Drought and Heat: Do Hybrids or Vinifera Handle Them Better?

How grapevines respond to heat and drought stress has become, um, a hot topic. We know that the earth is heating up. Regions that have been optimal for certain varieties and species of grapes are undergoing significant changes, often becoming more extreme. The future of wine may depend on us learning what varieties can best deal with extremes of heat and drought with the least impacts to grape production and quality.

In 2025, two important peer-reviewed studies were published that measured the drought and heat tolerance of hybrid grape varieties in comparison with popular vinifera varieties. They each used different techniques to measure the grapevines’ responses to these stresses, and each study got some press for their results. But they seemed to come to opposite conclusions. According to the press about them, one study showed that hybrids responded poorly to heat and drought stress while the other study showed that vinifera varieties responded poorly.

But did they? If you believed the press take-away that boiled these two studies down to the equations of hybrids + drought + heat = bad, or vinifera + drought + heat = bad, you’re missing some of the most important parts of these studies and over-simplifying a series of very complex questions. With the future of wine at stake, we can’t afford to rely on biased opinions that fuel gross assumptions. So in this article, I’m going to analyze these two studies, break them down by their differences, shine some light on the nuances that were overlooked by all the press, and ask some bigger questions about what these studies actually tell us.

The Big Differences

There were such major difference between both studies that in some ways the conclusions we might draw from either, if there even are any, represent apples-and-oranges comparisons. Even more, the data collected were interpreted and presented within different contexts, resulting in stark differences in messaging and understanding about the studies. One study took place in Bordeaux, and the other took place in Quebec, so I’ll refer to them as the French and Canadian studies respectively.

The French study looked at xylem embolism—the extent to which circulation within vines was disrupted by drought and heat.

The Canadian study looked at metabolic response, using metabalomic analysis to measure the regulation of over 200 metabolites—amino acids, phenolics, sugars, etc.—by the heat and drought stressed vines.

I will show that the combined data from both studies would be important, and even necessary, to draw better conclusions.

The French looked at 30 varieties of grapes, but only seven of them were hybrid grapes and two of those are used almost exclusively as rootstock. They also included one single species non-vinifera rootstock (RGM/Riparia Glorie or Vitis riparia). The rest were vinifera varieties.

The Canadians only studied four grapevines – two vinifera and two hybrids. All four are common in Quebec: Riesling, Cabernet Franc, Vidal Blanc, and Marquette. It’s worth noting that Riesling and Cab Franc were two of the vinifera studied by the French as well, but they didn’t study Marquette or Vidal.

The French grew the vines without rootstock on their own roots, while the Canadians grew all four varieties on the same rootstock. The problem is that on the one hand the French tested a lot of vinifera varieties growing in a way that they would almost never grow in a commercial vineyard, since phylloxera is near ubiquitous now in most regions that grow vinifera. On the other hand, the Canadians grew the hybrid grapes in a way that they also might not regularly grow in commercial vineyards since some hybrids, and these in particular do, have enough phylloxera resistance to grow own-rooted.

At the very least, the Canadian study reports findings that could be found in the field, since growers could put Marquette and Vidal on rootstock successfully. The findings from the French study, however, seem almost unusable in real viticultural applications since winegrowers don’t have the option of growing vinifera without rootstock in most areas. We already need another study to find out if putting all the same vines on rootstock affect the results of the first French study. And then we’d really need a third study to find out if growing the vines as they grow in the field—ie hybrids own-rooted when possible and vinifera on rootstock—affects the outcome if we really want to apply this to commercial viticulture.

Results and Interpretations

The Canadian study found, and this is simplifying things quite a bit, that the two hybrid grapes had a less active metabolic response to heat and drought. While the Cab Franc and Riesling began a cascade of metabolic responses, the Marquette and Vidal showed minimal metabolic change as conditions heated up and dried out. What does this mean?

