Cross pollination is done routinely by breeders to establish new cultivars. I'm not aware that any toxicity tests are done on them. If there was a chance that new cultivars could be toxic, we'd probably have a huge public health problem.

I can think of different plants in the same family that are either non-toxic or toxic (consider tomatoes and nightshade), but you're not going to come up with nightshade as a cultivar of tomatoes. They're different species.

I assume that someone with deep biological insight will be able to give a better answer.

Landrace gardening isn't a new concept by any means and has been discussed here many times in the past. One of many discussions the search pulls up is

http://forums2.gardenweb.com/discussions/1471369/getting-more-from-your-garden-with-landraces-and-local-varietes?n=29

And while many of the claims associated with it are debatable, many home gardeners practice some aspects of it, often unknowingly due to simple cross pollination.

The answer to your question about inadvertently creating a toxic cross, as in poisonous, is no. If it was safe to eat to begin with genetically it will remain so. Even if one begins with a hybrid variety that subsequently reverts to parent stock it remains safe to consume. As Dan said, new hybrids are created all the time, both intentionally and accidentally.

Now creating an unpalatable one? Yes. Many of us have done that. ;-) You need only look at all the "what on earth is this squash" discussions here as examples.

One caution when putting stock in the claim, "In theory, by doing this over and over again, you will have developed a/many culivar(s) that have adapted to your specific garden and can grow great there."

The cultivar itself is only one of many variables that determine success. And in many cases, it is a minor variable.

Dave

Just a word of caution. Be aware that there are poisonous varieties of wild curcurbits. I don't grow them, so I've never done all the research to separate what's true from what is not, but there are conflicting internet articles that say ornamental gourds also contain the toxic compounds.

So, while most other vegetables are fine for crossing, do your due diligence concerning curcurbits. Many seed savers (myself included) isolate pollen for squash. My reason is to maintain purity for an heirloom which is already acclimatized to my area. However, if you wish to let some cross pollinate freely, at the very least (and like I said, I'd research and take precautions) you should taste just a very small amount of any curcurbit that was produced through 'free' crossing. If it tastes bitter, think twice. This is wholly unscientific, and an ounce of prevention is worth a pound of squash in the belly. This though, is the only edible vegetable plant family *that I know of* (whatever that's worth) with cross-able toxic cousins.

That's interesting about cucurbits. But cucurbits are a *family*, and it's not clear that you can interbreed between different species in a family. That is the definition of "species", after all. But if these toxic cucumbers are really in the same species as Cucumis Sativus, which is the garden variety cuke, then I suppose there could be some danger. Are they? No question that cukes, like tomatoes, do have toxic compounds in them, and you can hurt yourself if you eat a lot of them. BTW, I believe that things called "wild cucumbers" are not really cucumbers, though they are in the same family.

Well, as i said, due diligence. I'm not a professional horticultural scientist, so I have to trust warnings issued from reliable sources. Here's an article from the University of Nebraska... I'm not a horticultural scientist, but they are...

Here's one from Mississippi State... Again, horticultural scientists...

There is a lot of info on the web. Some of it trustworthy, some not... I tend to look for the dot EDU sources, and just finding a few is enough to spur due diligence in me.

Thanks. Those are useful links. I'm certainly not a professional horticultural scientist either, but I do wonder how you get interspecies pollination. Not supposed to happen. But the issue here is the concentration of toxic compounds that I was referring to. I guess the lesson is that, if it tastes bad, don't eat it!