Evaluation of changes in the trend in physiological and morphological characteristics of sorghum (Sorghum bicolor L.) under different levels of salinity stress at different time intervals

Sorghum (Sorghum bicolor L. Moench), known for its high photosynthetic efficiency and biomass production, is utilized for various purposes, including food, animal feed, fiber, and fossil fuels. Salinity stress stands as a significant abiotic stressor that exerts numerous adverse effects on growth and crop yield. In order to investigate the physiological and morphological response of sorghum to salinity stress, a pot experiment was conducted in the greenhouse and laboratory of the University of Guilan, Iran, following a factorial split-plot design based on a randomized complete blocks design with three replications in 2021. The sorghum cultivars, Fuman and Sepideh, were subjected to salinity stress at four different levels, including control, 75 mM, 125 mM, and 175 mM NaCl, in the 4-5 leaf stage, with subsequent measurements taken at 24, 48, 72, and 96 hours after stress exposure. The results of the variance analysis demonstrated that the interaction between cultivars Fuman and Sepideh, various levels of salinity stress, and sampling times had a significant effect on the measured indices at the 1% level. Mean comparisons of treatment combinations indicated that proline, soluble sugars, ascorbate peroxidase, peroxidase, electrolyte leakage, and root length traits increased under salinity stress, showing a positive correlation with stress intensity. In contrast, chlorophyll a, chlorophyll b, carotenoid, protein, plant height, relative water content (RWC), leaf area, plant fresh weight, and plant dry weight decreased under salinity stress, with these traits declining as the stress level increased. In terms of the percentage of changes, soluble sugars had the greatest effect on stress, while RWC had the least impact. Based on the results, it can be concluded that sorghum employs mechanisms such as increasing the activity of antioxidant enzymes, proteins, and osmotic regulation through important osmolytes such as proline and soluble sugars to achieve tolerance to salinity stress. Additionally, the findings revealed that the Foman cultivar, known for its higher tolerance, exhibited a more favorable response to reducing oxidative damage caused by salinity stress compared to the Sepideh cultivar, making it a potential candidate for areas exposed to salinity stress through the implementation of appropriate management strategies.