According to Patrick McGovern in his book Ancient Wine: The Search for the Origins of Viticulture, “A SINGLE Eurasian grape species (Vitis vinifera L. subsp. sylvestris), among approximately 100 that grow wild in temperate zones of Asia, Europe, and North America, is the source of 99 percent of the world’s wine today.” It is quite remarkable that, of all the wild grape species around the world, only one has gone on to become dominant in agriculture.
As the principal species of wine grapes around the world, the evolution of Vitis vinifera has been studied at length (This et al 2006). Advances in modern genetics have introduced methods which have yielded many new theories as well as shedding new light on relationships between grapevine species and varieties. For example, there are now much clearer distinctions between the genes of different Vitis species that shows clustering linked to geography (Zecca et al., 2011).
Relationships between varietals. (Myles et al., 2011)
But within the cultivated vinifera species, genetic mapping has revealed the entire species to be basically one large pedigree – the result of limited crosses among “elite” cultivars that have been immortalized by vegetative propagation (Myles et al., 2011). But this is likely due to a number of other factors as well.
First degree relationships between “elite” varietals of table grapes and wine grapes in the USDA germplasm. (Myles et al, 2011)
Climate changes have been shown to have a major impact on natural selection and diversification. “Species extinction rate due to past climatic and orogenic changes was lower in Asia, higher in North America and highest in Europe” (Ricklefs, 2005). Recently, Wan et al. (2013) discovered that major climate changes in the past have caused spread and diversification of Vitis species that survived the shifts. So, because the pressures of natural selection varied quantitatively and qualitatively in different global regions, it is possible that the progenitors of V. vinifera were selected more rigorously.
Studying the DNA of widely cultivated varieties in comparison to wild grape species has also shown the impact of agriculture and human migration on the evolution of the grapevine. However, there are many conflicting hypotheses regarding phylogeny, speciation events, and biogeographic history of the genus Vitis (Zecca et al., 2011). Indeed, the identification of many “wild” Vitis sylvestris samples had been questioned because of the ease with which they cross and morphological similarities with vinifera. There were likely a multitude of crossover events between the species throughout history (Myles et al., 2011). Answers to these questions might have a valuable use in deciding which direction future breeding or genetic engineering could go.
While the narrow genetic diversity may be attributed to the evolution from few ancient progenitors, human movement and major events linked to globalization have certainly had a major impact as well. The major pest and disease outbreaks in Europe in the 19th century were likely to have drastically reduced the genetic diversity of cultivated and wild grapes just as their most popular cultivars were being spread around the world. Further globalization and commercialization of wine has further narrowed the cultivars outside of germplasm collections (This et al., 2006).
The majority of cultivated varieties today also share a common pedigree due to socio-economic forces through the ages of human agriculture. The reasons for most varieties’ success through history are usually linked to things like sugar content, drought tolerance, and/or yield. The goals of many viticulturists today have changed. So after thousands of years of selection for these traits it may make sense to look to diversity as a solution. Genetic variation is integral to crop improvement (This et al., 2006).
As agriculture advanced vegetative propagation became the norm. With it came the promise of more consistent vineyards and true breeding cultivars but also the loss of a source of unique cultivars from crossing. The market pressure to grow (and subsequently research) only a few, elite cultivars has caused many qualities of those lesser known to go undiscovered (Myles et al., 2011). These trends of narrowing genetic diversity can make the crops more vulnerable.
Major pathogen pressures continue to plague vineyards around the globe. The most logical way to solve these problems in the long term would be to look more deeply into the “tremendous” natural diversity of Vitis available to us (Myles et al., 2011).
As all vinifera populations have been shown to originate from eastern sylvestris (in the Near East) and most vinifera hybrids to date have been made with North American labrusca (Myles et al 2011), it could be interesting to explore hybridization with genotypes closer to the progenitors. So perhaps the recent increase in Chinese grapevine research due to their emerging wine market could have prospects for improvements and understanding of the current cultivars. Also, the vast germplasm collection around the world could generally be explored in more depth.
Although many other species may hold potential for genetic breeding value, it may be more logical to focus on the current vinifera germplasm and “wild” sylvestris varieties. Genetic evidence supports the idea that vinifera/sylvestris have survived and adapted to the more climatic changes than other species. This could be a clue that they have more evolved genotypes in some very important traits. Human impact has undoubtedly been significant in arriving at the current form of vinifera, but maybe this effect has masked its underlying superiority resulting from the right natural selection pressures. It’s difficult to know because of the unclear origins of sylvestris samples, but future research could explore this possibility.
Myles, S., Boyko, A.R., Owens, C.L., Brown, P.J., Grassi, F., Aradhya, M.K., Prins, B., Reynolds, A., Chia, J.-M., Ware, D., Bustamante, C.D. and Buckler, E.S. Genetic structure and domestication history of the grape. PNAS, 108(9): 3530-3535 (2011).
This, P., Lacombe; T., Thomas, M.R. Historical origins and genetic diversity of wine grapes. Trends in Genetics, 22:511-519 (2006).
McGovern, P.E. Ancient Wine: The Search for the Origins of Viniculture. Princeton University Press, 335p. (2003).
Ricklefs, R.E. Historical and ecological dimensions of
global patterns in plant diversity. Biologishe Skrifter (Royal
Danish Academy of Sciences and Letters), 55: 583–603 (2005).
Wan, Y., Schwaninger, H.R., Baldo, A.M. Labate, J.A., Zhong, G.Y., Simon, C.J. A phylogenetic analysis of the grape genus (Vitis L.) reveals broad reticulation and concurrent diversification during neogene and quaternary climate change. BMC Evolutionary Biology, 13:141. (2013).
Zecca, G., Abbott, J.R., Sun, W.B, Spada, A., Sala, F., Grassi, F. The timing and the mode of evolution of wild grapes (Vitis). Mol. Phylogenet. Evol., 62(2):736-47 (2011).