Abstract

[Background] Cymbidium tortisepalum var. longibracteatum is a Class II nationally protected endangered plant in China with significant economic value. [Aim] This study aimed to establish an efficient in vitro flowering system and identify key hormonal factors regulating flower bud differentiation. [Methods] Orthogonal experiments and hormone treatments were performed to evaluate the effects of TDZ, 6-BA, NAA, IBA, PP, ABA, and GA on flower bud induction in tissue-cultured plantlets. [Results] TDZ was identified as the key initiator of flower bud differentiation, as no flower buds were induced in TDZ-free treatments. The optimal hormone combination was 1.0 mg/L 6-BA + 0.4 mg/L TDZ + 0.8 mg/L NAA + 1.6 mg/L IBA, achieving a flower bud induction rate of 23.33% and a normal flower bud rate of 20.00%. PP inhibited flower bud differentiation but reduced malformation; at 0.2 mg/L PP, the normal flower bud rate reached 20.00%. GA pretreatment resulted in a flower bud induction rate of 12.04%, whereas ABA pretreatment showed no significant promoting effect on flower bud induction. [Conclusions] This study provides an efficient in vitro flowering system and key hormonal parameters for shortening the breeding cycle and elucidating orchid flowering mechanisms.