2002 Volume 71 Issue 6 Pages 818-825
In this study, flower-bud differentiation in nine Chinese tree peony cultivars from Zhongyuan Province, China, growing in the open field and then under protected cover (forcing) was investigated. Flower-bud differentiation of Chinese tree peony cultivars began during the last 10 days of June. Depending on when flower-bud differentiation began and when developmental process ceased, cultivars can be divided into following three groups : (1) cultivars in which flower-bud differentiation progressed rapidly and smoothly to flower formation under high summer temperature ; the gynoecium completely formed in early October, such as in 'Bai He Wo Xue', (2) cultivars in which flower-bud differentiation progressed at a moderate pace ; the gynoecium completely differentiated by mid-October, such as in 'Shan Hu Tai', and (3) cultivars in which flower-bud differentiation was slow ; the gynoecium was not completely differentiated even in early November, such as in 'Jin Xiu Qiu'. The percentage budbreak in a Japanese tree peony cultivar was quite low, even after being chilled at 4°C for 4 weeks, whereas almost 100% of the Chinese tree peonies sprouted after 4 weeks of chilling. Percentage of flowering of the Chinese 'Bai He Wo Xue' was sufficiently high before the end of the year so that the blooms could be marketed. Over 80% of 'Bai He Wo Xue', 'Feng Dan' and 'Shu Nu Zhuang' flowered for December shipping.