Abstract
Chimonanthus praecox is an important ornamental plant and cut flower material in China. It blooms in the freezing winter and its flower emits charming fragrance. However, in different region the flowering time is variable. In order to understand the flowering mechanism of Ch. praecox in the winter, we studied the flower bud differentiation in Spring City-Kunming using paraffin sectioning method in the present study. Meanwhile we compared the differentiation process difference from different regions. It was found that the temperature is the key factor for its flower bud differentiation and blossom of Ch. praecox. In the process of bud differentiation, the temperature 20 °C was the optimum for inducing changes from vegetative axillary buds to reproductive buds and subsequent morphological differentiation in Ch. praecox. Furthermore in the first three differentiation periods—tepal primordial stage, staminal primordial stage and pistil primordial stage, Kunming took the shortest time to finish the process due to very rapid temperature rise to 20 °C, whereas, in Zhengzhou the time for these differentiations was the longest, which may be caused by the slow temperature rise. After May, the high temperature stress forced the flower buds into the first long dormant period in all regions except Kunming. In Kunming, the average temperature was only 20–25 °C, so the flower bud continued to differentiate. In all regions, Kunming is the first to complete whole flower bud differentiation even on the early August, and started the second dormancy very early but very long. In the other regions, the plants went through a shorter dormancy and the low temperature broke the dormancy rapidly. Contrarily the plants of Kunming spent a longer period for the low temperature. Thus, the low temperature less than 10 °C is a key factor to breaking the second dormancy. Surely the regular effects of temperature on flower bud differentiation and blossom is very helpful for florescence regulation of Ch. praecox.
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