Rosa species are one of the most economically important ornamental plants. Their popularity as garden flowers and cut flowers, but also their use for cosmetics and perfume industry, is constantly increasing. The Rosa genus includes about 150 perennial species and shows a great diversity of ploidy levels. (di-, tri-, tetra-, penta-, hexa-, octo-, decaploid).
It has a small genome (about 560 MB or 4 times the genome of Arabidopsis thaliana), and international effort is underway to achieve its complete sequencing. The rose has a relatively short life cycle for a perennial plant (one year after germination of the seeds, the seedlings can flower) and its genealogy is well documented. Several teams around the world, particularly in France, are studying the molecular and genetic bases that govern certain characteristics of this plant, such as flowering date, flower shape and colour, vase life for the cut flower, resistance to pathogens and perfume.
These molecular and genetic data, as well as the development of genetics tools for the rose, make it a model of choice for ornamental plants.
Roses are self-incompatible. Pollination is entomogamous (meaning pollen is mainly carried by insects). The stamens are numerous and the carpels are inserted on a hollow receptacle, the hypanthium, which protects them and allows the styles and stigmas to emerge.
After fertilization, the carpels evolve into achenes, contained in the fleshy rosehip, resulting from the evolution of the hypanthium. Interspecific hybridization is frequent in nature and most polyploid species are derived from it, and for these we speak of an allopolyploid origin.
Ploidy differences are an important barrier to varietal improvement, since most cultivated varieties are tetraploid, which is a barrier to the introgression (dispersion of genes from one species to another, since the two are interfecund) of traits of interest from wild diploid species.
In nature, vegetative propagation is common. It takes place through the emission of specialized stems, the suckers, which, after the plant that emitted them has been freed, give an independent clone. The rose’s ability to be cut (vegetative propagation) is widely exploited for its industrial multiplication, as is the possibility of grafting an axillary bud onto a rootstock.
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« Scent evolution in Chinese roses. », Scalliet et. al., Proc Natl Acad Sci., 2008
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