Term for the lower part or rootstock of a grafted vine that originates from a phylloxera-resistant American vine. During grafting, the upper part (scion) 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 wild American varieties to the underground stages of phylloxera, or to the nodosities and tuberosities (growths) formed on the roots as a result of phylloxera infestation.

Lower part (root system): 1 = grafting point, 2 = lateral roots, 3 = root stem, 4 = foot roots

Upper part (scion): 1 = one-year-old wood, 2 = biennial wood (in the following year; is then usually removed), 3 = cordon(old wood), 4 = trunk (old wood), 5 = water shoots (one-year-old wood), 6 = grafting point

Quality criteria

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 (tolerance) to different and difficult soil types such as dry soil or limestone soil, good absorption of nutrients from the soil, as well as good grafting affinity to the grafted grape variety without promoting coulure.

Good intergrowth of the two foreign tissues at the grafting site and the harmonious coordination of the growth characteristics of the grafted grape variety with the rootstock selected according to the soil type ensure good vigour and grape quality with consistently high vine yields.

Vine species for rootstocks

The majority of rootstocks used in European countries are descendants of crosses of the three American species Vitis berlandieri x Vitis riparia, Vitis riparia x Vitis rupestris and Vitis berlandieri x Vitis rupestris. The greatest contribution was made by the US botanist Thomas Volney Munson (1843-1913). A rootstock with complete phylloxera resistance, approved in 1989, 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).

Extraction of rootstock wood

The rootstock is mainly harvested in specialised vine nurseries. A common method is Greiner-Decker's diagonal stake training, in which particularly long and well-matured annual canes are produced by pulling up the shoots at an angle. These are used as cuttings for rooting.

Suitability

Not every rootstock variety is equally suitable for the different soil types, site conditions, noble varieties and growth requirements. For this reason, there are official recommendations as to which rootstock harmonises best with which grape variety (top) on which soil and produces the required results.

The cuttings of most rootstock varieties root without any problems. However, shoots of the European Vitis vinifera root particularly easily. Therefore, when planting out grafted vines, make sure that the grafting point remains above the soil surface. If the European part of the scion were to be buried, it could form its own roots - and the vine would lose its phylloxera resistance.

Experience has shown that rootstock varieties with crosses of the American species Vitis cinerea var. helleri (old name Vitis berlandieri) or Vitis champinii root less well, so the ends of the cuttings are often treated with the growth hormone auxin to promote root formation.

Authorisation

Just like quality wine grape varieties, rootstock grape varieties are also authorised or classified by the state authorities (depending on the wine-growing region). Some (latent) vine diseases can be spread during grafting and cuttings propagation if plant material (rootstock or scion) infected with...