Pinot Noir: Rootstocks and Clones for West Sonoma County
By Mat Gustafson
Rootstocks are one American vine species or hybrids of several. Rootstocks are used to overcome soil pests, disease, or special soil conditions. The main reason rootstocks were developed was because of Phylloxera, which has been present in California since 1873. Vitus Vinifera (European) vines are not resistant to Phylloxera but American vines are resistant.
The rootstock AXR1 had been found so adaptable in California it was described in Winkler's textbook as the nearest approach to an all-purpose rootstock, despite Winkler's qualifying phrase "resistance to Phylloxera is not high". Most of the AXR1 had to be replaced in the 1980's but still is doing fine in many Sonoma County vineyards because of remote locations and sandy soils.
It is a given that all rootstock selections today have to be Phylloxera resistant. The other main considerations for rootstock are desired vigor levels and adverse soil conditions. High vigor can cause poor fruit set in the spring and too much vigor at the end of the growing season will have a detrimental effect on fruit ripening and wine quality. It is always better to error on the side of low vigor for your spacing and site. Too little vigor will not allow the vineyard to reach its potential yields.
Clonal selection was first discovered in Germany in 1926 and has been used extensively since in European countries. Through vegetative propagation, taking cuttings and rooting them or grafting, the exact same DNA of the mother plant will be produced. In California field selection was the norm for many years. Field selection is the practice of going into a vineyard and taking cuttings from the best vines in the vineyard to use for new plantings. This method does not give the consistency of clonal selection because many different mother vines are being used to supply bud wood.
Pinot Noir shows extreme variation between clones, which suggest that multiple selections were initially made from the wild and/or a high mutation rate. Spontaneous mutations can sometimes occur and cause small but perceptible changes to the vines genetic make-up. The vines can also be changed by viroid incidence that can lead to clonal variation. This is the principal that UC Davis adheres to and is why they are so adamant about releasing only virus free vines, mostly through heat treatment. Because of this it usually takes at least three years to clear clones through UC Davis.
The two factors in west Sonoma county that dictate rootstock selections are acidic soils and limited water supplies, especially in mid-summer to late fall. Rootstocks must be tolerant of the acidic soils to grow well. Any rootstock that is very susceptible to drought conditions will not do well in most west county vineyards.
The common rootstocks presently being used here are Riparia Gloire, 420a, and 101-14. Riparia Gloire is very phylloxera resistant and has very low vigor, providing for lower yields of improved quality fruit and early ripening. It does need a good water supply making it unsuitable for many sites in this area. Rootstock 420a is highly regarded for high quality vineyards, being a lower vigor rootstock that hastens maturity. It does very well in chalky or limestone soils that we do not have and is also susceptible to waterlogging. The most planted rootstock in this area is 101-14; it is the most tolerant of the acidic soils we have here. It is low vigor and early maturing and produces high quality wines. It has a shallow root system that works well in sites with little topsoil. The only weakness for this rootstock in this area is the ability to survive drought conditions.
The pinot Noir clones that have historically been used in Sonoma County are Beringer, Martini, Pommard, Calera, and Swan. Most of these were really field selections rather than true clones. These varieties are generally earthier, funkier, slightly higher yielding and later ripening than the new Dijon clones. They have shown deeper flavors but this could be a factor of older vines than clonal difference.
The new Dijon clones from France are true clones and include 113, 114, 115, 667, 777, and most recently 828. Dijon 115 was the first clone available and so far has proven to be the most consistent of the bunch. It is early ripening and very fruity but has enough structure and complexity to make a good wine on its own. Dijon 777 is the other new clone that has the ability to stand on its own. It is later ripening than 115, earthier, and a little more tannic.
Dijon 113 and 114 are fruity, early ripening, and can be a little tutti fruity. They are generally considered blending clones. Dijon 667 is later ripening, has a good balance of fruit and earth, and a bit of tannin. It is also considered a blending clone. Dijon 828 is said to be very similar to 777 with more fruit to go with the earthiness. It is highly regarded but has only been available here for a short period of time. The first vintage from the Dutton Ranch Manzana Vineyard was lighter with pretty fruit with good texture. I would expect it to be darker and more full bodied in the years to come.
The winemaker must decide what the style of wine it is they are hoping to produce to make proper clonal selections. If an earthy, funky, more traditional style is desired then the old clones would be the best choice. If a fruitier, more forward style is desired then the new Dijon clones are the ones. The site will determine the rootstock selection more than the particular clone choice. Clones and rootstocks are just a small part of the equation in wine quality but well planned combinations will produce the best wines.