Comprehensive evaluation and physiological responses of 20 table grape varieties to sole and combined salt and drought stress

Soil drought and salinization limit grape production, and the cultivation of salt and drought resistant table grape varieties can effectively solve this problem. In this study, the salt and drought tolerance of 20 table grape varieties was comprehensively evaluated by different methods. Under salt and drought stress the growth of grapes was inhibited; the stomatal resistance, relative conductivity, MDA, FRAP antioxidant activity, ABA, ABS/RC, TRo/RC, and DIo/RC in leaves increased; and the relative water content, content of photosynthetic pigments, Fv/Fm, PI abs, and ETo/RC in leaves decreased. The degree of damage was greatest under combined salt-drought stress, followed by sole salt stress and sole drought stress. Under various stress conditions, 'Munage' exhibited strong tolerance. Compared with the sensitive variety 'Sweet sapphire', the new shoot growth quantity and Fv/Fm of 'Munage' were respectively 146.67 % and 10.88 % higher under salt stress, 93.10 % and 3.63 % higher under drought stress, and 200.00 % and 13.31 % higher under combined stress. Correlations between indicators were observed, the shoot growth, stomatal resistance, Chla and chlorophyll fluorescence parameters of leaves could be used as reliable indicators for rapidly evaluating the salt and drought tolerance of grapes. Membership function analysis and principal component analysis were used to calculate the D-value (the comprehensive evaluation indicator). 'Munage', 'Manaizi', 'Thompson Seedless', and 'Hotan Red' were highly salt and drought-tolerant varieties. 'Kyoho', 'Red muscatel', 'Summer Black', 'Shine Muscat', and 'Sweet sapphire' were highly sensitive to salt and drought. Three stepwise regression models were also developed for the rapid screening and identification of salt and drought-tolerant grape varieties. In conclusion, key salt and drought tolerance indicators and comprehensive evaluation methods were proposed to identify salt and drought-tolerant grape varieties.