I ran across some interesting information…
It seems that Constance Spry and R. kordesii are diploids, and not tetraploids.
Is anyone surprised like me?
I am. I’ve always read that kordesii is tetraploid.
I think that it is a mistake. In the text of the thesis, he refers to R. kordesii as an ampidiploid several times. It is only in Table 5.1 that it is listed as a diploid.
Well, I have yet to send a rooted kordesii cutting to David-- but once I do… I’m sure he’ll figure out its ploidy eventually. Right now, it’s recovering from nearly being baked to death. It even made a flower today.
Enrique, I could look at its pollen. It does not take very much pollen to do a microscope determination of pollen diameter.
I really enjoy Leen and the work that she has done. I have found a number of discrepancies between her ploidy estimation using flow cytometry and the counts that I’ve made, but for the most part our results are pretty consistent. Perhaps there are different clones labeled under the same cultivar name? The amount of DNA in a cell (as estimated by flow cytometry) can be variable at a given ploidy level and overlap. In wide crosses (as most roses are involving multiple species) there is often some genomic rearrangement and alterations in genome size that occurs. Repetitive DNA might be removed in some regions making the size smaller or visa versa sometimes. I think this is probably a large part of the discrepancies. Root tip squashes and chromosome counts also just tell the ploidy of Layer III of the growing point because root tissue is typically derrived from this layer. However, flow cytometry can pick up chimeras, plants with a mixture of ploidy levels. The roses that are different in ploidy from Leens flow work and my direct counts are not ones she identified as ploidy chimeras. Flow is a very nice indirect estimation of ploidy, as is pollen diameter, but I doubt if direct chromosome counts can ever be completely replaced when accurate ploidy determinations are imperative.
Sincerely,
David
Is it possible to do chromosome counts on germinated pollen? For that matter, how about androecia and gynoecia tissue?
It seems like it would be very difficult to do chromosome counts on germinated pollen. The chromosomes need to be condensed so they can be distinguished from each other and seen and counted. There is one last mitotic division to produce the two generative nuclei in roses as the pollen tube germinated (one to fertilize the egg and one to fertilize the central cell for the endosperm). As the chromosomes condense and are ready for this division I think it could be possible. Otherwise overall meiosis can be observed and the chromosomes counted at the different stages and with enough counted and knowing what stages are being seen one can tell the ploidy of the parent. I got some flower buds in the mail just recently to try just that on a clone. I don’t have much success yet preparing and looking at meiotic cells and finding the different stages. Perhaps I should fix a bunch of buds from my garden and practice before looking at these samples.
The female tissue is much harder to isolate ane work with. Male tissue is so much easier to access and more abundant.
Hopefully I’ll have success with these samples. Otherwise from my chromosome doubling paper I found a couple diploids that produce 2n pollen and confirmed that instead of by observing the chromosomes during meiosis, counting diads and triads compared to tetrads. The original cell going through meiosis typically results in 4 pollen cells and before they break apart are joined together as a tetrad. If there are just 2, it is probably 2 pollen grains with twice as many chromosomes or 2n pollen. If there is a triad, two are probably normal and there is one 2n pollen grain.
Sincerely,
David