Changes of edogenous hormone levels during short-day inductive floral initiation and inflorescence differentiation of Chrysanthemum morifolium ‘Jingyun’

Duration of various stages of inflorescence differentiation and hormone levels in apical buds eventually decide the harvest time, flower uniformity and quality of ornamental plants. The progress in inflorescence differentiation process in the chrysanthemum cultivar ‘Jingyun’ can be divided into nine stages. Following short day induction, it took 4d to reach the growing point hypertrophy stage, 8d to finish involucre primordia differentiation, 12d to finish floret primordia differentiation and 10d to finish crown formation. Under inducible conditions, the level of indole acetic acid (IAA) initially decreased, but maintained a relatively high level during the whole period of inflorescence differentiation. Both N6-(Δ2-isopentenyl)-adenosine (iPA) and abscisic acid (ABA) levels increased markedly during floral induction and floral initiation, peaking at the final involucre primordia differentiation stage. Thereafter, the iPA level remained high, while the ABA level decreased. A large decrease in the level of gibberellic acid (GA3) occurred during floral induction, but this recovered by the final floret primordia differentiation stage. In conclusion, various stages of inflorescence differentiation take different time-span, the floret primordia differentiation takes the longest time-span, while time-span for involucre primordia differentiation is shortest. Moreover, an appropriate amount of IAA appears to be necessary for inflorescence differentiation, and a stable GA3 and ABA level for crown formation. iPA plays a positive role both in floral induction and inflorescence differentiation.