I’m growing some seeds this year from hardy citrus hybrids (Citremon, US-852, carolina lime, and some citrumelos). I’m mostly interested in seeing if I can grow out any unique seedlings with a pinch more hardiness. They’re in ziplocs right now, and the first couple to send out roots have 2-3 separate roots emerging. I’ve read that citrus seeds can be polyembryonic, but then there’s various rates of zygotic seeds - with the rest being clones of the mother.
My question is, if one seed makes multiple seedlings, are those all identical? or could there be multiple genetically distinct embryos in one seed?
It is possible that one seed makes multiple seedlings with many of those being clones of the mother plant but one being a genetically distinct seedling. One other thing to consider is that sometimes a clonal seedling could experience chromosome doubling or end up with a mutation that could give it a bit more hardiness.
There’s some oddness with the whole process, but in general seedlings from a polyembryonic seed are either all clones or at most one is a sexual seedling and the rest are clones. All the seeds start off with a single embryo, one that is sexually produced (though often it’s from self-pollination), but as the seed matures the placental tissue around the embryo differentiates in weird ways and starts producing new embryos. And since the placental tissue is all genetically the mother plant, those new embryos are all genetic clones of the mother. What’s more, they often outcompete the original sexual embryo in development, leaving you with a polyembryonic seed with no viable sexual embryo and just a bunch of clones.
For most varieties, the rate of nucellar (clonal) seed is very high, with most nucellar seeds also being polyembryonic, though pollen parent seems to make some difference. US-852 has a decent rate of zygotic seed so you’ve got some chance there.
6a is gonna be a really tall order though. 6b is where that madlad kumin is doing his massive trial. And even in 6b, most of the hardy varieties aren’t hardy enough.
This is a myth promoted by sellers of seedlings. It is only true for a small set of fruiting plants with polyembryonic seeds. There is a wide number of possible outcomes across the rest. In the UC breeding program of Mandarins, about half the seeds in fruits were true-to-type. This is why they hand-picked seeds based on morphology from the fruit.
All I know about for polyembryonic, is citrus seeds, and loquats. Each variety will vary in the percentage of seeds that are polyembryonic.
Polyembryonic seeds will look different than the seeds that are not polyembryonic, because polyembryonic seeds, each of them grow in to more than one plant, it’s like each polyembryonic seed gives birth to twins.
Some are identical twins, and some are not. Even the identical twins will grow up to not being 100% the same, just like the identical twins that people give birth to. Like has been already said the identical twins can vary in ways that are an improvement to the plant, like more cold hardiness.
Thanks for the info. I’ll have to grow em out a little more and just observe for a while.
I had read some of Kumin’s posts, and that is waaay more intense than what I had in mind. I was thinking of just exposing a few dozen seedlings to maybe 10 or 15F and moving from there. Making crosses could be fun over the next few years too. My area is on the edge of 6B now, so in-ground (and halfway edible) is a distant dream.
You’ll note I’m discussing specifically those within the set of citrus with polyembryonic seed, so there’s no need to say " It is only true for a small set of fruiting plants with polyembryonic seeds" as I’m already making that qualification (though without the inaccurate claim that it’s a small set of citrus).
As for it’s prevalence and importance in breeding, I’ll quote a write-up from James W. Cameron and Robert K. Soost, who I suspect you’ve heard of:
Nucellar embryony has been a major obstacle to
the systematic production of F1 hybrids and selfpollinated
progenies. Many cultivars produce almost
entirely nucellar embryos.
Also, didn’t UC use Wilking in a lot of their breeding lines? If I recall correctly, that’s one of the handful of tangors that is fairly zygotic. So yes, the breeding program did see high rates of zygotic seed, but that’s because they (intentionally) used a parent variety that is known to produce zygotic seed. In no way does that imply that other varieties of tangor and mandarin aren’t nucellar (as an analogy, the existence black swans does not imply white swans don’t exist or are rare…), so I’m not sure why you bring it up.
Anyway, this is all a somewhat useless quibble, so I think I’ll lay off it now.