Search Results (45)

Azospirillum is a well-studied genus of plant growth-promoting rhizobacteria (PGPR) and one of the most extensively researched diazotrophs. This genus can colonize rhizosphere soil and enhance plant growth and productivity by supplying essential nutrients to the host. Azospirillum–plant interactions involve multiple mechanisms, including nitrogen fixation, the production of phytohormones (auxins, cytokinins, indole acetic acid (IAA), and gibberellins), plant growth regulators, siderophore production, phosphate solubilization, and the synthesis of various bioactive molecules, such as flavonoids, hydrogen cyanide (HCN), and catalase. Thus, Azospirillum is involved in plant growth and development. The genus Azospirillum also enhances membrane activity by modifying the composition of membrane phospholipids and fatty acids, thereby ensuring membrane fluidity under water deficiency. It promotes the development of adventitious root systems, increases mineral and water uptake, mitigates environmental stressors (both biotic and abiotic), and exhibits antipathogenic activity. Biological nitrogen fixation (BNF) is the primary mechanism of Azospirillum, which is governed by structural nif genes present in all diazotrophic species. Globally, Azospirillum spp. are widely used as inoculants for commercial crop production. It is considered a non-pathogenic bacterium that can be utilized as a biofertilizer for a variety of crops, particularly cereals and grasses such as rice and wheat, which are economically significant for agriculture. Furthermore, Azospirillum spp. influence gene expression pathways in plants, enhancing their resistance to biotic and abiotic stressors. Advances in genomics and transcriptomics have provided new insights into plant-microbe interactions. This review explored the molecular mechanisms underlying the role of Azospirillum spp. in plant growth. Additionally, BNF phytohormone synthesis, root architecture modification for nutrient uptake and stress tolerance, and immobilization for enhanced crop production are also important. A deeper understanding of the molecular basis of Azospirillum in biofertilizer and biostimulant development, as well as genetically engineered and immobilized strains for improved phosphate solubilization and nitrogen fixation, will contribute to sustainable agricultural practices and help to meet global food security demands. Full article

Water scarcity can negatively affect crop yield, posing a significant threat to global food security, such as drought. Plant growth-promoting rhizobacteria (PGPR), either as single strains or synthetic communities (SynComs), has shown promise in alleviating drought stress in various plant species. In this study, we examined the effects of water limitation on Salvia officinalis and the potential of a SynCom composed of five phosphate-solubilizing, auxin-producing, and/or nitrogen-fixing Gram-negative bacteria to enhance plant growth and drought tolerance. Plant growth, morphology, physiology, and leaf metabolomic profiles were assessed using a combination of physiological measurements and LC-MS untargeted metabolomics. Mild water stress induced a conservative water-use strategy in S. officinalis, characterized by increased root-to-shoot ratio and altered leaf morphology, without compromising photosynthetic performance. SynCom inoculation under well-watered conditions elicited drought-like responses, including transient reductions in stomatal conductance. Leaf metabolomic analysis revealed that inoculation influenced the abundance of several metabolites, including biogenic amines and dipeptides, under both irrigation regimes. Notably, drought stress and SynCom inoculation increased histamine and α-ketoglutaric acid levels, highlighting potential impacts on food quality. Under reduced irrigation, inoculation further modulated leaf morphology and biomass allocation, promoting thicker leaves and increased root biomass allocation. These results demonstrate the ability of the SynCom to modulate plant physiology and metabolism in response to both optimal and reduced irrigation, potentially enhancing drought resilience without directly improving growth. The study also highlights the complex interactions among microbial inoculation, plant stress responses, and leaf metabolite profiles, emphasizing the importance of considering the effects on the production of bioactive compounds when developing microbial inoculants for edible plants. Full article

