But if they occur in the bud meristem they can produce a shoot that has different properties to the rest of the vine. If they occur in a cell that isn’t part of a bud meristem (the area of rapid cell division that forms new bits of plants) they are incidental because they won’t be passed on through cuttings. Most of the mutations will be invisible, and most will be neutral or deleterious. If you have 10 000 vines growing in a vineyard of the same variety, each starting out genetically identical, over the years various mutations will develop and there will be some genetic differences among the vines. Epigenetic changes also allow a vine to adapt to the environment, partly in concert with the TEs. Finally, there’s epigenetic modification, which involves changes to the material around DNA but not the DNA sequence itself, affecting how genes are turned on and off, and this can be heritable just as DNA changes are heritable. Their activity is heightened by environmental stress: it is becoming clear they are important for plant adaptation to the environment. TEs have been shown to be responsible for most clonal variation in grape varieties, and form around 20% of the DNA sequences in Vitis vinifera. The sorts of changes that can occur include single base changes in the DNA code, or insertions or deletions of bits of DNA (called ‘indels’: these are structural changes) or genes moving around (known as transposable elements TEs). These vines are standing out in a field, often in very sunny climates, and will be exposed to a lot of solar radiation. Then there are environmental stresses that can cause DNA mutations. There are molecular checks and balances, but occasionally mistakes are made. One of the sources of this mutation is the copying process itself: each time a cell divides by mitosis (as opposed to meiosis which occurs during the production of pollen or ovules in sex), a new strand of DNA is copied from the existing one. Over time, as grape vines of each variety are propagated vegetatively, spontaneous mutations will accumulate in their DNA. But if, over hundreds of years, people take cuttings from Chardonnay grapes and keep on propagating them, they will remain Chardonnay. If you take a seed from a Chardonnay grape, and grow it, you will have a new variety. That’s all you need to make a new variety, and it’s also the only way you can make a new variety. Each grape variety we have now consist of plants that are descended from that single seed, and which have been selected by humans, and have then been propagated over centuries or millennia by people layering the vines or taking cuttings (known as vegetative propagation, as opposed to sexual propagation).Īs Jose Vouillamoz, the grape geneticist puts it: every variety has a father and mother. Examples? Pinot Noir, Cabernet Sauvignon, Chardonnay, Sauvignon Blanc, Merlot, Syrah. So the 1500 or so commercial varieties of the single species Vitis vinifera grown worldwide are all the result of the germination of 1500 different seeds. A new grape variety is produced when a grape seed has grown into a plant. But what, precisely, do these terms mean? We talk a lot about clones and grape varieties.
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