Modern Rose Breeding
Director Lewis Feldman
The origins of modern-day roses can be traced to a complex series of hybridizations between seven to fifteen wild rose species, over three centuries. Two species in particular, Rosa gallica (European) and Rosa chinensis (Asian), figure prominently in the origins of modern-day domesticated cultivars of roses.
The recent completion of the genome sequence of one of those progenitors, R. chinensis, provides advanced molecular tools for developing roses with improved characteristics desired by breeders. These include longer bloom time (repeated versus once-flowering), “improvements” in petal color and number, enhanced fragrance and increased disease resistance.
Rose species that have the ability to flower again after the first, generally most showy, blooming period are said to be “recurrent bloomers.” We have a limited understanding of the genetic controls of bloom time(s); there is some evidence that the plant growth regulator gibberellin may regulate specific genes that control whether a rose is a repeat or one-time bloomer.
Increasing the number of petals – from the wild-type number of 5 to over 40 – has also been an aim of breeders. Several genes whose activities influence petal number have been identified. But there is also evidence that environmental signals, such as temperature, can influence petal number. The challenge now is to decipher how the environment affects petal number by controlling genes.
Petal color in wild roses plays a critical role in attracting pollinators. But for breeders, rose color has an additional, commercially important, allure. To date, hybridization of roses of different colors has led, by painstaking trial and error, to the development of orange, yellow and purple flowers. But a true blue rose has never been produced. With newly detailed genetic information, biochemical pathways influencing flower pigments may enable breeders to much more quickly produce new rose colors.
In addition to color, fragrance is the characteristic we most pleasurably associate with roses, and it invariably draws garden visitors in for a deep whiff. Some scents come from the petals whereas others derive from the stamens. However, despite an understanding of the many biochemical pathways associated with scent, there have been few studies of the genetics of fragrance production. Once the key genes for fragrance are known, investigators note, a “major challenge (will be) to understand their evolution…and how favorable and unfavorable genes were selected during evolution and domestication.”
Disease is an ongoing challenge for commercial and home growers. Mildew (Peronospora sparsa and Podosphaera pannosa) and black spot (Diplocarpon rosae) are among the two major diseases in roses. Yet despite ongoing research, only a few commercial rose varieties have significant levels of disease resistance. The recent availability of the complete rose genetic sequence will facilitate the discovery of candidate disease-resistance genes, so-called R genes. The many naturally disease-resistant wild roses offer a vast resource for the identification of new R genes.
For a deeper and more technical dive into genetic rose research see this recent review.
And don’t be surprised to see blue roses in the future!
Featured image: Rosae gallica