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 limestone soil, good absorption of nutrients from the soil, as well as good graft affinity to the grafted grape variety without promoting trickling. A 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 those of the rootstock variety ensure good shoot growth and grape quality with uniformly high vine yields.