I have a seedling of Country Dancer x Hansa. I believe Hansa is diploid. I assume Country Dancer and the other Buck roses are generally tetraploid, but I cannot seem to locate that information. If that were the case, am I correct in saying my seedling is probably triploid?
I would suspect your hybrid is triploid too as ‘Hansa’ is a confirmed diploid and ‘Country Dancer’ a confirmed tetraploid. I counted a number of Buck roses over time. Some are listed in this paper:
Additional ones are listed here: www.rosebreeders.org/Fall_2012_Zlesak_long_version.pdf
Is it not true that Theodosia’s seedling, while most likely triploid, does stand a reasonable chance of being either tetraploid or diploid based on our understanding that pollen comes in a spectrum of ploidies?
Country Dancer has triploids on both sides of its ancestry, so even if it is tetraploid it has a good chance of passing along triploidy. There is a good chance that your seedling is triploid. However, it may be fertile and produce useful seedlings.
Country Dancer has triploids on both sides of its ancestry
What’s that got to do with it?
According to research by Paul Barden and David Zlesak, tetraploids do not always behave as tetraploids. See their article “Conducting Chromosome Counts on the Bracteata hybrids” in the Winter 2004 RHA Newsletter. Muriel (itself a tetraploid) gives some triploid offspring and some tetraploid offspring in the same cross.
I think there is nothing surprising about this. Tetraploid roses which are closer to triploid-level ancestors are more likely to give triploid offspring than those which are from lines that have had nothing but tetraploids involved in their ancestry for the past 4-6 generations. Many of us have grown seedlings in which the color of an ancestor from 4 or more generations back reappears, but it is much more common to get a range of colors from the more recent ancestors. I see no reason to think that ploidy would not be similarly heritable. Many of the Pernetiana roses are triploids, and although GuinÃ©e (one parent of Muriel) is tetraploid, it is from a Pernetiana ancestry.
As I understand it, that is what triploid ancestry has to do with the ploidy of Country Dancer.
Tetraploid roses which are closer to triploid-level ancestors are more likely to give triploid offspring than those which are from lines that have had nothing but tetraploids involved in their ancestry for the past 4-6 generations.
Did I miss that in their paper or are you just …
I see no reason to think
Did I miss that in their paper or are you just … guessing?
I prefer to think of it as thinking rather than “guessing”. I’m applying what seems to be the general principle involved in these instances.
Chromosomes are not always stable, and the demonstrated instability of chromosomes in one complex hybrid suggests to me that instability of ploidy is no more surprising than the appearance of colors from a much earlier ancestor. In the article I referred to, David offers these thoughts about the instability of chromosomes:
Unexpected ploidy levels may be coming from tetraploids where uniform and consistent chromosome pairing during meiosis is not regularly occurring. For instance, among the chromosome-doubled polyanthas I generated there was pretty low fertility in general. They are autotetraploids instead of allotetraploids. All four sets of chromosomes theoretically should recognize each other well and be capable of pairing. Sometimes the four complements may pair two and two, sometimes three form a trivalent and there’s one loner, sometimes all four have parts of their chromosome arms pairing and join to form a tetravalent.â€
If that is “guessing”, so be it.