The Great Squash-Up

“One of these things is not like the others”

OK, that’s a trick header. Sort of like over-thinking an SAT logic question on the exam. It is supposed to read, “One of these squash is not like the others.” The coffee mug is just there for context. And caffeine.

The seeds for those squash all came from the same packet, ordered from a major commercial seed company. Those on the left are the really truly acorn squash as expected. The one on the right? Not so much. And, mind you, I’m not complaining! “Variety is the spice of life,” as they sing on Sesame Street. No, wait. That’s “One of these things (is not like the others)” they sing on Sesame Street. I am as confused as the squash.

Throw a pumpkin up in the air and it comes down squash

Squash are as American as apple pie. Well, no, come to think of it, that’s wrong too. Apples originated in Central Asia and were featured in fast food shops all along the Silk Road thousands of years ago. Before Ronald McDonald put on clown shoes. Squash is way more American. The archaeologist K. Kris Hirst has a wonderful review on the origins of squash, and its mutual dependence on pollinators, in ThoughtCo.

Squash are all part and parcel of the genus Cucurbita which grew wild in North and South American during the age of the megafauna. Indeed, squash were considered a delicacy by mastodons because they were so big (the mastodons, not the squash) that the bitter cucurbitacin toxins, couldn’t kill them like it would the little creatures. That bitterness persists to this day in some cucumber varieties, and cucurbitacins – long a focus of ethnic health strategies – have recently attracted modest attention for their clinical potential as anti-cancer agents.

When the megafauna began to die out about 10,000 years ago, the wild Cucurbita declined with them. But fortunately for pumpkin (not apple) pies, a host of young Johnny Squash Seed entrepreneurs had already begun to successfully domesticate the species. In fact, the domestication of squash beat out that of corn to the tune of about 4000 years. Why domesticate a toxic weed? Who knows. The mastodon liked them. They had big seeds, stored well, and the dried, hollowed out gourds were great for carrying water. And so why not make them edible. Today there are five broad agricultural species of squash, a.k.a. pumpkins, a.k.a. gourds.

Archaeological remnants of the great-great-ever-so-great-grandfather of butternut squash, C. machata, modern varieties of which I also grow in my garden, have been found at human sites in northern South America dating to around 10,000 years ago. Think approximately 400 human generations back. For all the genetic archaeology, however, the wild progenitor of the butternut squash remains incognito. We can do a little better for the acorn squash.

Acorn squash, the guys under the spotlight in our banner picture, are C. pepo spp. ovifera var. turbinata, (as in the shape of a turban, get it?) and in my garden they sit close to their origin story. C. pepo ovifera probably appeared in Midwestern U.S. between 5000 and 8000 years ago, independently domesticated from wild species like C. pepo spp. ozarkana. So acorn squash has a long, distinguished, thousands-of-years history. Why are they playing games in my garden?

Mix-up or mixed up?

We can rule out a couple of explanations for the orange squash. First, the only other winter squash seeds I’ve ever purchased or planted are for butternut. So it is impossible for me to have mixed up different packets of seeds in those squash hills. Second, the company from which I bought them is a long-time commercial supplier to farms across the country. It is highly unlikely someone there spilled bins of different squash seeds on the floor and then just swept them up together into sales packets. Third, our orange squash doesn’t look like anything in their seed catalog, squash or otherwise. And an internet search for “orange winter squash” turns up lots of Search Engine Optimized (SEO) links (“22 Varieties of Winter Squashes You Can Grow in Your Garden”), but it doesn’t turn up a candidate for our mystery squash.

Michelle McKenzie is one of the farmers at the Bellair Farm CSA, and she is also one of my go-to gurus on all things hands-in-the-dirt agricultural. I showed that picture to Michelle and she pointed out that our orange friend takes after modern day gourds rather than modern day squash. She emailed me:

This looks like an accidental cross! It could also be a mix-up but looking at it, it looks very gourd-like, which is an indicator of crossing.

So we are likely looking at the result of mixed up hanky-panky in the squash field, while the farmer wasn’t looking, and not a mix-up in packaging or handling, while the shift manager wasn't looking.

“Why can’t a cow have kittens?”

