Enhancing nutrient content in Maize: comparative effects of plant growth-promoting rhizobacteria across various Maize hybrids

Enhancing nutrient content in Maize: comparative effects of plant growth-promoting rhizobacteria across various Maize hybrids | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Enhancing nutrient content in Maize: comparative effects of plant growth-promoting rhizobacteria across various Maize hybrids Ahmad Asgharzadeh, Aidin Hamidi, Mohammad Akbari This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8211736/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The growing need for sustainable agricultural practices has driven interest in the use of Plant Growth-Promoting Rhizobacteria (PGPR) as a natural means to enhance crop productivity and nutrient content. Maize ( Zea mays ), a staple food crop worldwide, can greatly benefit from such biological interventions. This study explores the role of three PGPR species Azotobacter chroococcum (AZ), Azospirillum lipoferum (AS), and Pseudomonas fluorescens (PS) in boosting the mineral nutrient content of maize seeds, focusing on three different hybrids: SC704, SC700, and B73×K18. The experiment was conducted using a completely randomized design (CRD) to ensure robust and unbiased results. Maize seeds were inoculated with each PGPR strain individually, as well as in combination, and compared with a non-inoculated control group. The mineral content, including Nitrogen (N), Phosphorus (P), Potassium (K), Iron (Fe), Zinc (Zn), Magnesium (Mg), and Copper (Cu), was quantitatively analyzed. Statistical analysis was performed to assess the significance of the results. The results showed that the PGPR inoculation led to a significant increase in nutrient content across all maize hybrids compared to the control. The SC704 hybrid showed the highest improvement, with increases of X% in Iron, X% in Potassium, and X% in Nitrogen compared to the control. The combined application of AZ, AS, and PS yielded even greater enhancements, with a X% increase in Iron content in SC704, outperforming individual treatments. The study demonstrates that PGPR can effectively enhance the nutrient content of maize, with a notable dependency on the maize hybrid and the specific bacterial strain used. The SC704 hybrid, in particular, showed the most significant response. Corn PGPR macronutrients micronutrients SC704 sustainable agricultural Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Sustainable agricultural production fundamentally relies on the careful management of both genetic and environmental factors, including the formation of symbiotic relationships between plants and beneficial microorganisms [1]. Among these microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are particularly significant due to their ability to colonize the plant rhizosphere and establish mutually beneficial associations with a wide variety of plants, thereby enhancing growth and development. These bacteria are extensively utilized as biofertilizers, contributing to sustainable agriculture by minimizing the need for chemical inputs [2]. PGPR play a vital role in supporting plant growth under both stress and non-stress conditions, employing a range of direct and indirect mechanisms. Numerous studies have demonstrated that these bacteria can promote plant growth through diverse pathways, including nitrogen fixation [3], the production of volatile organic compounds that enhance plant defense and stress tolerance [4], and the synthesis of 1-Aminocyclopropane-1-carboxylate (ACC) deaminase, which reduces ethylene levels and mitigates stress-induced growth inhibition [5]. Furthermore, PGPR induce systemic resistance against pathogens [6], produce phytohormones such as auxins and gibberellins that regulate plant development, and secrete siderophores that enhance iron uptake [7, 8]. They are also known to solubilize phosphates, making this essential nutrient more accessible to plants [4]. Beyond these well-established mechanisms, PGPR may employ numerous other molecular pathways, many of which remain to be fully elucidated, that collectively contribute to their role in promoting healthier, more resilient plant growth [44, 45]. Maize (Zea mays L.) is a key global crop due to its increasing demand as both food and feed, as well as its vital economic importance, which has become particularly evident during recent geopolitical events such as the Ukraine-Russia war [9]. Based on the report of IFA (2021), the combination of successful Covid-19 vaccine development and improved management of the economic impact of the virus has enabled stronger-than-expected global performance in 2021. However, this increased production has been accompanied by a greater reliance on chemical fertilizers and pesticides, leading to detrimental effects on soil, water, and the broader food chain [10]. Organic agriculture, which avoids the use of chemical fertilizers, growth regulators, pesticides, and feed additives, offers a sustainable alternative by promoting the production of safe and healthy food while reducing negative environmental impacts [11, 45]. Biofertilizers, especially those based on PGPR, have emerged as a key component of organic farming systems. The use of biofertilizers, combined with beneficial microorganisms, has been suggested as an effective way to enhance plant growth, improve soil productivity, and maintain environmental health [12, 45]. A PGPR-based biofertilizer offers both environmental and agronomic advantages, increasing the efficiency of fertilizer use and improving economic yields under natural conditions. However, selecting the most effective bacterial strains that are compatible with specific plant varieties is crucial, as different strains can have varying effects on target plants [13, 45]. Studies have shown significant interactions between crop cultivars and bacterial strains in terms of biological nitrogen fixation in lentils [14], soybeans [15], peas [16], and beans [17]. Among the different types of PGPR, Azospirillum spp. are well-known for their application in maize and other cereals, producing phytohormones that encourage root growth and enhance nutrient and water uptake [18]. For example, Stancheva and Dinev [19] demonstrated that the interaction between Azospirillum brasilense and the corn root system leads to increased plant biomass and total nitrogen content. Inoculation with PGPRs such as Azospirillum lipoferum has been shown to improve the ability of crops to uptake mineral nitrogen. Although there are numerous successful examples of inoculating maize, tomato, wheat, and other crops with different PGPR strains such as Azospirillum, Enterobacter, Bacillus, and Pseudomonas, plants often exhibit varying responses to these bacteria within their rhizosphere. For instance, the floral and foliar application of Pseudomonas BA-8 and Bacillus OSU-142 on sweet cherry (Prunus avium L.) significantly influenced the content of N, P, K, Fe, Zn, and Mn (20(. Despite the well-documented effects of PGPR on host plants, there is limited research on the specific effects of PGPR inoculation on the mineral nutrient content of crops. Therefore, the present study aims to investigate the effects of inoculating three different hybrid maize varieties—SC704, SC700, and B73×K18—with Azotobacter chroococcum, Azospirillum lipoferum, and Pseudomonas fluorescens on the content of essential mineral elements, including Nitrogen (N), Phosphorus (P), Potassium (K), Iron (Fe), Zinc (Zn), Manganese (Mn), and Copper (Cu). By examining the interactions between these PGPR strains and maize hybrids, this study seeks to provide new insights into optimizing PGPR applications to enhance the nutritional quality and sustainable production of maize. Materials and Methods Plant Materials and Experimental Site The experiments were conducted using three maize hybrids: SC704 (single cross 704, B73 × Mo17), SC700 (single cross 700, K74/1 × K18), and B73 × K18, which were selected based on their economic importance and genetic diversity. The seeds of these hybrids were provided by the Maize and Forage Crops Research Department of the Seed and Plant Improvement Institute (SPII), Karaj, Iran. SC704 and SC700 are widely grown hybrids in Iran, known for their high yield potential and adaptability to local environmental conditions. The B73 × K18 hybrid was included in the study as a promising candidate for future cultivation. The field experiments were conducted at the experimental farm of the Seed and Plant Improvement Institute, Karaj, Iran, during the growing season. The site is located at 35.8308° N latitude and 50.9915° E longitude, with an altitude of approximately 1313 meters above sea level. The region has a semi-arid climate with an average annual precipitation of 250 mm and an average temperature of 14.5°C. Prior to sowing, soil samples were collected from the top 30 cm layer of the experimental field and analyzed for physical and chemical properties, including pH, electrical conductivity (EC), organic matter content, and available macronutrients and micronutrients (Table 1). Experimental Design and Treatments The study was arranged in a randomized complete block design (RCBD) with four replications to minimize the impact of spatial variability within the field. Each plot measured 3 meters in length with 5 rows, spaced 75 cm apart, and a plant-to-plant distance of 20 cm within each row. The treatments consisted of inoculation with three different plant growth-promoting rhizobacteria (PGPR) strains: Azotobacter chroococcum strain 5 (AZ), Azospirillum lipoferum strain 21 (AS), and Pseudomonas fluorescens strain 169 (PS), either individually or in combination, along with a non-inoculated control. The bacterial strains were obtained from the microbial culture collection of the Soil Microbiology Department of the Soil and Water Research Institute, Iran, and were selected based on their documented effectiveness in promoting plant growth in multiple field experiments. Preparation of Bacterial Inoculants and Seed Inoculation The PGPR strains were cultured separately in their respective growth media under sterile conditions. Azotobacter chroococcum was grown in Ashby's Mannitol Agar, Azospirillum lipoferum in Nitrogen-Free Malate Medium, and Pseudomonas fluorescens in King's B medium. The bacterial cultures were incubated at 28 ± 2°C for 48 hours to reach a concentration of approximately 10 8 colony-forming units per milliliter (CFU/mL). The bacterial suspensions were then diluted to a final concentration of 10 7 CFU/mL with sterile distilled water before inoculation. Maize seeds were surface sterilized by immersing them in a 1% sodium hypochlorite solution for 5 minutes, followed by thorough rinsing with sterile distilled water. The sterilized seeds were then soaked in the respective bacterial suspensions for 30 minutes, allowing the bacteria to adhere to the seed surfaces. Seeds were categorized into eight groups: ( 1 ) seeds inoculated with Azotobacter chroococcum (AZ), ( 2 ) seeds inoculated with Azospirillum lipoferum (AS), ( 3 ) seeds inoculated with Pseudomonas fluorescens (PS), ( 4 ) seeds inoculated with a combination of Azotobacter chroococcum and Azospirillum lipoferum (AZ + AS in a 1:1 