The truth is that we don’t really know. One interpretation is that the hybrids were less impacted, or less stressed, by the stresses, while the vinifera essentially started freaking out. Plants must use energy to regulate metabolites, and better conservation of energy might be generally associated with better rates of survival. And a chill response to heat and drought may signify that those factors aren’t really bothering the vine.

On the other hand, if you don’t raise your arms and cover your head as someone attempts to punch you in the face, you conserve energy but may not increase your chances of survival (unless you’re using your hands to get your knife out of your boot or something). In other words, freaking out metabolically might be an adaptation that helps you survive. These kinds of anthropomorphic analogies may not serve us in understanding how these plants actually behave, and I don’t intend them to be taken in any serious way. I use them to point out that we can look at the same data from very different perspectives.

To draw useful conclusions, this is why it would be important to combine the two studies. Riesling and Cab Franc performed mid to poorly, my words, in the French study, meaning they showed less than optimal vulnerability to xylem embolism under drought and heat stress. It would be very interesting if Marquette and Vidal had been studied by the French as well. If they had performed “well” in the xylem embolism tests, this would correlate well with the metabolic differences in the Canadian study. Or if the Canadians had studied Pinot Noir and Cabernet Sauvignon, which had some of the least vulnerability of the vinifera varieties in the French study, and found that these varieties also had low metabolic response… then we might begin to have some interesting findings suggesting that low metabolic response and less vulnerability toward xylem embolism seem to correlate. And that could begin to paint a better picture of how and which vines have adapted the best to deal with drought and heat. Alas, these cross-over studies weren’t done, and we don’t have that data.

If you’re beginning to wonder why I’ve spent so much time showing how inconclusive and inapplicable these studies are, I’m about to explain. I don’t mean to disparage either study, but they are the first baby steps, at most, to getting to answers of these important questions about drought and heat tolerance.

If we step back for a minute as look at the urgency of these questions, I think many of us care deeply about finding out what varieties of grapes might help us deal with the inevitable and already regularly occurring droughts and increasingly hot weather. But instead of just asking the question, “What grapes will help us survive these stresses?” there is in these studies an implicit or even explicit rivalry between two groups: vinifera vs. hybrid. Do we need that “versus”? Does it help us get the answers we actually, urgently need?

This sets up the findings from the French study. Oversimplifying again, the chart below ranks vulnerability to xylem embolism under drought and heat stress, with the most vulnerable varieties at the top and the least vulnerable at the bottom. The helpful color coding allows you to identify the hybrid varieties in Yellow, vinifera in Red, and rootstock in Green.

I don’t have proof, but knowing what I know about wine journalism, this chart was likely the cause of all the press that resulted from this study. Because if you don’t read the entire study and look at the methodology or have an extra minute or two to questions what you’re seeing, this graphic seems to show our “noble” varieties of vinifera “winning” while the hybrids are clearly the “losers” with the greatest vulnerability to drought and heat stress. That, essentially, was what was reported when this study was first published… and it was completely wrong.

In addition to all of the aforementioned issues with drawing any applicable conclusions from this study, let’s take a closer look at that chart. Yes, the popular vinifera varieties Pinot Noir, Cab Sauv, Merlot, and Syrah were some of the least vulnerable. And Floreal, Vidoc, and Voltis (hybrids) were some of the most vulnerable. As the study authors put it, “We also found that interspecific hybrid varieties that are resistant to mildews were significantly more vulnerable to xylem embolism than Vitis vinifera varieties.”

But let’s talk about some important but more nuanced things we see here. First, and this is something the authors of the French study mention, there seems to be a noticeable correlation in the results when we look at the color of the grapes. The white varieties, as you can see, had greater vulnerability across all species. Two of the hybrids that performed the worst, Floreal and Voltis, are white grapes. In fact, seven of the eight grape varieties with the greatest vulnerability are white grapes, while seven of the eight grapes with the least vulnerability are red (including the rootstocks). So did those hybrids perform poorly because they were hybrids, or because they were white grapes?

Did the authors’ own biases have an influence on how they interpreted the data? It’s entirely possible. They double down on their hybrid vulnerability claims, referring again to the “higher embolism vulnerability of hybrid varieties.”

