How many grape clones are there per variety?

I recently noted that the twin ideas of "varieties" and "clones" are basic to grape-growing, whether they are used for wine-making, table grapes, raisins, juice, jelly, canning, or rootstocks (Grape clones and varieties are not always what they seem). This leads me to ask the question posed in the title.

The number of clones is often related to the genetic mutation rate of the variety. Pinot noir is therefore recognized as one of the most mutable grape varieties. Indeed, it is so mutable that we have produced several different clones that we actually treat as being varieties, because they can be used to make very different wines (as discussed in the previous post). Indeed, Pinot noir itself also has more recognized clones than do most other varieties.

This is illustrated in the first graph. The data come from the list of varieties and clones currently approved for viticulture in France (Catalogue of vines grown in France). Each grape variety is listed horizontally, with the number of approved clones counted vertically. Only the 38 varieties with at least seven clones are shown — there are a total of 269 approved varieties, and 950 clones, although 161 of the varieties (60%) have only one listed clone.

As you can see, Pinot noir is way out in front. Its history is, of course, associated specifically with Burgundy, although it is now an international variety. It is therefore interesting to note that the second variety in the graph is Gamay, the red-wine grape from Burgundy's nearest neighbor, Beaujolais. The people of this part of France have had a long time to keep an eye out for potentially useful mutants among their vines.

We can, of course, separate the graph into both red- and white-wine grapes, and this is illustrated in the next graph, which shows the 30 varieties of each type with the most clones. It is immediately obvious that red-wine varieties tend to have more clones than do white-wine varieties. Presumably, this reflects the historically greater interest that has generally been shown in producing "fine" red wines compared to white wines.

As usual in this blog, we can search for simple patterns among these data. Mathematically, the data from the first graph most closely fits a Power model, as shown in the following graph, where the added line shows the model. The most obvious place the model does not fit the data is the first two varieties — both Pinot noir and Gamay actually have fewer clones than "expected" from the model!

If we fit the Power model to the red and white varieties separately, as shown in the next graph, then it is interesting to note that the model fits the white varieties very well, although the first white-wine grape (Chasselas) has too few clones. However, the model fits the red-wine varieties rather more poorly, and especially Pinot noir and Gamay have many too few clones for this model . The latter results from the greater number of clones for the remaining red varieties — red-wine grapes generally have more clones than we would "expect" from a simple mathematical model.

So, we may conclude that white grape varieties have clone numbers that fit a simple mathematical model, but red varieties have more clones than can be "explained" by any such model. This is likely to be because red wines have been preferred by consumers, so that the vignerons have been more keen to find "better" clones for lots of the red varieties but only a few of the white varieties.

Some comments

Lest anyone thinks that there is some restriction on the number of grape varieties that can be used in France, it is important to note that new varieties are being approved all the time (eg. for 2018: New grape varieties in France, some forgotten, some hybrids). The matter of hybrids is of particular interest, because they have long been detested in France but are now being seriously considered as a solution to viticultural problems like downy mildew (see French wine's hybrid dilemma).

However, the situation in France is quite formal:

Grapevine clonal material in France is subjected to extensive testing and certification under the aegis of the Ministry of Agriculture. The Institut Français de la Vigne et du Vin (IFV) is a national agency certified to manage and coordinate the French national clonal selection program. The responsibilities now entrusted to the IFV were formerly performed by an entity known as the Etablissement National Technique pour l’Amelioration de la Viticulture (ENTAV), and include maintenance of the French national repository of accredited clones, and administration of the ENTAV-INRA authorized clone trademark to protect the official French clones internationally.

The list of approved French cultivars is important, because only cultivars from this list can be used in wines given legal protection under the Appellation d'Origine Contrôlée (AOC) scheme administered by the Institut National de l'Origine et de la Qualité (previously INAO). Recently, INAO has allowed other varieties from the list to be used in AOC wines as "grape varieties for climate and environmental adaptation", which means that issues such as climate change can be addressed by trialling new varieties.

There has been some concern expressed about restricted use of clones in many vineyards, especially outside Europe (eg. Genetic instability and how it affects wine). In the past, vineyards tended to be a mosaic of clones, but modern agriculture (not just for grapevines) has shown a strong move towards using single clones — those that are seen as being "the best" in some ineffable way. For example, Cabernet sauvignon clones 07 and 08 have been the basis of many of the California Cabernet vineyards for decades (see The guide to wine grape clones).

However, this approach is asking for trouble — when problems occur in the field they are likely to affect all of the plants at the same time, because the clones are genetically identical. Resilience to the vagaries of different seasons (especially weather, pests) is based on diversity, not lack of it. As has been noted (Myles et al., Proceedings of the National Academy of Sciences of the USA 108:3530-3535):

Vegetative propagation [has] discouraged the generation of unique cultivars through crosses. The grape currently faces severe pathogen pressures, and the long-term sustainability of the grape and wine industries will rely on the exploitation of the grape’s tremendous natural genetic diversity.

To this end, of the known varieties, 7,200 are grown at the Centre de Ressources Biologiques de la Vigne (CRB-Vigne) de Vassal-Montpellier, near the town of Marseillan in southern France.

Perhaps at issue here for the growers is that some clones will produce mediocre wines when grown in certain regions but not others. For example, it has been noted that the original Chardonnay clones used in Oregon came from California, where the climate is warmer and drier, and that this situation was much improved when clones were imported directly from Dijon in Burgundy, where the climate is more similar (see The role of grape clones in planting grapes)

Also, there is the matter of intellectual property rights — the use of some clones requires the payment of royalties (see How wine clones are already taking over). The Foundation Plant Services Grape Registry currently lists 594 grape varieties used for all purposes in the USA, which is more than in France, but many of these are proprietary. The latter do include, of course, the ENTAV-INRA authorized clones.