نوع مقاله : مقالات پژوهشی
نویسندگان
1 گروه علوم و مهندسی خاک، دانشگاه رازی، کرمانشاه، ایران
2 استادیار گروه گیاه پزشکی، پردیس کشاورزی و منابع طبیعی، دانشگاه رازی کرمانشاه
3 گروه مهندسی تولید و ژنتیک گیاهی، دانشگاه رازی، کرمانشاه، ایران
کلیدواژهها
عنوان مقاله English
نویسندگان English
Introduction
Background and objectives: Drought stress is one of the most significant abiotic stressors, recognized as a major constraint on agricultural plant growth and productivity worldwide. It adversely affects soil physicochemical properties and plant physiological processes, altering soil microbial dynamics. Drought stress reduces crop yields and degrades soil health in arid and semi-arid regions, where water scarcity is a critical challenge. Plant growth-promoting rhizobacteria (PGPR) have emerged as a sustainable and eco-friendly strategy to enhance plant resilience against abiotic stresses, including drought. These beneficial microorganisms improve nutrient uptake, stimulate phytohormone production, and enhance stress tolerance mechanisms in plants, thereby mitigating the negative impacts of water deficit. Considering that most of the regions of Iran are located in arid and semi-arid climates and taking into account the advantages of plant growth-promoting rhizobacteria in reducing stress compared to other physical and chemical methods, this research investigated the effect of plant growth-promoting rhizobacteria on reducing drought stress in the tomato plant and biological characteristics of the soil.
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Materials and Methods
A greenhouse experiment was conducted in a randomized complete block design (RCBD) with four replications. Experimental treatments included four levels of drought stress (40, 60, 80, and 100% of FC) and five bacterial strains: B19 (Lysinibacillus sphaericus), B60 (Bacillus sp.), B103 (Lysibacillus sp.), B124 (Achromobacter sp.), and GB03 (Bacillus subtilis). A control treatment (without bacteria and drought stress) was also considered. To apply the treatments, 4 kg pots were prepared using soil passed through a 4 mm sieve. Nutrient Broth (NB) medium was used for cultivation to enhance the bacterial population. The bacteria were grown under controlled conditions at 30°C with continuous shaking at 120 rpm for 36 hours to ensure optimal growth. After incubation, a bacterial suspension with a concentration of 109 CFU/mL was prepared in sterile distilled water. Tomato seedlings' roots were then immersed in this suspension for 20 minutes to ensure proper colonization before being transplanted into the potted soil. A control treatment (non-inoculated seedlings) was also included in the experiment for comparative analysis. To ensure the establishment of the plants, all the pots were irrigated for 3 to 4 weeks. The desired drought stress was applied during the cultivation period by measuring soil moisture using the gravimetric method. In this method, the weight of the pots was measured every day, and irrigation was performed immediately after the soil moisture decreased. This method of applying treatments continued daily for three months. The greenhouse temperature was 25°C and the lighting period was 12 hours. The characteristics of the number of flowers, fresh weight of the aerial part and roots, stomatal resistance, fresh weight of the fruit, and the amount of the free proline content of the leaves were measured. In addition, soil biological characteristics, including organic carbon mineralization, microbial biomass carbon, substrate-induced respiration (SIR), and metabolic quotient (qCO2) after plant harvesting, were determined in the soil. Before performing the analysis of variance (ANOVA), the normality of the data was tested. In this study, Duncan's 5% probability level test was used for mean comparisons, Excel software was used for graphing, and SAS 9.4 was employed for data analysis.
Results
The results of this study showed that all five bacterial strains used caused significant increases in the fresh weight of the shoot, the number of flowers, and the fruit weight. The amount of free proline in the leaves increased significantly compared to the control treatment (no inoculation). The results showed that the value of stomatal resistance had a significant decrease compared to the control treatment (no inoculation). Also, the used strains improved the quality of soil biological characteristics, so that basal respiration, substrate-induced respiration (SIR), and microbial biomass carbon had a significant increase, but the metabolic quotient (qCO2) showed a significant decrease compared to the control treatment (no inoculation). Among the five strains used, three strains, B19, B60, and B103 showed the greatest effect in reducing the effects of drought stress.
Conclusion
Various stressful conditions, including the moisture stress prevailing in Iran's agriculture, cause a decrease in the growth and yield of agricultural products; therefore, the use of inoculants containing microorganisms, including plant growth-promoting rhizobacteria, whose activity has been proven to improve stress conditions, is essential.
کلیدواژهها English
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