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The use of rootstocks in viticulture has become an important consideration in quality wine production. Prior to the late-19th century, nearly all grapevines were "own rooted", meaning that the vines were grown on their own natural rootstock. When the Great French Wine Blight hit in the mid-19th century, the European Vitis vinifera vines were decimated by the phylloxera pest which fed on the root of the grapevine. It was soon discovered that American grapevine species, such as Vitis riparia, Vitis rupestris and Vitis berlandieri had some natural resistance to phylloxera. With the aid of American entomologist Charles Valentine Riley, several nursery owners in Missouri and Texas horticulturalist Thomas Volney Munson, suitable American rootstock varieties were identified for grafting onto vinifera scion (top part of the plant).

By 1990, nearly 85% of the world's commercial vineyards were made up of Vitis vinifera vines grafted onto rootstock from different Vitis species. Beyond just resistance to phylloxera, the development of hybrid and different clonal varieties of rootstock has allowed viticulturists to identify different rootstock varieties that can help control vigor, encourage or delay ripening and be better adapted to drought conditions or vineyard soils with high lime content. The influence of rootstock on potential yield and wine grape quality has made selecting the right rootstock for the vineyard site and the style of wine desired to be produced one of the most important decision in vineyard management.

Function of rootstocks

Along with the leaves in the canopy that conduct photosynthesis and clusters of grapes that provide the fruit/seeds, the roots of the grapevine are one of the most important organs in the plant. In addition to anchoring the plant into the ground, the roots absorb needed water and nutrients from the soil and is the location for the synthesis of important compounds such as growth hormones gibberellin (which can also be synthesis in the leaves and shoots) and cytokinins. As the vine enters the dormant phase of the growing season, the roots serve as important storage areas for reserves of carbohydrates that will be needed to sustain the vine through the beginning of next year's growth.

When vineyard pests such as phylloxera or nematodes feed on the roots of grapevines, they damage the vines by reducing the ability of the root system to absorb nutrients and water. They can also be vectors for viral grape diseases such as grapevine fanleaf virus which can further reduce the vigor of the vine as well as the yield and potential ripening ability. It if often the risk posed by these root-feeding pests that encourage vineyard owners to utilize resistant rootstocks.

While rootstock can have some influence on the yield, vigor and viability of a grapevine, it does not change the primary flavor characteristics of the scion (top part of the vine). So a Chardonnay or Merlot vine planted onto rootstock from a member of an American vine species, such as the Vitis labrusca variety Concord, will not "inherit" any of the characteristic "foxy" flavors or aromas of the Concord variety. Regardless of which rootstock variety is used, the grapevine will be recognized as a member of the scion variety (i.e. as a Chardonnay or Merlot vine).

History

While the process of grafting a scion vine onto an already planted rootstock has been known since at least the time of the Ancient Romans, this usually just a mean of propagation in the vineyard where a new vine variety was being "head grafted" onto an existing vine. The choice of rootstock was limited to what was already available and, in Europe at least, was almost always another member of the same Vitis vinifera family.

It wasn't until the phylloxera epidemic of the mid-19th century when the idea of grafting rootstock from different members of the Vitis family onto scions of vinifera varieties was considered as a viable option to combat the devastation of the root-eating louse. French grape growers Gaston Bazille and Leo Laliman were some of the first influential figures to recommend grafting in 1869 after noticing that American vine varieties succumbing the infestation like the European vinifera vines were. The French botanist Jules Émile Planchon was commissioned by the French government to find a solution to the phylloxera scourge. Planchon traveled to the United States where he met Charles Valentine Riley, an entomologist for the state of Missouri. Riley was able to confirm for Planchon that the louse that was damaging the European vine was the same variety that was native to the United State and of which the American vine varieties had developed a natural resistance too.

Riley was able to put Planchon and his colleague, Pierre-Marie-Alexis Millardet, in contact with several nursery growers in Missouri who helped shipped rootstocks of American varieties over to Europe. The Texas horticulturalist, T.V. Munson, also provided some assistance in identifying suitable rootstock varieties. Between 1873 and 1876, millions of American rootstock cuttings were shipped to France from species such as Vitis aestivalis, Vitis riparia and Vitis rupestris.

By 1880, around 2,500 hectares (6,200 acres) of French vineyards had been grafted over to American rootstock. In 1881, the International Phylloxera Congress based in Bordeaux, officially recognized the grafting of European vinifera vines to American rootstock as the best solution for dealing with phylloxera and soon the number converted vineyards rose to over 45,000 hectares (110,000 acres) by 1885. This rapid transition was aided by the work of French viticulturist Gustave Foëx who wrote a simplified manual on the grafting process and selecting rootstocks in 1882 that was widely disseminated among growers in the Languedoc wine region of France.

Grafting process and terminology

In viticulture, the rootstock is the bottom and largely below ground segment of the grapevine that contains the rooting system of the vine. It is grafted (joined) to the scion which is the top above ground segment that includes the fruiting parts of the vine. Where the rootstock and the scion meet is called the graft union. After grafting, the vine is identified by the scion variety.

The grafting process that joins the scion and rootstock together can be done by hand using a variety of methods (cleft grafting, green grafting, notch grafting or whip grafting) or by machine (often using an omega shape cut). The process can take place in the vineyard, such as the method of "head grafting" where the already planted scion is cut off and a new grape variety is grafted onto the existing rootstock. This method is usually only done as a means of replanting or switching over to a new scion variety when an existing vineyard is already planted to a suitable rootstock.

