Effect of natural cold acclimation on the cold resistance in wine grapes

Abstract:【Objective】Cold acclimation is an important physiological process for plants to increase cold resistance. The individual impact on the grape cold resistance from gene heredity and cultivation practice is quite stable, while the cold resistance of grape gained from cold acclimation in winter changes as the weather condition naturally varies with different years or places. Study on the responsive process of natural grape cold acclimation to low temperature and photoperiod is of great significance to reveal the formation process and physiological mechanism of grape cold resistance. It needs to build the relationship model between the cold resistance of grape and low temperature in order to analyze the low temperature indices for cold acclimation of grape.【Methods】In this paper, the annual ripe grape canes of Cabernet Sauvignon and Beihong at the eastern foot of Helan Mountain were taken and used as test materials to measure the physiological and biochemical response indicators, such as supercooling point, freezing point, soluble sugar, soluble protein, conductivity, Ca2 + , sucrose, ABA, etc. Thereafter, the effect of natural cold acclimation on grape cold resistance was quantitatively evaluated by analyzing the response process of physiological and biochemical parameters to low temperature with the methods of variance analysis, t test and numerical simulation. The supercooling point and the freezing point were measured in the experimental frost box of SDX-20, in which the temperature sensors were fixed on the canes and data were taken once every 10 seconds. The supercooling point and the freezing point were determined according to the heat releasing process of tested canes. The dropping process of temperature was set as referring to the natural process with a decreasing rate of 3.0 ℃· h- 1 from the room temperature to -25 ℃. Conductivity was measured with DDSJ-308F conductivity meter firstly and then it was put in the boiling water for 30 minutes after it was sealed with glass stopper. After it cooled down to room temperature, the conductivity was measure again under the condition where it kept still after it was shaken slightly. The water content in canes was measured with the heating and weighing method. Ca2 + content was measured by following the microwave digestion method. Cane sucrose content was measured with the method of resorcinol colorimetry. The ABA concentration was measured with ABA test toolkit.【Results】The results showed that: (1) The lowest temperature was the dominant factor in the cold acclimation process; Under the low temperature condition, grapes could reduce the water content in canes, increase Ca2+ content, and improve the osmotic regulation ability of the canes; Under the low temperature condition, grapes could also improve the cold resistance by increasing the sucrose content in canes. There was a significantly positive correlation between ABA content in canes and sunlight duration (photoperiod), but not closely related to the low temperature. Precipitation (irrigation) also played a significant role in the cold resistance of grape canes so that it reduced cold resistance of grape canes. (2) The indictor of cold resistance, which was calculated from the absolute difference value of maximum and minimum supercooling point values, showed that the cold resistance of Beihong canes was stronger than that of Cabernet Sauvignon. However, there was no significant difference in cold resistance for the physiological indicators between Cabernet Sauvignon and Beihong varieties in the same year, like supercooling points, conductivity and cane water content. There were significant differences in the supercooling point and the conductivity of Cabernet Sauvignon between different years, and there was a significant difference in the supercooling point of Beihong but there were no significant differences for other indicators, like conductivity and cane water content. (3) The grape cold acclimation was gradually accumulated, and the grape cold resistance increased as the cold acclimation temperature dropped. There was a typical nonlinear logistic relationship between the grape cold resistance and the low temperature. When the temperature was lower than 18.0 ℃, grapes triggered the cold acclimation process. The cold resistance increased with the decrease of temperature. When the temperature was lower than 12.0 ℃ , the grape cold resistance increased rapidly. When the temperature was lower than 3.0 ℃, the increase of the cold resistance of grape canes slowed down, and the grape cold resistance reached the strongest before grapes were buried in the soil.【Conclusion】It was very complex physiological process of cold acclimation of grape as the intensity of cold acclimation was determined jointly by indicators, like grape gene heredity, photoperiod, low temperature, precipitation or irrigation and other environmental factors. The low temperature was a major determinate factor in the cold acclimation of grape. With the decrease of temperature at the beginning of autumn, the cold resistance of grape canes increased logistically rather than linearly and this process was evolving gradually and cumulatively. Sunshine was the secondary factor to play a role in the process of grape cold acclimation by inducing ABA generation. It seemed that temperature and sunshine independently played roles in the process of grape cold acclimation.