Wine Grape Rootstocks
Choosing the Right Rootstocks
A fundamental decision in developing the vineyard is choosing the right rootstock best suited to the site and conditions. Ideally, vineyard management strategies should consider the site-specific properties of individual soils, the individual requirements of the rootstocks and the scion, as well as the relationship between the two. When choosing a rootstock, the wine grape grower must consider its resistance to phylloxera (Daktulosphaira vitifoliae), its resistance to nematodes, and other factors such as its environmental tolerance to drought, wetness, salinity, and lime as well as the influence on the scion in controlling vigor and ripening time. Generally, there is no single "universal" rootstock that is suited for all situations, and very likely some "fine tuning" is needed to identify the best rootstocks for each vineyard block.
Resistance to Soil-Borne Pests
The first criterion in choosing a rootstock is its resistance to grape phylloxera since rootstocks with V. vinifera parentage do not provide adequate phylloxera resistance. The phylloxera resistance of Native American and French-American hybrid varieties is variable, but rarely high. They have adequate resistance to phylloxera to grow and maintain adequate vine size when the initial phylloxera pressure is low. However, the yield potential of these varieties will increase when they are grafted onto a phylloxera resistant rootstock.
Even though grapevines are considered relatively tolerant to water deficits, grapevine growth and yield can be seriously reduced in drought-like conditions. Drought tolerant rootstocks are expected to enable the scion to grow and yield when water supply is limited. Drought tolerance is highly desirable if irrigation is unavailable.
In situations where there is an impermeable layer close to the soil surface and the site experiences high spring rainfall, there may be the potential for waterlogging.
Acidic soils are common in many viticultural growing regions, and liming to increase soil pH is a common practice at many vineyard sites.
The salinity of irrigation water and salinity associated with soils or rising water tables can affect productivity in grapevines and is detrimental to wine quality.
Vines growing on their own rootstocks will suffer from lime-induced chlorosis on soils rich in limestone (such as in Champagne, Cognac, and Burgundy) where calcium carbonate (CaCO3) in the soil locks up the iron, which is needed to produce the chlorophyll for photosynthesis.
Influence on the Scion
The ability of a rootstock to control the scion's vigor is one of the most desirable attributes of any rootstock, second only to phylloxera resistance. Rootstocks take up water and nutrients from the soil and provide them to the scion.
Rootstocks have a pronounced influence on the mineral nutrition of the fruiting variety. Vigorous stocks tend to reduce zinc levels but increase the uptake of potassium.
Rootstocks can influence fruit maturity hence ripening date can either be delayed or advanced. The relative length of the growing season varies among the rootstocks and it is considered this may influence the timing of grape maturity.
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