Different responses of rice cultivars to salt stress and the underlying mechanisms

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<p id="C3">The objective of this study is to elucidate the responses of physiological traits and yield with different salt stress to salt-tolerant and salt-susceptible rice cultivars. Five salt-tolerant rice cultivars and two salt-susceptible rice cultivars were grown in pots with five different salt concentration levels including 0, 1, 2, 2.5, and 3 g kg^-1 of per pot for two years. Results showed that the yields of salt-tolerant cultivars were less reduced than that of salt-susceptible cultivars, and salt-tolerant cultivars was able to tolerate higher salt concentration of 2.5 g kg^-1. Salt-tolerant varieties produced higher grain yield mainly due to the greater total spikelets per area and higher filled grain percentage under salt stress. Salt-tolerant rice cultivars also had higher activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), higher contents of osmotic substances such as fructose, trehalose, and sorbitol, and higher K⁺/Na⁺ ratio from mid-tillering to heading. The crop growth rate from tillering to jointing and from heading to maturity, and photosynthetic rate at heading stage were higher in salt-tolerant cultivars than in salt-susceptible cultivars. The above results revealed that the differences in grain yields between salt-tolerant and salt-susceptible rice varieties were mainly due to the performances of physiological traits at mid-tillering, panicle initiation, and heading stages. These growth stages were the key stages that determined the number of panicles, spikelets per panicle, and the percentage of filled grains. The better physiological traits in the salt-tolerant rice varieties during key stages were the basis for higher grain yield. The results of this study could be helpful for the physiological researches and the breeding of salt-tolerant rice.