In vitro flowering of the distylous plant Plumbago auriculata Lam

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Plumbago auriculata Lam., a typical distylous plant, undergoes heteromorphic self-incompatibility (HetSI). The use of in vitro flowering allows the early identification of a plant's style morphology, and this process can be used to increase the efficiency of the breeding process and expedite research on the flowering mechanisms of P. auriculata. Here, we used seeds of P. auriculata as explants; obtained plantlets; and assessed the effects of temperature, thermoperiod, photoperiod, and light intensity on the in vitro flowering of the plants. The optimum temperature treatment was a diurnal alternation of 35 °C for 12 h and 25 °C for 12 h. Under these conditions, flower bud formation occurred within approximately 33 d, and the flowering percentage was as high as 91%. A photoperiod of 16 h and a light intensity of 200 µmol m−2 s−1 also promoted in vitro flowering. Under these conditions, flower buds formed within approximately 33 d, and the flowering percentage was approximately 90%. However, relatively long photoperiods and high light intensity suppressed flower bud development, reduced flowering, and shortened flower lifespan. The in vitro flowers had a lighter colour and smaller petals than did the in vivo flowers, although their floral structures (including their reproductive structures) were intact. This work demonstrates a stable system for the induction of in vitro flowering in P. auriculata and describes suitable temperature (35 °C/25 °C) and light (16 h photoperiod and 200 µmol m−2 s−1) conditions for rapid in vitro flowering. This system allows the efficient identification of long and short P. auriculata morphs and allows the formulation of a reasonable cultivation plan. The methods described here provide technical support for the development, utilization, and rapid propagation of excellent new P. auriculata varieties.