Flower Bud Differentiation In Sweet Cherry And The Influence Of Temperature

In recent years, there has been a major expansion in sweet cherry production beyond the cool Bohai-sea bay region for the reason of great potential income. Most of these newly sweet cherry plantings are in warm regions which has been testified to the potential commercial orchard bases. Growers in the south of China have been interested in the introduction of sweet cherry. However, sweet cherry production has the troublesome problems of yield unsteability, shy fruit-bearing, and occurrence of fruit malformation. Temperature plays an important role which can regulate flower bud differentiation, dormancy, blossom, fruiting, and crop production. We attempted to obtain some important data which could redound to a better understanding of warm regions'introduction, greenhouse cultivation, and production difficulties. Three experiments about flower bud differentiation, including cultivars comparison, ecological regions comparision, and the high temperature effect, had been carried out consequently, and the results are as follows:(1) The whole process of flower bud differentiation in sweet cherry could be divided into six stages sequentially. Among these six phases, the first phase was the longest, the third, fourth, and sixth phase were relatively short, and the second and fifth phase were shorter than other four phases.(2) There was no direct correlation between the initiation time and the ripeness time. In'РубиноваяРанняяin', an extremely early-ripening cultivar, floral bud initiated on May 1, and the pistil primordia were evident on August 20. In'Hongdeng', a dominated early-ripening cultivar, floral bud initiated before May 1, and the pistil primordia formed on August 10. In'Lapins', a late-ripening cultivar, the initiation date was May 1, and the pistil primordia formed on September 10. Different cultivar had different progression of flower bud formation (FBF) in the three tested cultivars. However, the progression of FBF was almost in synchronization in'РубиноваяРанняя'and'Hongdeng', and both of their formation progression was faster than that of FBF in'Lapins'about 10 to 20 days. In'РубиноваяРанняя'and'Hongdeng', the flower bud differentiated rapidly in the period of mid-June and mid-July, and in'Lapins', the flower bud differentiated rapidly in the period of early-July, early and mid-August.(3) Compared with the flower bud formation in'Hongdeng'in Zhouzhou, the initiation date delayed to early-June, and the ending date delayed to mid-August in Yantai. So, the whole flower bud formation lasted for about 80 days, which was shorter than that of FBF in Zhenghzou about 20 to30 days. Although the experimental data in Jinhua was not satisfied completely with the original experiment design, we still could deduced that the initiation date of FBF in Jinhua was possibly later than that of FBF in Zhengzhou, and that the ending date in Jinhua was about August 20.Therefore, the progression of flower bud differentiation in'Hongdeng'changed obviously according to the locations.(4) High and low temperature (T) resulted in the retardance of the FBF and delayed the progression of FBF. In our experiments, the results indicated that the FBF in'РубиноваяРанняяin'and'Hongdeng'was inhibited when T was higher than the threshold of 27.0℃, and that the FBF in'Lapins'was inhibited when T was higher than the threshold of 29.0℃, and that the FBF in'Hongdeng'was inhibited when T was lower than the threshold of 20.0℃. It was supposed that the suitable T range for FBF in'Hongdeng','РубиноваяРанняяin'and'Lapins'was 20.0~27.0℃, 25.0~27.0℃, and 26.0~29.0℃respectively.There was a direct relationship between the occurrence of flower malformation and T. The occurrence of malformated flowers would increase remarkably if T became higher. The frequency of occurrence was different among cultivars.(5) Flower bud in sweet cherry finished the differentiation of ovule primordium and mother cell of microspores before dormancy, and showed little morphological change in dormancy, and achieved the formation of single-layer integument and ovule in bud's first swelling, and formed embryo sac in bloom. The observation in the paraffin-sections revealed that the mother cell of microspore(s) developed earlier than the mother of macrospore. In'Hongdeng', all the samples taken in full bloom developed the nucellus in three locations, and few flower samples(less than 5%) taken in Zhengzhou and Yantai were absent of embryo sac, and about 34.6% flower samples taken in post-bloom in Jinhua were lack of embryo sac. It was argued that the embryo sac abortion, induced by high temperature in bloom, might be a sound explanation.