Identification Of Cold Resistant Of Apple Seedling Rootstocks

Apple is the most popular fruit of China, which are the world's largest producer and consumer of apples. Apple's cold resistance is apparently different among different types and varieties. This difference, combined with different climates, often causes apple's suffering from freeze injury of varying degrees. The cold resistance is significant to apples. It determines the overwintering safety of the apple plants, the growth of the plants and the production of the apples, etc. In order to effectively enhance the resistance of the apple plants, people can correctly select the rootstocks, which are directly affect the growth and fruition of scions. Thus, they can achieve the cultivation goal of early fructification, high yield, stable yield and good quality. Therefore, it is of great significance to determine suitable cold resistance indexes for giving a proper evaluation to the cold resistance of apple rootstocks and providing instructional support for apple's regional cultivation.This research mainly used one-year-old branches of seedling offspring of apple rootstock as testing materials. Electrolyte leakage, electrical impedance method and electrical resistance measurement were used to study the mechanism of cold resistance during the dormant period of branches. This research aimed to provide theoretical basis for screening of apple rootstocks with different cold resistances by measuring soluble protein content, soluble sugar content, starch content, MDA content, cell membrane permeability, superoxide dismutase, and the activity of peroxides. Analysis of variance was used for data analysis. The main results are as follows:1. A primary comparison is made by conductivity and electrical impedance methods among 45 branches of apple rootstocks to test their resistance to cold. And the result shows that the more severe the rootstocks branches are treated by stress the more quickly relative membrane permeability is increased. However, the increase amplitude differs in various stages and there is also some discrepancy about cold-resistance between the result of conductivity method and electrical impedance method. The result of conductivity method shows that the rootstocks with strong cold resistance are as following: 230,2-2-7-9,2-2-4-4,3-7-21-1,2-5-35-4,172,3-7-15-1,2-6-29-4,3-7-9-3,2-2-15-4,2-2-3-8,2-6-32-3; and the electrical impedance method: 3-7-19-4,2-2-4-4,51,3-7-15-1,3-7-9-3,2-6-32-3,172.2. The relationship between non-frost-exposed shoots'electrical impedance spectroscopy (EIS) parameters and its frost hardiness of apple rootstocks (LT50 measured by the electrolyte leakage) was analyzed. The results showed that the shoots' EIS parameters, extremely high-frequency resistances (r), low-frequency resistances (r₁), extracellular resistance (r_e), and relaxation time (Ï„) had a observably negative correlation with its frost hardiness (r=-0.737^**--0.877^**) in three different period (Mar. Jul. and Nov.). Intracellular resistance (r_i) also had a markedly negative effect on the frost hardiness (r=-0.857^**) in November, which suggested that re was proved to be the best parameter for testing the shoots'frost hardiness by comparing the final path coefficients during the three periods.3. The extracellular resistance (r_e), intracellular resistance (r_i), the resistances (r₁) and relaxation time (Ï„) decreased with decreasing temperature. The frost hardiness which was evaluated from the EIS parameters of apple rootstock shoots, such as re, ri, and r₁, was highly correlated with that which was measured by EL method (r=0.838～0.906), but r₁ was not suitable for measuring the frost hardiness of apple rootstock shoots because there was a 10℃difference between it and the one by EL method.4. By simulated chilling stress, the trend variations in rootstock branches'physiological-biochemical index are basically identical. The fact that the branches of apple rootstocks'resistance to cold tested by relative conductivity can better show the changes of plasma membrane permeability and the severity of branch damage. With the lowering of temperature, there shows an increase in tendency in relative conductivity.5. The electrical conductivities of living apple shoots in different periods revealed that this method had a observably negative correlation with its frost hardiness by EL method (R²=0.605～0.82,r=-0.77^**～-0.90^**)。6. During the winter, the protection of enzyme activity, the level of soluble protein content, and the MDA were showing a trend of increasing as the temperature decreases. The soluble sugar and starch content was increasing first and then decreasing.7. The changes of the physiological and biochemical indexes of apple rootstock shoots with different cold resistances represented similar tendency under continuing low-temperature stress. But the SOD activity, POD activity, soluble sugar content, starch content and soluble protein content in apple rootstocks with strong cold resistance were higher than those in apple rootstocks with weak cold resistance. And with temperature reducing, the increasing rate of SOD activity, POD activity, soluble sugar content and starch content in apple rootstocks with strong cold resistance was higher than those in apple rootstocks with weak cold resistance.