I've never found them to be any different and honestly can't think of any reason why they would be just because they are labeled 'heirloom'. Many of the discussions over on the Tomato forum would seem to indicate just the opposite but it usually turns out to be a totally different cause.

So what specific symptoms are you seeing?

Dave

They seem to be more sensitive to the transition. .. wilting shortly after being outside, where the hybrids appear to be able to stay out longer without adverse effects.

Well Amish Paste is often described as a somewhat wispy plant in appearance so it could just be a plant appearance you aren't used to. I wouldn't expect it to look much like a Better Bush. In other words varietal appearances vary greatly regardless of if they are heirlooms or hybrids.

Don't know anything about Bison other than it is a dwarf determinate but if rapid wilting is the symptom then I'd sure be looking for other causes like over-exposure, less root development or root bound plants.

Dave

There could be a theoretical justification. Hybrids are a cross between two genetic lines, so you get the genetic contributions of both the mom and the dad. So-called 'heirloom' varieties are inbred lines - that's what keeps them a single consistent type. In genetics, the benefit of crossing two different lines is called 'heterozygote advantage.'

Another way to think of this phenomenon: many dog breeds suffer from genetic diseases that are the product of inbreeding. In order to get the dogs to look the way they do, you have to keep breeding the same types over and over, and eventually they get inbred. On the other hand, mutts are generally free of such medical conditions - being crosses between different types. they don't collect bad genetic mutations.

As much as the internet gardening world loves it's 'heirlooms,' hybrids have been used in agriculture and in animal breeding for a long time for good reasons.