This Is A Strange One

[Frax]

I have not seen what I will describe yet. It goes along with the other thread on crab apple leaf blights and that discussion.
My boss has seen instances of a certain type of crab apples in marked decline. These crabs show signs on the fruit that look like the manifestation of hawthorn/juniper rust - which is very common here. Apparently does not look like apple/cedar rust - which is not common here.
The kicker is that these declining trees are suckering from the root - as hawthorns! So these apples must have been grafted onto hawthorn rootstock. And seem to be showing signs of hawthorn/juniper rust on the apples!
I REALLY have to get a pic of this.
Anyone seen anything like this before?

 

[robinia]

I've seen it on an ornamental crabapple. The scion died and the suckers came up very different. At first I thought it was some wild plum rootstock because the spurs were so wicked - very thorny like hawthorn. Maybe it was. Come to think of it I'm not all that sure what it was, but definitely not hawthorn, probably some other Malus.

Grafting seems to work well between genera in the Rosaceae, even different Genus branches of the same tree.

I'm trying to think of exceptions - trees that are grafted accross families??

 

[KTSmith]

Crabapple is a recognized host for the cedar-hawthorn rust (caused by Gymnosporangium globosum). I expect that varieties differ in degrees of susceptibility.