North American Fruit Explorers mailing list at ibiblio

[Anton Callaway <marillen@earthlink.net>]

Megan,

The rootstock can affect the chill requirements of the scion.  Quite a bit of 
research was done on this and other aspects of dormancy onset & release.  It 
appears that the shoot bud is the active point of perception of cool 
temperatures (notice I said cool, not cold... temps 0 degrees C & below have 
no effect on dormancy release).  Therefore, one would expect that the larger 
the rootstock portion of the tree and the lower the chill requirement of that 
stock, the greater the effect and the influence would be significant on fruit 
crops like apple and pear, which have lots of shoot buds even on below-ground 
parts of the plant, whereas some other crops, like peaches would have minimal 
influence on the scion because they have few shoot buds on the lower part of 
the tree.  This has been borne out by university research.  

I don't believe that dumping ice around the base of the plant would have a 
significant effect unless you kept the ice on constantly for a sufficient 
period and the plant was small (therefore the proportion of the plant being 
chilled was significant).  Research has shown that the response of fruit 
plants to chilling temperatures is complicated and that short periods of 2-10 
degrees C (the range that satisfies chilling requirements) can be negated if 
they are followed by high temperatures (e.g. 24 degrees C).  Interestingly, 
the chilling requirements are satisfied more rapidly if the chill temperature 
period is alternated with a moderate temp, like 15 degrees C.  This kind of 
makes sense, when you think about it because in nature trees are exposed to 
alternating very cool and less cool temperatures in a night/day cycle.

Anton
Zone 8 


-----Original Message-----
>From: Spidra Webster <spidra@gmail.com>
>Sent: Sep 20, 2010 5:14 AM
>To: North American Fruit Explorers <nafex@lists.ibiblio.org>
>Subject: [NAFEX] Can Low-Chill Rootstock Affect Grafted Bits?
>
>Howdy,
>
>I rather stupidly bought 'Gravenstein' (a favorite) before checking into how
>many chill hours it requires. As I have moved from Berkeley to South
>Pasadena, CA, I fear this area won't get enough chill to set fruit most
>years. My favorite apples are Yellow Newton Pippin and Gravenstein. I like a
>lot of tart with my sweet. I'm assuming apples like 'Anna' and 'Dorsett
>Golden' don't really have this taste. However, if I grafted scions onto a
>low-chill apple rootstock, would they set fruit?
>
>I guess another question would regard chill cheating. Does the tree depend
>on the air chill being that cold or is it enough to put a bunch of ice on
>the ground near the trunk and try to give it a little local chill that way?
>
>Megan Lynch
>http://www.meganlynch.net
>
>South Pasadena, CA USDA Zone 9