Freezing Injury Index of Kiwifruit Branches for Main Varieties Under Simulated Low Temperature

Abstract

Low temperature freezing injury is the main meteorological disaster affecting the yield and quality of kiwifruit in China. To explore the damage mechanism of low temperature stress on kiwifruit and establish the indices of kiwifruit overwintering freezing injury, the impacts on fruit parent branches of kiwifruit are investigated by simulating natural freezing injury process with MSX-2F artificial simulated frost box system. Growth recovery method, tissue browning method, cell freezing point temperature method and cell membrane damage rate method are used to describe the characteristics of freezing injury quantitatively. By establishing the logistic analysis model of the relationship between freezing injury index and low temperature, the characteristics of freezing injury of 6 varieties are studied systematically. The results show that the response of different varieties to low temperature are significantly different. The supercooling point of Ruiyu and Hayward are lower, which are -3.4 ℃ and -3.2 ℃, respectively. The supercooling point of Xuxiang, Jinfu and Cuixiang are basically similar, which are -2.0 ℃, -1.7 ℃ and -1.7 ℃, respectively. The supercooling point of Hongyang is the highest, which is -1.4 ℃. The half-lethal temperature of buds of Hayward (-16.5 ℃) is the lowest. The half-lethal temperature of Ruiyu (-14.8 ℃), Xuxiang (-14.9 ℃) and Jinfu (-14.2 ℃) is intermediate. And the half-lethal temperature of Cuixiang (-13.4 ℃) and Hongyang (-13.8 ℃) are the highest. The differences in the degree and site of injury caused by different intensities of low temperature are significant. The freezing injury caused by -16 ℃ to -10 ℃ mainly affects the activity of the main bud of the resulting parent shoot. When the temperature is below -18 ℃, the low temperature damages the activity of main and secondary buds. And when the temperature is below -20 ℃, a large number of parent shoots are killed by low temperature injury. Among varieties, the frost resistance of Hayward is the strongest, Ruiyu, Jinfu and Xuxiang are the middle, and Cuixiang and Hongyang are the weakest. Taking the freezing injury index of the resulting parent branch bud as the main parameter, the 5-grade low temperature freezing injury index of the resulting parent branch is constructed by different varieties. Its freezing temperature ranges of level 1-5 are -11.0 ℃ to -10.5 ℃, -14.5 ℃ to -10.5 ℃, -16.5 ℃ to -12.0 ℃, -20.0 ℃ to -13.5 ℃, -20.0 ℃ to -15.0 ℃, respectively.

Keywords

• kiwifruit
• low temperature stress
• fruit branch
• lethal temperature
• index of freezing damage