In a talk that I saw recently, an experienced fruit grower indicated that grafting a low-chill variety onto one with higher chilling needs has the effect of reducing those needs.
Has anyone observed this behavior?
This is an Interesting topic that I look forward to hearing others experience/thoughts. If true this would open up opportunities to grow more high chill varieties in the warm south.
I don’t understand. Are you saying that grafting a low chill Scion might cause the fruit buds below the graft to become less chill needy?
That does not seem to pass the logic test.
The other way around (high chill onto low chill) maybe, but even that is questionable since we don’t see any changes in the fruit produced below a graft of a different variety.
Not a scientific conclusion… just ???
Mike
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I think that would be a fair conclusion from what I understood the speaker to convey.
Hmmm! That is definitely very interesting.
Please let us know if you hear as anything else on the subject.
Mike
There are been studies about transmission of flowering signal through grafts, so it may be possible. Would be easy to test, one tree non grafted and one with a branch/limb grafted with low chill cultivar
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Interesting hypothesis. Requires experimentation - haha, you know, double-blind, placebo-controlled crossover studies, jk. 
Seriously now, the way to find out is to jump in and try it. It may work for some combos and not others. Before the universities report you’ll have an answer. That, IMHO is one of the fun aspects of growing things. Just do it. 
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I’m not clear on exactly what your saying but I think you are saying that grafting low chill scion into a higher chill tree will lower the chill hour requirement of the rest of the tree. Is that correct? If so whom ever stated that is full of bull corn. This is easy to prove as well. Ask any one who has multi graft trees and they can tell you the early stuff will bloom early and the later stuff will bloom late. At least that has always been my experience. My mother has a multi pear tree I grafted for her and the lower chill Acres Home always blooms a good week and a half to two weeks before Leconte wakes up.
Drew
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That is the gist of what was presented.
Yes that is what I thought. In my opinion and experience this is grossly inaccurate.
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Hmm, I am not sure if they mean one scion on a grown tree or a graft closer to the ground? I cannot see one scion affecting a whole tree and I am not sure the rootstock would impart a lower or higher chill characteristic to a scion grafted on top. I don’t know much about chill other than it is chilly here most of the time.
I do know, however that the U of S has studies that conclude less hardy scions, when grafted onto a cold hardy crabapple, do become hardier partly because the rootstock forces the scion to enter dormancy earlier than it would if on a rootstock for a warmer zone. The scion is affected by the rootstock not the other way around.
So if the speaker meant that if you grafted a low chill cultivar onto high chill rootstock could it be possible that the rootstock may impart some of it’s characteristics to the scion? If you wanted to decrease the chill requirements then you will have to graft onto a variety that has lower chill requirements than your scion.
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I was reading a book once,but not sure of the name right now,about plant breeding,I think.
A section brought up how main thought was root stock controlling scion growth,but also mentioned that it can be the other way too.
I found these references after doing a short search online.They give observations about variations of stocks and scions.I didn’t see anything directly related to the original question though.Brady
http://www.bulbnrose.x10.mx/Heredity/King/StockScion.html
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The topic came up in the context of chill substitutes for (California) growers where the climate alone does not provide the desired amount. The meaning was that you could create the effect of chilling for a higher-chill cultivar by grafting a low-chill cultivar onto it, and rootstock did not come up in this contex.
A question came from the audience which was, in substance, the multi-graft tree example provided above, and the speaker remarked that the behavior observed there for the low-chill variety to wake up earlier than the high-chill variety on to which it was grafted would continue to be expected (notwithstanding the claimed chill-substituting effect).
So, I’m pretty sure that the speaker was referring to the interaction of two fruiting varieties, not with the rootstock.
The question that you raise @northof53, i.e., if one were to use a low-chill cultivar as a rootstock, would it provide chill-substituting effect to a high-chill variety as scion, I agree is a natural one, but didn’t come up.
@Bradybb, thanks for providing that link–the research history is interesting.
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I use three main rootstocks around the orchard, M27, MM102, and M111.
Of the three M27 has the lowest chill requirement, and so it’s ungrafted rootstocks wake up first, followed a few weeks by M111, then nearly a month later by MM102.
The varieties grafted to each are highly varied but there are a few I have on both M27, and MM102, and I can say for sure that the M27 grafted versions wake up 2 to 4 weeks earlier in most cases!
I’ve yet to try inter-stemming any of the rootstocks with Dorsett or Anna to see if it can be reduced even further, but suspect that so long as the interstem isn’t blind wood that it could reduce the CR by possibly another few weeks.
I’ve not tried the other way around, i.e adding Anna and Dorsett to MM102 or another high chill variety, but I can’t see why it wouldn’t effect the other varieties it’s grafted with at least somewhat, as when the low chill varieties wake up then they’d start pumping dormancy breaking hormones to the rootstock in order to get the rootstock to wake up and start supplying nutrients.
That’s definitely on my list of things to try next winter (July/August '23), so will let folks know what happens, even if just anecdotally.
Apples (M. domestica) were once thought to need chilling. It was proven false 20 years ago. Many production nurseries, including Dave Wilson have since changed their product descriptions.
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