ratio), ( 5 ) seeds inoculated with a combination of Azotobacter chroococcum and Pseudomonas fluorescens (AZ + PS in a 1:1 ratio), ( 6 ) seeds inoculated with a combination of Azospirillum lipoferum and Pseudomonas fluorescens (AS + PS in a 1:1 ratio), ( 7 ) seeds inoculated with a combination of all three PGPR strains (AZ, AS, and PS in a 1:1:1 ratio), and ( 8 ) a non-inoculated control group soaked in sterile distilled water. After inoculation, the seeds were air-dried for two hours under sterile conditions. Field Management and Growth Conditions The inoculated seeds were sown in the prepared field plots, and standard agronomic practices were followed throughout the growing season to maintain optimal growth conditions. The plants were irrigated regularly to maintain adequate soil moisture levels and were kept free of weeds by manual weeding. No additional chemical fertilizers or pesticides were applied to the plots to exclusively evaluate the effects of the PGPR treatments. The field was monitored daily for any signs of pest or disease infestations, and necessary protective measures were taken as required. Nutrient Analysis At maturity, maize seeds were harvested from each plot, oven-dried at 70°C for 48 hours, and ground into a fine powder for mineral analysis. Nitrogen (N) content was determined using the micro-Kjeldahl method as described by Bremner (1965). The concentrations of zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) were measured using an Atomic Absorption Spectrophotometer (AAS) at their respective wavelengths: Zn (213.7 nm), Fe (248.7 nm), Mn (279.5 nm), and Cu (324.6 nm). Phosphorus (P) content was determined spectrophotometrically using the indophenol-blue technique following a reaction with ascorbic acid (Murphy and Riley, 1962). Potassium (K) content was analyzed using a Flame Photometer after wet digestion of the dried samples in a mixture of sulfuric acid (H₂SO₄), selenium (Se), and salicylic acid. Statistical Analysis The data obtained from the experiments were subjected to analysis of variance (ANOVA) using SAS software (version 9.1) to assess the significance of differences among treatments. Duncan's multiple range test was employed to compare the means at a significance level of p < 0.05. Data from two consecutive years of experimentation were pooled, as no significant differences were observed between the years. Graphical representations of the results were prepared using Microsoft Excel 2016. Results Effects of PGPR Inoculation on Nitrogen Content in Maize Seeds The nitrogen (N) content in maize seeds was significantly affected by the inoculation with different strains of plant growth-promoting rhizobacteria (PGPR). The data presented in Fig. 1 illustrate the impact of seven different treatments (AZ, AS, PS, AZ + AS, AZ + PS, AS + PS, and AZ + AS + PS) on the N content of three maize hybrids: SC704, SC700, and B73×K18. The inoculation with a combination of all three bacterial strains (Azotobacter chroococcum [AZ], Azospirillum lipoferum [AS], and Pseudomonas fluorescens [PS]) resulted in the highest increase in N content across all three maize hybrids. The maximum increase was observed in the SC704 hybrid (4.0%), followed by SC700 (3.8%) and B73×K18 (3.5%). This suggests that the combined inoculation of these PGPR strains had a synergistic effect on enhancing N content in maize seeds, particularly in the SC704 hybrid. Among the single-strain treatments, the PS treatment led to the highest increase in N content, with values of 2.0%, 1.8%, and 1.5% for SC704, SC700, and B73×K18, respectively. The AS treatment showed the least effect on N content, with minimal increases observed in all hybrids (0.5% for SC704, 0.3% for SC700, and 0.2% for B73×K18). The dual-strain combinations also resulted in significant increases in N content compared to the control. The AZ + PS treatment showed the second-highest increase, with N content rising to 3.5% in SC704, 3.2% in SC700, and 3.0% in B73×K18. The AZ + AS treatment produced a moderate increase in N content (3.0% for SC704, 2.7% for SC700, and 2.5% for B73×K18). The AS + PS combination demonstrated a lower but still significant effect on N content, with increases of 2.5% in SC704, 2.2% in SC700, and 2.0% in B73×K18. Statistical analysis revealed that the differences in N content between the control and all PGPR treatments were significant (p < 0.05). Furthermore, among the different maize hybrids, SC704 exhibited the most substantial increase in N content following inoculation with the PGPR strains, particularly in the combined AZ + AS + PS treatment, where the increase was significantly higher than in the other two hybrids (p < 0.05). Effects of PGPR inoculation on Phosphorus content in the seeds The amount of P content in the seeds was increased in the treated plants compared to the control. The maximum P content was observed in AS + AZ + PS and the minimum amount observed in AS + PS (Fig. 2 ). Between the three studied maize hybrids no significant difference was observed concerning the Solubilization of P; while compared to the control, the SC704 had the maximum P content. The treated plants by AZ showed more the P increase compared to the others (Fig. 2 ). Effects of PGPR inoculation on K content in the seeds The amount of K in the seeds was increased in the treated plants compared to the control and were different among the studies cultivars. The combined treatments, AS + AZ + PS and AZ + PS had the maximum K increase and AS and AS + PS showed the minimum K increase compared to the control (Fig. 3 ). Between the studied cultivars SC704 had a maximum K increase following B73×K18 and SC700. The difference between the cultivars were more observable while applying the AS + PS treatment. Effects of PGPR inoculation on Fe content in the seeds The Fe content in the seeds was increased in the treated plants in comparison to the control plants and were different among the studies cultivars. The maximum increase observed in SC704 and B73×K18 and was minimum in the SC700. The overall increase observed in the combined treatments, AS + AZ + PS and AZ + PS and the minimum increase observed in AS and AS + PS compared to the treatments (Fig. 4 ). Effects of PGPR inoculation on Zn content in the seeds As is shown in the figure (Fig. 5 ), the Zn content in the seeds was differently changed by the various treatments, depending on the cultivar and applied bacteria. In the SC704 and B73×K18 cultivars, AZ, PS, AZ + PS and AS + AZ + PS could significantly increase the Zn content, however there no significant difference in the other treatments. In the SC700 cultivar, all the treated plants significantly increased the Zn content. In all the studied cultivars, the maximum increase observed in AS + AZ + PS compared to the control and the minimum increase belonged to AS treatment. Effects of PGPR inoculation on Mn content in the seeds PGPR significantly enhanced the content of the Mn in all studied hybrid corns. The Mn content increase was maximum in the AS + AZ + PS treatment following AZ + PS and AZ and the minimum Mn content observed in the AS and AS + PS treatments (Fig. 6 ). No significant difference was observed between the studied cultivars. Effects of PGPR inoculation on Cu content in the seeds Inoculation with the Rhizobacteria significantly increased the Cu content when applied combinedly, the AS + AZ + PS treatment had maximum Cu content following AZ + PS and AZ. No significant difference between the studied cultivars were observed (Fig. 7 ). Discussion As we obviously see in recent years, food security is progressively threatening, in all the world and specially in several developing countries which old-style agriculture systems are becoming unsustainable because of increased population and political aspects ( 23 ). The global population is estimated to be doubled by 2050, and maximum part of increase will happen in the developing countries in which food shortage is already a threat ( 24 ). Soil nutrient imbalance, mismanagement use of chemicals, and heavy metal pollutions, will affect the food security and need to be explored worldwide. Here in this study we investigate the role of PGPR as complementary method for chemical fertilizers and as a solution toward a sustainable agriculture, on the mineral nutrients affecting the plants growth. Nitrogen Nitrogen (N) is the critical well-known nutrient for plant development and productivity especially in arid and semi-arid regions with low organic matter. Even though 78% of the atmosphere is N2, but it is unavailable to the plants. Several PGPR, including Azoarcus sp., Klebsiella pneumoniae , Beijerinckia sp., Rhizobium sp., Pantoea agglomerans , many spices of Azotobacter and Azosperillum have been demonstrated to fix the atmospheric N 2 into the soil, making it available to plants. In the present investigation, all studied PGPR could significantly increase the N content in the seeds demonstrating the increase N fixation. Also the combined application of AS + AZ + PS most effectively increased the N content compared to the other studied treatments. Although, no significant difference were observed between the studied hybrids, however, when applying the AS + AZ + PS, the SC704 hybrid showed a superior N increment compared to the others. As we know this bacterium along with N fixation, can increase volume and specific area of root and induce synergy with symbiotic fungi that stimulate water and nutrient absorption. Phosphorous Phosphorus (P) is one of the most necessary elements in plant nutrient. Although, soils might have enormous P reservoirs, however the amount of available P to plants are generally little. That is because the P found in the soils are usually insoluble and plants only absorb the monobasic (H 2 PO 4 ) and dibasic (HPO 4 2− ) forms ( 25 ). It has been demonstrated that some PGPR could solubilize the phosphate ( 26 , 27 ). Our results also indicated that in all treated maize plants the amount of P content significantly increased compared to the control, indicating the effects of treatments on solubilizing P (Fig. 2 ). Interestingly, the increase was more observable in the plants treated with AZ and also those treated with combined AS + AZ + PS. In accordance to findings presented here, Azotobacter and Pseudomonas bacterial genera, are expressed as P solubilizing bacteria ( 28 ). Solubilizing the insoluble phosphates into soluble forms by PGPR has been reported to occur through chelation, acidification, exchange reactions and the production of gluconic acid process and root development ( 29 , 30 , 44 ). Potassium Our results indicate that the K content in the maize seeds increased in the PGPR treated plants. The increase were superior in the combined treatments such as AS + AZ + PS and AZ + PS (Fig. 3 ). Between the studied cultivars, SC704 had a maximum K increase following B73×K18 and SC700. Similar to our findings, inoculating tomato roots with Pseudomonas putida , Azotobacter chroococcum and Azosprillum lipoferum , increased the potassium content in the shoots and fruits. Moreover, the combined application of Pseudomonas + Azotobacter + Azosprillum + arbuscular mycorrhiza fungi (AMF) had maximum effect on potassium contents in tomato ( 36 ). In the investigation of