Effects of Intermittent Lighting for Night-Break and the Light Quality on Floral Inhibition in Chrysanthemum

Abstract

The efficiency of intermittent lighting for night-break (ILNB) with red (R) or red + far-red (R + FR) light was evaluated in the floral inhibition of chrysanthemum. ILNB schemes with various duty ratios had a lower efficiency on floral inhibition than continuous lighting with both R and R + FR. When ILNB (duty ratio: 0.5) was applied with the same accumulated amount of R light as in continuous lighting, the effect was the same. However, when the total ILNB irradiation was reduced by half, the effect was much lower than that after continuous R light irradiation. The results indicated that the effect of night-break depended on total irradiation. When the total lighting time was set at 18 min., the R ILNB effect of inhibition was same as continuous lighting, however, R + FR ILNB showed much stronger inhibitory effects than under continuous lighting. This could be because of the photoreversibility of responses by R and FR under continuous R + FR light conditions. In addition, the timing of night-break during the night affects the effectiveness of night-break. This should be considered when evaluating the effectiveness of ILNB. Nevertheless, we were unable to fully explain the effectiveness of ILNB schemes based on the results that were in accordance with the Pfr dark-reversion theory. Hence, in practice, one should not expect any advantage of ILNB schemes, because the photoreversibility of responses by R and FR light is not evident on long-term night-break irradiation under greenhouse cultivation.