BREEDING for WINTER HARDINESS and COLOR in ROSES
H. H. Marshall
Canada Department of Agriculture, Research Station, Morden Manitoba.
Roses have been cultivated and enjoyed for their beauty for at least 2000 years. Some of their history has been outlined in The Canadian Rose Annual, 1974. Since then we have learned more about R. arkansana Porter hybrids and about the pigments that give roses their distinctive colors.
Shrub roses can be useful landscape subjects but for some reason they have not become highly popular. They differ widely from the popular concept of what a rose should be and are seldom used where their characteristics could be an asset. Many of these shrub roses are sterile or highly infertile making them of little value for further breeding. Several are crosses between 14 and 28 chromosome species so would probably be sterile triploids. Other breeding irregularities have also been observed.
There seems to be several advantages to using R. arkansana as a hardy parent. It is well adapted to the harsh winter and summer of the Canadian prairies. It has the same chromosome number (28) as most Hybrid Tea and Floribunda roses. It is a low growing species that has adapted to frequent damage by grazing or fires by flowering on new growth originating at or below ground level. Superficially, this resembles the everblooming habit of tender roses but no flowers are produced on secondary branches until the following summer. This habit, however, permits an extended blooming period. While it may not be the most winter hardy species, it is tolerant of dry, moderately alkaline soils, rarely becoming chlorotic.
The main reason R. arkansana has not been used more often as a parent is probably because of difficulty in obtaining the first cross. There are strong interspecific sterility barriers between R. arkansana and cultivated roses but a few Floribunda roses such as 'Donald Prior' will accept R. arkansana pollen. First generation hybrids are often moderately fertile and may be crossed to sister plants or back to either parent.
A second peculiarity often causes a breeder to discard the real hybrids. Since the everblooming habit is recessive to June blooming or to the modified June blooming found in R. arkansana these hybrids are not truly everblooming but may produce scattered bloom in late summer. Also, because the seed parent is everblooming any stray pollen is likely to give everblooming seedlings. These occur so frequently as to suggest the possibility of apomixis or the production of seed without normal fertilization. In any case the everblooming seedlings are not hybrids of R. arkansana and, therefore, cannot carry its hardiness or any other character. However, a beautiful everblooming seedling is what one wants so one is tempted to retain the wrong seedling.
Our breeding program is based on using R. arkansana as the source of hardiness with Floribunda or Hybrid Tea varieties as the source of flower quality. Other species have been avoided as being probable sources of further. breeding irregularities. 'Assiniboine' is first generation 'Donald Prior x R. arkansana (red form), It has been backcrossed to both parental types and also to several hybrid teas and numerous combinations of the resulting hybrids have been made. Two selections from complex hybrids have been named 'Cuthbert Grant' and 'Adelaide Hoodless'. Many hundreds of seedlings and over 50 selections are under observation. The three named cultivars are not fully winter hardy, but they are sufficiently hardy to survive without special winter cover and are able to bloom freely each July and intermittently until late fall over most of the prairies.
Certain other facts about the performance of R. arkansana hybrids are becoming known. Fertility is impaired but many will produce seed in the right combination. 'Assiniboine' rarely bears seed but its pollen is effective on many cultivars or other seedlings. Some seedlings have no anthers or poor pollen while others such as 'Adelaide Hoodless' function as either male or female parent. 'Cuthbert Grant’ has given few seeds either way until its pollen was used on 'Prairie Princess'. Some of these problems appear to be due to the same fertility barriers that made the first cross difficult.
Flower color in roses and other plants have been studied by many scientists. Color in roses seems to be due to the interaction of several factors. These include white reflective surfaces both external and internal and three classes of pigments. Carotenoid pigments have been found in yellow roses and similar but white substances in white roses. Flavonoids and anthocyanins are similar chemically and are found in most, if not all, roses. Flavonoids are colorless or pale yellow and are most prominent in ivory white or pale yellow roses. Anthocyanins give various shades of red. Cyanin is by far the most common, occurring alone in many pink to blood red roses and together with one or both of two other pigments in other pink or red roses. Pelargonin, a scarlet pigment, as in scarlet geraniums (Pelargonium) occurs only in Hybrid Tea and Floribunda roses such as 'Independence', 'Queen Elizabeth' and 'Tropicana'. Peonin as in red peonies, is rare in these classes but is frequent in Section Cinnamomea and in R. arkansana. It appears in many of our R. arkansana hybrids including 'Assiniboine' and 'Adelaide Hoodless'. In these it usually gives a cardinal red shade but sometimes purplish red as in most R. rugosa hybrids. Many of the named varieties tested may be found in the following list:
Anthocyanin Pigments in Roses
Cultivars and species in which cyanin was the only red pigment observed
and species in which peonin was observed together with cyanin
*More peonin than cyanin
and species in which Pelargonin was observed together with cyanin
*More Pelargonin than cyanin
No anthocyanins were found in more than 30 yellow or white cultivars and species while all three were found in several hybrids between Floribunda varieties and R. arkansana, none of which are named. A large number of unnamed seedlings have also been analysed.
Cultivated roses are usually propagated by budding on a suitable seedling or clonal rootstock. Frequent winter killing of the rose variety and the absence of a fully satisfactory rootstock make this method unsatisfactory on the prairies. R. arkansana and most of its hybrids can be rooted from greenwood cuttings in mist. They root well in about 3 weeks even from leaf-bud cuttings, i.e. a single leaf with its bud and a short piece of stem. It is common to get over 90% established plants, therefore, there seems to be no reason for releasing selections that do not root.
The R. arkansana hybrids released to date have the same blooming habit as their wild parent. If the top survives over winter or is not pruned off, it will bloom as a shrub. If the entire top is cut off in early spring, they will flower on new growth but this takes place even if old wood is present. These flowers are produced later giving more or less continuous bloom from early July until hard frost.
The everblooming habit of their cultivated parent has reappeared among the hybrids. Since this character is recessive, it is easy to produce large numbers for further selection after the first few everblooming hybrids have been identified. The proportion of these in second generation crosses is very low. It is now known that these have more hardiness than Floribunda roses and that they will bloom continuously from the end of June until hard frost. They are usually small plants 2-2.5 feet in height with medium size flowers but some vigorous Hybrid Tea-like plants have been found. The generation time is short, many are highly fertile and they can be identified within a few weeks after germination.
R. arkansana hybrids can give us roses similar to the Floribunda with sufficient hardiness for the Canadian prairies. Many will bloom intermittently over an extended period and others will bloom continuously. Most root well from greenwood cuttings thereby eliminating the need for troublesome rootstocks. Many hybrids carry the peonin pigment which should permit the development of new shades of red. Good levels of resistance to leaf-spot, mildew and rust have appeared in some lines.