Investigation Of Freezing Injury And Freezing Resistance Of Six Varieties During Apple Florescence

Apple(Malus domestica Borkh.)is the most important fruit tree crops in our country,and the Loess Plateau is one of the best areas for the apple growth,and it is also the main apple planting district in China.However,apple flowering was often affected by "Late spring coldness",thereby affects the apple production and quality.In this study,6 apple varieties including 'Fuji','Ruiyang','Ruixue','Gala','Pink Lady' and 'Qinyang' cultivated in Baishui,Chunhua,Xunyi,Lingtai and Qingcheng in five counties of Shaanxi and Gansu province were used as test materials.After the nationwide severe low temperature on April6,2018,the freezing injury rate of flowers,fruit setting rate,fruit shape index and skewness index were investigated,the tissue structure of flowers were observed,the physiological indexes related to frost resistance were determined,and the frost resistance of 6 varieties were evaluated by principal component analysis.The main research results are as follows:1.The effect of freezing injury on terminal inflorescence was larger than axillary inflorescence,and terminal inflorescence had higher freezing injury rate and lower fruit setting rate.In the same inflorescence,the freezing damage rate of the central flower is higher than that of the lateral flower,and the fruit setting rate is lower.Among the six apple varieties,'Ruiyang' and 'Ruixue' had the lowest freezing injury rate and the highest fruit setting rate.The fruit shape index of the top fruit is higher than that of the axillary fruit during fruit development,more than 55% of ripe fruits are skew fruits,which the seed number of 'Ruiyang' is more and 'Fuji' is lower.After freezing injury,the fruit was small and the quality decreased.2.The flower organs at the late stage of development suffered from freezing injury,the carpel merges completely and no abdominal suture remains,and the ovary ventricle is formed with two or more ovules in the flower organs.The degree of injury in the pistil is in order: base of style(the connecting part in the middle of each ventricle),outer perianth,style,inside of calyx(the connecting part of calyx and style),embryo sac,ovary wall,indicates that the base of the style is the least resistant to freezing,which is the key part to prevent pollination and fertilization,and also the main reason of fruit deflective.3.A comparison among 6 cultivars in physiological indicators was made,the concentration of soluble sugar content(SSC),soluble protein(SP),proline(Pro),superoxide dismutase(SOD),peroxidase(POD),catalase(CAT)and malondialdehyde(MDA)in‘Ruixue' variety in different regions were relatively high,indicating that the flower of'Ruixue' had a certain degree of freezing resistance.4.Correlation analysis results show that the freezing injury rate,skewness index and MDA content were negatively correlated with other cold resistance indexes.Principal component analysis showed that SOD and POD in the antioxidant system and SP,Pro in the infiltrating substance are the main indexes of freezing injury in apple florescence.'Ruixue'is the most freeze-resistant variety in the comprehensive evaluation of freezing resistance of principal components.