Apple rootstocks can have a variety of desirable characteristics such as resistance to crown rot oomycetes (Phytophthora spp.), resistance to fire blight bacteria (Erwinia amylovora), resistance to Woolly apple aphids, dwarfing and tree branching modifications, increased precocity (early fruitfulness), increased productivity, and tolerance to apple replant disease (ARD). There are five major types of rootstocks used in the US. These include: Budagovsky (= Bud or B), Cornell/Geneva (=CG or G), Malling (=M) & Malling Merton (=MM), Michigan Apple Rootstock Clones (=MARK), and East Malling/Ashton Long (=EMLA) which are certified virus-free selections of Malling or Malling Merton. Rootstock names consist of the the type name or its abbreviation followed by the selection number. For instance, a Budagovsky selection 118 would be seen as either Budagovsky 118, Bud 118 or B.118. They all refer to the same stock material. As mentioned above, EMLA  are virus-free rootstocks derived from a corresponding M or MM selection. They have comparable characteristics to the uncertified material, but tend to be 5-10% more vigorous.

Tree size comparisons using different rootstocks.
Tree size comparisons using different rootstocks based on percent size of standard apple seedling.

Description of commonly available apple rootstocks

B.9 (Bud.9, Budagovsky 9) B.118 (Bud.118, Budagovsky 118) EMLA 7 EMLA 26 EMLA 106 EMLA 111 M.26 (Malling 26) G.11 (Geneva 11®) G.41 (Geneva 41®) G.890 (Geneva 890®) G.935 (Geneva 935®) M9-337 (Malling 9 virus certified #337) Nic 29®, RN 29 cv. (Malling 9 selection NIC 29) Supporter 4