Effect of GA and PP333 on autumn reflowering of two Chinese tree peony (Paeonia × suffruticosa Andrews) cultivars

Regulation of tree peony flowering time is a popular topic in tree peony research and is linked to a significant industry in China, in order to explore the mechanism of autumn flowering, we studied the effects of phytohormone and non-structural carbohydrate during autumn flowering of two cultivars of tree peony: the re-flowering cultivar ‘Chunqiu Hong’ and the once-flowering cultivar ‘Fugui Mantang’ within a single growing season. This investigation involved monitoring leaf emergence, as well as morphological and biochemical changes in flower buds, under three different treatment conditions: defoliation alone, defoliation combined with GA₃, and defoliation combined with Paclobutrazol (PP₃₃₃). The results indicated that flower bud differentiation occurred more rapidly in ‘Chunqiu Hong’ compared to ‘Fugui Mantang’. Notably, during the autumn season, some flower buds of ‘Chunqiu Hong’ exhibited natural bursting, whereas the flower buds of ‘Fugui Mantang’ showed minimal natural bursting. The combination of defoliation and GA₃ treatment stimulated bud development and the growth of new shoots, which was associated with elevated levels of GA₃ and soluble carbohydrates, alongside a reduction in abscisic acid (ABA) concentration. Furthermore, ‘Chunqiu Hong’ consistently demonstrated higher rates of flower bud bursting and more pronounced morphological changes in response to identical treatments when compared to ‘Fugui Mantang’. Consequently, we conclude that defoliation and the application of gibberellic acid significantly enhance the development of flower buds in the autumn re-flowering tree peony cultivar, attributed to increased levels of GA₃ and soluble carbohydrates, as well as a concurrent decrease in ABA concentration. However, it is important to note that the inhibitory effect of PP₃₃₃ on GA₃ biosynthesis was only temporary.