Ploidy of 'Cuthbert Grant'

Does anyone know what CG is?

I’d expect it’s tetraploid. It seems that all the parents and grandparents and great-grandparents are tetraploid.



I was looking at the parentage and couldn’t find anything but tetraploids going back a few generations like you found Peter but wasn’t sure because I’ve read of questionable fertility. I grew CG years ago and it’s back in my garden to use again. I don’t have a good recollection of what I found earlier as to its use as a parent.

Thank you for the link to your prior thread Henry. Any guess as to how it ended up as a triploid with all those tetraploid ancestors?

Hopefully I’m following ploidy discussions correctly. To get more fertility in a F1 it would be best to use diploid pollen on CG for a fertile diploid result or using CG pollen on a tetraploid and hope for a tetraploid or fertile triploid…is that correct? Thank you guys for the response.

I have a plant rooted from a cutting I took in for the winter that I hope to count the chromosomes of. With the low fertility documented by Henry and experienced by those of us who have tried it, I’d be very surprised if it isn’t triploid.

There were several roses that I came across (some my own seedlings) that are crosses between two tetraploid parents and are triploid. For instance, ‘Prairie Harvest’ is triploid and is reported to be a cross of ‘Carefree Beauty’ and ‘Sunsprite’, both I counted as tetraploid. It seems with all the diverse background in modern roses, during meiosis pairing can go astray sometimes and chromosomes are likely lost in some gametes.

Its also possible that we select triploids from seed batches without even knowing we have done so.

I think you are right Jadae. I think there are some advantages in growth rates and other factors that tend to be associated with lower ploidy levels (not completely of course) and we indirectly select triploids as we value those traits. It is interesting all the Knock Outs are triploid and most of the Flower Carpets, many of the Meidiland roses, and Home Run. Even more typical modern roses like ‘Tropicana’, ‘John F. Kennedy’, and ‘Incognito’ are triploid. Other Buck roses are triploid too like ‘Quietness’.

I’m suprised to read that “Prairie Harvest” is a triploid. I used it this year as a seed parent this year and it was a very good seed producer with over 21 seeds per hip. I believe David has confirmed another Buck rose “Hi Neigher” as a triploid as well, but I haven’t used it either way as a parent and it hasen’t produced any OP hips. Neither Prairie Harvest nor Hi Heighbor are very vigorous in my garden.

Could it be that we are actually selecting for defective gametogenesis on the female side, rather than triploidy per se? A clever commercial breeder might find it an advantage to cross a line of diploids to a line of tetraploids to get floriferous but sterile (relatively) flower makers. But I don’t think that’s how Knock Out was developed in the first instance. And the pollen of Rainbow Knock Out (which is not a sport of Knock Out but a different pedigree) seems very fertile in a variety of crosses I have done, though it sets less than one hip per hundred blooms by my estimate of 4 plants here on campus. It is visited by bees, but nearest neighbors tend to be K.O. or other low fertility types, so I can’t say for sure it is the female rather than male function.

Double Knock Out is a separate cross, not a sport of K.O., and Home Run came from Knock Out, according to published statements. But there is something in the pedigree that makes them behave as relatively female infertile. I’ve gotten relatively a lot more seeds from what I believe is H.R., than from K.O. in my area. I don’t think the problem is from Carefree Beauty, which is highly self-fertile. As for Prairie Harvest, how is the fertility of Sunsprite, the pollen donor?