History and Genetic Diversity of Wine Grapes adapted from recent article

Here is a short synopsis of an excellent review article by Patrice This in the journal, Trends in Genetics . The article covers how modern wine grapes were developed over time and the current status of research aspects of the genomics of the grapevine. 

The following is adapted and primarily sourced from the article cited below. Other references are listed at the end of the article.

https://www.sciencedirect.com

Historical origins and genetic diversity of wine grapes
Patrice This1, Thierry Lacombe1 and Mark R. Thomas2
1 INRA, UMR Diversite ́ et Ge ́ nomes des Plantes Cultive ́ es, 2 place P. Viala, 34060 Montpellier, France 2 CSIRO Plant Industry, PO Box 350, Glen Osmond, SA 5064, Australia

Current status of grape genomic resources

            What is the heck is “genomics” anyway? How is it different from “genetics”?  Genetics and genomics are two terms that are often incorrectly used interchangeably. Genetics is the study of single genes and their role in the way traits or conditions are passed from one generation to the next. Genomics describes the study of all parts of an organism's genes. This distinction/definitions are found at: https://www.healio.com/cardiology/genetics-genomics/news/online/%7B6cdf2745-8257-40e4-ae0c-4f1fa7193d03%7D/genetics-vs-genomics

            At any rate, the two terms differ. Although “back in day”, plant breeders I knew and worked for seldom dealt with a single gene. Most had to account and allow for the role of multiple genes when developing new varieties. However, here we defer to the term: genomics: the study of multiple genes and their interactions and as “study of all parts of an organism’s genes”, in our case, we are concerned with genes of the grapevine and its close relatives.

Historical overview

            Human culture has been associated with the grapevine since ancient times. Wine has captured humankind’s attention …devotion even, over the centuries. The ancient’s gods, Dionysus and Bacchus were gods of wine. The Italian cultivar, Sangiovese translated from Latin sanguis Jovis, means the “the blood of Jupiter” (Wikipedia).

             The Vitis genus within the Vitaceae family has 60 inter-fertile species (species is a community of individuals that can interbreed with one another, but not with members of other populations), see Figure 1. Vitis vinifera, or the ‘wine-bearer’, the species that originated in Eurasia about 65 million years ago, is most used in today’s worldwide wine industry.

             There are about 10,000 modern grape varieties and these cultivars are hermaphroditic, which in the case of grape means they possess perfect flowers with male and female reproductive structures and are self-fertile. However, hermaphroditic vines also “out-cross” easily. A few varieties dominate the wine industry: Airen, Grenache, Carignan, Merlot, Chardonnay, Cabernet Sauvignon, Pinot Noir, Tempranillo, Aligoté, Riesling, Rkaziteli, Sangiovese, Sauvignon Blanc, and Chenin Blanc. Grapes are classified by their end use as: table grapes, wine grapes, juice grapes (think Welch’s, made from the Vitis labrusca variety, Concord) or raisins. Most known cultivars are not planted commercially and exist only in germplasm collections, although there is some recently renewed interest in old landraces and local cultivars. 

Figure 1. Grapevine family tree with various species of the family Vitaceae and within the
   genus Vitis or Muscadinia. Note the single European species, Vitis vinifera, “the winebearer”.

            When the grape was domesticated, and likely made into wine, it was also selected for sugar production, yield, and regular production from year to year. The wild grapevine has/had a dioecious (Greek dis = double, oikos =house) flowering habit, meaning functionally male or female flowers occur on different individual plants. Cultivated types have functionally perfect flowers…the aforementioned hermaphroditic types. The grapevine’s seeds also changed and this characteristic is important when researching the age of seeds found in archaeological remains. The question arises…did these changes occur over a long period of time via natural sexual crosses and human selection, or in a short time with mutations noticed and propagated with cuttings by observant and enterprising humans?

            Wild grapes probably originated in the Near East, with early wine production in Iran near Hajii Firuz Tepe about 7400-7000 BP (before present). Although the earliest evidence of a functioning winery has been documented in Armenia (Barnard et al. 2010). Seeds of domesticated grapes dated from ~8000 ago have been found in Georgia and Turkey, and in bronze-age sites in France. From these sites, grape culture likely spread to Egypt, Lower Mesopotamia and on to the Phoenicians, Greeks, and Romans among others, and eventually to China and Japan. The Romans spread V. vinifera to Germany and throughout their empire. As Roman influence faded, the Catholic church spread wine and grape culture, and the Islamic faith spread table grape culture.

