Studying the history of floribunda and miniature roses, it seems that hybridizers have crossed diploids and tetraploids, and then crossed the resulting triploids with tetraploids (when fertile enough). However, I haven’t found any records where someone took the triploid and crossed it back to a diploid. Are there any known roses that are the result of a diploid x triploid cross?
I think ‘The Fawn’ is maybe a diploid from a triploid. It is a result from ‘The Fairy’ X ‘New Dawn’. Even ‘The Fairy’ itself is a diploid resulting from a cross between a diploid and a triploid as it is a cross between ‘Paul Crampel’ X ‘Lady Gay’. And I think many of the hybrid musks may be diploids from triploids, but they are so weird as a group. Many of them are fertile even when their parentage suggests that they are not soppose to be.
There is a research group headed by Dr. Debener that is doing some inheritance and molecular genetics work in roses. Off the top of my head I think they are in Germany. They have been working with a population of diploid roses that they obtained from open-pollinated triploids that are the result of crossing diploid R. multiflora with tetraploid modern roses.