One of the other uses of an interstem graft is to gain compatibility. There’s an apple cultivar someone discovered was compatible with pear for instance. Graft that to a pear limb, then graft some other apple cultivar onto it. You then have a pear tree also producing apples (of your desired variety), by way of that “interstem”.
As for seedlings I’m mostly using grocery store sourced Golden Delicious. I am guessing that they’re from a large commercial orchard, probably with crabapples providing pollen. If so they’re roughly 50% crab and GD. From seed they form a taproot whereas (to my knowledge) clonally propagated rootstock like MM111 does not. Just seemed like that might have better results…
If you use Pink Lady or Granny Smith seeds, they are stored so long that you don’t need to stratify the seeds and often the seeds are already growing inside the apples and they can go straight into pots.
I do like your thinking about being half crabapple though, that’s probably the best aspect of commercial apple seeds for rootstock.
Pears tend to take a few years longer to fruit so the tree usually stouter by the time it’s loaded up with fruit. Pear roots also get those beefy roots like molars (human teeth) that probably anchor the tree better. Quince is also probably the most dwarfing and it’s only in the neighborhood of 50% versus 60-80% on the most dwarfing apple rootstocks.
edit: I should note that a Quince interstem for dwarfing is probably a bad idea. Or at least I’ve never heard of it being done and working any better than grafting Quince onto Pear usually (doesn’t) work. Probably for that reason.
I’ve heard that quince can be a free standing tree, but according to my friend’s girlfriend, who is growing cider pears, she needs to stake her dwarf trees, but she’s new to this and might be being overly cautious.
I use seedling I start myself for rootstock too. I have a question about spraying them. I have been using random apples to get seeds from and it has worked fairly well until this year. Last year I planted seeds from Jonagold and Rome Beauty the Jonagold did real well but the Rome got powdery mildew so bad that some died and the rest didn’t grow enough to use them for rootstock. This year the seeds were from yellow delicious, Fugi, Pink lady, And empire. Out of 50 seedlings started I have 2 yellow delicious and 3 Empire that might make rootstock next spring. The rest either died from Powdery Mildew, Scab, and CAR. I either have to try to spray or pick varieties that have some disease resistance. Do any of you spray your seedlings that you start for rootstock or don’t you have a disease problem. I see that some of you are useing disease prone apples.
When I spray my mature trees I also spray the seedlings in the nearby “tree nursery” area. I therefore haven’t noticed much in the way of fungal problems with them. Since ultimately they will not have any trunk/limbs/leaves above ground, I hadn’t given that much consideration. Hmm…