Objective This paper aims to determine the characteristics of growth and development of secondary branches and their apical buds of cultivated Paeonia ludlowii as well as the differentiation process of flower buds in the cultivated site and the original site, then provide a reference for the introduction, cultivation, development and utilization of P. ludlowii.
Method Taking the adult P. ludlowii introduced and cultivated in Luanchuan, Henan Province of Central China as the object, the growth and development dynamics of the secondary branches and its apical buds were observed. And the apical bud floral differentiation process in introduction site (Luanchuan and Lhasa) and original site (Nyingchi) was observed by paraffin section method.
Result (1) In Luanchuan, the secondary branches of P. ludlowii grew from early May to mid-September, and the peak period was from early May to early June. However, some axillary buds of flowering branches were stagnant and did not develop into secondary branches. (2) In Luanchuan, the secondary branches of cultivated P. ludlowii had three growth types: the type 1, which accounted for 28.57%, its apical buds formed and began to differentiate in mid-July, blossom and bear fruits normally in following year. The type 2 was mainly located in the middle and lower parts of the flowering/fruit branches, apical buds formed but did not differentiate and there was only vegetative growth in the following year. The type 3 did not form apical bud, freeze-dried during winter and following spring. (3) In original site Nyingchi, 56.25% of the apical buds on the secondary branches of P. ludlowii differentiated and blossomed and bore fruits normally in following year, the secondary branches of type 3 were not observed. (4) The differentiation process of the apical bud on the secondary branches was the same in introduction site and original site. The apical bud finally formed a compound bud with a top flower bud, 2–3 lateral flower buds, axillary bud primordiums and leaf primordiums though six differentiation stages, the top flower bud differentiated earlier than the lateral flower buds. The axillary bud primordiums located at the base of the 3rd–4th leaf primordiums, which will develop new secondary branches on the flowering branches in the following year. (5) The start time and duration of flower bud differentiation in introduction site and original site were different. In Luanchuan, P. ludlowii began to differentiate late and lasted relatively longer (88–97 d), while in Lhasa and Nyingchi, it began to differentiate earlier and lasted relatively shorter (nearly 70 d).
Conclusion The flower bud differentiation ratio of cultivated P. ludlowii in Luanchuan is low, the differentiation begins late and lasts long but it could form a stable secondary branch with normal flower bud differentiation, blossom and bear fruit.The natural environment of it could be a reference for site selection to introduce and cultivate P. ludlowii.