Characterisation of flower colouration in 30 Rhododendron species via anthocyanin and flavonol identification and quantitative traits

• Floral color is a key reproductive character, often associates with environmental adaptation, and undergoes human intervention. A large number of Rhododendron species spread widely with various flower colors, which makes a good model for flower coloration. The chromatic features and anthocyanin compositions of 30 species from seven subgenera were systematically analyzed. • The Royal Horticultural Society Color Chart and CIE L*a*b* system were employed to describe and investigate flower colors. The UPLC-PDA/ESI-MSn system was used to identify and quantify anthocyanins in petal extracts. • The flower colors of 30 Rhododendron species were categorized into four groups—red, purplish pink, purple and white. Seven anthocyanins were identified and quantified in petals, including delphinidin, cyanidin and malvidin 3-O-arabinoside-5-O-glucosides, cyanidin 3,5-di-O-glucoside, 3-O-galactoside and 3-O-arabinoside, and delphinidin 3-O-glucoside. The red-flowered species mainly contained cyanidin monoglycosides and had much higher total anthocyanin contents than purplish pink- and purple-flowered species. Purplish pink- and purple-flowered species had similar anthocyanin types and contents. The chromatic differences were significant among groups, except the purplish pink and purple groups. Statistical analysis showed that Cy3Gal and Cy3Arb are characteristic for red-flowered species, and Mv3Arb5G and Dp3Arb5G play important roles in purple coloration; their contents were major components that greatly affected the chromatic parameters. In total, 21 flavonols derivates were identified. However, total flavonols content and copigmentation index showed no significant difference or correlation among /with color groups, suggesting that flavonols might not play a major role in coloration. • These results enhance our knowledge of the biochemical basis of flower coloration in Rhododendron species, and will lay a foundation for genetic variation study and aid the breeding of cultivars with novel flower colors. This article is protected by copyright. All rights reserved.