Metabolite profiling of violet, white and pink flowers revealing flavonoids composition patterns in Rhododendron pulchrum Sweet

Flower color is the major characteristics and critical breeding program for most Rhododendron species. However, little is known about their coloration mechanism and color inheritance. In this study, petal pigment constituents of three Rhododendron pulchrum Sweet cultivars with different colors were clarified based on L C- ESI-MS/MS method. Using a broad-targeted metabolomic approach, a total of 149 flavonoids and their glycosylated or methylated derivatives were identified, including 18 anthocyanins (Pg, Cy, Dp, Pn, Pt, and Mv) and 32 flavonols (mainly kaempferol 3- O- glycosides and quercetin 3- O- glycosides). Moreover, anthocyanins were mainly represented by anthocyanidin-3- O- glycosides (glucoside, rutinoside, galactoside, and di-glycosides). Flavone and C- glycosylated flavone were major second metabolites responsible for the difference among three different R. pulchrum cultivars. The accumulation of total flavonoids displayed a clear phenotypic variation: cultivars ‘zihe’ and ‘fenhe’ were clustered together, while ‘baihe’ was clustered alone in the HCA analysis. The composition and content of anthocyanins were more complex in colored flowers (‘zehe’ and ‘fenhe’) than in white flower (‘baihe’). This study further enhanced our understanding on the flavonoids profile of flower coloration and will provide biochemical basis for further genetic breeding in Rhododendron species.