Optimal photoperiod and floral transition of Eustoma grandiflorum ‘Tiramisu Double Cream’

• Growth and flowering traits of lisianthus were studied under 7 kinds of photoperiods.
• Critical and optimal photoperiods for flowering of lisianthus were estimated.
• Floral transition was distinguished before appearance of sepal primordia.
• Correlation of floral bud differentiation and vegetative growth was established.
• Leaf number was used to predict floral bud differentiation phase.

The aim of this study was to further our current knowledge of photoperiodic flowering traits in lisianthus. The effects of the photoperiod on the flowering traits of Eustoma grandiflorum ‘Tiramisu Double Cream’ (TDC) were investigated under 7 day-length treatments. TDC was deduced to be a facultative long-day plant, of which the critical day-length for flowering was 14 h. Compared with short-days, high flowering quality was available under day-lengths of 14 h and above, with no significant difference between long-days, except 24 h. Thus, the optimal photoperiod that promotes the flowering of TDC was the 14 h day-length. The floral transition in TDC was estimated through the identification of the floral bud differentiation phase (DP) and its correlation with vegetative growth traits (VGTs). The results show that the floral bud differentiation of TDC lasted approximately 3 weeks and was divided into 6 phases. The floral transition in TDC was distinguished before the appearance of sepal primordia. Significant correlations existed between DPs and VGTs, and the regression equations suggested that the floral transition of TDC occurred at the 21-leaf stage. Therefore, it is recommended that TDC be planted under a day-length of 14 h before the 21-leaf stage to promote flowering.