Comprehensive Evaluation Of Alkali Tolerance And Cold Resistance Of Different Hybrid Elites Of Apple Dwarf Rootstocks

Apple is one of the important fruit trees in the temperate zone.The north of China is the main area of apple production,but the development of apple industry is restricted by low temperature,saline-alkali and other abiotic stresses.Therefore,it is very important to improve alkali tolerance and cold resistance of apple trees.Apple rootstocks with strong stress resistance could effectively reduce the harm caused by stress on apple trees,and play an important role for apple plants in adapting to alkali environment and improving cold resistance.Therefore,it is necessary to carry out breeding of dwarf rootstocks with high resistance to alkali and cold,and to evaluate and screen dwarf rootstock hybrid elites with strong resistance to alkali and cold.In this study,two experiments were carried on.On the one hand,sand culture method was used to comprehensively evaluate the alkali tolerance of dwarf rootstocks and hybrid elites,through analyzing the changes of growth,active oxygen accumulation,antioxidant enzyme activity,membrane damage,proline and chlorophyll content,etc.On the other hand,cold resistance of dormant branches was evaluated by low temperature treatment,through the analysis of the reactive oxygen species accumulation,antioxidant enzyme activity,membrane damage,proline content and other indexes.Finally,some of hybrid elites of apple dwarf rootstocks with higher alkali tolerance and higher cold resistance were screened.The main results were as follows:1.Fourteen hybrid elites of apple dwarf rootstocks and dwarf rootstock M9T337 were selected and treated with alkaline solution for 50 days to analyze the changes of growth and physiological indexes.The results show that after alkali stress treatment,the plant height increment,new leaf number and biomass of C8,B6,H9 and H10 were less inhibited,the photosynthesis and biomass of B6 and C8 were less inhibited,the ROS accumulation of H10 and H4 was less,the membrane damage of F7 and D10 was lower,the osmotic regulatory substance content of A7 and B1 was higher,and E7 and H10 had higher antioxidant enzyme activity.According to the average subordinative function value(ASFV)of 13 indexes,15 materials could be divided into four groups according to the alkali resistance as highest,higher,medium and lower alkali resistance.At the same time,according to the value of the subordinative function value(SFV)of the measured indexes,these materials could also be divided into 4 groups by cluster analysis.Finally,based on the comprehensive evaluation results of alkali tolerance by SFV analysis and cluster analysis,15 materals were classed into3 group:(1)6 materials with higher alkali resistance,including A7,C8,E2,E7,H9 and H10;(2)6 materials with medium alkali resistance,including A9,B1,B6,D10,H4 and M9T337;(3)3 materials with lower alkali tolerance,including D6,E6 and F7.2.Twenty-one hybrid elites of apple dwarf rootstocks and dwarf rootstocks M9T337 and M26 were selected as materials,and the physiological indexes of apple annual dormant branches were analyzed after low temperature treatment.The results showed that after low temperature treatment,the membrane of F7,K1 and B13 was less damaged,the antioxidant enzyme activities of A3,E7 and E4 were higher,the proline(Pro)content of M26 was the highest,and the Pro content of E4 increased the most.By means of principal component analysis and SFV analysis,according to the D value of 8 indexes,23 materials could be divided into four groups according to the cold resistance: highest,higher,medium and lower cold resistance.At the same time,according to the value of SFV of the measured indexes,the materials could also be divided into four groups by cluster analysis.Finally,based on the comprehensive evaluation results of cold resistance by SFV,23 materals were classed into 4group:(1)1 material with highest cold resistance,which was E4;(2)6 materials with higher cold resistance,including A3,B13,E7,F7,H11 and M26;(3)10 materials with medium cold resistance,including A2,A7,A9,C5,C7,C8,E2,H6,G6 and K1;(4)6 materials with lower cold resistance,including B1,D10,G4,H4,H7 and M9T337.Based on the comprehensive evaluation,the hybrid elites of apple dwarf rootstocks with higher alkali resistance,including A7,C8,E2,E7,H9 and H10,and the elites with higher cold resistance,including A3,B13,E4,E7,F7 and H11 were screened.