Scary, huh???  ;o)

Several grafting threads going on right now.  I know grafting can be used to create dwarfism , etc.
What about cold hardiness?  What if one was to graft a “less cold hardy variety” onto a known cold hardy such as a MBVS or Malta black, etc??????
Anyone tried or heard of such????

Asks Greg as he stands there in his lab coat , feverishly rubbing his hands together , crazed look in his eyes,  muwahahahha !!

;))

I believe that the rootstock would not confer any cold-hardiness onto the scion, and the scion would die back at the appropriate temp, leaving you with a tree of the rootstock only. 

Brackishfigger is probably right

This has been discussed quite a bit on the forum already in multiple threads.  For example, see:

http://figs4funforum.websitetoolbox.com/post/Benefits-of-switching-out-the-rootstock-via-grafting-6205144

As far as I know the cold-hardiness question hasn't ever been rigorously tested - I would be glad to be proven wrong though.  However, I think I have seen on the forum where growers have shown that enhanced vigor can be added to a slow growing variety by grafting onto a fast growing/healthy rootstock.  Of course this approach is common in other fruit trees so it is not surprising.

LOL Pattee,  I actually was wearing a lab coat,  as I work in R&D in the food business.  ;o)

Rewton,  I was silly enough to think I had an original idea and did not think to search, Thanks

It would be great if cold hardiness could be transferred from the roots to the branches. But I don't think that's possible. I think that Vasile mentioned what he believes the reason Florea is more cold hardy is that the branches are more woody with less pith in the center.

LOL!

Grafting,creates a problem,that can be  resolved by making the graft as low as possible ,and under the soil line if possible,in cold climates.
That is because a graft,is not ever ,one unit,with the rootstock,and will die from frost first,and after the union is dead the scion will die.
If done the way I indicated,and if the rootstock is Fig mosaic virus resistant,then ,cultivars like Ischia Black will grow and produce a much better harvest.
That is because Fig mosaic virus,affect the  whole tree  roots included,and if I dig out my 9 years Ischia Black that is only one foot tall,I will find only 10 inches long roots,very poor root system.
If grafted on LSU Purple as an example the results will be much different,I am sure,the strong root system of LSUP,will feed the Ischia plant canopy,much better.

Herman, besides LSU purple, which other varieties do you think would be suitable as rootstock in the cooler parts of the country?  I was thinking of using Marseilles vs Black or Hardy Chicago.

Any fig that resist Fig mosaic well,and it grows  well,while diseased,because even if it is not when at graft time,it will be after .
Yes Hardy figs are a good start,like Marseilles vs black,HC,Atreano,and Sal Gene,which has Fig MV,but it is a strong grower.
However I had a Black Sicilian from Italian FT,that was identical to HC,but it did not grow at all because it was infected with a virus,similar to what Ischia Black have.
So I am sure ,that one need to experiment,with more than one rootstock to find one that can get infected with FMV,and be a strong grower at the same time.

Grafting does not alter genetics. It does have some causal relationship to such things as dwarfing, not by changing the genetics of the scion, but by affecting the flow of nutrients, etc., or by in imperfect interface (mild incompatibility) at the graft union.

Studies have shown that chill, for instance, is mostly about what the bud experiences, but what the roots or the rest of the tree experiences.

Pit, shouldn't there be a "not" somehere in that last sentence?

Not sure how the root system would effect figs, but it's well documented with citrus that hardy rootstocks increase the hardiness of the scion by a few degrees.  If one high grafts (say 4' up) Citrus on Poncirus the Poncirus rootstock can help drag the Citrus scion into deep dormancy and can hold it there until later in the spring.  With the trunk of the tree fully exposed to the environment being the hardy, strongly dormant Poncirus, and it making up a larger portion of the body of the grafted plant, its root system can hold the tree dormant because the root system controls the flow of water and nutrients to the shoot system.  The tree is much, much hardier while it is fully dormant.

It would be interesting if there was any equivalent combination with figs.  Do some figs wake up much later in the spring than others?  Not something I've noticed with my figs, but my plants are all potted and come in for the winter so they probably aren't getting the same cues as plants outside?

In the greenhouse, we graft tomatoes for vigour and also resistances to diseases and some viruses (if the root stock is resistant to tmv and tomv)  There is a transfer to varities with no resistance to the viruses etc but again it is only a resistance not magically curing it from virus.

The world is a complicated place.  One of my professors once told me that they gave the same tests year after year.  They never changed the questions, only the answers. 

As for Jon's missing "not", I believe it goes before the bud phrase.  From what I've heard (years ago) chilling hours required are needed by the roots.  In 10 years we'll find out that the bud also requires something.  I've always wanted someone to put a bunch of cooling pipes in Florida soil and plant a standard apple tree and see if it fruits.  I know a guy in OR who put heating pipes in the soil under a large greenhouse.  He said it helped a lot but he stopped using that greenhouse by the time I met him.

There are so many theories, but I believe experimenting will determine how a hardy rootstock will affect a cold sensitive variety. Rootstock for many fruit trees can affect dwarfing, disease resistance, and some cold hardiness. 
I can tell you that if the variety is sensitive to cold, it will die back to the graft union. For example I have grafted Asian Persimmons that are cold sensitive, into a Diospyros Virginiana rootstock which is known for its cold hardiness, The graft died a couple years later due to cold and sprouted back from the rootstock.