I’m a big fan of the Lawranceanas and Dwarf Chinas. Love their twiggy growth habit, lanceolate leaves, blooms and would like to breed some more. I’ve read that Rouletii is a sport of Old Blush and is genetically identical. I’ve also read that many believe Old Blush to have some genes responsible for miniaturizing.
My question is how much of Old Blush was retained in the Rouletii sport? In regard to Old Blush’s surprising cold hardiness (for a China), fragrance, and susceptibility to Powdery Mildew? To me, it’s their blooms are nearly identical, so that’s no question. But I wasn’t able to find much of this info on HelpMeFind. Any help is appreciated, thanks!
I can’t offer any suggestions to answer your questions, but would offer the question, what is your plant size goal? Rouletti is more likely to produce miniatures to polys while Old Blush is more likely to produce larger plants. If you don’t mind working with smaller plants and flowers, use Rouletti. If that isn’t your interest, Old Blush would probably serve you better. Personally, I’d use Rouletti over Old Blush. I grew Old Blush because of its place in history and breeding but it didn’t stick around as long as most of the minis did. Where I grew it, foliage spotting and MILDEW were always issues. VERY few minis ever provided such irritation and NON of the “Lawranceana” types.
I doubt that Roulettii is a dwarf sport of Old Blush. They are likely related, but I have doubts about a more direct relationship. At any rate, they will absolutely not behave the same in breeding. Old Blush will give you large plants, and Roulettii will give you small ones (depending on what you mate it with). Dwarfism in roses is a dominant traits, so crossing something like Roulettii with a large shrub will give you a percentage of dwarf seedlings. If your goal is to breed "new Lawranceanas”, then use Roulettii (or Oakington Ruby), IMO.
If it helps to picture what’s possible… I pollinated Nessie [(Brunonii X Gigantea) X Mlle Cecile Brunner] with Tom Thumb. Yes, THAT Tom Thumb. I got short to tall polys and a few which looked like regular floribundas. The majority of them repeated. Most were “pink” and all were scented. 'Nessie' Rose
Thanks for your reply and advice. I definitely want to stay away from passing down PM and foliage spotting susceptibility. Did you ever raise anything from it? And would you know how species roses breed with lawranciancas/chinas? I’ve on here that I should never use any rugosa/rugosa hyrbrids with chinas, but I’d like to get some better disease resistance in there.
Thanks for the advice. I’d like to keep the structure and habit of the Lawranceanas; do you find that breeding outside of China class reduces the China habit of the the offspring? I’d love to retain the habit but it seems to me that a lot of their outcrossed offspring resemble polyanthas.
I’ve not taken any of the Nessie X Tom Thumb seedlings further (too many irons in the fire). I wouldn’t know how healthy species crossed with these roses may be, but generally, first generation species x modern crosses tend to have health issues. You can usually expect fungal issues any time you mix deciduous and evergreen foliage types. They can require a number of generations to breed out (if ever). It seems to me, your best hope is finding one or a few of that type of cross which are acceptably healthy where you are as they will often NOT be healthy in other climates. Two examples… Joseph Pernet-Ducher raised the HT X Foetida crosses (Pernetianas) and was asked “what about the black spot?” He replied, “what black spot?” as they didn’t experience the issue in his nursery. Ralph Moore raised a number of rugosa hybrids, many of which I trialed in my Newhall garden. I reported back to him about rust issues with one, in particular. He responded, “what rust?” as it hadn’t rusted for him in the nursery…until he experienced a spring like those my area usually experienced.