Malus - Apple Trees
M27 - Very dwarf
MM106 - Semi-vigorous
Colt - Semi-vigorous
Pixie - Semi-dwarf
St Julian A - Semi-vigorous
SF - Self fertile
FG = flowering group that will pollinated each other
FG3 - Pollinated by flowering groups 2, 3 & 4
FG4 - Pollinated by flowering group 3, 4 & 5
These are all the rootstocks of the trees that control the growth rate.