The Evaluation Of Salt Tolerance And Relative Physiological Responses Of Malus Seedlings

Apple (Malus) owes the largest growing area and the highest yield in northern China. Salinization is one of the main obstacles to economic production that apple suffered in arid and semi-arid areas. For this reason, to explore apple resources with strong resistance to salt stress is of great significance. In our study, we collected 15 kinds of commonly grown Malus from several regions of China, then simulated soil salinization environment through hydroponic method. We compared their habitats, antioxidant systems, and membrane functions to determine which factors play roles in salt tolerance, and identified those that can be best adapted to high-saline based on a salt injury index (SI), adversity resistance coefficients (ARC), and cluster analysis. The objective was to explore growth and physiological response mechanism of different apple resources under salt stress, and meanwhile to provide a theoretical basis for apple production in the future.The results were as follows:(1) Salt (NaCl) stress obviously inhibited plant growth. Growth slowing, leaf wilting and yellowing, and other symptoms were found in the earlier stage, while leaf margins brown, severe leaf lossing, and even plant death occurred in the later stage. Under stress, their growth parameters mostly decreased compared with the control, with remarkable inter-specific differences among them. Malus roots were found to be less sensitive than shoots to salt stress.(2) Under NaCl stress, Electrolyte leakage, the contents of malondialdehyde (MDA), and the activities of peroxidase and catalase were all increased. For most Malus kinds, stress treatment decreased soluble protein contents and superoxide dismutase activity. But apple plants could mitigate the damage caused by salt stress to some extent through raising the activities of anti-oxidation enzymes and the amount of organic osmotica.(3) Sensitivities of the 15 kinds of apple to salinity were obviously different. Through a synthetical evaluation of their salt tolerance based on SI, ARC, and cluster analysis, M. prunifolia Borkh cv. dongbeihuanghaitang, M. sieboldii Rehd cv. daguohongsanyehaitang, M. prunifolia Borkh cv. qiuzi, and M. xiaojinensis Cheng et Jia were deemed as salt-tolerant apple kinds, whereas M. prunifolia Borkh cv. yingyehaitang, M. micromalus Hemsl, and M. sieboldii Rehd cv. lushihongguo were considered to be salt-sensitive.