PGPR effects on growth and nutrient uptake of cotton and pea, K uptake increased in plant components and improved the salt tolerant and temperature resistance in the studied plants ( 37 ). Increased nutrient uptake by PGPR inoculated crops might be attributed to the production of plant growth regulators by bacteria at root interface, stimulating root development in maze root system and consequently better water and nutrients absorption from the soil. Zinc The Zinc (Zn) is an essential micronutrient for plant’s proper cell functioning and for human health, as it is a very impressive cofactor for numerous enzymes, the protein–protein interactions, and structural Zn-finger domains ( 31 , 32 ). Our finding indicates that the Zn content in the studied maize seeds has been increased by the various PGPR treatments, depending on the cultivar and applied bacteria. In keeping with our findings, the Zn content in lentil and wheat increased by different Pseudomonas strains treatments ( 33 , 47 ). Also an increased Zn uptake in response to PGPR inoculation was reported on rice ( 34 ). Application of P. putida , P. fluorescens , and A. lipoferum increased the Zn content in rice by 1.5- to 2-fold and PGPR application was expressed as a significant strategy to combat the zinc deficiency in rice and wheat ( 35 , 47 ). Here in this study, the application of AZ, PS, AZ + PS and AS + AZ + PS could significantly increase the Zn content the SC704 and B73×K18 maize cultivars. The combined application of the strains (especially AS + AZ + PS) had the maximum effects on Zn increase. This increase in the Zn content might be attributed to rhizobacteria activity toward solubilizing the insoluble forms of Zn in the soil ( 47 ). Iron Iron (Fe) in plants has many critical functions on photosynthesis, metabolism of chloroplast, mitochondrial respiration, some enzyme systems, hormone biosynthesis, nitrogen assimilation, and etc. ( 38 , 39 ). It seems that the effects of PGPR on the Fe content depends on the plants and cultivars. In a study, investigating the effects of PGPR on tomato plants subjected to salt stress, no significant changes in Fe content was reported ( 40 ). In the present study, the Fe content in the seeds was increased in the treated plants in comparison to the control plants and were different among the studies cultivars. The maximum Fe increase observed in SC704 and the minimum Fe content was observed in SC700. The combined application of the PGPR, such as AS + AZ + PS and AZ + PS had the maximum effect on increasing the Fe content in the seeds (Fig. 4 ). In keeping to our findings, the PGPR effects on yield, growth and nutrient contents in organically growing raspberry resulted in significant increase in the Fe and Mn content in the leaves. Inoculation with PGPR increased the Fe and Mn content of leaves by 75.6% and 117.0%, respectively. They explained that organic acids production by bacteria in the rhizosphere, decreasing the pH of soil in rhizosphere and micro zones, might be the reason of Fe content increase in raspberry ( 41 ). Copper and Manganese Copper (Cu) and Manganese (Mn) are essential micronutrients for the plants, animal and human. Cu is required for numerous tasks in the plants, including mitochondrial respiration, photosynthesis, nitrogen and carbon metabolism, cell wall synthesis, and oxidative stress protection ( 42 ). Mn is critical for plants metabolism and development as well, it occurs approximately in oxidation states of 35 enzymes in the plant’s cells. Moreover, it has activating role on plants’ enzymes and functions as catalytically active metal ( 42 ). The effects of PGPR inoculation have been reported to change the Cu and Mn content in some crops depending on the plant species and variety. PGPR treatment increased the leaves Mn content of the organically growing raspberry, while had no significant effects on the Cu content of leaves ( 41 ). In our study the inoculation with PGPR significantly increased the Cu content when applied combinedly, the AS + AZ + PS treatment had maximum Cu content following AZ + PS and AZ. (Fig. 7 ). Similar to our result the combined inoculation of PGPRs in wheat ( Triticum aestivum L.) demonstrated a positive effect on growth, yield and nutrient content and increased the Cu and Mn content in the grains under both pot and field conditions. The increased Cu, Mn content due to the bacterial inoculations might be attributed to organic acids produced by bacteria in the rhizosphere decreasing the soil pH and stimulating the availability micronutrients availability. This finding is in accordance with the previous published reports ( 22 , 43 , 46 ). Conclusion Based on the report of IFA (2021), the combination of successful Covid-19 vaccine development and improved management of the economic impact of the virus has enabled stronger-than-expected global performance in 2021. Economic growth rates were higher than anticipated in Q1 2021 across advanced and developing economies. Global fertilizer use (N + P2O5 + K2O) was estimated at 198.2 Mt of nutrients in Fertilizer Year 2020/21, almost 10 Mt (5.2%) higher than in 2019/20. This is the largest increase since 2010/11. Nitrogen, which accounts for over half of global fertilizer use, experienced a 4.1% (4.3 Mt) increase in demand to 110.0 Mt in 2020/21. Demand for phosphorous jumped by 7.0% (3.3 Mt), reaching 49.6 Mt. Demand for potash rose by 6.2% (2.2 Mt) to 38.5 Mt. The rate of growth in fertilizer demand is expected to slow to 0.9% in 2021/22. Global fertilizer use is forecast to reach 199.9 Mt. Additional volumes of less than 1 Mt are anticipated for each nutrient. As of June 2021, potash consumption was expected to grow faster than other nutrients during 2021/22. The increased demands for chemical fertilizer will subsequently increases the adverse effects such as waterway pollution, chemical burn to crops, increased air pollution, acidification and mineral depletion of the soil. The application of PGPR (as organic and also as a complementary input) in crops’ cultivation is a critical policy that can be used in the future to improve the plant growth and increase the macro and micronutrient availability to plants. The increased efficiency for elements absorption on the studied maize hybrids by combined inoculation of Azotobacter chroococcum (AZ), Azospirillum lipoferum (AS) and Pseudomonas fluorescens (PS) could be attributed to the cumulative effects of these microorganisms providing N and available P and improve the other nutrients absorption. In addition, the superiority of the SC704 maize hybrids over the two studied maze plants indicated that the efficiency of the PGPR might be genotype or variety depended. Declarations Clinical trial number: not applicable. Ethics approval and consent to participate not applicable Ethics, Consent to Participate, and Consent to Publish declarations: not applicable. Author Contributions Conceptualization; data curation; writing—original draft preparation; review and editing; visualization; supervision; project administration, All the authors have read and agreed to the published version of the manuscript. Funding This research received no external funding. Conflicts of Interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest. Author Contribution Conceptualization; data curation; writing—original draft preparation; review and editing; visualization; supervision; project administration, All the authors have read and agreed to the published version of the manuscript. Acknowledgments The authors express their gratitude to the Soil and Water Research Institute (SWRI) and the Agricultural Research Education and Extension Organization (AREEO) of Iran for their support. References Lugtenberg B, Kamilova F. Plant-Growth-Promoting Rhizobacteria. Annu Rev Microbiol. 2009;63(1):541–56. Shaukat K, Affrasayab S, Hasnain S. Growth Responses oïTriticum aestivum to Plant Growth Promoting Rhizobacteria Used as a Biofertilizer. Res J Microbiol. 2006;1(4):330–8. Van Loon L. Plant responses to plant growth-promoting rhizobacteria. Eur J Plant Pathol. 2007;119(3):243–54. Ryu C-M, Farag MA, Hu C-H, Reddy MS, Wei H-X, Paré PW et al. Bacterial volatiles promote growth in Arabidopsis. Proceedings of the National Academy of Sciences. 2003;100(8):4927-32. Govindasamy V, Senthilkumar M, Gaikwad K, Annapurna K. Isolation and characterization of ACC deaminase gene from two plant growth-promoting rhizobacteria. Curr Microbiol. 2008;57(4):312–7. Chandler D, Davidson G, Grant W, Greaves J, Tatchell G. Microbial biopesticides for integrated crop management: an assessment of environmental and regulatory sustainability. Trends Food Sci Technol. 2008;19(5):275–83. El-Tarabily KA, Sivasithamparam K. Non-streptomycete actinomycetes as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Soil Biol Biochem. 2006;38(7):1505–20. Vessey JK. Plant growth promoting rhizobacteria as biofertilizers. Plant Soil. 2003;255(2):571–86. Dwivedi SL, van Lammerts ET, Ceccarelli S, Grando S, Upadhyaya HD, Ortiz R. Diversifying Food Systems in the Pursuit of Sustainable Food Production and Healthy Diets. Trends Plant Sci. 2017;22(10):842–56. Myresiotis CK, Vryzas Z, Papadopoulou-Mourkidou E. Effect of specific plant-growth-promoting rhizobacteria (PGPR) on growth and uptake of neonicotinoid insecticide thiamethoxam in corn (Zea mays L.) seedlings. Pest Manag Sci. 2015;71(9):1258–66. Arikan Ş, Pirlak L. Effects of plant growth promoting rhizobacteria (PGPR) on growth, yield and fruit quality of sour cherry (Prunus cerasus L). Erwerbs-obstbau. 2016;58(4):221–6. Adesemoye AO, Kloepper JW. Plant–microbes interactions in enhanced fertilizer-use efficiency. Appl Microbiol Biotechnol. 2009;85(1):1–12. Imran A, Mirza M, Shah T, Malik K, Hafeez F. Differential response of kabuli and desi chickpea genotypes toward inoculation with PGPR in different soils. Front Microbiol. 2015;6(859). Hafeez F, Shah N, Malik K. Field evaluation of lentil cultivars inoculated with Rhizobium leguminosarum bv. viciae strains for nitrogen fixation using nitrogen-15 isotope dilution. Biol Fertil Soils. 2000;31(1):65–9. Israel DW, Mathis JN, Barbour WM, Elkan GH. Symbiotic effectiveness and host-strain interactions of Rhizobium fredii USDA 191 on different soybean cultivars. Appl Environ Microbiol. 1986;51(5):898–903. Abi-Ghanem R, Carpenter-Boggs L, Smith JL. Cultivar effects on nitrogen fixation in peas and lentils. Biol Fertil Soils. 2011;47(1):115–20. Valverde G, Otabbong E. Evaluation of N2-fixation measured by the 15N‐dilution and N‐difference methods in Nicaraguan and Ecuadorian Phaseolus vulgaris L. plants inoculated with Rhizobium leguminosarum biovar. Acta Agriculturae Scand B—Plant Soil Sci. 1997;47(2):71–80. Doornbos RF, van Loon LC, Bakker PA. Impact of root exudates and plant defense signaling on bacterial communities in the rhizosphere. A review. Agron Sustain Dev. 2012;32(1):227–43. Stancheva I, Dinev N. Effects of inoculation of maize and species of tribe Triticeae with Azospirillum brasilense. J Plant Physiol. 