## 4 Discussion
### Expression of Genes Related to the Morphogenesis and Flowering  
The expression levels of _PHYA_ and _PHYB_ were the highest for plants in LD13 + 4B, and the expression level of _CRY1_ was the greatest for plants in LD13 + NI - 4B. Plants in these two treatments were also the tallest. It has been reported that cryptochromes and phytochromes affect the height of chrysanthemums [33]. In _Arabidopsis_, high _PHYB_ levels can increase the expression of _AtGAox2_, which controls the synthesis of gibberellins (GAs) [35]. Furthermore, it has been verified that both phytochromes and cryptochromes play a part in the regulation of the plant hormone GA levels [35; 44]. Thus, it is speculated that the high expression levels of _PHYA_, _PHYB_, and _CRY1_ found in plants grown in LD13 + 4B and LD13 + NI - 4B may promote the synthesis of GAs and eventually result in greater plant heights.  
It is well known that photoreceptors related to B light were involved in the flowering process [18; 20]. The CRY1 and CRY2 both mediate the flowering promotion by B light [45]. _PHYA_ mediates the flowering promotion by Fr light, and _PHYB_ mediates the flowering inhibition by R light in _Arabidopsis_[46; 47; 48]. Although _PHYA_ and _PHYB_ are R light receptors, it has also been shown that they also function under B light in _Arabidopsis_[49], and it has been proven that either _PHYA_ or _PHYB_, as well as cryptochromes, were required for responses to B light [24; 46; 50]. In this study, the number of flowers per plant was shown to increase with the B light treatments. This may be attributed to the high _CRY1_ expression levels. Similarly, [PERSON] et al. [11] reported that a greater number of flowers per plant was observed with light shifting from B during the NI, which may be attributed to a high light energy induction as well as shade avoidance responses, a behavior where plants evade darkness by lengthening the internodes. In rice, NI with B light delayed the flowering time, but this delay was not reproduced in the _PHYB-1_ mutant [51], which means _PHYB_ is a negative regulator for the flowering time. It was also observed that while chrysanthemum is a qualitative SD plant, those in the LD13 + 4B and LD13 + NI - 4B treatments still flowered. This indicates that high _PHYA_ and _CRY1_ expression levels may induce flowering. However, further research is necessary to verify this speculation.  
In summary, B light resulted in a greater height and promoted the flowering in chrysanthemum. The results of this study illustrate that a 4-h B light supplementation during the photoperiod promotedflowering and increased the number of flower buds formed. Hence, B light supplementation may be an optimal technique to induce flowering, and can be practically applied to commercial cultivation of SD plants. This study suggests that B light supplementation is an alternative practical technique to induce flowering in SD plants to using blackout curtains during LD seasons. Further research is still needed to optimize B light supplementation techniques for flowering induction of SD plants.  
[PERSON] and [PERSON] conceived and designed the experiments; [PERSON] performed the experiments; [PERSON] and [PERSON] analyzed the data; [PERSON] and [PERSON] contributed reagents/materials/analysis tools; [PERSON] and [PERSON] wrote the paper. All authors have read and agreed to the published version of the manuscript.  
The APC was funded by Gyeongsagn National University.  
The authors express their gratitude to [PERSON], [PERSON], and [PERSON] for their assistance.  
The authors declare no conflict of interest.