Designation for the lower part or rootstock of a grafted vine stock, which originates from a phylloxera-resistant American vine. In the grafting process, the upper part (noble vine) of European grape varieties of the species Vitis vinifera is grafted onto it. The main reason for such grafting is the low susceptibility or resistance of the roots of American wild species against the underground stages of the phylloxera, or against the nodosities and tubercles (growths) formed by phylloxera infestation on the roots.
Lower part (root system): 1 = grafting point, 2 = lateral roots, 3 = root shaft, 4 = foot roots
Upper part (noble vine): 1 = one-year-old wood, 2 = two-year-old wood, 3 = cordon old wood, 4 = trunk old wood, 5 = water shoots one-year-old wood, 6 = grafting point
Quality criteria
Regarding suitability for viticulture, rootstock varieties must also meet further breeding requirements. These include low susceptibility to both mildew types, low tendency to chlorosis, high resistance to bacteria and viruses, good wood structure and wood ripeness, good adaptation (compatibility) to various and difficult soil types such as dry soil or calcareous soil, good uptake of nutrients from the soil, as well as good grafting affinity to the grafted grape variety without promoting shatter.
A good fusion of the two foreign tissues at the grafting point and the harmonious coordination of the growth characteristics of the grafted grape variety with the rootstock selected according to the soil type ensure good shoot growth and grape quality with consistently high yields of the vine stock.
Grape species for rootstocks
The vast majority of rootstocks used in European countries are descendants of crossbreeds of the three American species Vitis berlandieri x Vitis riparia, Vitis riparia x Vitis rupestris and Vitis berlandieri x Vitis rupestris. The greatest merit was achieved by the US botanist Thomas Volney Munson (1843-1913). A rootstock approved in 1989 with complete phylloxera-resistance was created by Dr. Helmut Becker (1927-1990) from a cross of Vitis riparia x Vitis cinerea and named after the German oenologist Dr. Carl Börner (1880-1953).
Suitability
Not every rootstock variety is equally suitable for the various soil types, site conditions, noble varieties, and growth requirements. Therefore, there are official recommendations on which rootstock harmonizes best with which grape variety (upper part) on which soil and brings the required results.
The cuttings of most rootstock varieties root without problems, but the cuttings of the European Vitis vinifera still root best. Therefore, the European proportion of a grafted vine cutting should not be buried in the soil. The rootstock varieties with crosses of Vitis cinerea var. helleri (old name Vitis berlandieri) or Vitis champinii are known to root poorly, so the cutting ends are treated with the growth hormone auxin to induce root formation.
Approval
Just like quality wine grape varieties, rootstocks are also approved or classified by the state authorities (differently per wine-growing region). Some (latent) vine diseases can be further spread during grafting and cutting propagation if plant material (rootstock or noble vine) infected with viruses or bacteria is used. The effects often only become visible in older stocks. Therefore, the use of as healthy, virus-free planting material as possible is legally required in the EU. Proof must be provided through a standardized procedure (see under certification of vines).
Breeders
The development of special rootstocks began towards the end of the 19th century. Notable breeders include François Baco, Helmut Becker, Carl Börner, Maxime Cornu, Georges Couderc, Gustave Foëx, Victor Ganzin...
