Wine’s genetic diversity: Thank goodness we’re not coffee

Wine has a diversity issue. Wine actually has several diversity issues, but I’m not prepared to deal with the massive and significant question of non-white non-male winemakers (today). The much easier diversity question is about the wine grapes themselves. And even though it’s an issue, and one that’s been rightfully earning more press of late, wine grapes have the potential to be a good deal better off than most crops. The problem is of our own making, and we should be able to unmake it.

Arabica coffee varieties, according to a recent genetic survey, share 98.8% of their genes in common. That’s an estimate made by sampling both wild and cultivated plants (781 sequences in total) from around the world. So, even if coffee breeders try their darndest to increase the diversity of cultivated coffee plants – which they are, because genetic diversity means better resilience against threats like infectious diseases and climate change – they only have so much room to work. The survey found that wild plants were more genetically diverse than cultivated ones. The breeding stock can be improved. But compare coffee to maize, for which something like 30% of the genome varies across all of the plants on the planet, and there’s not that much room.

Wine grapes are like maize, not like coffee. Both maize and Vitis are, in fact, extraordinarily diverse. No shortage of room here. What’s most curious for wine grapes, though, is that the difference between the genetic diversity of wild and cultivated vines isn’t that great. When humans domesticate a species, we create a genetic “bottleneck” (Nature has a nice image here), reducing genetic variability in the new crop. For wine grapes, the bottleneck was “weak;” the reduction wasn’t that dramatic. (Coffee, by the way, suffered a very severe bottleneck.) And earlier this year, a genetic survey of wild and cultivated grapevines in the Republic of Georgia, where grapes were first domesticated to the best of our knowledge, still found plenty of diversity in wild grapevines that doesn’t overlap with cultivated varieties and which have yet to be explored.

Unlike coffee, the real problem with wine grapes isn’t that the genetic diversity isn’t available, in wild or even in cultivated plants. The problem is that we’ve artificially selected for an incredibly narrow set of vines, over and over again, through clonal selection to replicate what we think is the best of the best. To recapture the genetic diversity that might help wine combat disease and changing climates and whatever else the next century or three throws our way, we need to undo the relatively recent work of the modern wine world.

The numerous research teams working around the world on the grape diversity issue have a great big spectrum of possibility out in front of them. That’s a good reason to be hopeful. And to be sorry for the coffee guys.

Ampelography –> Genetics –> ? Varieties –> Clones –> ?

How much difference does clone make to flavor, and where do we draw the line between important and unimportant differences? The line might really be between interesting and uninteresting differences; any difference is important if we choose to make it so. I’ve written on Palate Press this month about variety, clone, and treating pinot gris like pinot noir, which provokes an unsettling argument about what differences are important differences.

Before the global phylloxera crisis in the late 19th century, precisely identifying varieties was less crucial from a viticultural standpoint, bottles didn’t routinely carry variety information until the mid-20th c., and many from the Old World still don’t. But where variety is the way consumers make purchase decisions, some now go a step further and heralding specific clones, at least on websites and to wine writers.

We have reasonably fixed definitions for what constitutes a variety and a clone. A variety is the unique progeny resulting from a fertilized egg involving genetic reassortment between the DNA of two parents. A clone is a variant of a variety resulting from small genetic changes (usually spontaneous changes from random mutations) involving just those genes, not full-on mixing. Fine.

But those definitions are essentially arbitrary, or at least they could be otherwise. The technology we have defines how we can define a species, or a variety, or a clone. Clones are only clones when those genetic changes produce some big, obvious physical change that a grower will notice and decide she likes enough to cut and reproduce. Most genetic changes aren’t like that. Most probably don’t result in any important change to grape quality, but there’s likely a whole category of mutations that affect ripeness, phenols, canopy development, or whatever that go unnoticed — because they’re not big and obvious, maybe because they deal with invisible chemicals — but that affect quality parameters we care about.

We’re developing precision viticulture techniques that map vineyards at a sub-block and perhaps even individual vine level for differences in development and quality. As genetic testing becomes easier, precision vit could easily include genetically typing individual vines. Purchased stock should fit the known genetic profile of a known and loved clone bought from a certified facility, but older vineyards are going to be full of endless numbers of new…clones? Do we call them clones when they’ve not been selected and propagated?

The resolution at which we can define species — actually, let’s make it simpler and just say define differences — changes with the technology we have to do so. So we moved from ampelography to Mendel to DNA sequencing to the Robinson, Harding, and Vouillamoz tome outlining the genetic relationships of darn near most grape varieties on the planet. A splendid article from 1938 outlining principles for doing ampelography — distinguishing grape varieties by their physical characteristics — observes that botanical and horticultural classifications of grape varieties are different. The botanists want to describe family relationships, the horticulturists to create practical guides for distinguishing varieties, so we have the genetic tree and the field identification guide. Different purposes, different resolutions, different differences called out as important.

Resolution isn’t about “natural” differences. It’s about the degree of difference we decide is important. I’ve tasted pretty profound differences amongst different clones from the same vineyard when they’ve been vinified separately and before they’re blended together. They’re striking. They’re wonderful. My little wine writer soul wants to proclaim over new-found differences. Those differences seem important. But in older mixed-planting vineyards full of whatever happened to be around at the time, harvested and made all together as a “field blend,” variety may not even be all that important.

On the one hand, people like Matt Kramer have been urging growers (of pinot noir in particular) to plant lots of different clones as a prayer against the curse of boring wine. And researchers looking to natural grape genetic diversity for breedable salvation from Pierce’s Disease, powdery mildew, and other expensive threats caution against limiting and losing living genetic pools that could be irreplaceable in our time of future need. And yet, if those researchers succeed, growers will have first one, maybe eventually a handful of clones carrying those disease resistance genes that they’ll want (or be pressured to) plant.

As many winemakers tell me that they don’t want to talk about clones and wish people would stop asking about them as want to talk about little else; I suspect that there’s a poetry competition for odes to chardonnay “Mendoza” and pinot noir “Abel” running somewhere in New Zealand. It’s part of your story or it’s not. Great. But we can say the same thing about variety, and maybe all of this consumer interest in genetic differences is merely a fad. A century from now we could be talking about micro-clones, or about clades, or about specific genes a vine does or doesn’t carry, or about famous vineyards planted with an especially successful mix. Wine evolution, made possible with the support of genetics, but brought to you by the eddies of our changing attention spans.