Clonal selection in vineyard plantings

Cabernet Sauvignon is the most planted grape variety in the world, with approximately 290,000 hectares of the vine planted worldwide in 2010 (Sereno). The grape, which is believed to have originated in the south of France, and has been recorded as growing in Bordeaux since the 17th century, is the result of a natural cross between the Cabernet Franc and Sauvignon Blanc varieties. To this date, fully 50% of the 53,000 hectares planted in France is located in its area of origin.

Many a Cabernet Sauvignon vine have been planted worldwide but the two poles of excellence, if one considers production volume and consumer spend, are definitively Napa and Bordeaux. In this exercise I examine the use of Cabernet Sauvignon clones in the two regions to determine whether there are any appreciable differences in type and/or application and, if so, how it manifests. But first, some background on clones.

Early vineyards were planted/replanted with cuttings sourced from successful vines in a vineyard, a process which is referred to as massal selection. The advantage of this method is that all the good qualities of the parent plants can be passed on to these new vines but the same is also true for negative characteristics. The more modern practice is to use clonal selections as the source for these new plantings and, in so doing, pass on the desirable characteristics while eliminating those that provide negative effects. Areas of potential clonal differentiation are shown in the table below.

Component Characters	Manifestations
Vine	Upright Weeping High yield Low yield
Leaf	More lobed Less lobed
Cluster	Compact Loose
Berry	Color Size Shape Maturity pH
Flavor	Anthocyanin levels Color Muscat character
Wine	Sensory perception

Source: Deborah Golino presentation on source of Cabernet Sauvignon clones, UCD course, 5/15/2008.

In the case of clonal selection, the source material has undergone a number of procedures "designed to isolate and provide premium stock to grape growers" (Jackson, Wine Science). The key objective of any clonal selection program is to improve crop yield and grape quality by providing virus-free (or impact-neutral) rootstock and scions to the grower. Viruses can negatively impact the vine in the following areas (Bisson):

• Vine
• Pruning weight
• Shoot numbers
• Yield
• Cluster numbers
• Berry
• Berry weight
• Sugar levels
• Titratable acidity
• pH
• Other measures
• Shoot weight
• Cluster weight
• Berries/cluster

In California, the body that is primarily responsible for certifying grape vine material is Foundation Plant Services, "a self-supporting service department in the College of Agricultural & Environmental Sciences at the University of California, Davis which produces, tests, maintains and distributes premium foundation level virus and disease-tested plant materials for use by California nurseries" (http://fpms.ucdavis.edu/). The FPS process is illustrated graphically in the figure below.

Source: Modified from Deborah Golino presentation on source of
Cabernet Sauvignon clones, UCD course, 5/15/2008

It normally takes 2 years for a vine to go through the process from end to end. If the vine is found to have a virus, that timeframe is extended to 7 years.

The heat therapy  identified in the Disease Elimination Phase involves exposing dormant cuttings to high temperatures (~ 38℃) for several weeks. This approach has been supplanted by shoot-tip culture, "a disease elimination technique whereby pieces of the apical growing point are excised from a plant and cultured in a sterile growth media apart from the plant. In microshoot tip therapy, as practiced at FPS, a growing tip that is less than 0.5mm is excised from the shoot tip. Many pathogens, including viruses and the crown gall bacterium, are eliminated by this technique" (http://iv.ucdavis.edu/files/72924.pdf).

The body responsible for certification of clones in France is the Institut Francais de la Vigne et du Vin (IFV; formerly ENTAV) and its regional vine selection partners (INRA Bordeaux, Chambre d'agriculture de Gironde, and Chambre d'agriculture des Pyrenees-Atlantiques for Cabernet Sauvignon). This organization began its work in the 1960s and has traversed two generations of clones with a third generation in its future (See figure immediately below). The IFV clone-certification process is illustrated in the second figure.

Jackson recommends that more than one clone be planted in a vineyard as a mechanism for increasing the variability and complexity of flavors in the finished wine. Boulton, et al. (Principles and Practices of Winemaking), suggests at least two clones should be planted in small plots and up to five or six in larger vineyards in order to avoid problems that may arise due to limited genetic variation in a single clone.

I will continue with the specifics of the Cabernet Sauvignon clones in my next post.


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