I’m very much a newbie, but I’ve been reading a lot. I think there are several bases for rebloom, beyond just Chinensis and ‘Autumn Damask’, and as has been posted, not all are compatible. In addition, some species seem more easily nudged into reblooming than others, indicating something more complicated than simple Mendelian genetics. I think there’s a dose-dependent factor as well. ‘Autumn Damask’ rebloom seems to be capable of “working” in F1 offspring with other European OGRs – sometimes. If the reported ancestries are correct, it worked on ‘Duchess of Portland’, ‘Rose du Roi’ and ‘Stanwell Perpetual’ despite being passed on from only one parent. Then consider ‘Autumn Damask’ itself – two ancestors (‘R. moschata’ and ‘R. fedtschenkoana’) have long bloom seasons. Somehow, the stars aligned and allowed for extended bloom in this Damask, but not as much in the others (though perhaps ‘Isphahan’ is just another expression of it).
Some other F1 hybrids of ‘R. moschata’ rebloom, despite expectations based on the other parent. I have ‘Reverend Seidel’, and while mine is still young and doesn’t bloom a lot, it does have flowers over an extended period, despite its other parent being assumed to be a once-blooming Synstylae Rambler (‘The Garland’). ‘Dupontii’ is reported to have some scattered Autumn blooms. ‘Yvonne Rabier’ is an F1 from ‘R. wichuraiana’. John Starnes got repeat bloom on an F1 from ‘R. brunonii’ with his ‘Lemon Zen’ seedling. My ‘Baltimore Belle’ has what could be called either “extended bloom” or “scattered repeat”. Perhaps this indicates that Synstylae roses are more easily coaxed into reblooming than some other species. Maybe this is an independent Synstylae “prediliction” for forming dwarf repeating plants, either as seedlings or sports.
Then there’s ‘R. rugosa’ rebloom, which also seems to “work” sometimes in F1 seedlings from once-blooming roses. ‘Basye’s Purple Rose’ is the first that comes to mind there. Does this mean that ‘R. rugosa’ rebloom is dominant? Maybe, sometimes. Maybe some rose species need more things “knocked down” genetically to induce rebloom than do others, and maybe the various “forms of rebloom” target different mechanisms. Perhaps it’s better to think of it as genetics for “preventing bloom period shut-down” rather than “causing rebloom.”
Then there’s another wild card – epigenetics. It could very well be that “surprise” reblooming offspring have, for whatever reason, the “stop blooming signals” shut down or diminished because of expression – rather than genetic – variation. I think of this as a possibility for ‘New Dawn’ sporting from ‘Dr. W. Van Fleet’. Both are triploid, and based on parentage, likely have three copies of “Chinensis Rebloom” and one copy of “Wichuraiana easily-nudged-into-rebloom”. In the sport, perhaps an epigenetic mechanism favored activity of the two chromosomes with “Chinensis Rebloom” and silenced the third member of the triad which lacked the “reblooming gene(s)”, and these epigenetic changes were maintained in gamete formation.
This is all just conjecture from an amateur. I became fascinated with rose ancestry and genetics since it’s so “fuzzy” for someone coming more familiar with animal genetics. My first season’s attempts at hybridizing have netted a total of three seeds, all from two ‘R. moschata’ hips – one with ‘Nigrette’ as the daddy, the other with ‘Chateau de Clos Vougeot’ providing paternity. If they grow, will my “red Noisettes” rebloom? I hope so.
~Christopher