Known hexaploid cultivars

I found

Hi Fred,

I wish I knew of some repeat flowering hexaploids… The only hexaploid roses I know of are one time bloomers. Perhaps that’s where we need to start. Pollen diameter can give a clue, but direct chromosome counts has been the best way. Separating diploids and tetraploids with pollen diameter has worked well for me, but not tetraploids and hexaploids.

R. alba semiplena is hexaploid, but it has what appears to be a variation on Caninae meiosis and has two sets of chromosomes in the pollen and four in the egg. So, as you select hexaploid parents it’s important to know what hexaploids are in the section Caninae or are derrived from it to know what’s going on in the gamates so you can carry through with the mating system you are intending.

If repeat flowering is your main concern and you want to pruduce tetraploids from mating hexaploids with diploids this is what I suggest. Cross your diploid species or cultivars with triploid repeat flowering roses like ‘Iceberg’, ‘Out of Yesteryear’, and ‘Tangerine Jewel’. These triploids are producing some 2n pollen (“unreduced” pollen and the grains have 3 sets of chromosomes). You will have more than tetraploids among your offspring, but as you select those offspring with fertility you can get to the next generation and will hopefully select out the fertile tetraploids and perhaps some fertile roses of other ploidy levels as well.

Sincerely,

David

Thank you for the reply David. My problem besides being limited space is that many of the non repeat blooming cultivars will not reliably bloom here due to the high temperatures during our winters (USDA zone 11). My aim is to be able to get some of the good qualities available in some of the old Chinas and Teas (some of which grow here with little spraying required although they all do better with it)and introduce those qualities back into the lines of modern Hybrid teas. I just collected some hips of crosses that I made with old blush but I am worried that the progeny will be sterile and therefore useless for future work. Any suggestions anybody?

Don’t give up too easily with triploids. Many make fabulous male parents. I have a couple very fertile ones that are producing very vigorous, well-branched seedlings. Perhaps you can find some older cultivars which are triploids from crosses of tea roses and tetraploids which could make a great bridge to hybrid teas. Chromosome doubling some tea seedlings wouldn’t be too hard either if you are interested. Good luck. Way up here in the North I can’t get teas to overwinter even with lots of protection, but I sure admire them for what I read about their general disease resistance and seeing some in Texas last summer.

Sincerely,

David