Physiological responses and relative tolerance by Chinese apple rootstocks to NaCl stress

The physiological responses and salt tolerance of apple rootstocks were evaluated under high salinity. Seedlings of 15 kinds of apple rootstocks were treated with 200 mM NaCl for 10 d to assess growth, biomass, and physiological responses. Under NaCl stress, their growth parameters decreased compared with the control, with the greatest changes in leaf number, plant height, and relative water content (RWC). In contrast, electrolyte leakage (EL) and activities of peroxidase (POD) and catalase (CAT) were increased. For most rootstocks, stress treatment decreased malondialdehyde (MDA) and soluble protein contents along with superoxide dismutase (SOD) activity. Their degree of salt tolerance was comprehensively evaluated based on salt injury index (SI), adversity resistance coefficients (ARC), and cluster analysis. Malus prunifolia Borkh cv. dongbeihuanghaitang, M. sieboldii Rehd cv. daguohongsanyehaitang, M. prunifolia Borkh cv. qiuzi, and M. xiaojinensis Cheng et Jia were salt-tolerant rootstocks, whereas M. prunifolia Borkh cv. yingyehaitang, M. micromalus Hemsl, and M. sieboldii Rehd cv. lushihongguo were salt-sensitive rootstocks. These differences in sensitivity were associated with variations in the activities of anti-oxidation enzymes and in the amount of organic osmotica.

Research highlights▶ Apple (Malus) is one of the most economically important fruits worldwide. But apple tree often encounters environmental stress in production. Salt stress is thought to be one of those important factors which restrict the development of apple in some regions. As an important center for apple production, China has abundant germplasm resources with strong resistance to adverse environments. Salt tolerance of some apple rootstocks had been previously evaluated and shown large differences among species. However, as far as we know, some apple rootstocks have not yet been well evaluated and characterized. Evaluation and screening salt-tolerance apple rootstock is of fundamental importance to regional recommendations for apple rootstock selections and apple breeding. In the present study, the seedlings of 15 kinds of apple rootstocks were comparatively studied to investigate the physiological response to NaCl stress and evaluate their relative tolerances.