In these days of magnificent achievement for the Hybrid Teas, it is probable that more than 95 per cent of the current work of rose breeders involves Hybrid Teas, Floribundas, and Grandifloras; all lines in which breeding has proceeded over a sufficient number of generations for the attainment of a certain compatibility between varieties likely to be crossed. Experience with such lines must tend to make rose breeders unaware of the hazards involved when attempts are made to hybridize species that are distant in relationship.
My own line of work in roses involves the hope of improving hardiness by bringing in the genes of species not ordinarily thought of as of value except for hardiness. There are many species capable of increasing hardiness, and when one tries them out, even though only on a random basis, one becomes appreciative of the enormous richness of the Genus Rosa, as well as of the tremendous distance travelled by breeders during the past century or two.
Who would have thought that a hybrid like Hansa would be of such high fertility? It may not be a hybrid, agreed. Its ancestry is not on record. Nevertheless, it is hard to resist the conclusion that Hansa is indeed of hybrid descent, if only because it so closely resembles Mrs. Anthony Waterer, which is known to be a hybrid. The latter Rugosa would probably be as fertile as Hansa if it were not a triploid, If the pollen parent of Mrs. Anthony Waterer was General Jacqueminot (a tetraploid), the pollen parent of Hansa may be a Chinensis rose; perhaps one now long lost, which resembled General Jacqueminot except in being a diploid. Hansa hips can have up to 80 seeds in each, which would indicate that it is both fertile and fecund.
If it is a marvel that Hansa should be so self-compatible, the marvel is compounded in its descendant Aylsham, which I bred by putting on Hansa pollen of the New England native rose R. nitida. It must be many millions of years since R. nitida became separated geographically from the two ancestors of Hansa, and yet Aylsham is fertile too. The hips are not so large, but are equally well packed with seeds.
Yet when I cross Aylsham with one of its sibs, the distance apart of the Asiatic and the North American parent becomes clear. Fertile as the first generation may be, the second generation is genetically unhappy. I do not know what their fertility is, because I have discarded most of them for lack of vegetative vigor. Doubtless if someone were to continue the line of breeding, in the fourth or fifth generation, he would find a few individuals in which both fertility and vegetative vigor were restored.
If one were to cross Aylsham with a different hybrid that had two further species in its make-up, say a Spinosissima-Foetida hybrid, he would almost certainly get a plant which would refuse to bloom, or bloom very sparsely. A hybrid with four grandparents of different species is quite unlikely to be satisfactory. It will lack vigor, or ability to make flowers, or fertility.
When one crosses two species, it is best not to use the immediate or first generation hybrid in further breeding involving still other species. The first task is to let the hybrid line "settle down" by raising a fourth or later generation in which the genes are no longer at war with one another. A fourth generation hybrid may closely resemble the first generation hybrid in all outwardly discernible characters, and yet differ greatly from it in genetic happiness and abilty to dominate in further crosses.
Some species, however, are capable of being crossed, and are fertile enough in the first-generation hybrid. Yet, when subsequent generations are raised, they lack intermediates. The progeny will largely resemble one parent or the other, but the equivalent of the first hybrid will scarcely appear. The following rules for hybridizers of distant species might not be foreseen by making a book study of the Mendelian principles, but they should be useful. They are: (1) Don't mix too many species at one time. That is, don't confuse the poor plant by eventually giving it too many genes alien to one another. You may be able to bring genes from distant ancestors into one line of descent, but don't hurry to do so. (2) Have a definite objective to start with. Plan where you want to go before you start out to go there, whenever you have the needful information, from books, correspondence, or your own previous experience, that will guide you. (3) And yet, after you have learned all you can about what is likely to happen, make a few crosses at random too. Not everything is cut-and-dried. Nature will have many surprises for you; some of them delightful ones.
When I put pollen of Rosa nitida on the pistils of the Rugosa Hybrid Hansa, it was a cross made at random, and yet the results were a valuable new rose variety. The flower form of Aylsham and its color also, are much more beautiful than the flower form or the color of Hansa. I'd never have had Aylsham if I had not been willing to make some interpollinatons without specific plan.