Environmental factors involved in colouration of flowers of Kangaroo Paw

Abstract

Environmental regulation of flower colouration has been examined for Kangaroo Paw ( Anigozanthos spp.) grown in protected cultivation. Two commercial ‘Bush Gem’ hybrids were grown in controlled conditions at various temperatures, irradiances and levels of ultraviolet-B radiation (UV-B). Based on spectral reflectance differences between vividly coloured and faded flowers, their colour depends on pigment(s) absorbing over the 520–630 nm waveband which should involve flavonoids including anthocyanins. This anthocyanin-like pigment, localised in the epidermal hairs of the flowers, was extracted and quantified spectrophotometrically. Flower colour (OD 535 nm g −1 FW) was greatest for plants grown at low temperature and decreased linearly as the growth temperature increased from 13 up to 28 °C. Increasing the photosynthetic irradiance to 550 μmol m −2 s −1 gave strong flower colour as did the addition of UV-B. Although the maximum exposure to UV-B (0.5 mW m −2 at 302 nm) may not have been saturating, this was slightly higher than that of a clear summer day at a latitude matching those occurring where Anigozanthos grows naturally. The maximum UV-B exposure caused leaf and stem tissue damage reminiscent of ‘Ink Spot’ disease. Flower colour could be manipulated only during flower development but differences were evident within 1–3 weeks of transfers between cool and warm conditions or within 1–2 weeks of exposure to UV-B. The data obtained in this study provide the basis for developing ways to manipulate flower colour to give the most vivid display in commercial production systems.