Biocontrol has emerged as an effective strategy for managing plant pathogens and pests. The use of plant growth-promoting rhizobacteria (PGPR) as biocontrol agents offers a sustainable alternative, enhancing plant morphology, biochemistry, physiology, and secondary metabolism. This study conducts a bibliometric analysis and systematic review of PGPR-based biocontrol research from 2019 to 2023, using the Web of Science (WoS) database. A total of 2823 publications were identified, with a significant increase in scientific output since 2019. Original research articles dominated the field, with India, China, the USA, and Pakistan leading in publication volume. Key contributors included Babalola (North-West University, South Africa), Kloepper (Auburn University, USA), and Shen (Nanjing Agricultural University, China), each with at least 25 publications. Co-authorship analysis revealed four major research networks centered in India, China, Brazil, and Canada. Bacillus and Pseudomonas were the most studied PGPR genera, recognized for their roles as bioinoculants, bioremediators, and biostimulants, mitigating the negative impacts of synthetic fertilizers and pesticides. This analysis underscores the growing global focus on PGPR-based biocontrol and its potential for sustainable agriculture. Strengthening international collaboration and accelerating applied research on PGPR formulations will be critical for optimizing their efficacy and scalability in real-world agricultural systems. Full article

Soilless cultivation allows for the exploitation of the benefits of plant growth-promoting rhizobacteria (PGPR) without the loss of efficacy observed with soil inoculation. In this study, we investigated the effects of a PGPR consortium on the plant growth, ecophysiology, and metabolic profile of lettuce (Lactuca sativa L.) grown in an aeroponic system under a low-nutrient regime. Overall, the plant biomass increased by 25% in the PGPR-inoculated plants due to enhanced leaf and root growth. The rise in the leaf biomass was primarily due to an increase in the leaf number and average leaf mass, coupled with a higher total leaf area. In addition, the inoculated plants exhibited an altered leaf anatomy characterized by an increased palisade parenchyma thickness and reduced airspace area, suggesting an improved photosynthetic efficiency and changes in the mesophyll conductance. The root morphology was also altered, with the PGPR-inoculated plants showing higher lateral root development. Furthermore, PGPR inoculation induced significant metabolic reprogramming in the leaves, affecting several pathways related to growth, development, and stress responses. These findings provide valuable insights into the intricate metabolic dialog between plants and beneficial microbes and demonstrate that the integration of soilless culture with an analysis of the ecophysiological, anatomical, and metabolomic plant responses can be a powerful approach to accelerate the design of new PGPR consortia for use as microbial biostimulants. Full article

Microbial plant biostimulants offer a promising, sustainable solution for enhancing plant growth and resilience, particularly under abiotic stress conditions such as drought, salinity, extreme temperatures, and heavy metal toxicity. These biostimulants, including plant growth-promoting rhizobacteria, mycorrhizal fungi, and nitrogen-fixing bacteria, enhance plant tolerance through mechanisms such as phytohormone production, nutrient solubilization, osmotic adjustment, and antioxidant enzyme activation. Advances in genomics, metagenomics, transcriptomics, and proteomics have significantly expanded our understanding of plant–microbe molecular communication in the rhizosphere, revealing mechanisms underlying these interactions that promote stress resilience. However, challenges such as inconsistent field performance, knowledge gaps in stress-related molecular signaling, and regulatory hurdles continue to limit broader biostimulant adoption. Despite these challenges, microbial biostimulants hold significant potential for advancing agricultural sustainability, particularly amid climate change-induced stresses. Future studies and innovation, including Clustered Regularly Interspaced Short Palindromic Repeats and other molecular editing tools, should optimize biostimulant formulations and their application for diverse agro-ecological systems. This review aims to underscore current advances, challenges, and future directions in the field, advocating for a multidisciplinary approach to fully harness the potential of biostimulants in modern agriculture. Full article

Biostimulants include a wide array of microorganisms and substances that can exert beneficial effects on plant development and growth, often enhancing nutrient uptake and improving tolerance against abiotic and biotic stress. Depending on their composition and time of application, these products can influence plant physiology directly as growth regulators or indirectly through environmental condition changes in the rhizosphere, such as nutrient and water availability. This review evaluated 48 case studies from 39 papers to summarize the effects of biostimulant application on fruit and tuber yields and on the quality of processing tomato and potato in open field conditions. For potato, PGPR bacteria were the main studied biostimulant, whereas the low number of studies on processing tomato did not permit us to delineate a trend. The yield and quality were greatly influenced by cultivars and biostimulant composition, application method, period, and dose. For processing tomato, a positive effect of the biostimulant application on the marketable yield was reported in 79% of the case studies, whereas for potato, the effect was reported in only 47%. Few studies, on processing tomato and potato, also reported data for quality parameters with contrasting results. The variability of crop response to biostimulant application in open field conditions highlights the need for more comprehensive studies. Such studies should focus on diverse cultivars, deeply understand the interaction of biostimulant application with agronomic management (e.g., irrigation and fertilization), and evaluate yield and quality parameters. This approach is crucial to fully understand the potential and limitations of biostimulant applications in agriculture, particularly regarding their role in sustainable crop production. Full article

