Effects of Some Stress Modulators (Methanol, Nano silicon, and Humic acid) on Yield, Activity of Some Antioxidant Enzymes and Biochemical Traits of Wheat in Different Irrigation Regimes

IntroductionDrought stress is one of the most common limiting factors for crop production. Due to its detrimental effects on numerous physiological and biochemical processes, this stress restricts the growth and development of plants. In this regard, the application of stress modulators (methanol, silicon and humic acid) has been found to enhance plant growth and grain yield while also increasing its resistance to abiotic stresses. On the other hand, stress modulators can lessen the effects of stress toxic by reducing malondialdehyde and hydrogen ‎peroxide accumulation and keeping the effectiveness of the photosynthetic apparatus‎. Therefore, measurement of traits of such as antioxidant enzymes activity, chlorophyll content, proline and soluble sugars content, malondialdehyde content, electrical conductivity are as indicators of plant response to environmental stress. Although, several strategies have been developed to decrease the effects caused by drought stress on plant growth. But, among them, the application of stress modulators (methanol, nano silicon, and humic acid) plays a very important role in yield improvement. The aim of this study was to evaluate the effects of foliar application of stress modulators (methanol, nano silicon and humic acid) on the activity of antioxidant enzymes, compatible osmolytes, photosynthetic pigments content and grain yield of wheat in different irrigation regimes.Materials and Methodsan experiment as factorial was conducted based on randomized complete block design with three replications in Agricultural and Natural Resources Research Station of Ardabil, Ardabil, Iran, in 2022-2023 growth season. The treatments were different irrigation regimes (normal irrigation as control; irrigation withholding at 50% of booting and heading stages) and foliar spraying of stress modulators (foliar spraying with water, foliar spraying of methanol (25% volume), nano silicon (50 mg.L-1), humic acid (300 mg.L-1), foliar spraying of methanol and silicon, methanol and humic acid, nano silicon and humic, methanol with nano silicon and humic acid). In each plot, there were six rows with two m long. In this experiment, the wheat cultivar ‘Hiran’ was employed. For this cultivar, 400 seeds.m-2 is the optimum density. The used nano silicon had an average particle size of less than 30 nm and the special surface of particles was more than 30 m2.g-1. They were product of Nanomaterial US Research which was provided by Pishgaman Nanomaterials Company of Iran. For a better solution, deionized water was mixed with nano Si powder and placed on a shaker with ultrasonic equipment (100 W and 40 kHz). Two phases of period growth, BBCH 21 and 30 were used for the foliar application of nano silicon.  In this study, the activity of antioxidant enzymes (Catalase, peroxidase, and Polyphenol oxidase), compatible osmolytes (Proline and soluble sugars), photosynthetic pigments content (Chlorophyll a, Chlorophyll b, total chlorophyll, and carotenoid), H2O2, MDA, protein content and grain yield of wheat were investigated.Results and DiscussionThe result indicated that both application stress modulators (methanol, silicon and humic acid) at irrigation withholding in booting stage decreased malondialdehyde content (39.79%) and electrical conductivity (31.25%), but increased activity of peroxidase (4.89%), polyphenol oxidase (7.73%) enzymes, soluble sugars (22.15%), chlorophyll a (33.48%), chlorophyll b (24.96%), leaf protein content (25.09%) and grain yield (36.21%) in compared to the no application of stress modulators under irrigation withholding in booting stage.ConclusionAccording to our findings, applying stress modulators (methanol, silicon and humic acid) under water limitation often reduced this damage by strengthening the defensive mechanisms, particularly antioxidant enzymes and compatible osmolytes (Proline and soluble sugars). In summary, our results indicated that application of stress modulators upgrade plant physiology and trigger the cellular defense of wheat plants against severe water limitation. Therefore, in can be suggested that applying stress modulators as individual and integrated could enhance grain yield of wheat under water limitation conditions due to improving of physiological and biochemical characteristics.