In graft hybridisation does a younger stock facilitate more extensive hybrid effects in the scion?

Question

There are anecdotes and articles where one kind of tree fruit scion has been grafted to the stock of another kind, perhaps with an interstock, and properties like flavour and shape have been affected (I have not linked to any, as I don't have enough rep yet).

In one case, a pear grafted to an apple has resulted in an apple shaped pear with a flavour in between. And in another case, peach stock grafted to an almond interstock, grafted to a peach scion, resulted consistently in oval shaped peaches - and in the accompanying trees where the almond interstock failed normal round fruit as expected from the scion cultivar. And one last study documented how reliably leaf colour of the stock combined with the leaf colour of the scion, to appear in the seedlings of the scion.

Then there is what is described as the old French technique of grafting "in and in". This is where a scion is grafted to an existing tree, and as the scion fruit exhibits desirable properties of the stock tree, a further scion is taken from the growth of that scion, and grafted to the stock tree. The process is repeated, with all scions of different stages available for comparison on the tree, in theory.

What I would like to know, is whether there is significantly more benefit to grafting a scion to a young new rootstock, as compared to grafting to a grown stock tree, in terms of the likelihood of more evident graft hybridisation effects?

Answer 1

In my experience this does not happen to people. The fruit is of course altered somewhat by the different rootstock, but the reason for grafting is to get a better, more resilient, hardier rootstock. Not to change the fruit. I grafted pears onto quince rootstocks many times, not once did the pears taste even any closer to quince fruit.

Even so, there are slight changes in the scion, especially habitwise, when grafting. The vigor is often lower (as in a dwarf tree) and the fruit size can differ, but overall quality stays about the same. And when one takes a scion off of a grafted dwarf apple, and grafts it onto a new standard rootstock, it will still retain its own genetic structure, and perform to the limits of the new rootstock. It will not retain any dwarf-ness from its prior time growing off of a dwarfing rootstock.

And when you said, "in the accompanying trees where the almond interstock failed normal round fruit as expected from the scion cultivar", I had to laugh. the interstock is between the scion and the rootstock, usually used when a cultivar of something, say a pear, isn't compatible with the necessary rootstock (say, a quince), and you have to use a compatible pear interstock in between. Now, if the interstock fails, everything above that point dies. That's why your above statement cannot make sense.

As for your question,

What I would like to know, is whether there is significantly more benefit to grafting a scion to a young new rootstock, as compared to grafting to a grown stock tree, in terms of the likelihood of more evident graft hybridisation effects?

I can only say that in my experience, you get only minimal changes to the scion genewise, and any changes will have to do more with the rootstock cultivar than to the age of the rootstock. And don't believe every article out there, many of them are hogwash or stories.