Comparative Studies on the Physiobiochemical, Enzymatic, and Ionic Modifications in Salt-tolerant and Salt-sensitive Citrus Rootstocks under NaCl Stress

A study was conducted to investigate the morphological, physiobiochemical, enzymatic, and ionic differences among four cultivated citrus ( Citrus sp.) rootstocks with different salt tolerances. Two salt-tolerant rootstocks [Rangpur lime ( C. limonia ) and Rubidoux ( C. trifoliata )] and two salt-sensitive rootstocks [Carrizo citrange ( Citrus sinensis × C. trifoliata ) and Sanchton citrumello ( C. trifoliata × C. paradisi )], were subjected to NaCl stress in greenhouse conditions. The 9-month-old plants were exposed to four different NaCl levels (0, 30, 60, or 90 m m ) in sand culture for 3 months. Plant biomass (fresh weight, dry weight, root length, shoot length, and leaf thickness), physiological attributes [number of stomata, stomatal size, number of epidermal cells, photosynthesis rate, stomatal conductance ( g S ), water use efficiency, and transpiration rate]. and ion content (Na + , K + , Ca +2 , Mg +2 , and Cl – ) were adversely affected by salt stress, but salt-tolerant cultivars were comparatively less affected. Salt stress also enhanced antioxidant enzyme activity (superoxide dismutase, catalase, and peroxidase), particularly in salt-tolerant cultivars. The salt-sensitive cultivars accumulated the greatest content of Na + and Cl – in their leaves, whereas the salt-tolerant cultivars accumulated the greatest content of Na + and Cl – in their roots, an adaptation to combat the highly saline conditions. Overall, it was concluded that the salt tolerance of rootstocks is associated with a greater antioxidant enzyme activity and differing accumulation patterns of Na + , K + , Cl – , Mg +2 , and Ca +2 in leaves and roots; these can be considered potential indicators of a cultivar's sensitivity to salt stress.