Study the Effects of Salicylic Acid and γ-Aminobutyric Acid on Some Physiological Characteristics of Seedling and Yield of Lycopersicum esculentum cv. Seyran

Introduction Recently, the market demand for high quality tomato fruit is increasing. This product is one of the most important vegetables produced all over the world, and in the last few decades, there has always been a growing trend for its production and consumption. Today, seedling production is considered as a specialized and profitable industry all over the world, which also has a good development speed in our country. The production of healthy and strong seedlings is a prerequisite for proper plant growth and economic production, and nutrition plays an important role in this. Today, the use of natural and organic compounds in various sectors of production and agriculture is increasing. One of these organic compounds, is γ-aminobutyric acid. Biofertilizers are used in order to reduce the consumption of chemical fertilizers and thus reduce the negative environmental effects and increase the yield of plants in agricultural systems. Salicylic acid is a natural phenolic compound and one of the endogenous plant regulators that exists in most plants and is an important component in the signaling pathway. Salicylic acid is effective in regulating the process of plant growth and development, germination, flowering, opening and closing of stomata, respiration, absorption and transfer of ions, photosynthesis, maintaining membrane integrity and plant growth rate. The objective of this study was to examine the influence of varying concentrations of γ-aminobutyric acid and salicylic acid compounds on the physiological attributes, photosynthetic components, and quality traits of Lycopersicum esculentum cv. Seyran seedlings. The aim was to identify the most effective concentration of these hormonal and pseudo-hormonal compounds under the specific conditions of this research.   Materials and Methods  This experiment was conducted in 2017 in the research greenhouse of Shahid Bahonar University of Kerman as a factorial in a completely randomized design with three replications. Lycopersicum esculentum cv. Seyran seeds were planted and after the seedlings reached the stage of three to four leaves and were well established, the first foliar spraying was done with complete NPK fertilizer containing other micronutrients. After 75 % of the seedlings reached the five leaf stage, foliar spraying of the treatments with γ-aminobutyric acid with concentrations of 0, 5 and 10 mg/l and half an hour later with salicylic acid with concentrations of 0, 0.5 and 1.5 mM was performed. After 15 days, the second foliar spraying steps of the treatments were repeated. Traits studied include; seedling stem diameter, ion leakage, relative water content, total chlorophyll, yield, stomatal conductance, net photosynthesis rate, catalase, peroxidase, proline and malondialdehyde.   Results and Discussion Based on the results of analysis of variance, the simple effect of GABA and the simple effect of salicylic acid on seedling diameter, ion leakage and total chlorophyll were significant at the level of one percent and their interaction was significant at the level of five percent. In the of relative water content and yield, the simple effects of GABA and salicylic acid, as well as the interaction of the two, were significant at the 1% level (Table 1). Results showed that the largest plant diameter and relative water content in GABA 10 mg/l and with the combined use of 1.5 mM salicylic acid and the lowest plant diameter and relative water content in the condition of not using GABA and using salicylic acid in the amount 0.5 mM was obtained. Also, the highest amount of ion leakage occurred in the control plants and the lowest amount of ion leakage is related to the treatment of 10 mg/l GABA combined with 1.5 mM salicylic acid. Investigations showed that a increase in performance compared to the control occurs when using the combination of GABA 10 mg/l along with 0.5 and 1.5 mM salicylic acid (Table 3). According to the analysis of variance results, both the individual effects of γ-aminobutyric acid (GABA) and salicylic acid on leaf stomatal conductance and net photosynthesis rate were found to be significant at the one percent level, with their interaction being significant at the five percent level. Furthermore, the analysis revealed that the individual and combined effects of GABA and salicylic acid on catalase enzyme activity were significant at the five percent level. Additionally, the individual effect of GABA at the one percent level, the individual effect of salicylic acid, and their combined effect on malondialdehyde levels were all significant at the five percent level (refer to Table 2). According to the average comparison results, the highest level of leaf stomatal conductance was observed in the concentration of 1.5 mM salicylic acid in all three application levels of GABA, and the interaction treatment of 10 mg/l GABA with 1.5 mM salicylic acid had the highest net photosynthesis rate and activity of catalase and peroxidase enzymes. The highest amount of proline accumulation occurred in the treatment combination of GABA 10 mg/l along with each of the three concentrations of salicylic acid. The highest accumulation of malondialdehyde was observed in the control sample (without the use of γ-aminobutyric acid and salicylic acid) and the lowest amount of this characteristic was obtained in the combined treatment of GABA 10 mg/l with 0.5 mM salicylic acid (Table 4).   Conclusion In summary, the utilization of γ-aminobutyric acid as a biological compound and salicylic acid as a growth regulator exhibited a beneficial impact on most of the studied traits in Lycopersicum esculentum cv. Seyran seedlings. This included enhancements in seedling diameter, relative water content, total chlorophyll levels, yield, catalase and peroxidase enzyme activity, proline content, as well as reductions in ion leakage and malondialdehyde levels. It appears that the highest applied concentration of GABA (10 mg/l) and the highest concentration of salicylic acid (1.5 mM) yielded the most favorable results, effectively improving seedling production while preserving its quality.