Abstract: Objective In this study, the growth and physiological responses of walnut seedlings with different genotypes to salt stress were studied, and their salt tolerance was comprehensively evaluated, which would provide reference for screening salt-tolerant varieties in saline-alkali areas.Method Seedlings derived from 4 genotypes of Juglans regia ‘Xinxin2’ (JX2), J. regia ‘Wen185’ (JW185), J. regia ‘Zha343’ (JZ343), and J. regia ‘Liaoning1’ (JL1) were used as test materials, and subjected to five NaCl concentration gradients (0, 50, 100, 200 and 300 mmol·L^?1). The photosynthetic parameters, membrane permeability, osmotic adjustment substances, enzyme activity and endogenous hormone content of the four genotypes were measured for different days (6, 12, 18 and 24 days), and the salt tolerance of the four genotypes was comprehensively evaluated.Result 1) Under salt stress, the growth of seedlings of four genotypes was affected to different degrees, and the leaves of all genotypes showed different degrees of salt damage symptoms, such as yellowing, curling and shedding. The growth indexes such as seedling height increment, ground diameter increment and plant dry weight showed a downward trend with the increase of NaCl concentration. Among the 4 genotypes, JX2 grew relatively better and was less inhibited. 2) With the increase of salt concentration and the prolongation of stress time, the chlorophyll content and photosynthetic parameters of each genotype generally showed a downward trend, and JX2 showed a smaller decline than the control, and performed better. 3) With the increase of salt concentration and the prolongation of stress time, relative electrical conductivity (REC) and malondialdehyde (MDA) content showed an overall upward trend. Among the 4 genotypes, JX2 had lower the REC value and MDA content, with a smaller increase compared to the control, while JZ343 was the opposite. 4) With the increase of salt concentration and the prolongation of stress time, proline (Pro) content generally showed an upward trend, soluble sugars (SS) and enzyme activities showed an overall increase followed by a decrease. Among the 4 genotypes, JX2 accumulated more Pro and SS, and had higher enzyme activity. 5) In terms of endogenous hormones, salt stress promoted the production of abscisic acid (ABA) and inhibited the synthesis of indole-3-acetic acid (IAA). Conclusion Salt stress significantly affects the growth and photosynthesis of walnut seedlings, by reducing the photosynthesis activity of leaf cells. Seedlings can cope with salt stress by increasing the content of osmotic adjustment substances, improving enzyme activity and regulating their endogenous hormone balance. The comprehensive evaluation of salt tolerance indicates the following order of magnitude of salt tolerance among the four genotypes: JX2 > JW185 > JL1 > JZ343.

Key words: walnut, salt stress, growth index, physiological response, principal component analysis