Part one of Ferocious Focus: Rootstocks, the first of a series that looks at the more technical parts of wine, was about phylloxera, the nasty insect that almost destroyed the global wine industry in the late 1800s, and the solution, grafting European varietals on American rootstocks.
The use of rootstocks developed as a solution to protect vines against phylloxera vastatrix. This remains the main reason for using rootstocks and a rootstock’s level of resistance to phylloxera is a major factor that a grape grower considers when choosing what type of rootstock to use in a vineyard.
In addition to phylloxera resistance, however, a grape grower may also consider a rootstock’s resistance or tolerance to other pests such as nematodes. The grape grower may also consider resistance or tolerance to certain soil conditions such as:
- high levels of limestone which can cause some rootstocks to suffer iron deficiency;
- excess acidity which can cause aluminum toxicity in some rootstocks;
- high levels of salinity which can disrupt water uptake and vine nutrition;
- incidents of drought or waterlogging; and
- fertility which can lead to high levels of vigour in the rootstock.
The principal rootstocks are the American vine species, V. riparia and V. rupestris. But there are several different rootstocks made by crossing those two principal rootstocks as well as crossing those with others such as V. berlandieri, V. vinifera and V. champini. I won’t get into all the varying crosses—the important thing to know is that rootstocks and their crosses, as discussed above, have varying strengths and weaknesses. If a grape grower’s principal problem is nematodes, he may choose to use a V. riparia and V rupestris crossed rootstock like Schwarzman or a V. rupestris and V. berlandieri crossed rootstock like 99R.
A grape grower may also consider vineyard conditions when selecting a rootstock. For example, rootstocks have varying preferences for soil type: V. riparia prefers humid, cool, fertile soils while certain V. berlandieri and V. rupestris rootstock crosses prefer poor, dry soils. In addition, some rootstocks have poor uptake of magnesium which can lead to coulure where berries do not develop after flowering (e.g., V. riparia x V. berlandieri SO4 Selection Oppenheim); some rootstocks are resistant to acid soils (e.g., V. riparia x V. berlandieri 161-49C); and some rootstocks may be used in quality vineyards (e.g., V. riparia x V. berlandieri 420A) and some are unsuitable for growing high quality grapes (e.g., V. champini Dog Ridge).
Rootstocks also have varying degrees of vigor, or growth rates. The vigour of a rootstock will affect the vigour of the scion to which it is grafted and affect canopy management (a topic for a later Ferocious Focus) during the growing season.
I referred to rootstocks as Frankenstein in the first part of this post, but they are really the unsung heroes of wine grape growing and wine making. Without American rootstocks, the wine industry would not exist or at least look taste very different. With that in mind, for the next post, I plan to take a look at Cahors, France, which I recently visited and which suffered greatly as a result of phylloxera. Check back soon.