SO4 (Selection Oppenheim 4) 

The 'definitive' rootstock for the UK, adapts to a very wide range of soil types. Tolerant of wet soil, especially suitable for fertile soils containing humus, which are not inclined to excessive dryness; it's performance in very dry soil is average. It produces a 'semi-plunging' root system.
Tolerant of limestone (CaCO3): will tolerate up to 30 (to 40)% total limestone with up to 18 (to 20)% 'active' limestone (i.e. the limestone part of the soil which the vine can take up; this is very dependent on the composition and structure of the soil). Excess active limestone generally has a detrimental effect on growth and causes chlorosis (a physiological ailment, due to various causes, resulting in yellowing of leaves and other green parts of the plant).
Strength of growth is quite vigorous but not as strong as 5BB or 125AA. It is especially suitable for varieties which are sensitive in flowering; it doesn't promote coulure or millerandage. It favours fruit-set, encourages early development and maturity, also good wood-ripening. It is more resistant to frost than 5BB.

Binova (an SO4 mutation) has similar characteristics to SO4: it is even more limestone-tolerant (up to 50% total, 30% active).

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