Yet look at the two hybrid varieties Artaban and Regent on the graph: Artaban is almost at the level of Syrah, and Regent is definitely less vulnerable than more than half of the varieties. And both of these hybrids showed less vulnerability than Riesling, Sauvignon Blanc, Grenache, Cab Franc, and Chardonnay… some of the most popular and widely planted vinifera varieties in the world.

Finally, the authors separated out the rootstock and seem not to have taken its performance into account when interpreting the results. The variety in this study that showed the greatest resistance to xylem embolism is a hybrid. It just happens to be a hybrid that contains zero vinifera genetics. The rootstock SO4 is an interspecific cross between V. berlandieri and V. riparia. And “third place” in resistance is rootstock 110R, which is a hybrid of V. berlandieri and V. rupestris. And then “fifth place” goes to the un-hybridized, non-vinifera rootstock RGM, which is pure V. riparia.

So to draw any conclusions related to hybrids being generally more vulnerable to drought and heat stress, or the process of hybridizing being the cause of making a “stronger” vinifera vine “weaker” is not something this study supports when examined without bias. Yet when the study was published, the press almost without exception talked about the greater drought and heat vulnerability of hybrids. And it’s unfortunate, because these are questions that we need to explore urgently and accurately.

Important Conclusions

I’m not trying to flip this rivalry on its head and say that hybrids are actually better at dealing with drought and heat than vinifera. I don’t think the data in these studies support that either. That chart, and the French study, shows hybrids and vinifera performing at every level from top to bottom. So it’s hard to make generalizations about any category related to genetics, based on the way this study was conducted.

One thing I will note, however, is that the French study tested nearly every globally important vinifera variety. But it only tested five hybrids that have been used for winemaking, and only ones used by the French. Some of the most popular hybrids in Europe and North America were not tested.

Additionally, hybridization gives us an ability that vinifera can never match… the ability to adapt. Pinot Noir’s performance is the best resistance that can be achieved by the major vinifera varieties within the parameters of this study. But we already know that there is greater resistance possible by looking at the performance of SO4. With hybridization we can start developing new grapes that incorporate and improve on something that’s already better than the best vinifera. And we don’t know if there are other hybrids or species of grape that might be even less vulnerable to drought and heat than SO4 that we can begin to breed into our wine grapes. This option does not exist if we keep growing the same vinifera varieties. We already know their limits.

Also, the French scientists should know better than to generalize about something with the infinite potential that hybrid grapes have. Hybrids are already too diverse a class to fit into easily defined boundaries. Selecting seven hybrids with a random assortment of genetic parentages seems an incredibly limited way to make comparisons between vinifera and hybrids, and their statements about the higher embolism vulnerability of hybrids read not as dispassionate assessments of data but as either sloppy or biased opinions. So I do blame the scientists a bit for the untrue press that resulted from their study. But the wine press needs to be much more careful, and critical, when reporting on these kinds of studies.

We need to consider that a grape that evolved in the US Southwest, like V. arizonica, is unlikely to have the same drought and heat tolerance of a species of grape from Manchuria in Northern China, like V. amurensis. How do these genetic histories impact the grapes that they parent? If we wanted to actually start understanding the genetic reasons behind drought and heat tolerance we may want to first study the native species to find out which have the characteristics we’re looking for, then begin seeing if and how those characteristics get transferred to their progeny when crossed with other species. And that’s just looking at the genetic variables. There are so many unexplored options and potentials, and we need to take care to be able to answer these vital questions with nuance and honesty, and not rely on the kind of thinking that can make our scientific studies look more like op eds.

Canadian Study:
Metabolic response of vitis vinifera and interspecific vitis sp. varieties to heat stress, water deficit and combined stress, using a metabolomic approach
Full - PDF download

French Study:
Quantifying the grapevine xylem embolism resistance spectrum to identify varieties and regions at risk in a future dry climate

Reference:
Rootstock Chart