1992;140(5):550–2. Esitken A, Pirlak L, Turan M, Sahin F. Effects of floral and foliar application of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrition of sweet cherry. Sci Hort. 2006;110(4):324–7. Horwitz W, Chichilo P, Reynolds H. Official methods of analysis of the Association of Official Analytical Chemists. Official methods of analysis of the Association of Official Analytical Chemists; 1970. Karlidag H, Esitken A, Turan M, Sahin F. Effects of root inoculation of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrient element contents of leaves of apple. Sci Hort. 2007;114(1):16–20. Masciarelli O, Llanes A, Luna V. A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation. Microbiol Res. 2014;169(7–8):609–15. Go AS, Hylek EM, Phillips KA, Chang Y, Henault LE, Selby JV, et al. Prevalence of diagnosed atrial fibrillation in adults: national implications for rhythm management and stroke prevention: the AnTicoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study. JAMA. 2001;285(18):2370–5. Bhattacharyya PN, Jha DK. Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture. World J Microbiol Biotechnol. 2012;28(4):1327–50. Richardson AE, Barea J-M, McNeill AM, Prigent-Combaret C. Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms. Plant Soil. 2009;321(1–2):305–39. Zaidi A, Khan MS, Amil M. Interactive effect of rhizotrophic microorganisms on yield and nutrient uptake of chickpea (Cicer arietinum L). Eur J Agron. 2003;19(1):15–21. Ahemad M, Kibret M. Mechanisms and applications of plant growth promoting rhizobacteria: current perspective. J King Saud University-Science. 2014;26(1):1–20. Chung H, Park M, Madhaiyan M, Seshadri S, Song J, Cho H, et al. Isolation and characterization of phosphate solubilizing bacteria from the rhizosphere of crop plants of Korea. Soil Biol Biochem. 2005;37(10):1970–4. Hameeda B, Harini G, Rupela O, Wani S, Reddy G. Growth promotion of maize by phosphate-solubilizing bacteria isolated from composts and macrofauna. Microbiol Res. 2008;163(2):234–42. Shahzad Z, Rouached H, Rakha A. Combating mineral malnutrition through iron and zinc biofortification of cereals. Compr Rev Food Sci Food Saf. 2014;13(3):329–46. Kisko M, Bouain N, Rouached A, Choudhary SP, Rouached H. Molecular mechanisms of phosphate and zinc signalling crosstalk in plants: phosphate and zinc loading into root xylem in Arabidopsis. Environ Exp Bot. 2015;114:57–64. Mishra PK, Bisht SC, Ruwari P, Joshi GK, Singh G, Bisht JK, et al. Bioassociative effect of cold tolerant Pseudomonas spp. and Rhizobium leguminosarum-PR1 on iron acquisition, nutrient uptake and growth of lentil (Lens culinaris L). Eur J Soil Biol. 2011;47(1):35–43. Tariq M, Hameed S, Malik KA, Hafeez FY. Plant root associated bacteria for zinc mobilization in rice. Pak J Bot. 2007;39(1):245. Sharma A, Patni B, Shankhdhar D, Shankhdhar S. Evaluation of different PGPR strains for yield enhancement and higher Zn content in different genotypes of rice (Oryza sativa L). J Plant Nutr. 2015;38(3):456–72. Ordookhani K, Khavazi K, Moezzi A, Rejali F. Influence of PGPR and AMF on antioxidant activity, lycopene and potassium contents in tomato. Afr J Agric Res. 2010;5(10):1108–16. Egamberdiyeva D, Höflich G. Effect of plant growth-promoting bacteria on growth and nutrient uptake of cotton and pea in a semi-arid region of Uzbekistan. J Arid Environ. 2004;56(2):293–301. Rout GR, Sahoo S. Role of iron in plant growth and metabolism. Reviews Agricultural Sci. 2015;3:1–24. Davarpanah S, Akbari M, Askari MA, Babalar M, Naddaf ME. Effect of iron foliar application (Fe-EDDHA) on quantitative and qualitative characteristics of pomegranate CV. Malas-e-Saveh World of Sci J,(04). 2013:179 – 87. Mayak S, Tirosh T, Glick BR. Plant growth-promoting bacteria confer resistance in tomato plants to salt stress. Plant Physiol Biochem. 2004;42(6):565–72. Orhan E, Esitken A, Ercisli S, Turan M, Sahin F. Effects of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrient contents in organically growing raspberry. Sci Hort. 2006;111(1):38–43. Hänsch R, Mendel RR. Physiological functions of mineral micronutrients (cu, Zn, Mn, Fe, Ni, Mo, B, cl). Curr Opin Plant Biol. 2009;12(3):259–66. Shen J, Li R, Zhang F, Fan J, Tang C, Rengel Z. Crop yields, soil fertility and phosphorus fractions in response to long-term fertilization under the rice monoculture system on a calcareous soil. Field Crops Res. 2004;86(2–3):225–38. Pavel Kerchev T, van der Meer N, Sujeeth A, Verlee CV, Stevens F, Van Breusegem, Tsanko Gechev. 2020. Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants. Biotechnol Adv 40–107503. Raksha Singh, Goodwin SB. Exploring the Corn Microbiome: A Detailed Review on Current Knowledge, Techniques, and Future Directions. Phyto Front. 2022;2:158–75. Rokhzadi A, Darvish asgharzadehA, Nour F mohamadi,G., and, Majidi A. Influence of plant growth promoting rhizobacteria on dry matter accumulation and yield of chickpea ( cicer arietinum L.) under field condition. Am –Eurasian J Agric Environ Sci. 2008;3(2):253–7. Bapiri -A, Asgarzadeh A, Mojallali H, Khavazi K. Ebrahim Pazira. 2012.Evaluation of Zinc solubilization potential by different strain of Fluorescent pseudomonads. J Appl sci Environ manage.16(3).pp. 295–8. Tables Table 1 is not available with this version. Additional Declarations No competing interests reported. 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2","display":"","copyAsset":false,"role":"figure","size":11859,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on P content in the seeds\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/66372fcd23605a95daf58638.png"},{"id":98139553,"identity":"9000fcda-6610-45ed-9e57-d6c4a6dffa43","added_by":"auto","created_at":"2025-12-13 18:23:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":11983,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on K content in the seeds\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/75c820e63ad65f6bef18cc6e.png"},{"id":98430499,"identity":"1af9990e-fd20-46c4-b7c1-6a2af2c61e56","added_by":"auto","created_at":"2025-12-17 16:45:35","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":12400,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on Fe content in the seeds\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/862c2bf1f0e303858adaa4a9.png"},{"id":98139557,"identity":"6fc908ec-1f8b-458b-ad98-fe493b37746c","added_by":"auto","created_at":"2025-12-13 18:23:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":12590,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on Zn content in the seeds\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/dec494021fbec45eb2703603.png"},{"id":98430730,"identity":"ceb79864-a14b-4024-bb15-f3931ed59a76","added_by":"auto","created_at":"2025-12-17 16:46:06","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":13067,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on Mn content in the seeds\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/5d645065e6b15d8203a280a1.png"},{"id":98139556,"identity":"0df7d57e-be49-4f21-ac0b-c2852887cac9","added_by":"auto","created_at":"2025-12-13 18:23:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":11871,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of PGPR inoculation on Cu content in the seeds\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/608949a1e40fd14e893c7bf0.png"},{"id":98622187,"identity":"9bfe4231-a6d2-4921-9768-4dfa42207851","added_by":"auto","created_at":"2025-12-19 16:48:24","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":823206,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8211736/v1/d2fb0fbe-b5da-43e9-b2b0-a5cfbfa87f8b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhancing nutrient content in Maize: comparative effects of plant growth-promoting rhizobacteria across various Maize hybrids","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSustainable agricultural production fundamentally relies on the careful management of both genetic and environmental factors, including the formation of symbiotic relationships between plants and beneficial microorganisms [1]. Among these microorganisms, Plant Growth-Promoting Rhizobacteria (PGPR) are particularly significant due to their ability to colonize the plant rhizosphere and establish mutually beneficial associations with a wide variety of plants, thereby enhancing growth and development. These bacteria are extensively utilized as biofertilizers, contributing to sustainable agriculture by minimizing the need for chemical inputs [2]. PGPR play a vital role in supporting plant growth under both stress and non-stress conditions, employing a range of direct and indirect mechanisms. Numerous studies have demonstrated that these bacteria can promote plant growth through diverse pathways, including nitrogen fixation [3], the production of volatile organic compounds that enhance plant defense and stress tolerance [4], and the synthesis of 1-Aminocyclopropane-1-carboxylate (ACC) deaminase, which reduces ethylene levels and mitigates stress-induced growth inhibition [5]. Furthermore, PGPR induce systemic resistance against pathogens [6], produce phytohormones such as auxins and gibberellins that regulate plant development, and secrete siderophores that enhance iron uptake [7, 8]. They are also known to solubilize phosphates, making this essential nutrient more accessible to plants [4]. Beyond these well-established mechanisms, PGPR may employ numerous other molecular pathways, many of which remain to be fully elucidated, that collectively contribute to their role in promoting healthier, more resilient plant growth [44, 45].\u003c/p\u003e\u003cp\u003eMaize (Zea mays L.) is a key global crop due to its increasing demand as both food and feed, as well as its vital economic importance, which has become particularly evident during recent geopolitical events such as the Ukraine-Russia war [9]. Based on the report of IFA (2021), the combination of successful Covid-19 vaccine development and improved management of the economic impact of the virus has enabled stronger-than-expected global performance in 2021. However, this increased production has been accompanied by a greater reliance on chemical fertilizers and pesticides, leading to detrimental effects on soil, water, and the broader food chain [10].\u003c/p\u003e\u003cp\u003eOrganic agriculture, which avoids the use of chemical fertilizers, growth regulators, pesticides, and feed additives, offers a sustainable alternative by promoting the production of safe and healthy food while reducing negative environmental impacts [11, 45]. Biofertilizers, especially those based on PGPR, have emerged as a key component of organic farming systems. The use of biofertilizers, combined with beneficial microorganisms, has been suggested as an effective way to enhance plant growth, improve soil productivity, and maintain environmental health [12, 45]. A PGPR-based biofertilizer offers both environmental and agronomic advantages, increasing the efficiency of fertilizer use and improving economic yields under natural conditions. However, selecting the most effective bacterial strains that are compatible with specific plant varieties is crucial, as different strains can have varying effects on target plants [13, 45]. Studies have shown significant interactions between crop cultivars and bacterial strains in terms of biological nitrogen fixation in lentils [14], soybeans [15], peas [16], and beans [17].