🌿 Rootstock

A rootstock is the root part of a grafted grapevine. The upper part, the scion, is the variety that bears the grapes. Rootstocks were developed by French viticulturalists in the late 19th century to combat grape phylloxera (Daktulosphaira vitifoliae), an insect that nearly devastated European vineyards. Most North American Vitis species resist phylloxera, so rootstocks are American species or their hybrids.

Most rootstocks are crosses of three species. Vitis riparia roots shallowly, Vitis rupestris is semi-drought tolerant, and Vitis berlandieri tolerates lime-rich soils. V. riparia and V. rupestris root easily from hardwood cuttings and graft well, while V. berlandieri roots poorly from dormant cuttings, so breeders crossed it with the other two. Three widely used hybrids are 110R (V. berlandieri x V. rupestris), Kober 5BB (V. berlandieri x V. riparia) and 101-14 Mgt (V. riparia x V. rupestris).

Today rootstocks serve more than one purpose. They are chosen for tolerance of nematodes, limited water, lime-heavy or saline soils, for erosion control, and to increase or decrease vigor. 101-14 Mgt gives moderate vigor and early growth, while 110R and Kober 5BB give high vigor and delay maturity. 110R tolerates drought, whereas 101-14 Mgt and Kober 5BB perform well in moist soils. Rootstocks based on V. riparia are not advised for saline soils, because yields decline there. A rootstock can also influence fruit characteristics.