I looked up online and I couldn’t find much on the topic, can you think of any fruit variety that grows from seed and make a very good rootstock.
Something like the Pistachio hybrid from UCD, a good rootstock and can be started from seed. Or even Mahaleb cherry.
Can you think of other examples please?
‘Lovell’ is what came to mind for me, but apparently there are several others that can be propagated from seeds.
I don’t think a one time seedling tree proves anything, but I’ve experienced something this year that I’ve found very interesting. I’m growing out my first ever seedling peach (an Indian Blood x unknown pollinator). This is it’s third year. I’ve been absolutely blown away by the health and vigor of this tree. It is by far the greenest, healthiest, fastest growing peach tree I have ever had. I’m well aware that the fruit may end up not being any good (though I’ve heard Indian Blood tends to be fairly true which is why I tried it). But even if the fruit isn’t good, I am very tempted to create more of these seedling peach trees and then graft a known variety onto them. Of course, the next 100 seedling peach trees may not be such robust trees. And there may be problems with this one down the line. But what I’ve seen so far sure makes me think peach seedlings would make good rootstock- if I know what the pollinator was so I could create the same seedling again, I’d REALLY be excited about the possibility of using them as rootstocks.
I’m hooked now, if I wasn’t in a low chill area, I would have asked for some seeds to try 
Well of course crabapple grown from seed is used as a rootstock, as is Antonova apple.
Common pear, mainly Bartlett from canneries, was once a very common pear rootstock. Though I don’t guess that would be real common where you are. I have a large rootstock pear with small astringent fruit that I’ve planted, grown and grafted. Adds a little special interest to the tree. Sue
For backyard growers seedlings work fine for many things. These days I use peach seedlings on all my new stone fruits besides cherries, they sprout all on their own beneath my trees and all I have to do is move them to my nursery bed and in a few years I have rootstocks. I also have several pears on seedling which I can’t appreciably tell apart from the OH rootstocks. For commercial growers where that extra 5% of precocity or production or consistency matters its a big deal, but not in the backyard. The one case where I really appreciate rootstocks is dwarf apple stocks - there really is a difference in vigor and precocity there.
Jujubes and persimmons are commonly sold on seedling root stock.
I have read that some seedling jujubes can be very invasive and send up suckers from the roots all over your yard, but this hasn’t been my experience (yet, at least!).
Things I start from seed for use as rootstocks include ;
Persimmons
Pawpaw
Peach
Pecan
apples
walnuts
Trifoliate orange -for citrus
Have not grafed any nut trees yet, but think it’s time I try.
Seedlings are commonly used for uncommon fruits like persimmons and pawpaws, but I think the key here is that they are uncommon, ie: Big Agriculture hasn’t had the incentive to develop fancy rootstocks for them. Somewhere out in the woods, there’s probably a dwarfing pawpaw that would be just perfect if only we could find it.
Asmina parviflora, aka dwarf or small-flowered pawpaw, might fit that bill… i had a selection of it from AL grafted on A.triloba understock for years. Think I might have a seedling or two of it (perhaps with A.triloba as pollen parent) stuck in the ground somewhere here on the farm, and sent one to Guy Sternberg several years back.
I’d also add mulberry to the list. I’ve had good luck grafting into Russian mulberry seedling root stock (purchased from Burnt Ridge), and I know many others that dig up volunteer seedlings and graft onto them.
Glad to read this thread as I have several seeds of both apple and pear planted right now and several apples that have already sprouted and growing! I have cherry, peach and various other seeds planted as well but nothing up as of yet. I have planted seeds of different things for years but not used much in the way of rootstock yet. I have only used sprouts for rootstock besides what I have bought.