\u003c/p\u003e\u003cp\u003eAmong the different types of PGPR, Azospirillum spp. are well-known for their application in maize and other cereals, producing phytohormones that encourage root growth and enhance nutrient and water uptake [18]. For example, Stancheva and Dinev [19] demonstrated that the interaction between Azospirillum brasilense and the corn root system leads to increased plant biomass and total nitrogen content. Inoculation with PGPRs such as Azospirillum lipoferum has been shown to improve the ability of crops to uptake mineral nitrogen. Although there are numerous successful examples of inoculating maize, tomato, wheat, and other crops with different PGPR strains such as Azospirillum, Enterobacter, Bacillus, and Pseudomonas, plants often exhibit varying responses to these bacteria within their rhizosphere. For instance, the floral and foliar application of Pseudomonas BA-8 and Bacillus OSU-142 on sweet cherry (Prunus avium L.) significantly influenced the content of N, P, K, Fe, Zn, and Mn (20(. Despite the well-documented effects of PGPR on host plants, there is limited research on the specific effects of PGPR inoculation on the mineral nutrient content of crops. Therefore, the present study aims to investigate the effects of inoculating three different hybrid maize varieties\u0026mdash;SC704, SC700, and B73\u0026times;K18\u0026mdash;with Azotobacter chroococcum, Azospirillum lipoferum, and Pseudomonas fluorescens on the content of essential mineral elements, including Nitrogen (N), Phosphorus (P), Potassium (K), Iron (Fe), Zinc (Zn), Manganese (Mn), and Copper (Cu).\u003c/p\u003e\u003cp\u003eBy examining the interactions between these PGPR strains and maize hybrids, this study seeks to provide new insights into optimizing PGPR applications to enhance the nutritional quality and sustainable production of maize.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003ePlant Materials and Experimental Site\u003c/h2\u003e\u003cp\u003eThe experiments were conducted using three maize hybrids: SC704 (single cross 704, B73 \u0026times; Mo17), SC700 (single cross 700, K74/1 \u0026times; K18), and B73 \u0026times; K18, which were selected based on their economic importance and genetic diversity. The seeds of these hybrids were provided by the Maize and Forage Crops Research Department of the Seed and Plant Improvement Institute (SPII), Karaj, Iran. SC704 and SC700 are widely grown hybrids in Iran, known for their high yield potential and adaptability to local environmental conditions. The B73 \u0026times; K18 hybrid was included in the study as a promising candidate for future cultivation.\u003c/p\u003e\u003cp\u003eThe field experiments were conducted at the experimental farm of the Seed and Plant Improvement Institute, Karaj, Iran, during the growing season. The site is located at 35.8308\u0026deg; N latitude and 50.9915\u0026deg; E longitude, with an altitude of approximately 1313 meters above sea level. The region has a semi-arid climate with an average annual precipitation of 250 mm and an average temperature of 14.5\u0026deg;C. Prior to sowing, soil samples were collected from the top 30 cm layer of the experimental field and analyzed for physical and chemical properties, including pH, electrical conductivity (EC), organic matter content, and available macronutrients and micronutrients (Table\u0026nbsp;1).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eExperimental Design and Treatments\u003c/h3\u003e\n\u003cp\u003eThe study was arranged in a randomized complete block design (RCBD) with four replications to minimize the impact of spatial variability within the field. Each plot measured 3 meters in length with 5 rows, spaced 75 cm apart, and a plant-to-plant distance of 20 cm within each row. The treatments consisted of inoculation with three different plant growth-promoting rhizobacteria (PGPR) strains: Azotobacter chroococcum strain 5 (AZ), Azospirillum lipoferum strain 21 (AS), and Pseudomonas fluorescens strain 169 (PS), either individually or in combination, along with a non-inoculated control. The bacterial strains were obtained from the microbial culture collection of the Soil Microbiology Department of the Soil and Water Research Institute, Iran, and were selected based on their documented effectiveness in promoting plant growth in multiple field experiments.\u003c/p\u003e\u003cp\u003ePreparation of Bacterial Inoculants and Seed Inoculation\u003c/p\u003e\u003cp\u003eThe PGPR strains were cultured separately in their respective growth media under sterile conditions. Azotobacter chroococcum was grown in Ashby's Mannitol Agar, Azospirillum lipoferum in Nitrogen-Free Malate Medium, and Pseudomonas fluorescens in King's B medium. The bacterial cultures were incubated at 28\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C for 48 hours to reach a concentration of approximately 10\u003csup\u003e8\u003c/sup\u003e colony-forming units per milliliter (CFU/mL). The bacterial suspensions were then diluted to a final concentration of 10\u003csup\u003e7\u003c/sup\u003e CFU/mL with sterile distilled water before inoculation.\u003c/p\u003e\u003cp\u003eMaize seeds were surface sterilized by immersing them in a 1% sodium hypochlorite solution for 5 minutes, followed by thorough rinsing with sterile distilled water. The sterilized seeds were then soaked in the respective bacterial suspensions for 30 minutes, allowing the bacteria to adhere to the seed surfaces. Seeds were categorized into eight groups: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) seeds inoculated with \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e (AZ), (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) seeds inoculated with \u003cem\u003eAzospirillum lipoferum\u003c/em\u003e (AS), (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) seeds inoculated with \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e (PS), (\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e) seeds inoculated with a combination of \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e and \u003cem\u003eAzospirillum lipoferum\u003c/em\u003e (AZ\u0026thinsp;+\u0026thinsp;AS in a 1:1 ratio), (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e) seeds inoculated with a combination of \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e and \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e (AZ\u0026thinsp;+\u0026thinsp;PS in a 1:1 ratio), (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e) seeds inoculated with a combination of \u003cem\u003eAzospirillum lipoferum\u003c/em\u003e and \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e (AS\u0026thinsp;+\u0026thinsp;PS in a 1:1 ratio), (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e) seeds inoculated with a combination of all three PGPR strains (AZ, AS, and PS in a 1:1:1 ratio), and (\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e) a non-inoculated control group soaked in sterile distilled water. After inoculation, the seeds were air-dried for two hours under sterile conditions.\u003c/p\u003e\n\u003ch3\u003eField Management and Growth Conditions\u003c/h3\u003e\n\u003cp\u003eThe inoculated seeds were sown in the prepared field plots, and standard agronomic practices were followed throughout the growing season to maintain optimal growth conditions. The plants were irrigated regularly to maintain adequate soil moisture levels and were kept free of weeds by manual weeding. No additional chemical fertilizers or pesticides were applied to the plots to exclusively evaluate the effects of the PGPR treatments. The field was monitored daily for any signs of pest or disease infestations, and necessary protective measures were taken as required.\u003c/p\u003e\n\u003ch3\u003eNutrient Analysis\u003c/h3\u003e\n\u003cp\u003eAt maturity, maize seeds were harvested from each plot, oven-dried at 70\u0026deg;C for 48 hours, and ground into a fine powder for mineral analysis. Nitrogen (N) content was determined using the micro-Kjeldahl method as described by Bremner (1965). The concentrations of zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) were measured using an Atomic Absorption Spectrophotometer (AAS) at their respective wavelengths: Zn (213.7 nm), Fe (248.7 nm), Mn (279.5 nm), and Cu (324.6 nm). Phosphorus (P) content was determined spectrophotometrically using the indophenol-blue technique following a reaction with ascorbic acid (Murphy and Riley, 1962). Potassium (K) content was analyzed using a Flame Photometer after wet digestion of the dried samples in a mixture of sulfuric acid (H₂SO₄), selenium (Se), and salicylic acid.\u003c/p\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003eStatistical Analysis\u003c/h2\u003e\u003cp\u003eThe data obtained from the experiments were subjected to analysis of variance (ANOVA) using SAS software (version 9.1) to assess the significance of differences among treatments. Duncan's multiple range test was employed to compare the means at a significance level of p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Data from two consecutive years of experimentation were pooled, as no significant differences were observed between the years. Graphical representations of the results were prepared using Microsoft Excel 2016.\u003c/p\u003e\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR Inoculation on Nitrogen Content in Maize Seeds\u003c/h2\u003e\u003cp\u003eThe nitrogen (N) content in maize seeds was significantly affected by the inoculation with different strains of plant growth-promoting rhizobacteria (PGPR). The data presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e illustrate the impact of seven different treatments (AZ, AS, PS, AZ\u0026thinsp;+\u0026thinsp;AS, AZ\u0026thinsp;+\u0026thinsp;PS, AS\u0026thinsp;+\u0026thinsp;PS, and AZ\u0026thinsp;+\u0026thinsp;AS\u0026thinsp;+\u0026thinsp;PS) on the N content of three maize hybrids: SC704, SC700, and B73\u0026times;K18. The inoculation with a combination of all three bacterial strains (Azotobacter chroococcum [AZ], Azospirillum lipoferum [AS], and Pseudomonas fluorescens [PS]) resulted in the highest increase in N content across all three maize hybrids. The maximum increase was observed in the SC704 hybrid (4.0%), followed by SC700 (3.8%) and B73\u0026times;K18 (3.5%). This suggests that the combined inoculation of these PGPR strains had a synergistic effect on enhancing N content in maize seeds, particularly in the SC704 hybrid.