Designation for the lower part or rootstock of a grafted vine that comes from a phylloxera-resistant American vine. During grafting, the upper part (grafting rice) of European grape varieties of the species Vitis vinifera is grafted onto this. The main reason for such grafting is the low susceptibility or resistance of the roots of American wild varieties to the underground stages of phylloxera, or to the nodosities and tuberosities (growths) formed on the roots by the phylloxera infestation.
Quality criteria
With regard to suitability for viticulture, rootstock grape varieties must also meet further breeding requirements. These are low susceptibility to both types of mildew, low tendency to chlorosis, high resistance to bacteria and viruses, good wood structure and wood maturity, good adaptation (compatibility) to different and difficult soil types such as dry soil or calcareous soil, good absorption of nutrients from the soil, and good grafting affinity to the grafted grape variety without promoting trickling. Good intergrowth of the two foreign tissues at the grafting point and the harmonious coordination of the growth characteristics of the grafted variety with those of the rootstock ensure good budding and grape quality with uniformly high vine yields.
The vast majority of rootstocks used in European countries are descendants of the three American wild species crosses Vitis berlandieri x Vitis riparia, Vitis riparia x Vitis rupestris and Vitis berlandieri x Vitis rupestris. The research of the US botanist Thomas Volney Munson (1843-1913) made a decisive contribution to this. A rootstock with complete phylloxera resistance, approved in 1989, was created by Dr. Helmut Becker (1927-1990) from a crossbreeding Vitis riparia x Vitis cinerea. He named it after the German oenologist Dr Carl Börner (1880-1953). Not every rootstock variety is equally suitable for the different soil types, site conditions, noble varieties and growth requirements.
For this reason, official recommendations exist as to which rootstock harmonises best with which grape variety (upper part) on which soil and produces the required results. The cuttings of most rootstock varieties root without problems, but the best ones still root the cuttings of the European Vitis vinifera. Therefore the European part of a grafted vine cuttings should not be dug into the soil. The rootstock varieties with crosses of Vitis cinerea var. helleri (old name Vitis berlandieri) or Vitis champinii do not root well, so that the cuttings ends are coated with the growth hormone auxin to induce root development.
Just like quality wine grape varieties, rootstock grape varieties are also approved or classified by the state authorities (varies by wine-growing region). Some (latent) grapevine diseases can be spread on a large scale during grafting and cutting propagation, for example if plant material infected with viruses or bacteria (rootstock or grafting rice) is used. The effects often only become apparent with older vines. For this reason, the use of plant material that is as healthy and virus-free as possible is required by law in the EU. This must be verified by a standardised procedure (see under Certification of vines).
Grower
The development of special rootstocks of larger size began in the last third of the 19th century. Among the most successful breeders are François Baco, Helmut Becker, Carl Börner, Maxime Cornu, Georges Couderc, Gustave Foëx, Victor Ganzin...
