The Effect of Foliar Applications of Fe and Salicylic Acid on Sesame (Sesamum indicum L.). under Water Deficit Conditions

IntroductionSesame, with the scientific name Sesamum indicum L., is a member of the Pedaliaceae family. It is one of the oldest and most popular oilseeds known in the world and has the highest oil and seed protein content among oilseed plants. This plant is typically cultivated as a drought-resistant plant in arid and semi-arid regions, however, there have been reports of a significant effect of deficit irrigation on sesame yield and a decrease in the number of capsules per plant, number of seeds per plant, thousand-seed weight, grain yield, and biological yield under drought stress compared to full irrigation. Plants are constantly exposed to various stresses, and drought stress is the most important factor limiting crop yield in many parts of the world. Given that most of Iran's oil needs are imported and the limited water resources, the development of water-resistant oilseed crops is essential. The application of micronutrients through foliar application can improve plant growth under stress conditions. Among the micronutrients, Fe is particularly important for many metabolic activities in plants; therefore, plants require sufficient amounts of this element to continue their growth. Fe deficiency causes a significant reduction in the yield and quality of the crop. Salicylic acid is a plant regulator that is effective in increasing plant tolerance to stresses such as drought and plays a fundamental role in regulating plant physiological processes. Increased germination, induction of flowering, improved growth and development, increased yield and fruit yield, inhibition of ethylene synthesis, and effects on plant activities including stomatal opening and closing, water relations, membrane stability, nutrient absorption, and activation of disease resistance factors are some of the cases attributed to the use of salicylic acid. Given Iran's arid and semi-arid climate, and the importance of sesame as a valuable crop in tropical and subtropical regions with wide applications in the food and cosmetic industries, this study aimed to investigate the effects of foliar application of iron (Fe) and salicylic acid on the growth and yield of sesame under deficit irrigation conditions. Despite the significance of ecological approaches, limited research has addressed drought stress mitigation in sesame cultivation using such inputs.Materials and MethodsIn order to investigate the response of sesame to drought stress, and especially the effect of foliar spraying with iron and salicylic acid, an experiment was conducted as a factorial split-plot based on a randomized complete block design with three replications at the research farm of the Faculty of Agriculture, Gonabad University in 2020-2021. Three different irrigation levels (full irrigation, cut-off irrigation at the podding stage, and cut-off irrigation at the flowering stage) were applied to the main plots and a factorial combination of foliar spraying and non-foliar spraying of salicylic acid and Fe (iron) was applied to the subplots. At the end of the growing season, with the beginning of the seed ripening stage and the drying of the plant's aerial parts, plants of 0.1 m-2 from each experimental plot were randomly selected and traits such as plant height, shoot dry weight, number of pods per plant, number of seeds per pod, number of seeds per plant, seed weight per plant, and 1,000-seed weight were measured. To determine the seed yield, biological yield, and harvest index, after removing the marginal effect, plants from the entire experimental plot were harvested and their total and seed weights were determined. Data analysis of variance (ANOVA) and graphing were performed using Ver. SAS 9.4 and MS Excel Ver. 11 and comparison of treatment means was performed using Duncan's multiple range test at a probability level of 5%.Results and DiscussionThe maximum plant height was observed under the combined application of salicylic acid and Fe with full irrigation (82.6 cm), while the minimum plant height was recorded in the treatment without salicylic acid and Fe application under cut-off irrigation at the flowering stage (42.6 cm). The highest number of seeds per capsule was obtained in the treatment with combined foliar application of salicylic acid and Fe under cut-off irrigation at the podding stage (56.6), whereas the lowest value for this trait was observed in the absence of salicylic acid and Fe application under cut-off irrigation at the flowering stage (22.7 seeds per capsule). Cut-off irrigation at the podding and flowering stages led to a reduction in seed yield by 39% and 55%, respectively, compared to full irrigation. Foliar application of iron increased seed yield by 18% compared to the non-application of Fe. The treatment involving cut-off irrigation at the podding stage, combined foliar application of salicylic acid and Fe, and separate foliar application of salicylic acid and Fe increased the harvest index by 16%, 7%, and 6%, respectively, compared to the non-application of foliar treatments.ConclusionIn general, it appears that foliar application of 1 mM salicylic acid and 5 in 1000 Fe mitigated the adverse effects of cut-off irrigation at podding and flowering stages in sesame.