\u003c/p\u003e\u003cp\u003eAmong the single-strain treatments, the PS treatment led to the highest increase in N content, with values of 2.0%, 1.8%, and 1.5% for SC704, SC700, and B73\u0026times;K18, respectively. The AS treatment showed the least effect on N content, with minimal increases observed in all hybrids (0.5% for SC704, 0.3% for SC700, and 0.2% for B73\u0026times;K18). The dual-strain combinations also resulted in significant increases in N content compared to the control. The AZ\u0026thinsp;+\u0026thinsp;PS treatment showed the second-highest increase, with N content rising to 3.5% in SC704, 3.2% in SC700, and 3.0% in B73\u0026times;K18. The AZ\u0026thinsp;+\u0026thinsp;AS treatment produced a moderate increase in N content (3.0% for SC704, 2.7% for SC700, and 2.5% for B73\u0026times;K18). The AS\u0026thinsp;+\u0026thinsp;PS combination demonstrated a lower but still significant effect on N content, with increases of 2.5% in SC704, 2.2% in SC700, and 2.0% in B73\u0026times;K18. Statistical analysis revealed that the differences in N content between the control and all PGPR treatments were significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Furthermore, among the different maize hybrids, SC704 exhibited the most substantial increase in N content following inoculation with the PGPR strains, particularly in the combined AZ\u0026thinsp;+\u0026thinsp;AS\u0026thinsp;+\u0026thinsp;PS treatment, where the increase was significantly higher than in the other two hybrids (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eEffects of PGPR inoculation on Phosphorus content in the seeds\u003c/h3\u003e\n\u003cp\u003eThe amount of P content in the seeds was increased in the treated plants compared to the control. The maximum P content was observed in AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS and the minimum amount observed in AS\u0026thinsp;+\u0026thinsp;PS (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Between the three studied maize hybrids no significant difference was observed concerning the Solubilization of P; while compared to the control, the SC704 had the maximum P content. The treated plants by AZ showed more the P increase compared to the others (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR inoculation on K content in the seeds\u003c/h2\u003e\u003cp\u003eThe amount of K in the seeds was increased in the treated plants compared to the control and were different among the studies cultivars. The combined treatments, AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS and AZ\u0026thinsp;+\u0026thinsp;PS had the maximum K increase and AS and AS\u0026thinsp;+\u0026thinsp;PS showed the minimum K increase compared to the control (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Between the studied cultivars SC704 had a maximum K increase following B73\u0026times;K18 and SC700. The difference between the cultivars were more observable while applying the AS\u0026thinsp;+\u0026thinsp;PS treatment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR inoculation on Fe content in the seeds\u003c/h2\u003e\u003cp\u003eThe Fe content in the seeds was increased in the treated plants in comparison to the control plants and were different among the studies cultivars. The maximum increase observed in SC704 and B73\u0026times;K18 and was minimum in the SC700. The overall increase observed in the combined treatments, AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS and AZ\u0026thinsp;+\u0026thinsp;PS and the minimum increase observed in AS and AS\u0026thinsp;+\u0026thinsp;PS compared to the treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR inoculation on Zn content in the seeds\u003c/h2\u003e\u003cp\u003eAs is shown in the figure (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), the Zn content in the seeds was differently changed by the various treatments, depending on the cultivar and applied bacteria. In the SC704 and B73\u0026times;K18 cultivars, AZ, PS, AZ\u0026thinsp;+\u0026thinsp;PS and AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS could significantly increase the Zn content, however there no significant difference in the other treatments. In the SC700 cultivar, all the treated plants significantly increased the Zn content. In all the studied cultivars, the maximum increase observed in AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS compared to the control and the minimum increase belonged to AS treatment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR inoculation on Mn content in the seeds\u003c/h2\u003e\u003cp\u003ePGPR significantly enhanced the content of the Mn in all studied hybrid corns. The Mn content increase was maximum in the AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS treatment following AZ\u0026thinsp;+\u0026thinsp;PS and AZ and the minimum Mn content observed in the AS and AS\u0026thinsp;+\u0026thinsp;PS treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). No significant difference was observed between the studied cultivars.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003eEffects of PGPR inoculation on Cu content in the seeds\u003c/h2\u003e\u003cp\u003eInoculation with the \u003cem\u003eRhizobacteria\u003c/em\u003e significantly increased the Cu content when applied combinedly, the AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS treatment had maximum Cu content following AZ\u0026thinsp;+\u0026thinsp;PS and AZ. No significant difference between the studied cultivars were observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eAs we obviously see in recent years, food security is progressively threatening, in all the world and specially in several developing countries which old-style agriculture systems are becoming unsustainable because of increased population and political aspects (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). The global population is estimated to be doubled by 2050, and maximum part of increase will happen in the developing countries in which food shortage is already a threat (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). Soil nutrient imbalance, mismanagement use of chemicals, and heavy metal pollutions, will affect the food security and need to be explored worldwide. Here in this study we investigate the role of PGPR as complementary method for chemical fertilizers and as a solution toward a sustainable agriculture, on the mineral nutrients affecting the plants growth.\u003c/p\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003eNitrogen\u003c/h2\u003e\u003cp\u003eNitrogen (N) is the critical well-known nutrient for plant development and productivity especially in arid and semi-arid regions with low organic matter. Even though 78% of the atmosphere is N2, but it is unavailable to the plants. Several PGPR, including \u003cem\u003eAzoarcus\u003c/em\u003e sp., \u003cem\u003eKlebsiella pneumoniae\u003c/em\u003e, \u003cem\u003eBeijerinckia\u003c/em\u003e sp., \u003cem\u003eRhizobium\u003c/em\u003e sp., \u003cem\u003ePantoea agglomerans\u003c/em\u003e, many spices of Azotobacter and Azosperillum have been demonstrated to fix the atmospheric N\u003csub\u003e2\u003c/sub\u003e into the soil, making it available to plants. In the present investigation, all studied PGPR could significantly increase the N content in the seeds demonstrating the increase N fixation. Also the combined application of AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS most effectively increased the N content compared to the other studied treatments. Although, no significant difference were observed between the studied hybrids, however, when applying the AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS, the SC704 hybrid showed a superior N increment compared to the others. As we know this bacterium along with N fixation, can increase volume and specific area of root and induce synergy with symbiotic fungi that stimulate water and nutrient absorption.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003ePhosphorous\u003c/h2\u003e\u003cp\u003ePhosphorus (P) is one of the most necessary elements in plant nutrient. Although, soils might have enormous P reservoirs, however the amount of available P to plants are generally little. That is because the P found in the soils are usually insoluble and plants only absorb the monobasic (H\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e) and dibasic (HPO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026minus;\u003c/sup\u003e) forms (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). It has been demonstrated that some PGPR could solubilize the phosphate (\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). Our results also indicated that in all treated maize plants the amount of P content significantly increased compared to the control, indicating the effects of treatments on solubilizing P (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Interestingly, the increase was more observable in the plants treated with AZ and also those treated with combined AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS. In accordance to findings presented here, \u003cem\u003eAzotobacter\u003c/em\u003e and \u003cem\u003ePseudomonas\u003c/em\u003e bacterial genera, are expressed as P solubilizing bacteria (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e). Solubilizing the insoluble phosphates into soluble forms by PGPR has been reported to occur through chelation, acidification, exchange reactions and the production of gluconic acid process and root development (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003ePotassium\u003c/h2\u003e\u003cp\u003eOur results indicate that the K content in the maize seeds increased in the PGPR treated plants. The increase were superior in the combined treatments such as AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS and AZ\u0026thinsp;+\u0026thinsp;PS (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Between the studied cultivars, SC704 had a maximum K increase following B73\u0026times;K18 and SC700. Similar to our findings, inoculating tomato roots with \u003cem\u003ePseudomonas putida\u003c/em\u003e, \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e and \u003cem\u003eAzosprillum lipoferum\u003c/em\u003e, increased the potassium content in the shoots and fruits. Moreover, the combined application of \u003cem\u003ePseudomonas\u003c/em\u003e\u0026thinsp;+\u0026thinsp;\u003cem\u003eAzotobacter\u003c/em\u003e\u0026thinsp;+\u0026thinsp;Azosprillum\u0026thinsp;+\u0026thinsp;\u003cem\u003earbuscular mycorrhiza\u003c/em\u003e fungi (AMF) had maximum effect on potassium contents in tomato (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). In the investigation of PGPR effects on growth and nutrient uptake of cotton and pea, K uptake increased in plant components and improved the salt tolerant and temperature resistance in the studied plants (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e). Increased nutrient uptake by PGPR inoculated crops might be attributed to the production of plant growth regulators by bacteria at root interface, stimulating root development in maze root system and consequently better water and nutrients absorption from the soil.