This study investigated the combined effects of novel plant growth-promoting rhizobacteria (PGPR)—Agrobacterium pusense NC2, Kosakonia oryzae WN104, and Phytobacter sp. WL65—and Ascophyllum nodosum seaweed extract (ANE) as biostimulants (PGPR-ANE) on rice growth, yield, and rhizosphere bacterial communities using the RD79 cultivar. The biostimulants significantly enhanced plant growth, shoot and root length, and seedling vigour; however, seed germination was not affected. In pot experiments, biostimulant application significantly increased the richness and evenness of bacterial communities in the rhizosphere, resulting in improvements in rice growth and yield, with increases in plant height (9.6–17.7%), panicle length (14.3–17.9%), and seeds per panicle (48.0–53.0%). Notably, biostimulant treatments also increased post-harvest soil nutrient levels, with nitrogen increasing by 7.7–19.2%, phosphorus by 43.4–161.4%, and potassium by 16.9–70.4% compared to the control. Principal coordinate analysis revealed distinct differences in bacterial composition between the tillering and harvesting stages, as well as between biostimulant treatments and the control. Beneficial bacterial families, including Xanthobacteraceae, Beijerinckiaceae, Acetobacteraceae, Acidobacteriaceae, and Hyphomicrobiaceae, increased in number from the tillering to harvesting stages, likely contributing to soil health improvements. Conversely, methanogenic bacterial families, such as Methanobacteriaceae and Methanosarcinaceae, decreased in number compared to the control. These findings highlight the dynamic responses of the rhizosphere microbiome to biostimulant treatments and underscore their potential benefits for promoting sustainable and productive agriculture. Full article

The use of plant growth-promoting rhizobacteria presents a promising addition to conventional mineral fertilizer use and an alternative strategy for sustainable agricultural crop production. However, genotypic variations in the plant host may result in variability of the beneficial effects from these plant–microbe interactions. This study examined growth promotion effects of commercial vegetable crop cultivars of tomato, cucumber and broccoli following application with five rhizosphere bacteria. Biochemical assays revealed that the bacterial strains used possess several nutrient acquisition traits that benefit plants, including nitrogen fixation, phosphate solubilization, biofilm formation, and indole-3-acetic acid (IAA) production. However, different host cultivars displayed genotype-specific responses from the inoculations, resulting in significant (p < 0.05) plant growth promotion in some cultivars but insignificant (p > 0.05) or no growth promotion in others. Gene expression profiling in tomato cultivars revealed that these cultivar-specific phenotypes are reflected in differential expressions of defense and nutrient acquisition genes, suggesting that plants can be categorized into “microbe-friendly” cultivars (with little or no defense responses against beneficial microbes) and “microbe-hostile” cultivars (with strong defense responses). These results validate the notion that “microbe-friendly” (positive interaction with rhizosphere microbes) should be considered an important trait in breeding programs when developing new cultivars which could result in improved crop yields. Full article

This study investigates arbuscular mycorrhizal fungi (AMF), plant growth-promoting rhizobacteria (PGPR), and their combined application under salt stress (200 mM NaCl), emphasizing their synergistic potential to enhance plant resilience. Conducted in a controlled climate chamber, key parameters such as plant height, biomass, SPAD values, ion leakage, relative water content (RWC), osmotic potential, and mineral uptake were assessed. Salt stress significantly reduced plant growth, chlorophyll content, and nutrient absorption. However, AMF and PGPR improved plant performance, with co-inoculation showing the highest efficacy in increasing RWC, nutrient uptake, and maintaining membrane stability. AMF and PGPR treatments enhanced potassium retention and reduced sodium and chloride accumulation, mitigating ionic imbalances. The improved chlorophyll content and water relations under co-inoculation demonstrate the potential of these biostimulants to boost photosynthesis and plant resilience. These findings highlight AMF and PGPR as eco-friendly solutions for sustainable agriculture, promoting crop productivity and stress tolerance under saline conditions. Full article

