The Vine

The grapevine forms part of the family of plants that climb, and in its natural state the vine uses trees for support. It is a member of the genus Vitus, which includes several different species used for wine, although fine wine is made from the species vinifera. This species comprises 90% of world production and an examination of other species is unnecessary here. Many of the other species are native to North America and are not used for fine wine because of their marked “foxy” aromas, but have better resistance to pests (particularly phylloxera), disease, weather and soil conditions than V. vinifera. This makes them useful as rootstocks for the grafting of the vinifera wine grapes. The grapes in the V. vinifera species are subdivided into varieties, such as Cabernet, Chardonnay, Bombino Bianco, etc.

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These varieties are distinct groups of vines within V. vinifera that share the same general characteristics. A clone is a unique example of a variety. Each plant of a given clone shares the identical genetic makeup, which varies from other clones of the same variety because of genetic mutation over time, disease, or manmade selection for desired characteristics. The older a variety is the more variation is noted; there is much less difference between clones of Cabernet than between clones of Pinot Noir, for example, because Cabernet is a younger variety. Examples of the differences between clones include greater or lesser yields, greater or lesser resistance to disease, the greater or lesser ability to ripen grapes, variations in acid levels, aromatic character, and the size and color of the berries. Comparing these differences in vines grown in controlled environments can produce hardier vines with less viral infection. This process is known as clonal selection.

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Many different clones of Chardonnay exist, some of which were developed in Burgundy, and others in California at UC Davis. The Wente clone, also known as UCD 4 is one of the most widely planted of the New World clones. This clone, along with UCD 5 crop well but give big berries that can lack intensity. Another clone, UCD 6 shares many traits of 4 and 5, and is also prone to excessive vigor. Finally, UCD 7 and 15 produce smaller, looser bunches with berries that have thicker skin. For this reason, these clones are less prone to rot. They also have the benefit of maturing fairly early.

Clones developed in Burgundy are referred to as Dijon clones. Widespread Dijon clones include 95 and 96. In general, Dijon clones give smaller clusters and berries. Crop levels are moderate, and the grapes can produce wine that is concentrated. Since they are not well adapted to the heat in California, acidity can drop sharply at the end of ripening. Another Chardonnay clone is Mendoza or McRae. This clone is prone to millerandage or shatter, giving bunches with irregularly sized berries. Some winemakers prefer this clone because of this trait, since it provides naturally lower yields.

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Pinot Noir is the other grape where clonal difference is fairly important and there are many types on the market. 113, 114 and 115 produce relatively small clusters and ripen early, giving average yields, sugar levels and acidity. 113 and 115 can be prone to excessive vigor, however, and 114 to shatter. These are considered high quality clones. 667 and 777 give fruit in small clusters with small berries. They bud late, but flower and ripen with other clones, and 777 sometimes before. These are among the best clones of Pinot Noir. Several clones have also been developed at Davis, including UCD 4 (Pommard) and UCD 1A and 2A (Wadenswil).

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Not all growers plant vines that are the product of clonal selection. Some feel that this decreases wine complexity by leading to homogenization in the vineyard. One alternative is massal selection. Here cuttings for new planting are taken from the grower’s own vineyard. The cuttings are taken from the most successful vines, but they are not kept distinct in the same was as they are for clonal selection.

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The vine that produces the grapes, whether it comes from clonal or massal selection, is referred to as the scion. Because of the phylloxera root louse in the vast majority of the world’s vineyards, it has become necessary to graft this fruiting variety to a rootstock resistant to the pest. There are several types of grafts, but the essential distinction is between types of bench grafts, where the vines are done in the nursery during the winter and planted out in the spring, or the field grafts, which are done in the vineyard the year before. Field grafts are less expensive and quicker, but they are also less reliable.

Since grafting is necessary to combat phylloxera, it is important to choose the correct combination of rootstock and scion. There are considerations other than phylloxera resistance that help determine the proper match. Vigor is one important consideration, because some rootstocks tend to produce more foliage. This can shade the fruit, and draw the vine’s resources away from ripening the fruit, slowing the ripening process. Rupestris and 110R are examples of rootstocks with good phylloxera resistance but excessive vigor.

Tolerance of alkalinity in the soil is another factor. This is quite important in the vineyards of Champagne, because the chalk is very alkaline. Some rootstocks absorb iron less well in alkaline soils, interfering with the vines ability to conduct photosynthesis (an effect called chlorosis). Fercal 41B and 333 EM are resistant to this effect. Other varieties, such as 5 BB, are better adapted to heavy clay soils that can provide too much water to others. In spite of the largely positive benefits of widespread grafting, it has also led to increase in viral diseases (such as leaf roll virus).

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The trunk is the permanent portion of the vine, connecting the roots and the canes while getting thicker each year. The root system spreads through the soil, although not as deep as some people believe. Most of the root system is found between 2–6 feet, although it can go twice as deep as that if conditions are right. The roots serve to anchor the vine and provide a means to deliver water. This role in water absorption is the most important function of the roots, and the absorption of minerals is comparatively unimportant.

Photosynthesis is carried out in the leaves, combining water and CO2 from the air to form sugars, using the energy of the sun. This sugar is used as food by the vine for growth. The sugar that is not used by the shoots or the fruit is stored as starch or cellulose. The process of breaking down these sugars is referred to as respiration. This happens as oxygen combines with hydrogen and the carbon of the sugar to form water and carbon dioxide. During this process, the acidity of the grapes is reduced. This process of respiration happens more quickly in hotter temperatures, which is why grapes lose more acidity in warm climates.

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