A rootstock vine; see there.
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.
With regard to suitability for viticulture, rootstock grape varieties must also fulfil 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-up 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 grape variety with those of the rootstock generally 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 pioneering research of the US botanist Thomas Volney Munson (1843-1913) made a decisive contribution to this. A rootstock with perfect phylloxera resistance, approved in 1989, was created by Dr. Helmut Becker (1927-1990) from a crossbreed 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 have been made by the authorities 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 vine. 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 (better known under the old name Vitis berlandieri) or Vitis champinii have a poor rooting record, so that the cuttings ends are coated with the growth hormone auxin to induce root development.
Just like quality wine grape varieties, rootstock vines are also approved or classified by the state authorities (this can also vary from one wine-growing region to another). Some (latent) grapevine diseases (see also under grapevine enemies) can be further spread on a large scale during grafting and cutting propagation if, for example, plant material infected with viruses or bacteria (rootstock or scion) is used. The effects often only become visible 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).