Modern roses are the products of intensive breeding among a small selection of species in the widespread, northern hemisphere genus Rosa. The long history of our association with the rose has meant that picking apart the parentage of the garden rose has been a complex, intricate process which remains unfinished. We know the DNA of the modern rose includes genes from European species such as Rosa gallica and Rosa moschata, and Chinese species, such as Rosa chinensis and Rosa gigantea.
In its native south-west China, Rosa chinensis is shrub to 2m tall with single, semi-double or double flowers with red, pink, white or purple petals. Chinese roses were cultivated in their native lands for millennia before Europeans got to know them. The first inkling Europeans had of these oriental treasures came from dried specimens returned to Britain by the botanical explorer James Cunningham in 1702. Living material was introduced to Europe during the late eighteenth century, as the flood of Chinese garden plants into European gardens started.
Chinese roses were immediately popular with gardeners and rose breeders since they flowered repeatedly throughout the summer. In contrast, European roses flowered once, briefly, in the early summer. During the elaborate breeding programmes of the Victorian era, Hybrid Tea roses emerged with European rose characteristics such as cold and disease resistance, and Chinese rose characteristics such as perpetual flowering.
Roses attract gardeners not only for their colour and vibrancy but for their scents. Floral scent are one of the ways that flowers lure insects to act as unwitting pollinators and perhaps get a nectar, pollen or oil reward. Scent is particularly important when there are poor visual cues for pollinators.
Tea roses get their name from the distinctive tea-like scent of their flowers, something acquired from the Chinese rose. The major compound responsible for this scent is the phenolic methyl ether (PME), 3,5-dimethoxytoluene (DMT). In contrast, the scents of European roses are produced by 2-phenylethanol and monoterpenes. Once restricted to the Chinese roses, the PME metabolic pathway is now found in many rose cultivars. The synthesis of DMT is catalysed by two very similar enzymes, OOMT1 and OOMT2. Detailed genome analyses have shown that only Chinese roses have the genes that code for these enzymes. Furthermore, OOMT1 genes appear to have evolved from OOMT2 genes, and this evolutionary step appears to have been crucial in the evolution of scent production by Chinese roses.
Potter J 2010. The Rose. A true history. Atlantic Books.
Scalliet G et al. 2008. Scent evolution in Chinese roses. Proceedings of the National Academy of Sciences 105: 5927-5932.