Abstract
The short flowering period of ornamental cherry trees is the main factor limiting their use in gardens. Determining the secondary flowering characteristics of ornamental cherry trees is required to prolong their flowering period. In this experiment, Cerasus subhirtella 'Autumnalis' was used as the experimental material. The phenological differences in their annual growth cycle were observed using the BBCH coding system. The cooling requirements of the flower buds were evaluated by the chilling hours model (temperature between 0 and 7.2 °C) and the Utah model. The expression of the core gene involved in bud dormancy regulation DAM (dormancy-associated MADS-box) from the completion of flower bud differentiation in one year until the following year was measured by performing real-time fluorescence-based quantitative PCR. The results showed that the flowering duration of C. subhirtella 'Autumnalis' from November to December was longer than that of C. yedoensis 'Somei Yoshino', which was from March to April. The progress from seed bud-break to flower bud opening took about 10 days for C. subhirtella 'Autumnalis', while the same stage for C. yedoensis 'Somei Yoshino' took around 20 days. Additionally, the flower buds of C. subhirtella 'Autumnalis' needed only the chilling temperature unit of 54.08 to satisfy the chilling requirement, while C. yedoensis 'Somei Yoshino' required a chilling temperature unit of 596.75. After the completion of flower bud differentiation, during low-temperature storage, the expression of DAM4 and DAM5 genes first increased and then decreased, whereas, the expression of the DAM6 gene continued to decrease, and the expression of DAM4, DAM5, and DAM6 in C. yedoensis 'Somei Yoshino' increased rapidly and was maintained at a high level. This showed that the upregulation of the expression of the DAM4, DAM5, and DAM6 genes can inhibit the flower bud germination of Cherry Blossom. The relative expression of the DAM gene of C. subhirtella 'Autumnalis' was significantly lower than that of the DAM gene of C. yedoensis 'Somei Yoshino' from the end of October to the beginning of December, leading to its secondary flowering in autumn. These results might elucidate why the flower buds of C. subhirtella 'Autumnalis' can break their internal dormancy and bloom in the autumn and then again in the following year. Our findings might provide a reference for conducting further studies on the mechanisms of secondary flowering and bud dormancy in cherries.