Date Published: June 13, 2019
Publisher: Public Library of Science
Author(s): Jiaping Zhang, Dong Zhang, Jianfen Wei, Xiaohua Shi, Huaqiao Ding, Shuai Qiu, Juan Guo, Danqin Li, Kaiyuan Zhu, David P. Horvath, Yiping Xia, Zhenhai Han.
Expanding the southern range of herbaceous peony (Paeonia lactiflora Pall.) is a meaningful and worthwhile horticultural endeavor in the Northern Hemisphere. However, high temperatures in winter seriously hinder the bud dormancy release and flowering of peony in the more southern areas of subtropical and tropical regions. Resource introduction and hybridization can contribute to creating new cultivars with high adaptability in a warmer winter climate. In this study, three representative cultivars of P. lactiflora were screened for flowering capabilities and their annual growth cycles were observed to provide information needed for hybridization. Among these three cultivars, ‘Hang Baishao’ is the best adapted cultivar for southern growing regions and is unique in its ability to thrive in southern areas of N 30°00’. Pollen viability of ‘Hang Baishao’ was 55.60% based on five measuring methods, which makes it an excellent male parent in hybridization. Hybrid plants among these three cultivars grew well, but all of their flower buds aborted. Additionally, the ability of three growth regulators that advance the flowering of ‘Hang Baishao’ to promote an indoor cultivation strategy for improving peony application as a potted or cut-flower plant was tested. 5-azacytidine could impact the growth of ‘Hang Baishao’ and induce dwarfism and small flowers but not advance the flowering time. Gibberellin A3 promoted the sprouting and growth significantly, but all plants eventually withered. Chilling at 0–4°C for four weeks and irrigation with 300 mg/L humic acid was the optimal combination used to hasten flowering and ensure flowering quality simultaneously. These results can lay the foundation for future studies on the chilling requirement trait, bud dormancy release and key functional gene exploration of herbaceous peony. Additionally, this study can also provide guidance for expanding the range of economically important plants with the winter dormancy trait to the low-latitude regions.
Artificially extending the planting range of economically important plants is an important subject in horticultural research. Unsuitable climatic conditions, such as high winter temperatures in a new planting region can be problematic and may prevent or reduce growth and flowering due to the loss of vernalization and/or dormancy breaking conditions [2–4]. With the trend of global warming, research on the detrimental impact of high winter temperatures has been of significantly greater focus compared with research on high summer temperatures in the recent years. Warm winters lead to a serious deficiency of chilling accumulation, incomplete dormancy release, weak growth or low yield for deciduous fruit trees, tea trees, ornamentals and other economically important plants with winter dormancy traits[1,6–8]. Taking the herbaceous peony (Paeonia lactiflora Pall.), for example, this is a valuable ornamental flower that is widely cultivated in European, Asian and North American regions in the Northern Hemisphere with a temperate or cool climate [9,10]. Partial cultivars of herbaceous peony can grow in the northern subtropical regions; however, most cultivars cannot be cultivated or grown well in the low-latitude areas, such as central and southern subtropics and tropics. Although a few cultivars can be planted in these regions, they bloom very poorly[1,11,12].