The SOMM Journal

April / May 2018

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Page 96 of 108

96 { THE SOMM JOURNAL } APRIL/MAY 2018 TOMATOES "BREED TRUE"; when self- fertilized, the seeds from an individual plant's fruit will spawn offspring that are essentially identical. Grapevines, on the other hand, are not true-breeding, as self-fertilized vines always give rise to distinct plants that are more susceptible to environ - mental stressors. In order to clone a plant, commercial vines are almost always propagated vegetatively with cuttings taken from a se- lected parent. Grapes lose their leaves every year in the fall; on each bare cane where a leaf once lived, a node remains that can either be left on the vine to create a new shoot or cut to create a new plant. So how is it possible, then, that a clone— which, by definition, is identical to the or - ganism from which it came—can yield the many different types of grape varieties we hear about when visiting vineyards? As they develop over the course of a season, each bud at every node on a vine carries a high potential for genetic mutation. This means that every new shoot in every new vintage of every vine in the history of Vitis vinifera has a high probability of be - ing slightly genetically distinct from the wood it grew from—wood which is itself different from the wood that preceded it, all the way down to the seedling vine for a given variety. This would also mean that, as vines take about three years to yield their first fruit, the first-ever Syrah grape cluster may have been genetically distinct (al - beit minutely) from the original seed-grown Syrah vine it grew on. So, in the most literal sense, clones are not really clones! This is actually fantastic for wine, as it leads to the great variety of clonal selections with which grapegrowers can fine tune their vineyards. { what somms should know } A DEEPER DIVE INTO THE VARIATION WITHIN CLONAL DEVELOPMENT by Alex Russan IMAGE BY TETIANA SHEVELENKO VIA THINKSTOCK BREAKING DOWN MUTATION I'll leave it to the experts to ex- plain the various mechanisms that cause mutations, but the primary class are called transposons, or "jumping genes." Lest I make all of these yearly, individual mutations sound significant, they usually are not. While there are roughly 500 million places in the grape genome where genetic muta - tion can take place, the majority don't manifest any physiological changes. But, as previously noted, there is potential for change dur - ing every season in every bud on every vine on earth, and those changes accumulate over time. If a vine is 50 years old, a cutting taken from it for com - mercial use may have developed noteworthy differences from an adjacent vine or another of the same variety planted 100 miles away. This is how, little by little, the clonal selections we know have developed their differences in aromatics, phenolics, growth habits, environmental preferences, and so on . . . and they will keep changing. So, the next time you look out at a vineyard, if all the different blocks of Pinot look the same to you, remember that grape clones' DNA can vary from 1-5 per - cent—the same range, coinciden- tally enough, found by research- ers comparing the genomes of humans and chimpanzees. Talk about Planet of the Grapes! Evergreen Evolution

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