Softball size green apple used as crabapple rootstock
My parents planted a flowering crabapple almost 20 years ago. The tree only lived a few years and died. The stump sprouted and grew into full sized tree. They let it grow because they thought it might be the crabapple, but when it started to bear large apples it became obvious it was the rootstock of a grafted tree that survived.
I have never seen apples like these before. They are unusually large. The skin is green and rough, like bartlett pear, with a red blush. The flesh is hard/crispy with course texture. It is very juicy and sweet without any tart (low acid). When cooked it breaks down completely and sooner than any other apple variety I've cooked. They are only good for a sweetener in cider, apple sauce, and spreads.
Any idea what this apple might be? Since it has low desert quality, I can see why it never became popular. Its use for rootstock might be related to its cold hardiness. Other than pears, it is the only fruit tree in the area that had fruit buds to survive the brutal 2013-2014 winter. In fact the tree is loaded.