Thanks for posting this information, everybody, and particularly to Drew for the explanation about the Ottawa 3 ancestry of the problematic Geneva rootstocks. I had originally ordered G 935 rootstock for the grafting that I'm planning to do with my dad this spring, having read very positive reviews of it's performance from others here. But after reading this and the earlier thread about virus-infected scion wood, I decided to change my order to G 41, which sounds like it doesn't have the same issues with virus sensitivity. (I'm aware that there's some question about how big of a problem viruses are likely to be in a home orchard setting. On the other hand, it sounds like home grafting is more likely to lead to problems with susceptible rootstocks down the road.)
@scottfsmith, it sounds like you've had particularly bad results with (some of) the Geneva rootstocks. Just to confirm, was it particularly G16 and G30 that turned out badly for you? Do you attribute that mainly to multi grafting with infected scions, or do you suspect that there were other factors involved?
@Vohd, very interesting article, thank you for posting the link. It seems like the takeaways are (1) viruses are suspected to be a problem with G 935, (2) but they may not be the only or even the primary culprit for the problems that have been observed - possibly poor rooting? (3) certain strains and varieties may be particularly problematic on G 935, others less so. (Honeycrisp in particular sounds like it can be less than fun.) Of course, the results they're reviewing come from a commercial orchard setting and don't speak directly to the issue of grafting traded or open-sourced scions.
Anyhow, thank you all for guiding me away from a potential Marvin the Martian moment down the road. I will find many more ways of getting there, I'm sure...
Oh, and by the way, Drew - Go Hawks! I was born in Iowa City - my dad got his MFA in art there.