Effects of different dwarfing interstocks on cold resistance of‘Changfu 2’apple in Longdong area

Abstract:【Objective】A study was conducted in attempting to screen the cold- resistant dwarf inter- stocks suitable for the‘Changfu 2’apple tree in the Longdong area of Gansu province, and to establish the method for evaluation of cold resistance of apples with different dwarfing interstocks【. Methods】In this study, annual dormant branches from‘Changfu 2’‘( Changfu 2’/ interstocks / Malus sieversii) of nine dwarfing interstocks (SH6, SH38, SC1, SH1, M26, M9, M7, T337 and JM7) were used as the experimental materials, which were even in size and free from diseases and pests. 8 physiological indexes, including relative electrical conductivity (REC), malondialdehyde (MDA) content, soluble sugar content, soluble protein content, anthocyanin content and superoxide dismutase (SOD) activity, peroxidase (POD) activi- ty and catalase (CAT) activity of annual dormant branches were determined under different temperature treatments (-15, -20, -25, -30, -35, and -40 °C), and the temperature at time of harvesting in the or- chard was used as the control temperature. According to the change in each index in response to low temperature stresses, difference in cold resistance of‘Changfu 2 ’with nine dwarf interstocks was ana- lyzed【. Results】As the treatment temperature droped, the relative electrical conductivity increased and  showed a "slow-fast" trend. The relative conductivity of‘Changfu 2’/JM7/ Malus sieversii was always the highest, while that of‘Changfu 2 ’/SH6/ Malus sieversii was always the lowest. Based on REC, the semi-lethal temperatures (LT50) of‘Changfu 2 ’with different interstocks were calculated by logistic equation, and the order of LT50 was SH6 >SH38 >SC1 >SH1 >M26 >M9 >M7 >T337 >JM7. With the decrease in temperature, the soluble sugar content of all interstock treatments showed an increasing trend, but there were differences among interstocks‘. Changfu 2’/SH6/Malus sieversii had the largest in- crease (196.99%);‘Changfu 2’/T337/Malus sieversii had the smallest increase (132.97%); the other sev- en had an increase between 142.46% and 174.97%. Soluble protein content in all treatments increased sharply and then decreased slowly, but with an overall rising trend with the decrease in temperature. The peak appeared at -30 °C, the highest peak was found in‘Changfu 2’/ SH6 / Malus sieversii, and the lowest peak in‘Changfu 2’/JM7 / Malus sieversii. The variation pattern of anthocyanin content with temperature drop in the treatments was basically the same, increasing first and then decreasing. Except for‘Changfu 2’/ T337 / Malus sieversii which peaked at -20 °C, all other treatment peaked at -25 °C, and the peak values of each sample were in the rank of SC1 >SH6 > SH38 > M26 > SH1 >M9 >T337 >M7 > JM7. Except for‘Changfu 2 ’/T337/ Malus sieversii,‘Changfu 2’/ M26 / Malus sieversii and‘Changfu 2’/ SH1 / Malus sieversii whose MDA content decreased under treatment at -40 °C, all the treatments had an MDA content increasing with the decrease in temperature. The MDA contents‘Changfu 2’/ T337 / Malus sieversii and‘Changfu 2’/ JM7 / Malus sieversii were always higher than those of the other 7 treatments under various low temperatures; the contents of‘Changfu 2’/ SH38 / Ma- lus sieversii and‘Changfu 2’/ SH6 / Malus sieversii increased steadily but remained at a low level. The activities of SOD, POD and CAT the nine treatments increased first but decreased later and the peak ap- peared at the critical temperature of -30 or -35 °C. Then, as the temperature continued to decrease, the degree of damage on the plant increased, and the enzyme activities decreased. All the 7 physiological in- dexes could reflect the cold resistance of‘Changfu 2’with different interstocks, but there were correla- tions among various physiological indicators, and the information reflected by the statistics overlapped to some extent. Therefore, in order to simplify the indicators and more accurately compare the differenc- es in cold resistance between‘Changfu 2’of the nine interstocks, a principal evaluation system was established using principal component analysis. The principal component analysis of the original data showed that the two principal components were extracted from the eight physiological indicators with an eigenvalues of 5.832 and 1.128, respectively, and the contribution rates were 72.896% and 14.103%, respectively. The cumulative contribution rate was 86.998%, and the factor analysis results were ideal. A total of 86.998% of the total variance of the original variables was explained, covering most of the in- formation of the original variables. The first factor reflected the soluble protein, antioxidant enzyme, and semi-lethal temperature, and the second factor soluble sugar and anthocyanin. Then, we used the membership function method to calculate the membership value of each comprehensive index, and the weights of the two comprehensive indicators were obtained according to the contribution rate of the comprehensive index, and were 0.838 and 0.162 respectively. Using the formula, the D value of each intermediate anvil Fuji was obtained. The D value was a comprehensive evaluation value of cold resis- tance, reflecting the difference in cold resistance of each intermediate anvil Fuji. The higher the D val- ue, the stronger the cold resistance. Among the nine interstock, the D value of SH6 was the highest, 0.947, and the cold resistance was the strongest; the D value of JM7 was the lowest, 0.140, and the cold resistance was the weakest. The D values of the interstock was clustered by the inter-group connection method, and the clustering tree diagram was established.【Conclusion】The results showed that the nine interstocks were classified into three categories according to the cold resistance. The first type in- cludeed SH6, SH1, SH38 and SC1, which had the strongest cold resistance; the second type consisted of M7, M26 and M9, which had strong cold resistance; and the third type included JM7 and T337, which had weak cold resistance.