink alcohol, after getting his PhD in nutrition.)
“Wine processes are always changing throughout history, and can be connected to different empires that ruled and how it impacted things differently,” said Drori. “One of the interesting things about wine and grape vines is that they were so important that the dispersion of humankind was almost simultaneous with the distribution of wine. Once people moved into new territories and built civilizations, they always brought the wine.”