It is more common to see bench grafting taking place in the nursery on one year old vines known as rootlings. Here both the scion and rootstock are cut to expose the cambium which contains a zone of undifferentiated cells. With the exposed scion and roostock positioned opposite each other, and matching diameter, the two segments are joined in a graft union which is often secured by paraffin wax to protect the union as the cells of the callus develops and fuse the two segments. To insure that the grafting takes, this process often takes place in humid (90-100% relative humidity) and warm (24-30°C/75-86°F) conditions in the nursery.

While grafting has done much to improve viticulture from some hazards, poor hygiene in the grafting process and the use of diseased material has also done much to propagate the spread of several viral grape diseases (such as leaf roll virus), which rarely show symptoms as rootlings.

List of notable rootstocks

Rootstock	Pedigree	Vigor	Phylloxera	Nematode	Lime	Drought	Notes
101-14 Millardet et de Grasset	V. riparia-rupestris hybrid	Low to Moderate	High	Moderate	Low	Very low	Produces a very shallow root system and can promote earlier ripening. Well suited for cool, damp soils with high fertility
110 Richter	V. berlandieri-rupestris hybrid	Very High	High	Low to Moderate	Moderate	High	Developed in 1889 by Franz Richter. Well suited for Mediterranean climates with clay-calcareous soils. Can delay ripening. Difficult to root in nursery.
1103 Paulsen	V. berlandieri-rupestris hybrid	Very High	High	Moderate	Moderate	High	Developed in Sicily. Very easy to graft and take root in the nursery. Very saline resistant. Well suited for dry, relatively compact soils
125AA (Kober)	V. berlandieri-riparia hybrid	High	High	Moderate	Moderate	Moderate	Adaptable to a wide range of soils but not ideal for varieties that are sensitive to coulure. Good rooting in the nursery and very resistant to chlorosis
140 Ruggeri	V. berlandieri-rupestris hybrid	Very High	High	Moderate	High	High	Developed in Sicily and well suited for Mediterranean climates. In fertile, moist soil can produce excess vigor. Good resistance to chlorosis
1613 Couderc	Solanis x Othello complex hybrid	Low	Low to Moderate	Moderate to High	Low	Low	Developed in 1881 by Georges Couderc. Best used in fertile, loam and sandy soils. Mostly found in California
161-49 Couderc	V. berlandieri-rupestris hybrid	Low	High	Low	High	Very low	Well suited for acidic soils with high resistance to chlorosis. Easy to graft and take root in the nursery. Widely planted in France & Germany
1616 Couderc	Solanis x Riparia cross	Low	High	High	Low	Low	Developed in 1881 by Georges Couderc. Best used in humid climates. Known to promote earlier ripening
3309 Couderc	V. riparia-rupestris hybrid	Moderate	High	High	Low	Very low	Developed in 1881 by Georges Couderc. Easy to graft and take root in the nursery. Well suited for acidic soils.
333 EM	Cabernet Sauvignon x V. berlandieri hybrid	Moderate	Moderate to High	Low	High	High	Developed in Montpellier, France. One of the few major rootstocks with V. vinifera parentage. Susceptible to coulure but resistant to chlorosis
41 B	Chasselas x V. berlandieri hybrid	Moderate	Low to Moderate	Low	High	Moderate	Developed in 1882 in Bordeaux and widely used in the Champagne and Cognac regions of France. Well adapted for calcareous soils
420A Millardet et de Grasset	V. berlandieri-riparia hybrid	Low to Moderate	Very High	Moderate	Moderate	Very low	Developed in 1887 and known as the "riparia for chalky soils" with high resistance to chlorosis. Known to promote earlier ripening
5 BB Kober/Teleki	V. berlandieri-riparia hybrid	High	High	High	Moderate	Low	Best used on clay soils in humid climates. Not well suited for varieties that have issue with coulure. Can have potassium and magnesium deficiencies
5 C Teleki	V. berlandieri-riparia hybrid	Moderate	High	High	Medium	Very low	Developed in 1922 by Andre Teleki with similar qualities to SO 4. Well adapted to vineyards in northern wine region. Can have potassium deficiency
99 Richter	V. berlandieri-riparia hybrid	Very High	Very High	Moderate to High	Moderate	Moderate	Developed in 1889 by Franz Richter. Can delay ripening when planted in cool climates. Well suited for deep, permeable soils of southern France
AXR1	V. vinfera-rupestris hybrid	High	Very low	Low	High	Moderate	Developed by Victor Ganzin in 1879. Responsible for the California phylloxera outbreak of the 1980s. Easy grafting
Dog Ridge	V. champini	Very High	Low to Moderate	Very High	Low	Low	Best used on light texture, relatively infertile soils. More often used for table grapes than high quality wine production
Fercal	V. berlandieri x Colombard x 333 EM hybrid	Moderate	Moderate	Moderate	Very High	High	Developed in Bordeaux for vineyard soils with high lime content. Easy grafting but can have magnesium deficiency if soils have excess potassium
Harmony	V. champini x 1613 Couderc hybrid	Moderate to High	Low	High	Low	Low	Developed in Fresno, California in 1966
Riparia Gloire de Montpellier	V. riparia	Low	Very high	Moderate	Low	Low	One of the earliest rootstocks developed during the French phylloxera crisis. Known to promote earlier ripening. Prefers moist, loose soils
Rupestris St. George	V. rupestris	High	High	Moderate	Low	Moderate	Developed during the French phylloxera crisis. Known to promote longer growing seasons. Prefers loose soils and very sensitive to coulure.
Schwarzmann	V. riparia-rupestris hybrid	Low to Moderate	High	Very High	Low	Very low	Best used on deep, moist soils. Grafts well but very sensitive to chlorosis
SO 4	V. berlandieri-riparia hybrid	Moderate	High	Low to Moderate	Moderate	Very Low	Developed in Oppenheim, Germany. Known to promote earlier ripening but prone to magnesium deficiency. Several clonal variations developed