| Frost index in apple blossom is the foundation for frost forecast, warning and defense in orchard. This paper taking the Fuji, Jonagold and Gala as the test objects, utilizing the artificial frost simulating boxes to set up the cooling simulation test and 20 experimental treatments with 5 temperature gradients and 4 duration times, have been simulated and researched the frost sensitive indexes in apple blossom. The results showed that: The average supercooling point was from -3.51℃ to -3.27℃ for the petal in bud period and blossom, ovary and young fruit stage. The change range of freezing point was -2.94℃ to -2.65℃. The low sensitive temperature in apple blossom was -2.5℃ to -3.5℃. There were some difference between different floral organs, varieties, low temperature duration and developmental stage. Among them, for all floral organs, the petal was the most intolerant to frost than other floral organ as ovary, stamens and pistils. The variation was rather big with temperature decrease for the ovary, stamen and pistil. The order of resistance to cold for different flower type was bud>semi flowering> full flowering. The death rate was obviousness with increasing the duration, under the temperature treatment of -2.5℃～-3.0℃. While the duration had little effect on death rate when the temperature was higher or less this range of -2.5℃ to -3.0℃. In three test varieties, the Fuji was the most intolerant to cold, the second was Jonagold and Gala. |