Quantification of Pretreatment Effects of Potassium Silicate on Germination and Growth Indices of Faba Bean (Vicia faba L.) under Salinity Stress Using Empirical Models

IntroductionSalinity stress is one of the limiting factors for plant growth and production in arid and semi-arid regions of the world. The use of potassium silicate as the second most common element in soil is one of the strategies used to reduce the effects of environmental stresses such as salinity. Considering the increasing challenge of water and soil salinity and its limiting effects on the growth, development, and production of faba bean, the aim of this study was to investigate the effects of potassium silicate on improving germination and growth indices, and to determine the tolerance threshold of faba bean seeds to salinity stress. Materials and MethodsA factorial experiment was conducted based on completely randomized design with four replications at the Laboratory of Ilam University, Iran, in 2024. The experimental factors were included potassium silicate at four levels (0, 50, 100, and 150 mg.l-1) and five levels of salinity stress (0, 1, 4, 8, and 10 dS.m-1). The germination criterion was the protrugen of a radicle length up to 2 mm. At the end of the experiment, germination indices (germination percentage, germination rate, seed vigor index) and seedling growth (root and seedling dry weight and length) were measured. Results and Discussion The application of potassium silicate under non-salinity stress conditions (salinity of 0 and 1 dS.m-1) had no significant effect on the germination percentage of faba bean seeds; however, the germination percentage increased by 20.7, 23.8, and 26.7 percent with the application of 150 mg.l-1 of potassium silicate under salinity stress conditions of 4, 8, and 10 dS.m-1, respectively. The germination rate of faba bean seeds under non-salt stress conditions was not affected by pretreatment with potassium silicate. The germination rate of faba bean seeds with application of 150 mg.l-1 of potassium silicate under salinity stress conditions of 8 and 10 dS.m-1 was 23.9 and 26.7 percent higher than without its application, respectively. Under non-salinity stress conditions, application of 100 mg l-1 potassium silicate increased the vigor index of faba bean seeds by 25.4% compared to the control. Under salinity stress conditions of 8 dS.m-1, application of 50 and 150 mg l-1 potassium silicate improved the vigor index of faba bean seeds by 73.7% and 79.0%, respectively. Salinity stress at levels of 1, 4, 8, and 10 dS.m-1 reduced the length of faba bean rootlets by 21.8, 39.7, 44.2, and 60.0%, respectively, compared to the absence of salinity stress. The highest shoot dry weight (0.414 g.plant-1) was observed with the application of 100 mg.l-1 potassium silicate under non-salt stress conditions, which was 8.5% higher compared to the control. Under 10 dS.m-1 salt stress conditions, the application of 100 and 150 mg.l-1 potassium silicate improved the shoot dry weight of faba bean by 86.5 and 66.5% compared to the control. The highest root dry weight (0.419 g.plant-1) was observed with the application of 100 mg.l-1 potassium silicate under no salt stress conditions, which was 11.5% higher compared to control. Under 10 dS.m-1 salt stress conditions, the application of 100 and 150 mg l-1 potassium silicate improved the dry weight of faba bean root by 60.1 and 65.6% compared to the control. According to the Moss and Hoffman’s equation, the tolerance threshold to salinity stress in faba bean based on relative germination without the application of potassium silicate was 0.52 and its decreasing slope was 5.48. The threshold of tolerance to salinity stress in faba bean with the application of 50, 100, and 150 mg.l-1 of potassium silicate was 0.62, 0.22, and 1.32 and its decreasing slope was 5.5, 93.4, and 22.4, respectively. Based on the three-parameter sigmoid model, the salinity stress that reduced bean seed germination by 50% by applying different amounts of 0, 50, 100, and 150 mg.l-1 of potassium silicate was 8.75, 9.41, 9.38, and 10.10 dS.m-1, respectively. ConclusionsIt can be concluded that the faba bean plant is sensitive to salinitySeed priming with potassium silicate at concentrations of 100 and 150 mg.l⁻¹ effectively mitigates salt stress in faba bean and significantly enhances the plant's tolerance to salinity.