Effect of Drought and Salinity Stress on Yield, Biochemical Properties, and Activity of Antioxidant Enzymes in Forage Sorghum

In the present study, the effect of different levels of water and salinity stresses was investigated on dry matter production, biochemical attributes, and activity of antioxidant enzymes in sorghum [Sorghum bicolor (L.) Moench] in Marvdasht and Arsanjan regions in 2017. The treatments included four levels of water stress: 100%, 85%, 70%, and 55% of field capacity (FC) in the main plots and four levels of salinity stress: 1.5, 4.5, 7.5 and 10.5 dS m-1 in the sub plots, which were arranged in split plots based on randomized complete block design, with three replications. The results showed that water and salinity stresses in both regions were associated with decreased dry matter production and concentrations of chlorophylls a and b and carotenoids, while the concentration of free proline and the activity of antioxidant enzymes catalase, peroxidase and superoxide dismutase were increased depending on the stress level. Ascorbic peroxidase activity was increased only under water stress. The highest dry matter yields were obtained from 100% FC irrigation with 4.5 dS m-1 salinity and were 1.292 and 1.198 kg ha-1 in Marvdasht and Arsanjan, respectively. Non-significant effect in 85% FC irrigation regime showed that only 70% and 55% FC irrigation regimes led to water stress in sorghum. On the other hand, no significant difference was observed between non-saline conditions and 4.5 dS m-1, which indicates salinity tolerance of sorghum, at least up to this level. In both regions, the intensity of changes due to water and salinity stress was correlated with the intensity of that stress. The results of this research showed that due to antagonistic effects, drought and salinity stresses have a greater effect on reducing plant yield; therefore, water deficit irrigation strategies are not recommended in case of using water with salinities of 7.5 dS m-1 and more for sorghum irrigation.