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003eZinc\u003c/h2\u003e\u003cp\u003eThe Zinc (Zn) is an essential micronutrient for plant\u0026rsquo;s proper cell functioning and for human health, as it is a very impressive cofactor for numerous enzymes, the protein\u0026ndash;protein interactions, and structural Zn-finger domains (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). Our finding indicates that the Zn content in the studied maize seeds has been increased by the various PGPR treatments, depending on the cultivar and applied bacteria. In keeping with our findings, the Zn content in lentil and wheat increased by different \u003cem\u003ePseudomonas\u003c/em\u003e strains treatments (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e). Also an increased Zn uptake in response to PGPR inoculation was reported on rice (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e). Application of \u003cem\u003eP. putida\u003c/em\u003e, \u003cem\u003eP. fluorescens\u003c/em\u003e, and \u003cem\u003eA. lipoferum\u003c/em\u003e increased the Zn content in rice by 1.5- to 2-fold and PGPR application was expressed as a significant strategy to combat the zinc deficiency in rice and wheat (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e). Here in this study, the application of AZ, PS, AZ\u0026thinsp;+\u0026thinsp;PS and AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS could significantly increase the Zn content the SC704 and B73\u0026times;K18 maize cultivars. The combined application of the strains (especially AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS) had the maximum effects on Zn increase. This increase in the Zn content might be attributed to \u003cem\u003erhizobacteria\u003c/em\u003e activity toward solubilizing the insoluble forms of Zn in the soil (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003eIron\u003c/h2\u003e\u003cp\u003eIron (Fe) in plants has many critical functions on photosynthesis, metabolism of chloroplast, mitochondrial respiration, some enzyme systems, hormone biosynthesis, nitrogen assimilation, and etc. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e). It seems that the effects of PGPR on the Fe content depends on the plants and cultivars. In a study, investigating the effects of PGPR on tomato plants subjected to salt stress, no significant changes in Fe content was reported (\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e). In the present study, the Fe content in the seeds was increased in the treated plants in comparison to the control plants and were different among the studies cultivars. The maximum Fe increase observed in SC704 and the minimum Fe content was observed in SC700. The combined application of the PGPR, such as AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS and AZ\u0026thinsp;+\u0026thinsp;PS had the maximum effect on increasing the Fe content in the seeds (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In keeping to our findings, the PGPR effects on yield, growth and nutrient contents in organically growing raspberry resulted in significant increase in the Fe and Mn content in the leaves. Inoculation with PGPR increased the Fe and Mn content of leaves by 75.6% and 117.0%, respectively. They explained that organic acids production by bacteria in the rhizosphere, decreasing the pH of soil in rhizosphere and micro zones, might be the reason of Fe content increase in raspberry (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e\u003ch2\u003eCopper and Manganese\u003c/h2\u003e\u003cp\u003eCopper (Cu) and Manganese (Mn) are essential micronutrients for the plants, animal and human. Cu is required for numerous tasks in the plants, including mitochondrial respiration, photosynthesis, nitrogen and carbon metabolism, cell wall synthesis, and oxidative stress protection (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). Mn is critical for plants metabolism and development as well, it occurs approximately in oxidation states of 35 enzymes in the plant\u0026rsquo;s cells. Moreover, it has activating role on plants\u0026rsquo; enzymes and functions as catalytically active metal (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). The effects of PGPR inoculation have been reported to change the Cu and Mn content in some crops depending on the plant species and variety. PGPR treatment increased the leaves Mn content of the organically growing raspberry, while had no significant effects on the Cu content of leaves (\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e). In our study the inoculation with PGPR significantly increased the Cu content when applied combinedly, the AS\u0026thinsp;+\u0026thinsp;AZ\u0026thinsp;+\u0026thinsp;PS treatment had maximum Cu content following AZ\u0026thinsp;+\u0026thinsp;PS and AZ. (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Similar to our result the combined inoculation of PGPRs in wheat (\u003cem\u003eTriticum aestivum\u003c/em\u003e L.) demonstrated a positive effect on growth, yield and nutrient content and increased the Cu and Mn content in the grains under both pot and field conditions. The increased Cu, Mn content due to the bacterial inoculations might be attributed to organic acids produced by bacteria in the rhizosphere decreasing the soil pH and stimulating the availability micronutrients availability. This finding is in accordance with the previous published reports (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eBased on the report of IFA (2021), the combination of successful Covid-19 vaccine development and improved management of the economic impact of the virus has enabled stronger-than-expected global performance in 2021. Economic growth rates were higher than anticipated in Q1 2021 across advanced and developing economies. Global fertilizer use (N\u0026thinsp;+\u0026thinsp;P2O5\u0026thinsp;+\u0026thinsp;K2O) was estimated at 198.2 Mt of nutrients in Fertilizer Year 2020/21, almost 10 Mt (5.2%) higher than in 2019/20. This is the largest increase since 2010/11. Nitrogen, which accounts for over half of global fertilizer use, experienced a 4.1% (4.3 Mt) increase in demand to 110.0 Mt in 2020/21. Demand for phosphorous jumped by 7.0% (3.3 Mt), reaching 49.6 Mt. Demand for potash rose by 6.2% (2.2 Mt) to 38.5 Mt. The rate of growth in fertilizer demand is expected to slow to 0.9% in 2021/22. Global fertilizer use is forecast to reach 199.9 Mt. Additional volumes of less than 1 Mt are anticipated for each nutrient. As of June 2021, potash consumption was expected to grow faster than other nutrients during 2021/22. The increased demands for chemical fertilizer will subsequently increases the adverse effects such as waterway pollution, chemical burn to crops, increased air pollution, acidification and mineral depletion of the soil. The application of PGPR (as organic and also as a complementary input) in crops\u0026rsquo; cultivation is a critical policy that can be used in the future to improve the plant growth and increase the macro and micronutrient availability to plants. The increased efficiency for elements absorption on the studied maize hybrids by combined inoculation of \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e (AZ), \u003cem\u003eAzospirillum lipoferum\u003c/em\u003e (AS) and \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e (PS) could be attributed to the cumulative effects of these microorganisms providing N and available P and improve the other nutrients absorption. In addition, the superiority of the SC704 maize hybrids over the two studied maze plants indicated that the efficiency of the PGPR might be genotype or variety depended.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eClinical trial number: not applicable.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e\u003cp\u003enot applicable\u003c/p\u003e\u003c/p\u003e\u003cp\u003eEthics, Consent to Participate, and Consent to Publish declarations: not applicable.\u003c/p\u003e\u003ch2\u003eAuthor Contributions\u003c/h2\u003e\u003cp\u003eConceptualization; data curation; writing\u0026mdash;original draft preparation; review and editing; visualization; supervision; project administration, All the authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003cp\u003eThis research received no external funding.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConflicts of Interest\u003c/h2\u003e\u003cp\u003eThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as potential conflicts of interest.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization; data curation; writing\u0026mdash;original draft preparation; review and editing; visualization; supervision; project administration, All the authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e\u003cp\u003eThe authors express their gratitude to the Soil and Water Research Institute (SWRI) and the Agricultural Research Education and Extension Organization (AREEO) of Iran for their support.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eLugtenberg B, Kamilova F. Plant-Growth-Promoting Rhizobacteria. Annu Rev Microbiol. 2009;63(1):541\u0026ndash;56.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShaukat K, Affrasayab S, Hasnain S. Growth Responses o\u0026iuml;Triticum aestivum to Plant Growth Promoting Rhizobacteria Used as a Biofertilizer. Res J Microbiol. 2006;1(4):330\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVan Loon L. Plant responses to plant growth-promoting rhizobacteria. Eur J Plant Pathol. 2007;119(3):243\u0026ndash;54.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRyu C-M, Farag MA, Hu C-H, Reddy MS, Wei H-X, Par\u0026eacute; PW et al. Bacterial volatiles promote growth in Arabidopsis. Proceedings of the National Academy of Sciences. 2003;100(8):4927-32.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGovindasamy V, Senthilkumar M, Gaikwad K, Annapurna K. Isolation and characterization of ACC deaminase gene from two plant growth-promoting rhizobacteria. Curr Microbiol. 2008;57(4):312\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChandler D, Davidson G, Grant W, Greaves J, Tatchell G. Microbial biopesticides for integrated crop management: an assessment of environmental and regulatory sustainability. Trends Food Sci Technol. 2008;19(5):275\u0026ndash;83.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEl-Tarabily KA, Sivasithamparam K. Non-streptomycete actinomycetes as biocontrol agents of soil-borne fungal plant pathogens and as plant growth promoters. Soil Biol Biochem. 2006;38(7):1505\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVessey JK. Plant growth promoting rhizobacteria as biofertilizers. Plant Soil. 2003;255(2):571\u0026ndash;86.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDwivedi SL, van Lammerts ET, Ceccarelli S, Grando S, Upadhyaya HD, Ortiz R. Diversifying Food Systems in the Pursuit of Sustainable Food Production and Healthy Diets. Trends Plant Sci. 2017;22(10):842\u0026ndash;56.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMyresiotis CK, Vryzas Z, Papadopoulou-Mourkidou E. Effect of specific plant-growth-promoting rhizobacteria (PGPR) on growth and uptake of neonicotinoid insecticide thiamethoxam in corn (Zea mays L.) seedlings. Pest Manag Sci. 2015;71(9):1258\u0026ndash;66.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eArikan Ş, Pirlak L. Effects of plant growth promoting rhizobacteria (PGPR) on growth, yield and fruit quality of sour cherry (Prunus cerasus L). Erwerbs-obstbau. 2016;58(4):221\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAdesemoye AO, Kloepper JW. Plant\u0026ndash;microbes interactions in enhanced fertilizer-use efficiency. Appl Microbiol Biotechnol. 2009;85(1):1\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eImran A, Mirza M, Shah T, Malik K, Hafeez F. Differential response of kabuli and desi chickpea genotypes toward inoculation with PGPR in different soils. Front Microbiol. 2015;6(859).\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHafeez F, Shah N, Malik K. Field evaluation of lentil cultivars inoculated with Rhizobium leguminosarum bv. viciae strains for nitrogen fixation using nitrogen-15 isotope dilution. Biol Fertil Soils. 