Rootstock

A rootstock is a plant, and sometimes just the stump, which already has an established, healthy root system, used for grafting a cutting or budding from another plant. The tree part being grafted onto the rootstock is usually called the scion. The scion is the plant which has the properties desired by the propagator, and the rootstock is the working part which interacts with the soil to nourish the new plant. After a few years, the tissues of the two parts will have grown together, producing a single tree although genetically it always remains two different plants.

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The use of rootstocks is most commonly associated with fruiting plants and trees but is the only way to mass propagate many types of plants that do not breed true from seed or are particularly disease susceptible when grown on their own roots.

Although grafting has been practised for many hundreds (if not thousands) of years, most orchard rootstocks in current use were developed in the 20th century.

A variety of rootstocks are used for the same scion species because they impart different properties to it, such as vigour, fruit size and precocity. Rootstocks are also selected for traits such as resistance to drought, root pests, and diseases.

The rootstock can be a different species from the scion, but must be closely related. Grafting can also be done in stages; a closely related scion is grafted to the rootstock, and a less closely related scion is grafted to the first scion. Also, a serial grafting of several scions may produce a tree that bears several different fruit cultivars. The same rootstock takes up and distributes water and minerals to the whole system.

Grapevines for commercial planting are grafted onto rootstocks, while vines available for sale to back garden viticulturists are usually not. Grape growers prefer not to take the risk of purchasing or growing a whole plant, when it is safer to establish a number of healthy rootstocks and then graft vines onto them as they desire. This provides an extra measure of control over the growth of the plant, since the quality and characteristics of the resulting fruit are so important.

It can be hard to match a plant to the soil in a certain field or orchard. Growers want a rootstock which is compatible with the soil; the fruiting characteristics of the scion can be considered later, once the rootstock has proved successful. Rootstocks are studied extensively and sold with a complete guide to their ideal soil and climate. Growers determine the pH, mineral content, nematode population, salinity, water availability, pathogen load and sandiness of their particular soil, and select a rootstock which is matched to it. Genetic testing is growing more common, and new cultivars of rootstock are always being developed.

AxR1

AxR1 is a grape rootstock once widely used in California viticulture. Its name is an abbreviation for "Aramon Rupestris Ganzin No. 1", which in turn is based on its parentage: a cross (made by a French grape hybridizer named Ganzin) between Aramon, a Vitis vinifera cultivar, and Rupestris, an American grape species, Vitis rupestris - also used on its own as rootstock, "Rupestris St. George" or "St. George," referring to a town in the South of France, Saint Georges d'Orgues, where it was popular.

It achieved a degree of notoriety in California when, after decades of recommendation as a preferred rootstock -despite repeated warnings from France and South Africa about its susceptibility (it had failed in Europe in the early 1900's), it ultimately succumbed to phylloxera in the 1980s, requiring the replanting of most of Napa and Sonoma, with disastrous financial consequences.