Recent progress in night-break lighting technique based on photoperiodism of chrysanthemum

Abstract

Flowering control is one of the most important techniques in floriculture. The control of day length makes year-round cut-chrysanthemum flower production possible. Night-break is the most widely used flowering control method in both cut flower and pot chrysanthemum production. In this study, we investigated the effects of night-break, night-break time, and light quality on chrysanthemum flowering. On comparing the wavelengths of red (R) light used for night-breaks, it was observed that the inhibition effect on flowering was higher in the wavelength range of 620-640 nm than at 660 nm, in which the conversion efficiency of phytochrome is high. The effect of R light and R + far red (FR) light on the inhibition of flowering changes with the length of night-break. The effect of R light is higher with a short night-break. On the other hand, when the duration of night-break is long, both R and R + FR light showed equivalent inhibition effects, and the effect of R + FR light was higher than R light in some varieties. The most effective time for night-break was not the middle of the dark period, but near the end of the cultivar-specific critical dark period. As the night-break time was extended, the inhibitory effect on flowering initially increased with night-break time up to a certain time period, beyond which the effect decreased again. The results obtained here are contrary to current perspective on night-break. Based on these findings, we propose a new night-break protocol for the inhibition of flowering in chrysanthemum.