Effect of light quality of long-day treatments on flowering in <i>Delphinium</i>

Abstract

The effects of light quality on the flowering need to be investigated for the efficient use of light-emitting diodes (LEDs) in cut flower production because of the environmentally friendly features of LEDs. Assuming long-day treatments in cut flower production, we used Delphinium species, popular long-day plants, and treated the plants at night with relatively weak light to investigate the effects of light quality. We used reproductive experimental conditions with phytotrons and long-day treatments, mainly monochromatic light, to establish an experimental system to elucidate physiological and molecular mechanisms in the near future. Before investigating the effect of monochromatic light, we first performed a long-day treatment with a widely used white LED. A similar effect to the incandescent lamp on bolting was observed, suggesting the possibility that red or blue light, but not far-red light, are adequate to promote flowering from the spectra of both light sources. Next, long-day treatments were performed with LEDs emitting monochromatic blue, red, and far-red light. In the model plant Arabidopsis thaliana, flowering is well known to be promoted by far-red and blue light and inhibited by red light. However, long-day treatment with red light for Delphinium effectively promoted flowering. Treatment with far-red light, which shows an opposite flowering response to red light in A. thaliana, also promoted the flowering of Delphinium. As for blue light, the flower budding rate of D. grandiflorum reached 100%, and that of D. elatum was lower. Compared to far-red and blue lights, long-day treatment with red light did not negatively impact cut flower quality, including cut flower length and number of florets. Our results on light quality impact on flowering response will contribute to technology for regulating Delphinium flowering and potentially also lead to the elucidation of the mechanism of unique flowering promotion by red light.