How to manipulate hydrangea flower colour (Hydrangea macrophylla Thunb.)?

Abstract

In recent years, hydrangea (Hydrangea macrophylla), which has common usage as cut flowers, potted plants and garden plants, has been gradually increasing in both popularity and production in the world. The colour of hydrangea’s sepals varies from blue to purple and red depending on soil pH, sucrose content, metal content as well as temperature. It is possible to see different colours in the flowers which are located on the different stems of the same plant depending on the pH value of the growth medium and the additional aluminium (Al) level. When the pH value of the growth medium is between 4.5 and 5.0, the uptake ability of Al increases and the colour of the sepals becomes blue. In the event that pH value is 6.5, the uptake of Al becomes restricted and the sepals turn into pink and red colour. In neutral conditions, the sepals are purple. Anthocyanin has a particular importance on the colour change of hydrangeas. In the structure of these compounds, as the number of -OH group (hydroxyl) increases, the blue colour increases; but as the number of OCH3 groups (methoxylated hydroxyl) increases, the redness increases. Anthocyanin, delphinidin 3-glucoside and co-pigments have an effect on blueness in hydrangeas. Both pink and blue sepals contain the same anthocyanin pigment (delphinidin 3-monoglucoside). Al in the sepals binds the pigments and 3-caffeoyl and 3-p-coumaroylquinic acids serving as co-pigments, and this complex formation of Al/pigment/co-pigment is the reason for the colour transition of sepals from pink to blue. In this report, information about manipulation of flower colour is provided. © 2019 International Society for Horticultural Science. All rights reserved.