The application of biostimulants in vegetable cultivation has emerged as a promising approach to enhance the nutritional quality of crops, particularly in controlled environment agriculture and soilless culture systems. In this study, we employed a rigorous methodology, applying various biostimulants amino acids, Plant Growth-Promoting Rhizobacteria (PGPR), fulvic acid, chitosan, and vermicompost along with mineral fertilizers, both foliar and via the roots, to soilless greenhouse tomatoes during spring cultivation. The experiment, conducted in a coir pith medium using the ‘Samyeli F1’ tomato cultivar, demonstrated that plants treated with biostimulants performed better than control plants. Notable variations in nutritional components were observed across treatments. PGPR had the best effects on the physical properties of the tomato fruit, showing the highest fruit weight, fruit length, equatorial diameter, fruit volume, fruit skin elasticity, and fruit flesh hardness while maintaining high color parameters L, a, and b. PGPR and fulvic acid demonstrated significant enhancements in total phenolics and flavonoids, suggesting potential boosts in antioxidant properties. Amioacid and vermicompost notably elevated total soluble solids, indicating potential fruit sweetness and overall taste improvements. On the other hand, vermicompost stood out for its ability to elevate total phenolics and flavonoids while enhancing vitamin C content, indicating a comprehensive enhancement of nutritional quality. In addition, vermicompost had the most significant impact on plant growth parameters and total yield, achieving a 43% increase over the control with a total yield of 10.39 kg/m². These findings underline the specific nutritional benefits of different biostimulants, offering valuable insights for optimizing tomato cultivation practices to yield produce with enhanced health-promoting properties. Full article

Maize, a globally significant cereal, is increasingly cultivated under challenging environmental conditions, necessitating innovations in sustainable agriculture. This study evaluates the synergistic effects of a novel technique combining a Bacillus velezensis A6 strain with a plant extract from the Lamiales order on maize growth and stress resilience. Employing a pilot field trial, this study was conducted on the “La Añoreta” experimental farm of the ECONATUR group, where various biostimulant treatments, including bacterial and plant extract applications, were tested against a control group. The treatments were applied during key vegetative growth stages (V10-Tenth-Leaf, VT-Tassel, R1-Silking) and monitored for effects on plant height, biomass, and fumonisin content. The results suggest that the combined treatment of Bacillus velezensis A6 and the plant extract increases maize height (32.87%) and yield (62.93%) and also reduces fumonisin concentrations, improving its resistance to stress, compared to the control and other treatments. This study highlights the potential of microbial and botanical biostimulants and its novel combination for improving crop productivity and sustainability, suggesting that such synergistic combinations could play a crucial role in enhancing agricultural resilience to environmental stresses. Full article

Portulaca oleracea L. is a wild edible plant with high potential for exploitation in commercial cropping systems due to its nutritional value and great adaptability to abiotic stress conditions. The present study aimed to investigate the response of purslane plants grown under drought stress conditions (100%, 80%, and 60% of field capacity (FC)) and the implementation of biostimulant amendments (control without amendment, plant growth-promoting rhizobacteria (PGPR), mycorrhiza, and effective microorganisms (EMs)) for two consecutive years. In the two-year experiment, the greatest height was recorded in plants grown under no-stress conditions and inoculated with PGPR. The highest branch number, and fresh and dry weight of aboveground and underground parts were observed under no-stress conditions at the mycorrhiza treatment. Moreover, mycorrhiza application in plants growing under 100% FC resulted in the highest N, P, total carbohydrates, and vitamin C and the lowest nitrate and proline contents in leaves. Purslane plants grown under 100% FC and inoculated with PGPR treatment resulted in the highest K and total chlorophyll leaf contents. Additionally, growing plants under mild drought stress (80% FC) combined with biostimulant application (e.g., inoculation with mycorrhiza, PGPR, and EM) may improve plant growth characteristics and mitigate negative stress effects. In general, the applied biostimulant amendments alleviated the adverse effects of drought on plant growth and leaf chemical composition indicating the importance of sustainable strategies to achieve high yield and sufficient quality within the climate change scenario. Full article

