Spectral sensitivity of flowering and FT-like gene expression in response to night-break light treatments in the chrysanthemum cultivar, 'Reagan'

A night-break (i.e., a short exposure to light near the middle of the dark period) inhibits flowering in chrysanthemum (Chrysanthemum morifolium Ramat.), a short-day plant. We studied the effect of night-break light quality (wavelength) on flowering and on expression of the FLOWERING LOCUS T (FT)-like gene, CmFTL3. Night-break treatments with the yellow-to-red wavelength range showed strong inhibitory effects on flowering. Further studies using monochromatic light from panels of light emitting diodes (LEDs) showed that the maximum effect on the inhibition of flowering was around 596 nm, and that levels of CmFTL3 mRNA were reduced in a pattern consistent with the observed inhibition of flowering. Wavelengths from ultraviolet-A to blue, and far-red, had no inhibitory effects on flowering. Our results also showed that the inhibitory effect of red light on flowering responses could be reduced by far-red light. These results suggest that phytochromes are involved in night-break responses, and the absorption spectrum of leaf extracts indicated that the effect of wavelength might be distorted by the screening effect of the other pigments found in green leaves. We also discuss further developments of lighting techniques for commercial production of chrysanthemum.