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Effect of anthocyanin profile and petal pH on flower coloration in evergreen azalea

Nakatsuka, A., Hitomi, M., Tsuma, M., Ito, A., Mizuta, D., Kobayashi, N.
Acta horticulturae 2015 no.1104 pp. 357-362
Machaeranthera, Rhododendron, anthocyanidins, anthocyanins, color, corolla, cultivars, flavonols, horticulture, hybridization, hybrids, pH, wild flowers
In this study, the flower colors of selected wild azalea species were grouped as follows based on the Royal Horticultural Society color charts (RHSCC): red, red-purple, purple, purple-violet, and violet. The main pigment profiles of wild azalea are classified as cyanidin-type anthocyanidin (Cy), Cy + flavonol (Fl), and Cy + delphinidin-type anthocyanidin (Dp) + Fl. The flowers of the Cy and Cy + Dp types were red colored, and flowers with colors ranging from red-purple to violet also contained the flavonol (Fl) pigment. Natural hybrids between Rhododendron kaempferi and R. kiusianum, and the Kurume azalea cultivars were grouped as red, red-purple, and purple by the RHSCC and exhibited Cy, Cy+Dp, Cy+Fl, and Cy+Dp+Fl pigment types. The pH value of the petal tissue of red flowers of the wild species ranged from 3.17-3.35, while that of the purplish flower of R. macrosepalum (pH 4.55) and R. ripense (pH 3.96-4.12) was the same or higher than that of R. sataense (pH 3.26), R. eriocarpum (pH 3.40-3.70), and R. kiusianum (pH 3.40-3.42). The pH of the Kurume azalea cultivars was 3.3. These results suggest that the anthocyanidin and flavonol composition as well as the pH of the petals are specific to each wild species. These characteristics were combined through hybridization and lead to a variety of flower colors in Japanese azalea cultivars.