After the Renaissance, V. vinifera was carried to the new world, and missionaries introduced it to the Americas. Cuttings were spread to South Africa, Australia and New Zealand in the 19^th century. By the end of the 19^th century, the fungal diseases: powdery mildew, downy mildew, and black rot and the root louse phylloxera were carried to Europe from North America and spread across the continent devasting its vineyards. Sadly, there are few surviving native or wild grapevines in Europe today. European viticulture was salvaged and began to thrive again when American, non-vinifera, Vitis species were used as rootstocks and for breeding disease resistant, inter-specific hybrids (see Table 1, from Keller, the Science of Grapevines)

 
Figure 2. Wild Vitis (above) and fairly modern wine grapes (below): Muscat Blanc 9middle) and Muscat Noir (bottom).
Images from Kew Science website: http://www.plantsoftheworldonline.org/taxon/urn:lsid:ipni.org:names:325876-2

Trait	Eurasian Species	American Species
Fruitfulness	Good	Poor or highly variable
Fruit quality	Good	Poor
Usefulness	Highly diverse products	Niche products
Propagate capacity	Good	Variable
Lime tolerance	Good	Highly variable
Phylloxera tolerance	Poor	Good or variable
Disease tolerance	Poor	Good or variable

Table 1. Viticultural traits of American and Eurasian grapevine species. Table from Keller, 2010, The Science of Grapevines

Hybrids were popular until the 1950’s, but are scarce today because hybrids seldom have produced fruit and wine that satisfies most European winegrowers or the hopes of the breeders themselves. As M. Keller explains in his comprehensive textbook, The Science of Grapevines, “the only unequivocal success story thus far has been the grafting of phylloxera-susceptible European wine grape cultivars to rootstocks that are usually hybrids of tolerant American Vitis species”.

From the wild grapevine to varieties

            Wild European grapevines provide clues to the origin of modern cultivars. The question is: are they true-to-type wild vines, i.e. Vitis silvestris types, or simply escapes from vineyards or out-crossed hybrids between wild and cultivated types. Modern genetic techniques such as DNA analysis can help determine whether the collected individual vines are truly wild or whether they possess some genetic contribution from cultivated types. Wild ancestors and modern varieties differ in: sugar content, flower sex, berry and bunch size.

             

Early domestication and propagation by seed

            Early on, grapes were spread and distributed by seed. Seedling plants result from sexual crosses with new combinations of genes that could then be spread by cuttings (vegetative propagation) when desirable traits occurred. Patrice This and her co-authors, in the source article: Historical origins and genetic diversity of wine grapes, reminds us that the Pinot and Gouais varieties produced progeny maintained and adapted to the environment in northeast France and exist to this day. But they go on to explain that it is unlikely that there is gene mixing between wild and cultivated types, as the flowering times of the two are not the same.

Was there a single domestication event or many domestication events?

            Was there more than one genetic pool that generated modern varieties? The Muscat group of varieties, with their distinct flavors and aromas, support the likelihood of multiple genetic sources. Some researchers maintain a difference between European and Near Eastern grapes. For example, Chardonnay, considered a French variety from a cross of Pinot and Gouais of Croatian origin, demonstrates a mix of genes from different regions. Syrah, another example, long thought to be of eastern origin, has been determined to be of French origin.

How old are modern grape varieties?

            Speculation about the historical origins of current cultivars is common in popular publications but no evidence supports the notion that varieties from antiquity or the middle ages exist today, although the analysis of ancient DNA has been much improved lately. For instance, grape seeds from between 2600 and 1700 years ago have been successfully analyzed. Seeds are important as they can be a result of crosses, and coupled with the analysis of ancient wood, can characterize the identity of old cultivars and provide comparison with modern cultivars. The old variety, Mission, that is believed to be the first grape of European origin grown in New Mexico was brought to the Americas by the Spanish missionaries as seeds. It is believed that the Mission variety found in South America in the 16^th century was vegetatively propagated and transported as cuttings to various American countries where it was renamed with local names such as: Païs, Criolla chica, Rosa del Peru, and Negra corriente. Vegetative propagation of grapevines to plant new vineyards and move vines from region to region has been common for many hundreds of years. However, despite the importance of vegetative propagation, recent genetic characterization of cultivars has shown mutations frequently have had a role in generating genetic diversity.

