Currently studying my diploma and trying trying to find a source where I can find information on typical rootstocks used in different regions, the Medoc for example and how producers go about clonal selection in different regions.
When I took the Unit 2 exam, the only question(s) pertaining to rootstocks were covered in the Unit 2 book. Which types are more nematode resistant, drought tolerant, chlorosis resistant, for example. For your own knowledge, and to continue your studies in the future, it is useful to ask growers in different regions what they use and why.
Most of the rootstocks used today are hybrids of 3 species: v. riparia, v. rupestris, adn v. berlandieri (e.g. SO4, 8B, 99 Richter, 110 Richter, 1103 Paulsen are all v. berlandieri x v. riparia while Riparia Gloire is v. ruparia and Rupestris du Lot is v. rupestris).
Of course, an example of a rootstock to know is the A x R1 that was rupestris x Aramon, which is V. vinifera x V. rupestris. The vinifera in the rootstock made it susceptible to phylloxera and that rootstock is very clearly associated with California.