A rootstock vine (also Millardet et de Grasset 420 A); see there.
Name for the lower part or rootstock of a grafted vine that originates from a phylloxera-resistant American vine. In grafting, the upper part (scion) 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 varieties to the underground stages of phylloxera, or to the nodosities and tuberosities (growths) formed on the roots by 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 chalky soil, good absorption of nutrients from the soil, as well as good graft affinity to the grafted grape variety without promoting the coulure. A good intergrowth of the two foreign tissues at the grafting site and the harmonious coordination of the growth characteristics of the grafted grapevine variety with those of the rootstock variety ensure good shoot growth and grape quality with uniformly high vine yields.
The 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 cross of 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.
Therefore, there are official recommendations as to which rootstock harmonises best with which grape variety (top) on which soil and produces the required results. Cuttings of most rootstock varieties root without problems, but cuttings of European Vitis vinifera still root best. Therefore, the European part of a grafted vine cutting should not be dug into the soil. The rootstock varieties with crosses of Vitis cinerea var. helleri (old name Vitis berlandieri) or Vitis champinii root poorly, according to experience, so the cuttings ends are coated with the growth hormone auxin to induce root formation.
Just like quality wine grape varieties, rootstock vines are also approved or classified by the state authorities (differently per wine-growing region). Some (latent) vine diseases can be spread on a large scale during grafting and cuttings propagation if, for example, plant material (rootstock or scion) infected with viruses or bacteria is used. The effects often only become visible in older canes. For this reason, the use of plant material that is as healthy as possible and free of viruses is prescribed by law in the EU. In this respect, proof must be provided by means of a standardised procedure (see under certification of vines).
The development of special rootstocks on a larger scale 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,...
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