hearing the gras grow…
recently I’ve read an article about the correlation of seed size and the ploidy of roses.
Yesterday, after harvesting one of my crosses, I got a lot of small seeds inside the ‘Sympathie’ x ‘Ghislaine…’ cross:
the ratio of big to small is about 1:2.
Will this still indicate a lot of di/triploids and some tetraploids ? 'never observed this before when breeding with this motherplant.
cheers
Bernhard
Interesting idea, Bernhard. I’ve not considered that before, always chalking it up to immature or not viable seed. I’ll have to try more of the smaller ones to see what they do. Thanks!
If you do discover that some of the smaller seeds give lower ploidy plants then it will be a coincidence.
Seed size - dimensions of the achene - is a maternal trait. In fact, the achene often (maybe even most often) reaches its final size before the embryo is large enough to be visible to the naked eye. The lumen of the achene is filled by a loose wet tissue that gradually condenses and recedes as the embryo grows into the space.
For that matter, an embryo is not even needed for an achene to form. Almost always at least some of the seeds from a normal-looking hip are empty and sometimes all of them are.
In my experience smaller seeds like those pictured are less likely to contain embryos than the larger ones but chances are still good that some of them do.
I have found that very small seeds have an advantage over larger ones in cold climates when the hip remains exposed to the elements during the winter. In these cases it is often the embryos of only the smallest seeds that remain viable.
The reason that this happens is, I think, because the smallest seeds can completely dry out while the larger ones retain enough moisture to cause damage when they freeze.
Gigantea is diploid and its achenes are enormous.
Gigantea is diploid and its achenes are enormous.
But how big are it’s embryos? The largest embryos that I have seen are from R. moyesii, which is supposed to be octaploid, yet the seeds are about the same size as those from HT’s though more ovoid.
It is the relative size of the embryos from a hip that suggest differing ploidy levels. For that reason I have been noting when relatively small embryos turn up.
Small… but that’s not the point… am just saying you can’t judge a book by its cover.
Bernhard,
I agree with Don and Kim, the smaller seeds probably are not viable seeds, but you could try to germinate them anyway to find out. Are the smaller seeds hard or are they fairly soft and you can indent them with you thumbnail? If so they
Thanks for reply to all,
I
A fun experiment could be to germinate the smaller ones separately, to see whether the resulting seedlings reflect any particular pattern (eg. could some smaller be the result of a different pollen parent to the larger ones?).
The seeds from the chinenses Mutabilis and Hume’s Blush (Pickering) are also large, about the size of HT seeds.
In at least some cultivars, achene size is determined more by the number than anything else. For instance in Knock Out, or Silver Moon, a single achene may be 1/4 inch diameter with an open empty space surrounding it, in a large fleshy hip. But the same size hip may have up to 7 achenes, all quite a bit smaller and packed together so they are not round but more like sections of a citrus fruit. Other CV have fairly thin hips with overall size in proportion to seed #. When I dissected out 4000 or so seeds from 200 hips of Country Dancer last winter, there were achenes in a wide range of sizes, often both large and smaller in the same one. I got over 50 % germination, but have not done a size sort on the nongerminators. I can do that (for some anyway, if I don’t get too bored). They were in vermiculite so they are easy to sort out, and in lots of 200 hips/ treatment, so I can get a decent % estimate for at least one CV. One of my complex mini plants (Pink single, Carefree Beauty x Rise N shine) always makes rather small seeds, independent of #/hip, but they are very vigorous in both germination and growing.
Maybe we should consider species relativity rather than genus relativity. Maybe we are thinking too much in absolute terms.
In at least some cultivars, achene size is determined more by the number than anything else.
This makes a lot of sense. There is a finite amount of photosynthate that can be pumped into a hip and it has to be shared among all developing seeds.
“…Maybe we should consider species relativity rather than genus relativity…”
Jadae, 'agree, in this case it will be the better point of view.
“…A fun experiment could be to germinate the smaller ones separately, to see whether the resulting seedlings reflect any particular pattern (eg. could some smaller be the result of a different pollen parent to the larger ones…”
Thanx for the hint George, thats still in work 
“…have not done a size sort on the nongerminators. I can do that (for some anyway, if I don’t get too bored)…”
that would be great!.. to have an idea if the large one or small one will better work. Wilhelm Kordes wrote in his book that the ‘biggies’ are mostly the duds…
regards
Bernhard
Just an observation from another Genus that may or may not be useful…
In bearded Iris, for several years now I’ve noticed that tetraploid seed parent pollinated by diploid pollen gives mostly undersized/shriveled seeds with sometimes 1 or 2 large (fairly normal looking) seeds per pod. The reverse cross (tetraploid pollen on diploid) has always given nothing but chaffy completely aborted seeds for me (no germinations).
The most surprising thing though, is that I have never been able to germinate (not even one of) the larger, normal looking seeds from any of the mixed ploidy crosses. The only ones that regularly give me decent germination are the ones you would think are too small to be viable. So, I would be careful not to throw the small rose seeds away without testing some first.