The role of mutations

Figure 3. Pinot Noir with somatic mutation evident on individual berries

            Sexual crossing and natural mutations have driven grapevine evolution. The appearance of hermaphrodite flowers, the most important genetic development, seems to be the result of a mutation. It is not known when this trait was found and first used by humans. However, it is assumed that the adoption of such uniformly flowering and fruiting plants was rapid. Another mutation, berry skin color, was quickly made use of in development of modern cultivars. Because wild grapes are believed to have had black berries, white berries were probably selected and maintained during domestication.

            Somatic mutations that do not originate from sexual gene mixing but from vegetative tissue, can be stably maintained and vegetatively propagated over time. The Pinot family is notorious for many vegetative and floral mutants. Pinot noir has a black berry, Pinot gris a grey berry, and Pinot blanc has a white berry, all likely from a mutation.

            The seedless trait in Thompson Seedless, Emperor Seedless and Chasselas apyrène all probably occurred separately. Humans selected this seedless trait for their table grapes.

Vitis vinifera germplasm and genetic diversity

            Molecular geneticists tell us that sexual and asexual multiplication and mutations have helped expand and diversify the grapevine. As mentioned earlier, the number of varieties in various germplasm collections around the world is likely ~10,000. Nearly every wine growing country has its own grapevine germplasm collection that maintains quarantines and the material in the field as living plants. Many variety names are applied to the same cultivar as explained with the example, Mission. But often it works the other way around, and the same name can be applied to different cultivars, adding to the confusion. This is where microsatelitte (a bit of the DNA strand that repeats itself, https://en.wikipedia.org/wiki/Microsatellite) marker studies, available since the 1990s, are very useful and effective in identifying and differentiating varieties and determining the true extent of genetic diversity. With new genetic tools, it is estimated that the number of vinifera varieties will prove to be closer to 5,000 than it is to 10,000 (This et al., 2006)

            This et al. (2006) also point out that collections around the world need to cross correlate all their information to accurately identify cultivars. This burgeoning effort is available at http://www.montpellier.inra.fr/vassal. Additional data and coding are being accomplished and will assist in the development of an international database that will aid estimation of diversity in Vitis and V. vinifera: http://www.genres.de/eccdb/vitis.

            Somatic mutations and vegetative propagation have increased the genetic diversity in grapevine. The use of mutations in genomic studies will help assign roles to specific genes. Identifying and maintaining these mutants is crucial and the collection at Vassal, France has been doing this for many years and has cataloged over 200 mutants (This et al. 2006).

Conclusion

            Various collections can be defunded, and varieties can be lost. DNA profiling and a common database are needed to determine the true number of varieties, their relationships, genetic diversity and identification of unique individuals. Such data is also helpful for historical investigation of domestication.

            Wild grapevines are poorly characterized, and extensive analysis of wild individuals from a broad geographical area are crucial to understand the role of Vitis silvestris in the domestication process. Recent DNA studies and application of genomic techniques has increased characterization of the genes and genetic control of important traits. This detailed genetic analysis should help us understand the biology of the grape, and if properly and thoughtfully utilized in the field, can improve viticulture around the world.

References

Barnard, H., Dooley, A. N., Areshian, G., Gasparyan, B., and K.F. Faull. 2010. Chemical evidence for wine production around 4000 BCE in the Late Chalcolithic Near Eastern highlands. Journal of Archaeological Science. 1-8. http://www.elsevier.com/locate/jas

Keller, M. 2010. In the Science of Grapevines: Elsevier Inc., London, UK.

This, P., Lacombe, T., and M.R. Thomas. 2006. Historical origins and genetic diversity of wine grapes. Trends in Genetics. Vol 22. 9:511-519.  https://www.sciencedirect.com