I noticed something odd today. I have a random seedling crab apple, to
which I have grafted six branches of eating apples. (Karmijn x2, Cox,
Ribston, Ashmead, and Tydeman's late orange) Most of the leaves of the
crab have fallen, and the rest have all turned yellow. But five of the
six grafted branches are still fully green, and the other looks like it
has died (the cox). So I would say that dormancy is definitely not
controlled by the rootstock, although I suppose it might have an
influence.
Note that this is the same tree that frustrates me every year as the
crab branches flower and fruit, and the grafted branches just grow
leaves. Note also that except for the cox, the grafted branches look
quite healthy, and some of them have gotten very large. (especially
the Ashmead and Ribston, which are on the sunniest side) So the tree
looks irregular, and a little sad, when it is in bloom. The grafts
were done in 1999 and 2000. The tree only gets a few hours of full sun
each day, which is my working hypothesis for the troubles getting it to
bloom.