Wine Grape Rootstocks
Choosing the Right Rootstocks
A fundamental decision in developing the vineyard is selecting the right rootstock, best suited to the site and its 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 it is likely that some “fine-tuning” is needed to identify the best rootstocks for each vineyard block.. There are four characteristics of rootstocks that should be considered when making a selection:
Resistance to Phylloxera
Grape phylloxera, Daktulosphaira vitifoliae, is an aphid-like insect that feeds aggressively on grape roots. The soil-borne form of grape phylloxera is found in almost every major grape-growing region worldwide, with the notable exception of Chile and some isolated areas with specific soil conditions, such as high sand content. The root form of this pest prefers vines growing in heavy clay soils. Phylloxera is native to the eastern and southeastern United States, where native American grape species coevolved with the insect. The American grape species Vitis rupestris, V. berlandieri, and V. riparia are resistant to phylloxera.
Resistance to Nematodes
Many soils also harbor plant-parasitic nematodes, which are microscopic worms. There are several types of parasitic nematodes, including both free-living (ectoparasites) and those that spend part of their lives in vine roots (endoparasites). In some viticultural regions, such as parts of Australia and Chile, nematodes pose a greater threat to vine production than phylloxera. In these regions, phylloxera resistance is secondary to nematode resistance when selecting rootstocks for vineyards.
Environmental Tolerance
Drought Tolerance
Even though grapevines are considered relatively tolerant to water deficits, grapevine growth and yieldvcan be seriously reduced in drought-like conditions. Drought tolerant rootstocks are expected to enablevthe scion to grow and yield when water supply is limited. Drought tolerance is highly desirable ifvirrigation is unavailable.
Waterlogged Soils
In situations where there is an impermeable layer close to the soil surface and the site experiencesvhigh spring rainfall, there may be the potential for waterlogging.
Soil Acidity
Acidic soils are common in many viticultural growing regions, and liming to increase soil pH is a common practice at many vineyard sites.
Soil Salinity
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.
Calcareous Soils
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
Vine Vigor
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.
Mineral Nutrition
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.
Ripening Tendency
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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