North American Fruit Explorers mailing list at ibiblio

["edforest2010" <edforest55@hotmail.com>]

Tom,
I think the reason no one has responded is because either no one knows 
for sure or because it is a long answer.
Here is what I have learned, for what its worth:
> 
> What part of the tree is responsible for dormancy?  Roots or 
framework, or
> the whole tree?  

There are hormones that migrate down the tree in he fall from the tips 
of the branches, they are responsible for rooting and, when days get 
shorter and cooler, (unless unusually fertilized and watered) I 
suspect these hormones also, in addition to controling rooting, signal 
the rest of the tree to shut down. (I once saw a stretch of books in 
the ag library all dealing with dormancy and leaf absicion, so I may 
be naive in my simplicity)

>From memory, I have different takes on the initiators of spring 
growth, some have said that the tree can't grow if the roots are 
frozen. But one experimentor mulched one tree and left the other 
unmulched and they both leafed out at the same time. 
But I seem to recall someone saying that both the root temp and 
frame/branch temp play a role in determing the wake up time.

Ungrafted ranetkas break bud 10 days later than ungrafted antonovka. I 
had some sweet 16 grafted to both ranetka and antonovka. The 
rootstock had no influence on the date that Sweet 16 leafed out. 
However, on the Sweet 16 grafted to ranetka, ranetka suckers at 
the base of the tree leafed out two weeks earlier than the Sweet 16 on 
the same tree. So the shoot tips do determine the date of leafing 
out. That seems to suggest that there isn't an interplay between the 
top and the roots, that they are independent of each other in 
signaling dormancy. No matter what roots they were on, they broke bud 
at the same time, but as we know, (from the sandwiching phenomenon), 
if we change the shoot tips to another cultivar, that leafs out later, 
this can definately delay growth in spring. 
Seems to me its all up to the shoot tips in signaling spring growth. I 
wish we had some expert on this. If no one shows up to clarify this I 
will make a note to ask some people at the UW next time I go over to 
bother them.
Kevin B
> 

> >


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