Effects of far-red light and photoperiod during early growth stages on flower bud development of seed-propagated strawberry seedlings

The effects of far-red (FR) light and photoperiod on flower bud development in seed-propagated strawberry (Fragaria xananassa) 'Elan' and 'Yotsuboshi' cultivars seedlings were investigated to determine lighting condi-tions that would ensure high-quality strawberry plugs in a controlled environment. The strawberry seedlings were grown for 25 days in a growth chamber under LED illumination with or without FR light. Photoperiod was set at 16 h or 24 h After the light treatment, the seedlings were transplanted into the greenhouse to determine the emergence of their flower buds. In 'Elan', FR light and longer photoperiod both promoted flower bud devel-opment. However, in 'Yotsuboshi', the effect of the light treatment was weaker than in 'Elan': only FR light plus longer photoperiod promoted flower bud development. This difference may be due to cultivar differences in the juvenile period. The percentage of seedlings that had developed flower buds at the end of the light treatment was similar to that of seedlings that emerged flower buds after transplanting in most treatment groups. However, in 'Yotsuboshi' seedlings transplanted during the relatively high-temperature season, the percentage of seedlings with an emerged bud after transplanting was much smaller than that of seedlings that developed flower buds by the end of the light treatment. This may be because exposure to high temperatures after transplanting suppressed the development of immature flower buds, which in turn suppressed bud emergence.