Plant biostimulants have received attention as sustainable alternatives to chemical fertilizers. Extracellular polymeric substances (EPSs), among the compounds secreted by plant growth-promoting rhizobacteria (PGPRs), are assumed to alleviate abiotic stress. This study aims to investigate the effect of purified EPSs on rice under abiotic stress and analyze their mechanisms. A pot experiment was conducted to elucidate the effects of inoculating EPSs purified from PGPRs that increase biofilm production in the presence of sugar on rice growth in heat-stress conditions. Since all EPSs showed improvement in SPAD after the stress, Enterobacter ludwigii, which was not characterized as showing higher PGP bioactivities such as phytohormone production, nitrogen fixation, and phosphorus solubilization, was selected for further analysis. RNA extracted from the embryos of germinating seeds at 24 h post-treatment with EPSs or water was used for transcriptome analysis. The RNA-seq analysis revealed 215 differentially expressed genes (DEGs) identified in rice seeds, including 139 up-regulated and 76 down-regulated genes. A gene ontology (GO) enrichment analysis showed that the enriched GO terms are mainly associated with the ROS scavenging processes, detoxification pathways, and response to oxidative stress. For example, the expression of the gene encoding OsAAO5, which is known to function in detoxifying oxidative stress, was two times increased by EPS treatment. Moreover, EPS application improved SPAD and dry weights of shoot and root by 90%, 14%, and 27%, respectively, under drought stress and increased SPAD by 59% under salt stress. It indicates that bacterial EPSs improved plant growth under abiotic stresses. Based on our results, we consider that EPSs purified from Enterobacter ludwigii can be used to develop biostimulants for rice. Full article

To optimize the application of plant growth-promoting rhizobacteria (PGPR) in field trials, tracking methods are needed to assess their shelf life and to determine the elements affecting their effectiveness and their interactions with plants and native soil microbiota. This work developed a real-time PCR (qtPCR) method which traces and quantifies bacteria when added as microbial consortia, including five PGPR species: Burkholderia ambifaria, Bacillus amyloliquefaciens, Azotobacter chroococcum, Pseudomonas fluorescens, and Rahnella aquatilis. Through a literature search and in silico sequence analyses, a set of primer pairs which selectively tag three bacterial species (B. ambifaria, B. amyloliquefaciens and R. aquatilis) was retrieved. The primers were used to trace these microbial species in a field trial in which the consortium was tested as a biostimulant on two wheat varieties, in combination with biochar and the mycorrhizal fungus Rhizophagus intraradices. The qtPCR assay demonstrated that the targeted bacteria had colonized and grown into the soil, reaching a maximum of growth between 15 and 20 days after inoculum. The results also showed biochar had a positive effect on PGPR growth. In conclusion, qtPCR was once more an effective method to trace the fate of supplied bacterial species in the consortium when used as a cargo system for their delivery. Full article

As climate change is an imminent threat to the environment and agriculture, there is an increasing need to find immediate solutions capable of compensating for water deficits even in semi-arid conditions. This study is focused on the evaluation of the vegetative growth of grapevine plants Vitis vinifera L., of the Greek variety “Debina” in a water deficit environment, with the application of two bacterial-based formulations: one with Bacillus amyloliquefaciens (strain QST 713) and one with Sinorhizobium meliloti (strain cepa B2352). The two formulations were tested under rational irrigation (100% of Available Water) and deficit irrigation (57% of AW). After 140 days, plant growth parameters, such as total plant growth length, leaf area, roots, shoots, and leaves dry biomass showed better performance on treatments with plant growth-promoting rhizobacteria (PGPR) formulations under either rational or deficit irrigation conditions. In addition, the metabolic response of the grapevine plants to the deficit irrigation stress, such as the total chlorophyll, leaf relative water, total phenolic, and proline content, proved to be enriched on the treatments with PGPR formulations during this experiment. The two formulations, in conditions of abiotic stress, achieved to almost compensate for the irrigation deficit, boosting the plant metabolism. This study reveals the need for further research on PGPR biostimulants, as this first trial of these formulations on grapevine could be significant in the case of water scarcity and climate change. Full article