Effects of Red: Far-Red Light Ratio of Night-Break Treatments on Growth and Flowering of Eustoma grandiflorum (Raf.) Shinn

To investigate growth and flowering responses of Eustoma grandiflorum, long-day treatments (night-break treatments) with different red (R: 660 +/- 30 nm) to far-red (FR: 730 +/- 30 nm) ratios were applied to plants using various light sources. Compared with the controls, which were not subjected to night-break treatments, flower budding and flowering were promoted by night-break treatments with low R:FR ratios, but delayed by those with high R:FR ratios. Compared with the controls, plants with promoted flowering and budding had fewer nodes on the main stem at anthesis of the first floret, whereas plants with delayed flowering and budding had more nodes. The difference between the date of flower budding in plants receiving night-break treatments and that of controls was accurately approximated by the sigmoid function of the logarithms of the R:FR ratio. The threshold of the R:FR ratio demarcating the promotion and delay of flower budding was approximately 5.3 under these experimental conditions. The R:FR ratio of the light sources used for night-break treatments affected stem elongation in E. grandiflorum; a low R:FR ratio resulted in longer mean internode length of the main stem, whereas a high R:FR ratio resulted in shorter internode length. We evaluated the effects of various commercially available lights on flowering time and cut flower length. In addition, a blue-light night-break treatment promoted flowering of E. grandiflorum.