Salinity is one of the most adverse abiotic environmental stresses that limit the production of agricultural crops in many arid and semi-arid regions of the world. Strawberry (Fragaria × ananassa Duch) is one of the most important small fruits of temperate regions that is very sensitive to salt stress and its yield is reduced by low-quality irrigation water. In recent years, melatonin has received much attention as a phytohormone with important effects on growth and stress tolerance in plants. Therefore, this experiment was conducted in greenhouse conditions to eva‎luate the effect of melatonin on the vegetative and physiological traits of strawberries under salt stress. Treatments in this experiment included four levels of sodium chloride (0, 15, 30, and 45 mM) and various concentrations of melatonin (0, 50, 100, and 200 μM). The experimental design was 4⨯4 factorial in a completely randomized design with four replications and two plants in each replication. The results showed that the injury index of the strawberry plant increased significantly as the salinity level was raised. In melatonin-treated plants, the injury index was decreased significantly compared to controls. Also, salt stress reduced vegetative growth parameters (fresh and dry weight of shoots and roots) in strawberries. The application of melatonin at a concentration of 50 μM caused a significant increase in fresh and dry weight of shoots compared to the control treatment, while no significant effect on the fresh and dry weight of roots was observed. Proline, malondialdehyde (MDA), and soluble carbohydrate content were increased when salt concentration was enhanced. Application of melatonin increased proline (at 50 μM) and soluble carbohydrate (at 100 and 200 μM); however, the MDA (at 50 and 100 μM) level decreased significantly. When salt concentration increased, the chlorophyll fluorescence index and relative leaf water content decreased; while ion leakage increased significantly. The application of 100 μM melatonin significantly increased leaf chlorophyll fluorescence index. Also, all applied concentrations of melatonin significantly improved ion leakage. The activity of antioxidant enzymes was increased significantly by salt stress. In addition, the use of melatonin increased the activity of antioxidant enzymes such as superoxide dismutase, catalase, and guaiacol peroxidase. The highest increase in the activity of these enzymes was related to the melatonin at the concentration of 50 μM. Salinity stress also caused a significant increase in the ratio of sodium ion to potassium ion both in the root and shoot of strawberries. The application of melatonin significantly reduced the ratio of sodium ion to potassium ion in shoots (at all concentrations) and roots (at 100 and 200 μM). Due to the positive effect of melatonin on some vegetative and physiological characteristics of strawberries, the use of this plant hormone can be beneficial in salinity stress conditions. However, further studies are recommended to find the optimal melatonin concentration and underlying mechanisms of actions

بهرام باني نسب

مهديه غلامي

نعمت اله اعتمادي، محمد حسين اهتمام