Document Type : Research Article
Authors
Department of Genetics and Plant Breeding, University of Mohaghegh Ardabili, Ardabil. Iran
10.22067/jcesc.2026.96731.1435
Abstract
Introduction
Wheat (Triticum aestivum L.) is a strategic global cereal, providing over 20% of human calorie intake. However, climate change, increased drought frequency, and declining irrigation water resources seriously threaten sustainable wheat production. In many agricultural regions, including Iran, drought stress is a primary factor limiting wheat yield. Therefore, finding biological strategies to enhance wheat's tolerance to water stress is a research priority in sustainable agriculture. Utilizing low-cost and environmentally friendly approaches to increase plant resilience to environmental stresses is essential. Among these, employing beneficial rhizosymbionts like Arbuscular Mycorrhizal Fungi (AMF) and Plant Growth-Promoting Rhizobacteria (PGPR), such as Pseudomonas and Azospirillum, has garnered significant research interest. AMF form extensive hyphal networks in the soil, dramatically increasing the root absorption surface area and improving plant access to water and less mobile nutrients like phosphorus. PGPR enhance plant growth and abiotic stress tolerance through various mechanisms, including producing plant growth hormones (e.g., auxins), synthesizing siderophores, fixing nitrogen, and inducing systemic resistance. While many studies have focused on the individual effects of AMF or PGPR, research on their combined impact on wheat growth and performance under limited irrigation conditions is scarce. This study aimed to evaluate the individual and combined effects of mycorrhizal fungi and plant growth-promoting bacteria on photosynthetic pigments, antioxidant enzymes, biochemical resistance traits, and ultimately, the yield of wheat under different irrigation regimes.
Materials and Methods
This research was conducted during the 2021-2022 growing season at a research farm in the Arshaq region, Meshgin Shahr County, Ardabil Province, Iran. The experiment was arranged as a factorial based on a Randomized Complete Block Design with three replications. The first factor was biofertilizer type at four levels: control, mycorrhizal fungi (Rhizophagus intraradices), PGPR (Pseudomonas fluorescens and Azospirillum brasilense), and a combination of both mycorrhizal fungi and PGPR. The second factor was irrigation regime at three levels: no irrigation (rainfed), irrigation at 50% of plant water requirement, and full irrigation (100% water requirement). Measured traits included root colonization percentage, chlorophyll a, b, and carotenoid content, activities of the antioxidant enzymes catalase (CAT), peroxidase (POX), and superoxide dismutase (SOD), number of grains per spike, thousand-kernel weight, and grain yield. Root colonization was assessed using staining and microscopic examination. Photosynthetic pigments were extracted with acetone and measured spectrophotometrically. Enzyme activities were determined using specific spectrophotometric assays: CAT activity by monitoring H₂O₂ decomposition at 240 nm, POX activity by monitoring guaiacol oxidation at 470 nm, and SOD activity by measuring the inhibition of nitroblue tetrazolium reduction at 560 nm.
Results and Discussion
The analysis of variance indicated that the main effects of biofertilizers and irrigation regimes, as well as their interaction, were significant for all measured traits. The highest root colonization (79.6%) was observed in the full irrigation × combined biofertilizer treatment. Drought stress reduces carbohydrate allocation to roots, limiting the carbon source for fungi and hindering colonization. Biofertilizers, especially the combination, provided direct inoculation and improved the root environment, facilitating higher colonization. The maximum chlorophyll a (2.55 mg/g), chlorophyll b (0.85 mg/g), and carotenoid (0.204 mg/g) contents were recorded in the full irrigation × combined biofertilizer treatment. The minimum values were under severe drought without biofertilizers. Drought degrades chloroplasts and activates chlorophyll-degrading enzymes. Biofertilizers, by improving water and nutrient (especially phosphorus) uptake, helped maintain pigment synthesis and protect the photosynthetic apparatus from oxidative damage. The highest activities of CAT (32.5 U/mg), POX (4.88 U/mg), and SOD (28.8 U/mg) were found in the no irrigation × no biofertilizer treatment. Conversely, the lowest enzyme activities were consistently observed in the full irrigation × combined biofertilizer treatment. Elevated antioxidant enzyme activity under drought stress without biofertilizers is a physiological response to high oxidative stress caused by increased Reactive Oxygen Species (ROS) production. The application of biofertilizers, particularly the combination, mitigated water and nutrient deficits, thereby reducing ROS generation and the need for high antioxidant enzyme activity, indicating better physiological equilibrium. Increased significantly from 2501.7 kg/ha under severe drought without biofertilizers to 4891.6 kg/ha under full irrigation with combined biofertilizers. This demonstrates that the synergistic effect of AMF and PGPR in improving water relations, nutrient status, and oxidative stress management translated into superior yield performance.
Conclusion
The findings of this study demonstrate that the combined application of mycorrhizal fungi and plant growth-promoting bacteria is an effective strategy for mitigating the adverse effects of drought stress and enhancing wheat yield. This biological combination acted synergistically to significantly increase root colonization, preserve the photosynthetic system by maintaining higher chlorophyll and carotenoid levels, and reduce oxidative stress by modulating antioxidant enzyme activities. These improvements ultimately led to a significant increase in yield components. Therefore, employing these bio-inputs can serve as a sustainable and eco-friendly approach, paving the way for reduced chemical fertilizer use, increased plant resilience to water scarcity, and enhanced food security.
Keywords
Subjects
