Below is an excerpt from my blog. To read the whole potato discussion, about toxicity, diversity, variety registration, and more : Potato page.

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You probably heard more than once about toxic green potatoes.
All potatoes are known to contain certain levels of glycoalkaloids, namely chaconine and solanine; they are bitter tasting and toxic (depending on the dosage) and are mainly present in greened potatoes and potato foliage (1) .« Potato has a bitter taste when the levels exceed 14 mg/100g [total glycoalcaloids]» fresh weight (1).
(…)
The starting potato population used in our selection at the farm contains only parent tubers known to be edible and while we do taste and eat our seedling spuds and have not noticed a bitter tuber yet, we actually CANNOT tell you it is safe to do so because each seedling plant will yield different characteristics. And some people may be more or less tolerant to the GA’s. (Or maybe we are mutants and are able to breakdown or digest toxic spuds. Who knows. Okay, sorry, I could not keep from saying that… ) But you get it, in Canada any new variety of tuber (seedling) is NOT an edible thing until it has been tested and approved.

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