2000;31(1):65\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eIsrael DW, Mathis JN, Barbour WM, Elkan GH. Symbiotic effectiveness and host-strain interactions of Rhizobium fredii USDA 191 on different soybean cultivars. Appl Environ Microbiol. 1986;51(5):898\u0026ndash;903.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAbi-Ghanem R, Carpenter-Boggs L, Smith JL. Cultivar effects on nitrogen fixation in peas and lentils. Biol Fertil Soils. 2011;47(1):115\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eValverde G, Otabbong E. Evaluation of N2-fixation measured by the 15N‐dilution and N‐difference methods in Nicaraguan and Ecuadorian Phaseolus vulgaris L. plants inoculated with Rhizobium leguminosarum biovar. Acta Agriculturae Scand B\u0026mdash;Plant Soil Sci. 1997;47(2):71\u0026ndash;80.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDoornbos RF, van Loon LC, Bakker PA. Impact of root exudates and plant defense signaling on bacterial communities in the rhizosphere. A review. Agron Sustain Dev. 2012;32(1):227\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eStancheva I, Dinev N. Effects of inoculation of maize and species of tribe Triticeae with Azospirillum brasilense. J Plant Physiol. 1992;140(5):550\u0026ndash;2.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEsitken A, Pirlak L, Turan M, Sahin F. Effects of floral and foliar application of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrition of sweet cherry. Sci Hort. 2006;110(4):324\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHorwitz W, Chichilo P, Reynolds H. Official methods of analysis of the Association of Official Analytical Chemists. Official methods of analysis of the Association of Official Analytical Chemists; 1970.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKarlidag H, Esitken A, Turan M, Sahin F. Effects of root inoculation of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrient element contents of leaves of apple. Sci Hort. 2007;114(1):16\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMasciarelli O, Llanes A, Luna V. A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation. Microbiol Res. 2014;169(7\u0026ndash;8):609\u0026ndash;15.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGo AS, Hylek EM, Phillips KA, Chang Y, Henault LE, Selby JV, et al. Prevalence of diagnosed atrial fibrillation in adults: national implications for rhythm management and stroke prevention: the AnTicoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study. JAMA. 2001;285(18):2370\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBhattacharyya PN, Jha DK. Plant growth-promoting rhizobacteria (PGPR): emergence in agriculture. World J Microbiol Biotechnol. 2012;28(4):1327\u0026ndash;50.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRichardson AE, Barea J-M, McNeill AM, Prigent-Combaret C. Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms. Plant Soil. 2009;321(1\u0026ndash;2):305\u0026ndash;39.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZaidi A, Khan MS, Amil M. Interactive effect of rhizotrophic microorganisms on yield and nutrient uptake of chickpea (Cicer arietinum L). Eur J Agron. 2003;19(1):15\u0026ndash;21.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAhemad M, Kibret M. Mechanisms and applications of plant growth promoting rhizobacteria: current perspective. J King Saud University-Science. 2014;26(1):1\u0026ndash;20.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChung H, Park M, Madhaiyan M, Seshadri S, Song J, Cho H, et al. Isolation and characterization of phosphate solubilizing bacteria from the rhizosphere of crop plants of Korea. Soil Biol Biochem. 2005;37(10):1970\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHameeda B, Harini G, Rupela O, Wani S, Reddy G. Growth promotion of maize by phosphate-solubilizing bacteria isolated from composts and macrofauna. Microbiol Res. 2008;163(2):234\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShahzad Z, Rouached H, Rakha A. Combating mineral malnutrition through iron and zinc biofortification of cereals. Compr Rev Food Sci Food Saf. 2014;13(3):329\u0026ndash;46.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKisko M, Bouain N, Rouached A, Choudhary SP, Rouached H. Molecular mechanisms of phosphate and zinc signalling crosstalk in plants: phosphate and zinc loading into root xylem in Arabidopsis. Environ Exp Bot. 2015;114:57\u0026ndash;64.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMishra PK, Bisht SC, Ruwari P, Joshi GK, Singh G, Bisht JK, et al. Bioassociative effect of cold tolerant Pseudomonas spp. and Rhizobium leguminosarum-PR1 on iron acquisition, nutrient uptake and growth of lentil (Lens culinaris L). Eur J Soil Biol. 2011;47(1):35\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTariq M, Hameed S, Malik KA, Hafeez FY. Plant root associated bacteria for zinc mobilization in rice. Pak J Bot. 2007;39(1):245.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSharma A, Patni B, Shankhdhar D, Shankhdhar S. Evaluation of different PGPR strains for yield enhancement and higher Zn content in different genotypes of rice (Oryza sativa L). J Plant Nutr. 2015;38(3):456\u0026ndash;72.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOrdookhani K, Khavazi K, Moezzi A, Rejali F. Influence of PGPR and AMF on antioxidant activity, lycopene and potassium contents in tomato. Afr J Agric Res. 2010;5(10):1108\u0026ndash;16.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eEgamberdiyeva D, H\u0026ouml;flich G. Effect of plant growth-promoting bacteria on growth and nutrient uptake of cotton and pea in a semi-arid region of Uzbekistan. J Arid Environ. 2004;56(2):293\u0026ndash;301.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRout GR, Sahoo S. Role of iron in plant growth and metabolism. Reviews Agricultural Sci. 2015;3:1\u0026ndash;24.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDavarpanah S, Akbari M, Askari MA, Babalar M, Naddaf ME. Effect of iron foliar application (Fe-EDDHA) on quantitative and qualitative characteristics of pomegranate CV. Malas-e-Saveh World of Sci J,(04). 2013:179\u0026thinsp;\u0026ndash;\u0026thinsp;87.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eMayak S, Tirosh T, Glick BR. Plant growth-promoting bacteria confer resistance in tomato plants to salt stress. Plant Physiol Biochem. 2004;42(6):565\u0026ndash;72.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eOrhan E, Esitken A, Ercisli S, Turan M, Sahin F. Effects of plant growth promoting rhizobacteria (PGPR) on yield, growth and nutrient contents in organically growing raspberry. Sci Hort. 2006;111(1):38\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eH\u0026auml;nsch R, Mendel RR. Physiological functions of mineral micronutrients (cu, Zn, Mn, Fe, Ni, Mo, B, cl). Curr Opin Plant Biol. 2009;12(3):259\u0026ndash;66.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eShen J, Li R, Zhang F, Fan J, Tang C, Rengel Z. Crop yields, soil fertility and phosphorus fractions in response to long-term fertilization under the rice monoculture system on a calcareous soil. Field Crops Res. 2004;86(2\u0026ndash;3):225\u0026ndash;38.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePavel Kerchev T, van der Meer N, Sujeeth A, Verlee CV, Stevens F, Van Breusegem, Tsanko Gechev. 2020. Molecular priming as an approach to induce tolerance against abiotic and oxidative stresses in crop plants. Biotechnol Adv 40\u0026ndash;107503.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRaksha Singh, Goodwin SB. Exploring the Corn Microbiome: A Detailed Review on Current Knowledge, Techniques, and Future Directions. Phyto Front. 2022;2:158\u0026ndash;75.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRokhzadi A, Darvish asgharzadehA, Nour F mohamadi,G., and, Majidi A. Influence of plant growth promoting rhizobacteria on dry matter accumulation and yield of chickpea (\u003cem\u003ecicer arietinum\u003c/em\u003e L.) under field condition. Am \u0026ndash;Eurasian J Agric Environ Sci. 2008;3(2):253\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBapiri -A, Asgarzadeh A, Mojallali H, Khavazi K. Ebrahim Pazira. 2012.Evaluation of Zinc solubilization potential by different strain of Fluorescent pseudomonads. J Appl sci Environ manage.16(3).pp. 295\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTable 1 is not available with this version.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Corn, PGPR, macronutrients, micronutrients, SC704, sustainable agricultural","lastPublishedDoi":"10.21203/rs.3.rs-8211736/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8211736/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe growing need for sustainable agricultural practices has driven interest in the use of Plant Growth-Promoting Rhizobacteria (PGPR) as a natural means to enhance crop productivity and nutrient content. Maize (\u003cem\u003eZea mays\u003c/em\u003e), a staple food crop worldwide, can greatly benefit from such biological interventions. This study explores the role of three PGPR species \u003cem\u003eAzotobacter chroococcum\u003c/em\u003e (AZ), \u003cem\u003eAzospirillum lipoferum\u003c/em\u003e (AS), and \u003cem\u003ePseudomonas fluorescens\u003c/em\u003e (PS) in boosting the mineral nutrient content of maize seeds, focusing on three different hybrids: SC704, SC700, and B73\u0026times;K18. The experiment was conducted using a completely randomized design (CRD) to ensure robust and unbiased results. Maize seeds were inoculated with each PGPR strain individually, as well as in combination, and compared with a non-inoculated control group. The mineral content, including Nitrogen (N), Phosphorus (P), Potassium (K), Iron (Fe), Zinc (Zn), Magnesium (Mg), and Copper (Cu), was quantitatively analyzed. Statistical analysis was performed to assess the significance of the results. The results showed that the PGPR inoculation led to a significant increase in nutrient content across all maize hybrids compared to the control. The SC704 hybrid showed the highest improvement, with increases of X% in Iron, X% in Potassium, and X% in Nitrogen compared to the control. The combined application of AZ, AS, and PS yielded even greater enhancements, with a X% increase in Iron content in SC704, outperforming individual treatments. The study demonstrates that PGPR can effectively enhance the nutrient content of maize, with a notable dependency on the maize hybrid and the specific bacterial strain used. The SC704 hybrid, in particular, showed the most significant response.\u003c/p\u003e","manuscriptTitle":"Enhancing nutrient content in Maize: comparative effects of plant growth-promoting rhizobacteria across various Maize hybrids","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-13 18:22:58","doi":"10.21203/rs.3.rs-8211736/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"1a5bab32-c0bf-4690-8ed3-825a4deb4446","owner":[],"postedDate":"December 13th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-12-15T08:40:00+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-13 18:22:58","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8211736","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8211736","identity":"rs-8211736","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}