The American Rose, March 1978, p. 23.
Unexploited Genes in Rose Species
Percy H. Wright
Saskatoon, Saskatchewan, Canada
The topic suggested in the title is such a big one that a book should be written on it. I then must select only a few comments that are crying for recognition, and must do so in hopes that at least a few readers will follow up with a study of the literature of the larger topic. The specific recommendations I am able to make will, I hope, be worth the attention of rose breeders who are seeing the limitations in stirring up once more the old brew of genes which have been exploited so often and so industriously by recent enthusiasts. The simple truth is that so much has been achieved in the improvernent of form, petal substance, and long, strong necks, that our hope for further advance lies now in the improvernent of plant, rather than flower, characteristics.
We need fewer thorns (or none at all), greater hardiness, and better resistance to insects and diseases.
No one seems to have made it a special aim to breed for resistance to the rose curculio, or snout-beetle, which devastates shrub roses in an enormous area of the Great Plains, in both the U.S. and Canada, and the reason for this appears to have been the lack of a realization that roses do exist which do not attract this pest, even when their period of bloom coincides exactly with the maximum abundance of the pest. The two species which I have observed to be immune to attack, or nearly so, are Rosa laxa Retzius and the as-yet-unnamed species which has the everyday appellation of Ross Rambler. It is high time that the taxonomists got around to giving their best attention to this rose, which is surely unique in its combination of three highly desirable characters: hardiness, height, and everblooming. It is so like R. laxa that it may well be classified as a mere subspecies, but, from the practical standpoint of the breeder, its possession of a gene for everblooming means that the difference is important.
These two roses seem to be almost completely resistant to rose scale, at least to the commonest one. In addition, I have never seen blackspot or mildew on either of them. I have occasionally observed a little rust. The difficulty in making statements on disease resistance which will apply to all parts of our continent is compounded by the probability that different strains of these diseases exist and that they most abound in certain areas to which adaptation or chance has assigned them.
Both R. laxa and Ross Rambler are so hardy that I have never seen the slightest loss of tip growth, even when winter temperatures have reached -50°F. What is more, they seem able to transmit this remarkable hardiness to their descendants with considerably more success than that shown by other hardy rose species, even such hardy ones as R. blanda. From this it would seem that we can argue, for example, that a new cultivar with one-eighth of the ancestral material of these species would be as effective in inducing as great a hardiness as another cultivar with one-fourth of the ancestral material of some other hardy rose species, say R. blanda.
It is a pity that we cannot call upon R. blanda for more of the characters we seek, since it has that prized feature of complete thornlessness. However, it donates susceptibility to mildew and rust, as well as once-blooming, to its descendants, and imposes the additional handicap of the diploid condition. The same remarks apply to R. suffulta (or arkansana) which, though it is a tetraploid like most of our valued cultivars, is even more subject to rust.
There are two other rose species to which I should like to see some attention given. One, a native of Europe, is R. arvensis, which seems to have been overlooked by European rose breeders and of which a thornless strain exists. The other is R. foliolosa, a native of Oklahoma, which American breeders seem likewise to have overlooked.
In my far north location, I do not have the firsthand experience to enable me to comment on the genes of more southern roses, even such semi-hardy ones as R. hugonis and R. alpina. However, my purpose is to open up the whole topic of unexploited genes in Rosa, where future development undoubtedly lies hidden. There is a rich vein of gold in mines yet to be explored, and it is time we got to it.