Introduction of flare tree peonies(Paeonia rockii) to Chifeng district of Inner Mongolia and their cold resistance

The 2-year-old grafts of 11 flare tree peony (Paeonia rockii) cultivars and 5-year-old seedlings were firstly introduced to Chifeng district of Inner Mongolia from Lanzhou of Gansu Province, China, and their cultivation, domestication and observation were carried out for three years. Comparing with P.suffruticosa ‘Luo Yang Hong’, a traditional cultivar of common tree peonies, the cold resistance of P. rockii was studied. The results showed that: 1) flare tree peonies were able to adapt to the cold climate in Chifeng and normally grow and overwinter in open field under appropriate winter protection. The growth was obviously increased from the second year after introduction and in the third year most of cultivars except for only one had bloomed with a good quality of flowers. The plants sprouted from late March to mid-April, flowered at mid-May and fell into dormancy from early November to the next sprouting. Compared with the place of origin of the species, the dates for sprouting and flowering were delayed for one month and 20 days, respectively. The time interval from sprouting to flowering was shortened and the period of dormancy was prolonged significantly. 2) The thickness ratio of the palisade tissues to spongy tissues in the leaves of P. rockii reflected a link with the cold resistance of the species and could be used anatomically to evaluate the cold resistance of the cultivars. 3) The relative conductivity of leaves was increased with the decreasing temperature and the cultivars with lower leaf conductivity were more resistant to coldness. 4) Adaptability and cold resistance of P. rockii were apparently different from P. suffruticosa ‘Luo Yang Hong’ and the former was stronger than the latter. The adaptability and cold resistance of tested cultivars ordered from high to low as ‘Lan He’, ‘Mei Gui Hong’, ‘Zi Guan Yu Zhu’, ‘Qing Chun’, ‘Zi Lou Shan Jin’, ‘Tao Hua San Zhuan’, ‘Yu Ban Xiu Qiu’, ‘Gao Yuan Sheng Huo’, ‘He Ping Lian’, ‘Xue Li Cang Jin’, ‘Hong Lian’ and ‘Luo Yang Hong’.