Toxic Squash prevalence, and who profits from gardeners' fear of saving squash seeds

I'm part of a local gardening group on facebook (don't even get me started on this, it's really a festering pit of regurgitated "conventional wisdom" with a healthy dose of self-appointed experts telling everyone they're doing it wrong, but it's a good way to find out about local seed swaps and stuff), and one of the topics that seems to pop up again and again, nearly on a weekly basis, is some form of

"Hey guys, what is this volunteer squash? OMG You MUST pull it out RIGHT NOW did you know that volunteer squash can be TOXIC"

"Can I save seeds from my squash? OMG NO, the result will be TOXIC!!!"

"Hey guys, OMG I heard that any squash you don't grow from a seed you buy from a reputable source could be TOXIC"

Now, I'm not trying to say that no squash will ever turn out bitter and toxic. And I'm not even trying to refute the fact that commercial squash seed is saved with a lot better isolation practices than anything that I save or which volunteers in my garden, and is therefore probably a lot less likely to have the toxic bitter genes.

But I've been saving squash seed on a small scale for a while (I dunno, 6 or 8 years maybe), and, while I often get funny surprises caused by the outbreeding habits of squash or from saving seeds from some unstable hybrid, I can't say that I've ever come across a squash with the toxic bitter gene. I'm wondering what is actually the mechanism by which squash acquires the toxic bitter gene. Clearly it isn't coming from everyone else's garden where the commercially-available squash seeds are growing. I've read vague things about squash crossing with some wild squash-relative or a manroot or something like that, and that is how you end up with toxic bitter squash, but how prevalent are these bitter-carrying squash-crossing-plants? Does their prevalence vary across different regions and types of urban/rural environments? Have I just been especially lucky that I've saved thousands of squash seeds and grown out at least hundreds of them over the years, and ended up with none that are bitter (I live in a pretty urban area, so if these bitter squash-relatives live only in rural areas, maybe that has kept this from occurring)?

The frequency with which this toxic bitter squash topic comes up in this local gardening group and the fervor with which local gardeners insist that no one can save squash seed or allow volunteer squashes to live confuses me, since I have never had the bitter toxic squash happen, or even met anyone who has had it happen. So, I'm wondering if this is something that, while technically a true possibility, is fairly unlikely, but is played up to instill fear in small-scale gardeners and keep them coming back to buy squash seed year after year. It feels like it may be in a similar vein to the much-repeated oversimplifications discouraging saving seeds (e.g. "you can't save seeds from hybrids" or "you have to isolate your plants by 1/2 mile if you are going to save seeds or WHO KNOWS what you may get"), which as far as I can tell only serve to build a sense of rigidity in the practice of growing plants, while discouraging small-scale backyard seed-savers. I don't know if there's actually any diabolical conspiracy perpetrated by seed companies or "big agriculture" with the explicit goal of discouraging seed saving, or if gardeners just like to repeat as absolute truth oversimplifications that may contain some shred of fact, but I'd like to find out more about the mechanism by which the squash bitter toxic gene contaminates regular squash, and find out just how risky or overblown this actually is.

An excerpt from an internet search.

A study published in Clinical Toxicology in 2018 published a study from France that found 353 cases of reported adverse effects reported from eating bitter squashes. ... If your volunteer pumpkin looks the same as those raised by your daughter last year and a taste test is not bitter your pumpkin is probably OK to eat.

It is not likely that a squash "gets" a toxic gene.  More likely is that the "bitter gene" is heterozygous in the hybrid and suppressed, but upon breeding, some of the offspring are either bitter+ homozygosis, or bitter- homozygosis.

I've never worried about it and I save lots of squash seeds.  If I get one that turns out bitter, I won't eat it and I'll throw the seeds away.  That's as much caution as I'm willing to give it.  Your mileage may vary.

as a landrace grower, i am constantly re-hybridizing my squash. i have never run into a bitter/toxic one.

I have run into toxic squash in my breeding projects. It happens. But, as long as you have working taste buds, the toxin is very easy to detect. Just do a taste-test before using the squash, and you'll be fine.

(If there is a person in the household with a sharper sense of taste than anyone else, have them do the test.)

Easiest way to test is, when first cutting the raw squash open, shave a thin piece of the meat, about the size of your thumbnail. Hold it on your tongue for a minute. If it tastes bitter, acrid, or otherwise foul, spit it out immediately, and rinse out your mouth. The amount of toxin in that sliver wouldn't be enough to make you sick, even if you did swallow it. It just irritates your throat enough to be inconvenient. You would have to eat a lot more than that in order to get a high enough dose to make you sick.

A toxic squash is not a disaster. At most it's an annoyance.

In my area the most likely source of the "bitterness gene" is an ornamental squash, not a wild one. There are a lot of gourds out there that are actually C. pepo squash.

(Edited for clarification.)

don't know anything about the scientific part. but if your picking a squash and bite into it and taste buds tell you something is not right you will probably spit it out and not want to save those seeds. in experimenting with many different varieties you have to dedicate lots of space to plant many different varieties so you can still have a good harvest of good stuff and eliminate the stuff that deserves to be spit out. but I'm no expert just my opinion.
when I grew lots of stuff and went to farmers markets I would rely on mostly johnny's for my seeds so I had good idea of what the plants would produce. my my hats off to you for experimenting, this is where the great varieties come from that end up at johnny's and other good seed sellers.

I never stress out about what plants might do as it is just part of what mother nature does.

If I don't like the taste of what my squash plants produce I can always give the fruit to my wildlife or compost it if I had a compost pile.

Gardening is supposed to either be fun or feed my family.

Let's all go plant some squash seeds, of course when the time is right.

If anyone grows ornamental varieties close by then bitter squash is quite likely, if not then it is unlikely. Last year there were several commercial companies that had to recall squash seeds in the UK as cross pollination had happened in their growers. Of course by the time anyone knows it's happened it's really way to late to recall most of the seeds are now plants.
I have tasted a bitter squash and you really cannot miss it. just lick the end of the first one from each plant and you'll soon know.

growing species of squash that rarely cross with the ornamentals should work pretty well, too. are all those ornamental gourds pepo species?

Yes, those ornamental gourds used for autumn decorations in the US are all C. pepo. For more useful gourds that are not as ornamental, and cannot cross with any of your other cucurbits, try Lagenaria gourds, called "bottle gourd" in Indian English. In Indian and Italian cuisine they are eaten immature, where they are like zucchini but firmer. Left to ripen completely, they are those waterproof vessels you've seen in tropical cultures.