Critical Period Affecting Fruit Setting Of Sweet Cherry In Nanjing And Its Mechanism

Sweet cherry has the characters of bright color, rich nutrion, early listed and high economic benefit. It is very suitable for green food production because of short fruit development period and rarely use of pesticides. Its cultivated regions have enlarged from Yantai, Dalian and other regions around the Bohai Sea gulf to Longhai railway sides and the southwest high altitude regions. In recent years, peasants and research institutes in warm south regions such as Shanghai, Nanjing where the year average temperature was over 15℃, tried to introduce sweet cherry continually. But, so far, there are not successful large commercial planting cultivation examples in these regions because of the low setting rate. In order to find out the key period and environmental factors that can result in low fruit setting rate in the south, we took the ‘РубиноваяРанняяand’ ‘Summit’ as experimental material which planted both in Zhengzhou and Nanjing, then exchanged in different phenological period. Comparing the development of the bud, embryo sac and fruit set to find out the key period. We studied the relative expression of PaMADS2, PaMADS3, PaMADS4, PaMADS5 which belongs to MADS-box gene family by Fluorescence Quantitative Polymerase Chain Reaction in different phenological period in Zhengzhou and Nanjing. By analyzing the temperature, rainfall and the gene expression, we studied the mechanism of fruit setting. The main results are as follows:1. The exchanging was between Zhengzhou and Nanjing. ‘РубиноваяРанняя’ Treatments: 1. all in Zhengzhou, 2. moving to Nanjing when defoliation, 3. moving to Nanjing after dormancy, 4. all in Nanjing, 5. moving to Zhengzhou when defoliation. The fruit setting rates of these treatments respectively were 38.2%, 14.7%, 12.9%, 8.9% and 31.7%. Material ‘Summit’ Treatments: 6. all in Zhengzhou, 7. growing at Zhengzhou before defoliation, then moving to Nanjing to go dormancy and moving back to Zhengzhou after dormancy. The fruit setting rates of these treatments respectively were 13.9% and18.8%. The results indicated that the blooming and setting stage may be the key stage result in low setting rate in warm regions, not bud differentiation. Dormancy had little effects on fruit setting rate in the south.2. Observe embryo sac at blooming stage.The percentage of the bud that had ovule but no embryo sac were 41.5%, 55.6%, 57.7%, 74.5% and 50.0%, respectively. The rate of no embryo sac was not entirely consistent to fruit setting rate. The development of embryo sac may relate to the environmental factors in bud differentiation period and winter.3. Compared the temperature and rainfall at the bud differentiation stage, dormancy stage and blooming stage from July, 2013 to April, 2014 between Zhengzhou and Nanjing. In summer, the temperature of Nanjing was higher than that in Zhengzhou and so was the rainfall. In winter, the average temperature of Nanjing was higher than that in Zhengzhou. The rainfall in Nanjing was 65.2 mm but was 20.4 mm in Zhengzhou, both the rainfall was less. In budding and blooming period, the average temperature in Zhengzhou was 14.87 ℃ and in Nanjing it was 14.52 ℃, but the rainfall of Zhengzhou was a half of Nanjing. The results showed that temperature in budding and blooming stage had little on fruit set and rainfall had influence on fruiting set. The temperature and rainfall at budding and blooming stage affected bud differentiation. Rainfall had little influence on fruit set in dormancy.4. Contrasted the relative expression of PaMADS2, PaMADS3, PaMADS4 and PaMADS5 which belongs to MADS-box gene family in different phenological period both in Zhengzhou and Nanjing. PaMADS2, PaMADS4 and PaMADS5 may affect embryo sac development in dormancy and budding stage, respectively. In dormancy period, the rainfall of Nanjing was more than it in Zhengzhou, the expression of PaMADS2, PaMADS5 in Nanjing was higher than it in Zhengzhou and the expression of PaMADS4 in Nanjing was lower than it in Zhengzhou. In bud differentiation period, the temperature in the two places was similar but the rainfall in Nanjing was more than it in Zhengzhou, the expression of PaMADS2, PaMADS3, PaMADS4 and PaMADS5 were higher than them in Zhengzhou. The expression of PaMADS2 was up-regulated in Nanjing but was down-regulated in Zhengzhou along with the progress of phenological period. Combining the fruit setting rate in different phenological phase showed that high expression of PaMADS2, PaMADS3, Pa MADS5 and lower expression of PaMADS4 due to the differences in ecological factors such as rainfall, which led to embryo sac abortion may be the mechanism of fruit setting rate.