Flowering, morphological observations and FT expression of Curcuma kwangsiensis var nanlingensis bud in development process

• The flowering percentage of rhizomes was measured.
• We observed the anatomic morphology of different development stage.
• We analysed FT gene expression to clarify flowering induction.
• High temperature treatment in the initial differentiation phase is a key procedure.

Curcuma kwangsiensis var nanlingensis is an attractive tropical ornamental plant in China with high ornamental and commercial value. The effects of temperature on the flowering percentage of its rhizomes were studied. High temperature induced bud differentiation in Curcuma kwangsiensis var nanlingensis. The flowering percentage of rhizomes cultured at 30 °C was 100%, which was significantly higher than those of rhizomes cultured at 25 °C or 20 °C. Rhizomes that underwent a low temperature treatment after being hydroponically cultured at 30 °C until stage IV also achieved a flowering percentage of 100% and good ornamental quality. Observations of the appearance and anatomic morphology during the stages of flower bud differentiation were made using paraffin sections and a scanning electron microscope (SEM). The results showed that the rhizomes of different developmental stages cultured at 30 °C could be divided into five phases: initial differentiation phase, inflorescence and bract primordium differentiation phase, flower primordium differentiation phase, small floral primordium differentiation phase and flower organ differentiation phase. The differential expression of the FT gene was examined in the bud during the different developmental stages and organs under different temperature conditions using the real-time PCR technique. FT expression in the Curcuma kwangsiensis var nanlingensis bract and inflorescence axis was higher than that in the petiole and leaf. Under a high temperature treatment, FT expression reached a sharp peak at the beginning of bud differentiation and declined slightly between differentiation and maturation of the bud. FT expression at 30 °C was clearly higher than expression at 25 °C or 20 °C. The results of the FT expression and anatomic morphology observations suggest that FT expression is associated with flowering differentiation. High temperature treatment in the initial differentiation phase led to the highest expression of the FT and is a key procedure to ensure a high flowering percentage in Curcuma kwangsiensis var nanlingensis.