Flowering Responses in the Cut Rose ‘Vital’ to Non-Optimal Temperatures

Temperature stress is the primary cause of flower quality degradation of cut roses. A previous study showed that although low temperatures delay flowering, they can significantly increase the number of petals by promoting stamen petalody. In this study, we determined how excessively high or low temperatures influence flower development and floral organ differentiation in Rosa hybrida ‘Vital’ in the range of 10 to 35°C with three sub-ranges of optimal day/night temperatures (OT, 25/18°C), low temperatures (LT, 18/10°C; sub-optimal temperatures), and high temperatures (HT, 35/25°C; supra-optimal temperatures) and whether the differentiation is related to flowering function gene expression. The flowering time of shoots in OT (45 days) was delayed by 96% in LT (88 days) but accelerated by 31% in HT (31 days). However, the flower quality response was opposite. The flowers became larger and longer with additional biomass accumulation during the extended flowering period in LT. In addition, floral organ differentiation was suppressed under LT and HT stress conditions. Notably, HT stress reduced the formation of whole floral organs by 61.4%; however, LT stress stimulated petal formation at a rate of 9.8% and inhibited stamen formation by 1.8%. A quantitative real-time polymerase chain reaction analysis revealed that both RhAP1 (A-function gene) and RhAG (C-function gene) play essential roles in determining the number of petals, partly in association with RhAP3 (B-function gene). Our results highlight the impact of temperature stress on rose flower development and petal number determination, as determined by the expression of flowering function genes.