بهبود رشد و جذب عناصر غذایی ذرت با محلول‌پاشی باکتری‌های محرک رشد فیلوسفر در شرایط مزرعه

Background and Objectives: The phyllosphere microbiome represents an extraordinary ecological niche that harbors diverse microbial communities with immense potential for agricultural applications. As a unique aerial habitat, the phyllosphere supports bacterial populations that have evolved sophisticated mechanisms for plant growth promotion and stress mitigation. While rhizosphere bacteria have been extensively exploited in agricultural practices, the systematic utilization of phyllosphere-derived plant growth-promoting bacteria (PGPB) as foliar bioinoculants remains comparatively under-investigated, particularly under real-field conditions. This knowledge gap assumes critical importance given the increasing global demands for sustainable agricultural intensification and food security. The current investigation was designed to address this research vacuum through a comprehensive evaluation of three meticulously selected phyllosphere-originating bacterial strains Enterobacter hormaechei (AC. MN099393), Stenotrophomonas maltophilia (AC. MN099392), and Microbacterium arborescens (AC. MN099379) for their efficacy in enhancing maize (Zea mays L.) productivity, nutrient acquisition efficiency, and overall nutritional quality through foliar application. The study specifically aimed to elucidate the effects of these bacterial inoculants on shoot dry and fresh weight, nutrient uptake, while establishing correlations between observed phenotypic improvements and the documented plant growth-promoting attributes of the selected bacterial strains.




Materials and Methods: A rigorously designed field experiment was implemented during the 2020-2021 growing season at the Soil and Water Research Institute in Karaj, Iran, utilizing a randomized complete block design with three replications to ensure statistical robustness. The experimental matrix comprised four distinct treatments: (1) Absolute control (non-inoculated); (2) E. hormaechei inoculation; (3) S. maltophilia inoculation; and (4) M. arborescens inoculation. Soil characteristics were thoroughly analyzed before experiment establishment, revealing a loam texture with specific chemical properties. For the cultivation of maize, the seed variety 704 was used. The area of ​​each plot was 30 m², comprising 4 ridges with a distance of 75 centimeters and a length of 10 m. Bacterial suspensions were prepared to achieve optimal concentration (10⁹ CFU mL⁻¹) and applied at the critical V3 phenological stage (4-6 leaf stage) during evening hours to maximize phyllosphere colonization efficiency and minimize UV-induced bacterial mortality. The application method involved careful dilution protocols and uniform spraying using sterilized equipment to ensure consistent coverage. Comprehensive assessments included detailed analysis of shoot dry and fresh weight and precise quantification of macronutrient (N, P, K) and micronutrient (Fe, Zn, Cu, Mn) concentrations through standard protocols. Statistical analyses of the data were performed using the SAS software. Mean comparisons were conducted using Fisher's Least Significant Difference (LSD) test at the 5% probability level.
Results: The foliar application of phyllosphere bacteria significantly influenced maize growth parameters. Shoot dry weight was markedly increased by both bacterial treatments (S. maltophilia and E. hormaechei ) compared to the non-inoculated control (14289 kg ha⁻¹). Application of S. maltophilia resulted in a shoot dry weight of 15859 kg ha⁻¹, representing a significant increase of 11.0%. Similarly, E. hormaechei treatment yielded a dry weight of 15813 kg ha⁻¹, an increase of 10.7%. Nutritional analysis revealed significant biofortification effects, particularly for E. hormaechei. This treatment increased nitrogen concentration by 26.66% (1.33% versus control 1.05%), iron content by 37.3% (53.4 mg kg⁻¹ versus 38.9 mg kg⁻¹), and manganese concentration by 39% (35.3 mg kg⁻¹ versus 25.4 mg kg⁻¹). The S. maltophilia treatment also significantly enhanced nitrogen and iron concentrations by 19.02% and 33.16%, respectively. Phosphorus, potassium, zinc, and copper levels showed non-significant responses across treatments. M. arborescens application showed limited efficacy across most measured parameters, potentially attributable to suboptimal environmental adaptation mechanisms or reduced phyllosphere colonization capacity.




Conclusion: This research provides compelling evidence that targeted foliar application of specific phyllosphere-derived PGPB strains, particularly E. hormaechei and S. maltophilia, constitutes an innovative and highly effective strategy for enhancing maize productivity and nutritional quality under field conditions. The demonstrated improvements are mechanistically linked to the bacteria's multifunctional plant growth-promoting attributes, including enhanced nitrogen fixation capacity, sophisticated phytohormone modulation, and efficient siderophore-mediated iron sequestration. The significant enhancement of nutrient concentrations represents a major advancement toward sustainable nutrient management practices. These findings establish a robust scientific foundation for developing next-generation foliar bioinoculant technologies that can significantly reduce dependence on chemical fertilizers while simultaneously addressing global food security and nutritional challenges. The study opens new avenues for sustainable agricultural innovation through strategic manipulation of phyllosphere microbiomes and provides crucial insights for optimizing application protocols, strain selection criteria, and integration with existing agricultural practices. Future research should focus on elucidating molecular mechanisms underlying plant-bacteria interactions in the phyllosphere and developing commercial formulations for large-scale agricultural implementation.