tetraploid

‘Seedless’ Watermelon and Other Fruit

Seedless fruit rarely occurs in nature. This makes sense, of course: Nature is in the business of creating and furthering life. The seedless fruit you will find in the grocery store is the result of a manipulation developed by plant breeders years ago.

Now for some science: Different organisms have differing numbers of copies of genetic material or chromosomes, in their cells. Humans, for example, have two copies of chromosomes  in their cells; the genetic term for two chromosome organisms is called diploidic.  In nature, there are almost always an even numbers of chromosomes in cells: diploid (2x), tetraploid (4x), hexaploid (6x), etc. This way, when cells reproduce by splitting, each daughter cell receives an equal share of half of the parent cell’s chromosomes. If ploidies were odd, there could be no even split of chromosomes.

Seedless fruit is made by creating an odd-ploidy plant. Seeds cannot be produced from odd-ploidy plants, simply because there’s no way to evenly split the chromosomes. Thus odd-ploidy plants do not generally manufacture seeds at all, and if they are made by the plant, they are entirely nonviable (they themselves will not create seeds for further reproduction of their own genes, and don’t become fully mature seeds. ‘Seedless’ watermelon is an excellent example of this – there are very few seeds in a seedless watermelon and the seeds that are there are small, flimsy, and hollow.

Read More at thebestgardening / © The Best Gardening


More on plant breeding, polyploidy, and seed morphology.

Swedish whitebeam (Sorbus × intermedia)

This tree was making me crazy: I knew the berries looked like Rowan or Mountain Ash, but the leaves looked bafflingly oak-like. I’d never seed anything like it before coming to Denmark; and up until now, actually assumed it was a Hawthorn (Crataegus spp). That estimation wasn’t too far off, considering they are both in the subtribe Malinae.

I only recently found out that the Eastern coast of Denmark is home to a sizable population of this complex Swedish Sorbus hybrid. The three-way parentage of these trees is purported to be S. aucuparia, S. torminalis, and S. aria. It’s what you call a ‘tetraploid apomictic species,’ in that it produces viable seeds without pollination; this basically means it clones itself through seeds!

Here you can see it growing alongside a European Mountain Ash (Sorbus aucuparia), one of it’s parent species.

Swedish Whitebeam above, European Mountain Ash below.

Like Rowan, the red pome fruits are edible (barring the seeds, which contain cyanide). Unlike Rowan, they’re actually large enough to make harvesting interesting.

I put some of these seeds up in my shop for anyone interested. This species has already been introduced in North America, and not regarded as invasive: it’s an excellent forest gardening selection to try growing in Northern climes!


Support my writing and photography by buying seeds from my shop!