I think a lot of people are like I was this morning. That is, I had an unexamined mental image of “genetic modification” as something that’s only been possible either through selective breeding1 or some sort of computer-heavy process starting in the 90s.
Well, there is more middle ground than morning-Maya knew. I came across this while traipsing around in the Hybrid fruit category on Wikipedia2. And – just because it sort of blows my mind – remember when reading this that this technique has been around since at least the 1940s.
Colchicine is widely used in plant breeding by inducing polyploidy in plant cells to produce new or improved varieties, strains, and cultivars. When used to induce polyploidy in plants, colchicine cream is usually applied to a growth point of the plant, such as an apical tip, shoot, or sucker. Seeds can be presoaked in a colchicine solution before planting. Since chromosome segregation is driven by microtubules, colchicine alters cellular division by inhibiting chromosome segregation during meiosis; half the resulting gametes, therefore, contains no chromosomes, while the other half contains double the usual number of chromosomes (i.e., diploid instead of haploid, as gametes usually are), and lead to embryos with double the usual number of chromosomes (i.e., tetraploid instead of diploid). While this would be fatal in most higher animal cells, in plant cells, it is not only usually well-tolerated, but also frequently results in larger, hardier, faster-growing, and in general more desirable plants than the normally diploid parents. For this reason, this type of genetic manipulation is frequently used in breeding plants commercially.
When such a tetraploid plant is crossed with a diploid plant, the triploid offspring are usually sterile (unable to produce fertile seeds or spores), although many triploids can be propagated vegetatively. Growers of annual triploid plants not readily propagated vegetatively cannot produce a second-generation crop from the seeds (if any) of the triploid crop and need to buy triploid seed from a supplier each year. Many sterile triploid plants, including some trees and shrubs, are becoming increasingly valued in horticulture and landscaping because they do not become invasive species and do not drop undesirable fruit and seed litter. In certain species, colchicine-induced triploidy has been used to create “seedless” fruit, such as seedless watermelons (Citrullus lanatus). Since most triploids do not produce pollen themselves, such plants usually require cross-pollination with a diploid parent to induce seedless fruit production.
The ability of colchicine to induce polyploidy can be also exploited to render infertile hybrids fertile, for example in breeding triticale (× Triticosecale) from wheat (Triticum spp.) and rye (Secale cereale). Wheat is typically tetraploid and rye diploid, with their triploid hybrid infertile; treatment of triploid triticale with colchicine gives fertile hexaploid triticale.
I know that’s a lot of text, so I want to call out a list of things that are just wild about this to me:
- Polyploidy means having extra sets of chromosomes, which of course we’re all familiar with from awful conditions that can cause in people, but plants just… use all the chromosomes they have sitting around? The more ploidy they are, the better they get?
- We can do polyploidy math to determine fertility?
(2 + 4)/2 = 3, so odd so it’s infertile,
* 2for colchicine becomes
6again, so it’s fertile? This cannot be how it works. Je refuse.
- Oh, and it’s saying they use the triploid infertility to do plant DRM. Of course they fucking do.
- You’re telling me that every seedless watermelon I’ve ever eaten had the same backstory as the Hulk and no one bothered to advertise this?
- And they just rub Dr. Dioscorides’ Patented Mutant Cream on the plants? Captain America didn’t need to get in the iron maiden after all?
- It is “increasingly valued” that we broke the reproduction of a kind of plant because it’s so inconvenient to deal with fruit and seed litter. Somewhere there is a very dark metaphor here, though one to only be made carefully.
- Wheat is so civilizationally important, and rye is so civilizationally important, and they made a mashup and I didn’t even know. At least we are not letting down our ancestors in the sense that yes, someone has made it into a beer.
- Durum wheat is a non-colchicine-induced polyploid variety of wheat that you’ll likely have heard of: it’s-a what they make-a the pasta from. Instead of being diploid like you or me or basic bitch wheat, which means two sets of chromosomes, it has four sets of chromosomes. Wheat was so good they made a Wheat 2
The Anglo world, particularly Britain, has shown an impressive ability to forget just how into eugenics it has been. The timing of all those dog breed clubs: not an accident. You will find in literature “good breeding” referred to without irony decades after That War Fought Over Such Things. Someone really needs to explain to me how this was memory-holed so effectively. ↩
As one does. ↩