SO4 Rootstock — Moderate to Vigorous; Early Ripening; Widely Planted; Suited to Moist and Limestone Soils

SO4 is a hybrid rootstock whose full name is Sélection Oppenheim No. 4 de Teleki. It derives from a cross between Vitis berlandieri and Vitis riparia, first bred from seeds sent by the French nursery of Euryale Rességuier to Hungarian winegrower Sigmund Teleki in 1896. In 1912, Heinrich Fuhr, the director of the research station in Oppenheim, Germany, imported Teleki's selections from Hungary, and in 1919 selected out of those plants the clones SO4, SO5, and SO8. This history makes SO4 a product of Hungarian breeding talent and German institutional selection, refined for European viticultural conditions.

• Selected in 1919 by Heinrich Fuhr at the viticultural research station in Oppenheim from Teleki's 1896 Vitis berlandieri x Vitis riparia crosses
• SO4 stands for Sélection Oppenheim No. 4 de Teleki, reflecting its institutional and breeding origins
• Belongs to the same Berlandieri x Riparia family as Teleki 5C, Kober 5BB, 420A Millardet et de Grasset, and 161-49 Couderc
• Binova, a mutation of SO4 with hermaphrodite rather than male flowers, shares similar viticultural characteristics and offers even higher limestone tolerance

SO4 is one of the dominant rootstocks in both France and Germany, and its use is documented across all French wine-growing regions. Its combination of moderate vigor, reliable fruit set, advancement of maturity, and broad soil compatibility has made it a pragmatic default across diverse viticultural contexts. In Germany, SO4 and its close relative Binova are among the most commonly used rootstocks. In France, SO4 remains among the most widely planted, alongside 3309 Couderc and 161-49. Viticulturists in Alsace note that SO4 ripens fruit earlier than Fercal by roughly one week, and earlier than 3309 by up to two weeks, a meaningful advantage in marginal climates.

• One of the main rootstocks used in Germany alongside Binova, 5C, 5BB, and 125AA
• Estimated 180,000 hectares of French vineyard grafted to SO4, found in all French wine-growing areas
• Main rootstocks in France include SO4, 3309, and 161-49, with Fercal, Gravesac, and 34EM growing in popularity
• Advances ripening relative to Fercal by approximately one week and relative to 3309 by up to two weeks, according to Alsace growers

SO4 is classified as a moderate to vigorous rootstock, less powerful than Kober 5BB or 125AA but comparable to Couderc 161-49. A key characteristic is that it develops slowly in the first years of vine establishment before vigor increases significantly thereafter. It is especially well suited to varieties sensitive during flowering because it does not promote coulure or millerandage. SO4 favors fruit set, encourages early development and maturity, and supports good wood ripening. However, some growers report that SO4 can induce excess vegetation, shading berries and increasing susceptibility to grey rot and oidium. Canopy management is therefore important on more fertile sites.

• Moderate to vigorous scion growth; slower to establish than some alternatives but increases in vigor over time
• Does not promote coulure or millerandage, making it reliable for varieties with sensitive flowering such as Gewürztraminer
• Favors fruit set and advances phenological maturity, including good lignification of canes for winter hardiness
• Can induce excess vegetative growth in fertile soils, requiring active canopy management to avoid shading and disease pressure

SO4 tolerates up to 30 to 40 percent total limestone in soils, with up to 18 to 20 percent active limestone, making it suitable for many European calcareous sites, though excess active limestone can still cause iron chlorosis. It performs well in moist, even compact or poorly drained soils, and is considered a reasonable choice for waterlogged conditions. Crucially, SO4 is not suited to dry conditions and is not classified as drought tolerant, distinguishing it from berlandieri x rupestris crosses such as 110 Richter or 140 Ruggeri. It is also prone to magnesium deficiency, and grafting varieties with high magnesium demand onto SO4 can result in deficiency symptoms and inflorescence necrosis.

• Tolerates up to 30 to 40 percent total limestone and up to 18 to 20 percent active limestone before chlorosis risk increases
• Suited to moist, compact, and even poorly drained soils; a reasonable option for waterlogged vineyard conditions
• Not drought tolerant; not recommended for dry conditions without reliable irrigation or significant water-holding soil capacity
• Prone to magnesium deficiency; varieties with high magnesium demand should not be grafted to SO4

Despite its widespread use, SO4 has well-documented limitations that should guide rootstock selection decisions. Its tendency to promote vigorous vegetative growth in fertile soils can complicate canopy management and increase disease pressure from grey rot and oidium. Magnesium deficiency is a consistent concern, particularly when potassium levels are high, as elevated K to Mg ratios are associated with SO4. It is also susceptible to ring nematode. In Bordeaux, concerns about SO4's susceptibility to eutypiose (grapevine trunk disease) have led some producers to reconsider its use, particularly for Cabernet Sauvignon.

• Excess vegetative growth on fertile sites can shade fruit, delay ripening, and increase grey rot and oidium pressure
• Prone to magnesium deficiency, particularly where soil potassium is high; the K to Mg ratio can become strongly imbalanced
• Susceptible to ring nematode; moderate resistance to other nematode species should be assessed site by site
• Susceptibility to eutypiose has been noted in Bordeaux, particularly with Cabernet Sauvignon, where its otherwise useful traits may be outweighed by trunk disease risk

Understanding SO4 is easier when placed alongside its relatives. Within the Berlandieri x Riparia family, SO4 sits in the moderate to vigorous range, more vigorous than the lower-performing 420A Millardet et de Grasset but less so than 5BB Kober or 125AA Kober. Its sibling Teleki 5C is slightly more vigorous than SO4, with an intermediate position between 5BB and SO4. Binova, a mutation of SO4, shares its viticultural profile while offering improved limestone tolerance of up to 50 percent total and 30 percent active limestone. For sites requiring strong drought tolerance, berlandieri x rupestris crosses such as 110 Richter or 140 Ruggeri are more appropriate alternatives.

• Less vigorous than 5BB Kober or 125AA Kober; more vigorous than 420A Millardet et de Grasset
• Teleki 5C is closely related, slightly more vigorous, and shares many agronomic characteristics
• Binova, a mutation of SO4, offers similar attributes with greater limestone tolerance (up to 50 percent total, 30 percent active)
• For drought-prone sites, berlandieri x rupestris crosses such as 110 Richter or 140 Ruggeri are better suited than SO4