Here is an article I found
on Bud 9/antonovka interstems and the relationship of planting depth to
frost resistance and trees size. Also yield efficiency:
Acta Horticulturae 243: IV International Symposium on Research and
Development on Orchard and Plantation Systems- Effect of New
Rootstocks of Polish, Russian and Czechoslovakian Breeds and Two Depth of
Planting of Trees with Interstems on Growth and Cropping of 3 Apple
Cultivars. Written by A. Czynczyk, B. Omiecinska:
Interstem B9 on antonovka rootstock were similar in size to M9.
(M9 produces a tree that tops out at roughly 8 feet high) but produced
significantly higher crops than those planted on M9. Whether
planted with the interstem above the ground or whether planted with the
lower end (the interstem/rootstock union) of the interstem 15 cm below
the ground, Bud 9 interstem on antonovka rootstock was also among
the most yield efficient of those tested. Those planted with the
interstem 15 cm below the ground produced fewer suckers and also showed
higher frost resistance in the severe winter of 1986/87.