I was going through some of my photocopied journal articles and came across an article from 1969 I thought I lost. It was about a rose that has 77 chromosomes (11 sets!!!). It was in Euphytica (volume 18 pages 178-182) and is by A.E. Zeilinga. This person crossed R. canina with R. pendulina and got this unusual hybrid. They reason through the various options that this rose could have 11 sets of chromosomes and decide that the most probable option is that there was a 2n egg in their R. canina parent.
The R. canina parent they used was pentaploid (5x) and R. pendulina hexaploid (6x). In meiosis the Canina section roses typcially produce an egg with 4 sets of chromosomes and the pollen has one. So, perhaps with premature cytokinesis after Meiosis I the egg ended up with 8 sets of chromosomes and then along with the 3 sets from R. pendulina this hybrid is able to have 11 sets. The other option that they considered was that the microspore mother cell in the female did not go through reduction at all and then had all 5 sets of chromosomes and the R. pendulina male had a 2n gamete (6 sets) to come up with 11 sets. Due to the morphology of the hybrid being much more like R. canina and that the second option is more unlikely, the first senerio is what the author favored.
It’s interesting that the rose with the most number of chromosomes that has been reported arose as a fluke from a cross in a breeding program and without human intention of generating such a high ploidy plant (no colchicine or trifluralin).
Sincerely,
David