Concentration-dependent emission of floral scent terpenoids from diverse cultivars of Chrysanthemum morifolium and their wild relatives

Floral scent is an important trait that has a significant influence on the reproduction of many flowering plants and the market value of several ornamental crops. The family of Asteraceae is well known for its unique floral structure (capitulum) that consists of many florets. Although the constituents of either floral essential oils or emitted floral volatiles have been reported in many species of Asteraceae, little information is available on the mechanisms that determine floral volatile emission. In the present study, a total of 44 species/varieties of Chrysanthemum were analyzed to determine the relationship between the internal accumulation of floral terpenoids and their release as volatiles. By performing both headspace collection and organic extraction, it has been found that the emission rates of floral terpenoids are largely correlated to their internal concentrations. Particularly, the flowers of cultivated C. morifolium, when compared to their wild relatives, were found to exhibit lower emission rates that contain lowered concentrations of floral terpenoids. The differences were largely determined by six monoterpenes and five sesquiterpenes that were revealed by principal component analysis. Besides, the relationship between concentrations and emission rates of floral terpenoids as well as the sizes of capitulum was studied in detail. Separated into three different parts, disc florets were found to have a larger contribution to floral volatile emission than ray florets, whereas the phyllaries and receptacles are the main parts of volatiles accumulation. Finally, the potential biosynthetic pathway of the floral terpenoids produced in capitula of Chrysanthemum was proposed. In summary, our findings on the diversity and variations of floral terpenoids in Chrysanthemum reveal correlations between their production and emission. These findings can be useful to develop different plant breeding methods to create novel aromatic cultivars of Chrysanthemum.