I haz a big melon:
And it’s seedless!!
There’s nothing better on a hot summer day than digging into the sweet, scarlet, crunchy meat of a chilled watermelon. And it’s even better when the watermelon is seedless: no spitting and less mess. We didn’t have seedless watermelons when I was a kid, so it’s still a great treat for me to eat one. And it’s even better when they’re like the one above, which I got at the produce store this morning. It must weigh at least 12 pounds, and cost only $3.59. I’ll get at least seven evening treats out of that puppy.
Seedless watermelons are in fact a triumph of genetics, for you can really design them de novo. You just double the chromosome number of a regular watermelon, so that instead of two sets of chromosomes it has four. The methods, outlined in this article, are simple: they involve treating watermelon seedlings with colchicine, a chemical derived from crocuses that inhibits cell division. By so doing, you can produce watermelon plants that have cells with 44 instead of the normal 22 chromosomes. These plants are called “tetraploids,” for they have four instead of the normal two sets of chromosomes (“diploids”).
When those cells produce flowers, the pollen (or eggs) in those flowers will have ½ X 44, or 22 chromosomes, while the pollen or eggs of a normal diploid watermelon will have ½ X 22 = 11 chromosomes. If you cross pollen of the latter to eggs from an engineered tetraploid melon, the zygote, or fertilized seed, will have 11 + 22 = 33 chromosomes. That seed can grow into a normal plant: a watermelon with three sets of chromosomes, called a triploid.
But when that triploid melon itself tries to make seeds, it has to do so through the process of meiosis, the same way we make sperm and eggs. That process begins with the members of chromosome sets pairing together in the cell before they split up for the reduction division. And if you have three representatives of each chromosome instead of the normal two, they don’t pair properly. When that happens, a normal female egg cell can’t form, and you get tiny, aborted seeds. In other words, triploid melons are sterile. They are the mules of fruit. (This is exactly how modern bananas are produced as well: they are also triploids, engineered to get rid of the seeds of their wild ancestors. When you cut across a banana and see those black specks in the middle, those are the aborted banana seeds.)
Ergo, we have a tasty triploid melon that lacks seeds: just what we want. The only problem is this: how do we grow more of them if they are sterile? Farmers get the triploid seeds from horticultural companies that produce them by the colchicine + crossing process. (Farmers can’t be bothered with all that technical stuff.)
The process is also described in a “Fun facts” FAQ from the National Watermelon Promotion Board. Their description starts out okay:
Where do seedless watermelons come from?
Seedless watermelons were invented over 50 years ago, and they have few or no seeds. When we say seeds, we are talking about mature seeds, the black ones. Oftentimes, the white seed coats where a seed did not mature are assumed to be seeds. But this isn’t the case! They are perfectly safe to swallow while eating, and don’t worry – no seeds will grow in your stomach.
So, how are seedless watermelons grown? Chromosomes are the building blocks that give characteristics, or traits, to living things including plants and watermelons. Watermelon breeders discovered that crossing a diploid plant (bearing the standard two sets of chromosomes) with a tetraploid plant (having four sets of chromosomes) results in a fruit that produces a triploid seed. (Yes, it has three sets of chromosomes). This triploid seed is the seed that produces seedless watermelons!
But then they screw it up. Can you spot the error, or at least the confusion, in the following paragraph?
In other words, a seedless watermelon is a sterile hybrid which is created by crossing male pollen for a watermelon, containing 22 chromosomes per cell, with a female watermelon flower with 44 chromosomes per cell. When this seeded fruit matures, the small, white seed coats inside contain 33 chromosomes, rendering it sterile and incapable of producing seeds. This is similar to the mule, produced by crossing a horse with a donkey. This process does not involve genetic modification.
Note too the somewhat duplicitous statement that seedless watermelon is not a genetically modified food. It sure is! Colchicine treatment, crossing, and so on, are all modifications of the genetic complement of a melon, and what you finally eat has three sets of chromosomes instead of two. How is that not genetic modification? The fear of GMOs, always greatly exaggerated, has gone too far, scaring even the National Watermelon Promotion Board.
At any rate, eating watermelon is much better for you than eating the other summer treat I love: ice cream (Breyer’s strawberry, please). Watermelon is nutritious and rich in lycopene. Here’s the nutritional information for a “standard serving”: two cups. (I probably eat twice that much.):
Note: only 80 calories. By comparison, a small pot of Greek yogurt (125 g) has about 144 calories.
Oy vey! I intended to just show the picture of my bargain watermelon, and look what happened. I went too far. But that reminds me of a joke, one I’ve told before:
An elderly rabbi, having just retired from his duties in the congregation, finally decides to fulfill his lifelong fantasy–to taste pork. He goes to a hotel in the Catskills in the off-season (not his usual one, mind you), enters the empty dining hall and sits down at a table far in the corner. The waiter arrives, and the rabbi orders roast suckling pig.
As the rabbi is waiting, struggling with his conscience, a family from his congregation walks in! They immediately see the rabbi and, since no one should eat alone, they join him.
Shocked, the rabbi begins to sweat. At last, the waiter arrives with a huge domed platter. He lifts the lid to reveal-what else?–roast suckling pig, complete with an apple in its mouth.
The family gasp in shock and disgust, and quickly turn to the rabbi for an explanation.
“This place is amazing!” cries the rabbi. “You order a baked apple, and look what you get!”
I’ll be here all year, folks.