In all of my previous â€śWhoâ€™s Your Daddyâ€ť posts, I examined the parentage of one individual grape.Â Todayâ€™s â€śWhoâ€™s Your Daddyâ€ť is a bit different in that Iâ€™ll be discussing the parentage of, well, all grapes (specifically, all those that are in the USDA grape germplasm collection).Â To read past â€śWhoâ€™s Your Daddyâ€ť posts, click here and itâ€™ll take you to all of the posts under the â€śWhoâ€™s Your Daddyâ€ť tag.
Several studies have determined that grape domestication happened in the Near East about 6,000 to 8,000 years old, specifically originating in South Caucasus between the Caspian and the Black Seas.Â There are thought to be over 10,000 varieties of grapes throughout the world today (both table and wine grapes), which appear to have a very high level of genetic diversity compared to other organisms.Â Genetic diversity is important for several reasons, one of which isthe ability for grape-growers to selectively develop genetic strains that are resistant to pathogens.Â Problems can start to arise when there is too much selection for one particular genetic lineage, ultimately decreasing genetic diversity and increasing the chance of widespread crop loss if a new pathogen rips through the nonresistant population.Â Maintaining different lines of genetic diversity is important to avoiding these total wipe-out situations.
Though there are thought to be over 10,000 varieties of grapes throughout the world, identifying them can become very confusing, particularly with all of the misidentified clones, synonyms, and other errors associated with plant misidentification.Â The United States Department of Agriculture (USDA) has a â€śgrape germplasm collectionâ€ť, which essentially is a collection of grape seeds that can be used to resupply the industry with a particular type of grape, should something devastate the current plantings.Â The USDA keeps a germplasm collection of not only grapes but as many plants as possible, in order to maintain enough genetic diversity to help avoid mass die-offs and sudden shortages of the food supply when the plants are exposed to new pathogens of which they have no resistance.Â Out of the thousands of varieties of grapes, the USDA maintains a library of 950 vinifera germplasms.Â Of these 950 germplasms, 58% of them are clones of at least 1 other germplasm in the collection, with 583 of them being unique cultivars.
One really fascinating thing about grape breeding practices is that since it is a vegetatively propagated outcrossing perennial species of plant, very old cultivars spanning back thousands of years can still coexist with newer, younger cultivars.Â Â This can lead to a lot of genetic diversity if many new crosses are established, though relatedness between cultivars still remains relatively close.Â Specifically, a massive collaboration between researchers from all over the world found that in the USDA collection, 74.8% of the cultivars are related to at least one other cultivar in the collection directly (i.e. â€śfirst-degree relationshipâ€ť). Â (NOTE: The study of which I am referring to for all these facts is linked at the end of this post). Â The pedigree stemming from these crosses is therefore very complex, and was determined to have very interesting relationships.Â In terms of relatedness between cultivar types, it was found that 89.3% of relationships connected table grapes to other table grapes, and similarly wine grapes to other wine grapes.Â Interestingly, only 6.1% of the connections were between eastern and western grape cultivars, indicating a strong separation at one point in history between the two (Iâ€™m thinking the move across the ocean).
From the direct relationships mentioned above, 47.6% of them were calculated to be parent-offspring relationships, while the other 52.4% of them were calculated to be siblings or some equivalent thereof.Â Â Analysis also confirmed a probable Near-East origin of the domesticated grape, with all vinifera cultivars being more closely related to Eastern sylvestris cultivars than Western sylvestris cultivars (sylvestris = wild grapes).Â In terms of East versus West genetic diversity, diversity in the Western vinifera cultivars were found to be less genetically diverse than Eastern vinifera cultivars, suggesting some sort of population bottleneck, which can occur in extreme climate changes or human activities, or also due to geographical isolation (as is likely occurring in this scenario due to the transport of grapes from East to West during global expansion).Â After this bottleneck, it seems to be that propagation of different cultivars remained relatively low in the West, thus keeping the numbers of unique cultivars lower that they were in the East when their propagation practices were more complex.
As I mentioned previously, nearly 75% of the vinifera cultivars in the USDA collection were found to be related to at least one other cultivar directly (i.e. in a â€śfirst-degree relationshipâ€ť).Â What about table grapes?Â In fact, the same researchers found that an even greater percentage of table grapes had first-degree relationships compared with wine grapes.Â In other words, this suggests that table grapes were more intensely bred than wine grapes, with more purposeful crosses and fewer spontaneous mutations compared to wine grapes.Â In terms of wine grapes, the one grape that has the most first-degree relationships is the Traminer grape, which appeared to have 20 of these direct first-degree relationships with other cultivars in the collection, and what is believed to be one of the oldest cultivars that was used for propagation purposes (see Figure 3 above).
So, what does all this mean?Â Well, even though there appears to be a high level of genetic variation in vinifera grape cultivars, their inter-relatedness is extremely close; indicating that overall the percentage of possible genetic variants in the population is very low.Â In order to adjust to a changing climate with unknown roadblocks ahead, it may be very important to maintain a greater genetic diversity of wine grapes (as well as other agricultural products) so as to avoid possible total wipe-outs of entire pedigrees of grapes in the future.Just look at what happened starting in the 19th century with the Phylloxera crisis in France (and eventually, the globeâ€¦): The vineyards in France had been nearly eliminated by the invasive pest known as Phylloxera.Â None of the cultivars were able to protect themselves against this attacker.Â Since they all were so tightly interrelated, not a single cultivar had the genetic makeup necessary to provide resistance against the pest.Â In fact, only a small number of native grapevines from North America were resistant against the pest.Â Had there been greater genetic diversity in the wine grapes of France (and elsewhere in the world where Phylloxera devastated their vines), perhaps certain cultivars would have survived and they could have kept the industry going without having to search the globe for alternatives.Â If we want to avoid another Phylloxera or any other crisis that could potentially wipe out the entire wine industry, we may need to plan ahead and start creating much more genetic diversity in the wine grape.
With a changing climate, it is very possible that certain grape cultivars will not survive, so developing many new and more genetically diverse cultivars from the current stock may allow the wine industry to have a better chance at keeping vineyards thriving regardless of what mother nature throws in the way.Â In order for the wine industry to be successful in the future, it may very well be crucial for us to have developed many new genetic variants than what is currently in existence.Â We are already seeing some progress in this area, particularly with the Grape Genetics Research Unit in the Finger Lakes region of New York in the USA, though much more needs to be done.Â Iâ€™m encouraged by the work that has been done so far, and only hope this type of work continues and becomes more mainstream in wine industries around the globe.
Source: 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. 2011. Genetic structure and domestication history of the grape. Proceedings of the National Academy of Sciences 108(9): 3530-3535.