Whenever it comes to inheritance, I hear Harry Belafonte singing “Why ‘n’ Why” in the background of my mind’s ear.

Members of the squash family have 20 pairs of chromosomes. And, just like humans, they can send a sample plug from a leaf off to the genomics company “20andme.com” for analysis. Well, maybe not directly to my made-up company, but actually to research labs – where the chances of a data breach may be lower. Those 20 chromosomes from one C. pepo plant (a total of over 250 million DNA base pairs) can recombine, rearrange, and re-assort in bazillion ways with the 20 chromosomes of another C. pepo plant.

Squash plants are “monoecious”; that is, each plant produces both male and female flowers.Very convenient. But the challenge is that the pollen from the male flower has to find its way to the female flower, and that requires those pollinators I mentioned above, chiefly bees.

Now if my acorn plants each had their own personal Bee Uber delivery service flying back and forth exclusively between the plant’s own male and female flowers, the seeds produced would always breed true; all the progeny squash would be the acorn squash on the left of our picture. But bees are kind of free spirits, with a dance of their own, and they are known to roam as much as five miles from home looking for pollen.

So imagine I’m a farmer raising a field of acorn squash for seed, if there are fields of other C. pepo species within a few miles of me, like zucchini, summer squash, or pumpkins, I’m in for trouble. The bees are bound to bring pumpkin pollen to fertilize my acorn squash flowers. The result of that fertilization has 20 acorn squash chromosomes hooking up with 20 pumpkin chromosomes, followed by replication, recombination, meiotic nuclear divisions, segregation, and wild square dance moves, all to produce seeds for a Pumpcorn Frankensquash.

The thing is, Farmer Me won’t know about this problem until it’s too late. The mixup will all be in the seeds; the adult acorn squash will look fine. So myself the farmer will go out, harvest the squash, collect the seeds, and ship them off to my favorite seller. Nobody will be the wiser until myself the gardener plants the seeds and gets a big surprise when one of them produces something like our orange squash friend in the picture.

And all of this is good

You can thank your lucky squash gratin on this botanical intermingling.

Without its huge variation in traits, and the plasticity of the recombining genomes, poor Cucurbita would have perished with the mastodons 10,000 years ago. The ability of green squash to surprise with orange squash, of deadly bitter squash-like things to yield sweet wonders, this ability is the reason why our Johnny Squash Seed, our New World Gregor Mendel, succeeded in domesticating a family of agricultural staples that, as of 2019, gave the world 22.9 megatons of squash and pumpkins.

And it’s not done. The threats are here before us: climate change, new pests, new viruses, new fungi. But modern day Cucurbita breeders have it rough. And, consequently, there aren’t many left.

First, it takes a lot of real estate to grow a squash. Expensive real estate. This year I have 5 butternut squash plants in my garden and by mid-way through the growing season they seized over 400 square feet of garden terrain. By harvest time, the leading tendrils will have long ago jumped the fence and be found thumbing a ride to Albuquerque, New Mexico. And 5 plants doesn’t even tickle the needle on the demands of the breeding statistical meter.

Second, it’s tedious. In the field, you have to identify male and female flowers and do the pollination by hand, all while humming a buzzing sound to put them in the mood; the bees don’t care diddlysquat about your breeding experiment and will happily mess up the crosses if you don’t manually seal up the flowers with tape.

And finally, it takes time and a lot of detailed observation. My acorn squash – a bush variety! Hey! Cucurbita started out as vines! – is the result of maybe 8000 years of selection by untold generations of dedicated farmers and, later, additional scientists, who fortunately got there before Monsanto did.

Some help may be on the horizon. With the advent of complete genome DNA sequences for some of the Cucurbita, new technologies are being developed to facilitate more efficient and deliberate trait selection in breeding. Fingers crossed. Please tip the faculty and staff, and local extension agents, at an agriculture college near you.

So here I am, in awe at my thriller, “The Great Squash-Up!” As you can tell. Maybe if I were a commercial farmer, growing for market, I’d be pretty pissed off. Pissed off at bees, at monoecious sexual reproduction in Cucurbits, at mastodons. But I’m not! I’m a backyard gardener and, damn, this is fun!