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The use of environmental-stress resilient plant growth promoting rhizobacteria (PGPR) offers an organic solution to sustainable agriculture, under rapid climate change. Our laboratory has previously reported the drought-ameliorating property of an exopolysaccharide-secreting PGPR strain, Bacillus endophyticus J13 on Arabidopsis thaliana. In this study, A. thaliana roots were inoculated with J13 under well-watered and water-stressed conditions (under controlled plant growth conditions). To understand the mechanism of drought amelioration, impact of J13 on plant ABA biosynthesis and signaling was analyzed. It was found that the ABA levels in water-stress, inoculated plants were lower than the water-stressed plants, without inoculation. Also, the expression of ABA biosynthesis genes: NCED3, AAO3 and ABA2, was downregulated in inoculated treatments under water-stress as compared to non-inoculated, water-stress treatments. J13 did not cause any modulation in the expression of ABA-dependent signaling gene SnRK2 and the ABA-independent signaling gene, DREB2A, under water-stress in Arabidopsis shoots. On treating the bacteria with EDTA (which negatively impacts biofilm levels), we observed that J13 fails to impart stress tolerance to plants under water deficit conditions. The soil moisture content in soil adhered to roots and exopolysaccharide (EPS) content was significantly higher in the plants under water-stressed, inoculated treatments than the non-inoculated plants. This study unravels the mechanism of drought amelioration by J-13 on Arabidopsis by modulating soil moisture content through EPS secretion, thereby eliminating the need for enhanced ABA biosynthesis and signaling. [ABSTRACT FROM AUTHOR]

Background: Oxidative stress mediated by reactive oxygen species (ROS) is a common denominator in arsenic toxicity. Arsenic stress in soil affects the water absorption, decrease stomatal conductance, reduction in osmotic, and leaf water potential, which restrict water uptake and osmotic stress in plants. Arsenic-induced osmotic stress triggers the overproduction of ROS, which causes a number of germination, physiological, biochemical, and antioxidant alterations. Antioxidants with potential to reduce ROS levels ameliorate the arsenic-induced lesions. Plant growth promoting rhizobacteria (PGPR) increase the total soluble sugars and proline, which scavenging OH radicals thereby prevent the oxidative damages cause by ROS. The main objective of this study was to evaluate the potential role of Arsenic resistant PGPR in growth of maize by mitigating arsenic stress. Methodology: Arsenic tolerant PGPR strain MD3 (Pseudochrobactrum asaccharolyticum) was used to dismiss the 'As' induced oxidative stress in maize grown at concentrations of 50 and 100 mg/kg. Previously isolated arsenic tolerant bacterial strain MD3 "Pseudochrobactrum asaccharolyticum was used for this experiment. Further, growth promoting potential of MD3 was done by germination and physio-biochemical analysis of maize seeds. Experimental units were arranged in Completely Randomized Design (CRD). A total of 6 sets of treatments viz., control, arsenic treated (50 & 100 mg/kg), bacterial inoculated (MD3), and arsenic stress plus bacterial inoculated with three replicates were used for Petri plates and pot experiments. After treating with this MD3 strain, seeds of corn were grown in pots filled with or without 50 mg/kg and 100 mg/kg sodium arsenate. Results: The plants under arsenic stress (100 mg/kg) decreased the osmotic potential (0.8 MPa) as compared to control indicated the osmotic stress, which caused the reduction in growth, physiological parameters, proline accumulation, alteration in antioxidant enzymes (Superoxide dismutase-SOD, catalase-CAT, peroxidase-POD), increased MDA content, and H2O2 in maize plants. As-tolerant Pseudochrobactrum asaccharolyticum improved the plant growth by reducing the oxidation stress and antioxidant enzymes by proline accumulation. PCA analysis revealed that all six treatments scattered differently across the PC1 and PC2, having 85.51% and 9.72% data variance, respectively. This indicating the efficiency of As-tolerant strains. The heatmap supported the As-tolerant strains were positively correlated with growth parameters and physiological activities of the maize plants. Conclusion: This study concluded that Pseudochrobactrum asaccharolyticum reduced the 'As' toxicity in maize plant through the augmentation of the antioxidant defense system. Thus, MD3 (Pseudochrobactrum asaccharolyticum) strain can be considered as bio-fertilizer. [ABSTRACT FROM AUTHOR]

Abiotic stress refers to the diverse range of environmental challenges that plants encounter. Environmental stressors such as salt, temperature, nutritional deprivation, and heavy metal toxicity can lead to problems in the functioning of seedling adaption systems. Furthermore, they can hinder the formation of plumules and radicles in seedlings, as well as their subsequent development and growth, both of which can lead to reduced crop production. Soil salinity poses a significant challenge to global food supply since salt stress dominates as a primary determinant constraining agricultural productivity. By the year 2050, it is projected that drought stress will result in a 50% reduction in global productivity. Multiple methodologies, including biotechnological approaches, conventional breeding methods, conservative breeding, agronomical approaches, and priming techniques, have shown effectiveness in reducing the negative impacts of abiotic stress and adapting to its severe conditions. The use of seed priming treatments regulates the production of antioxidants and promotes the accumulation of osmolytes to mitigate the negative consequences of various abiotic stress responses. When subjected to abiotic stress, crop plants cultivated from primed seeds respond rapidly at the cellular level. The major emphasis of this review is on the impact of abiotic stress on plant physiology and productivity, strategies for its management, and possible solutions. Furthermore, it explores several methods of priming, namely bio priming with PGPR, a biological technique that entails the introduction of bacteria. [ABSTRACT FROM AUTHOR]

Plants have limited resources to allocate to defences against infection and herbivory. While interactions between plant responses to microbial and herbivore attack are complex, it is often the case that the induction of one response will act antagonistically to the other. Recent studies have shown that plant growth promoting rhizobacteria, which improves overall plant health and general stress resistance, can enhance both anti-microbial and anti-herbivore defences. We investigated how soil application of the biofungicide Serenade ASO (Bacillus subtilis strain QST 713), which primes plant defences against fungal and bacterial infection and promotes plant growth, affects anti-herbivore defences by measuring both constitutive and induced defences. We applied Serenade one or two times to the soil of tomato plants and measured the numbers of type IV glandular trichomes on leaves, the weight gain of a generalist caterpillar (beet armyworms; BAW), and the activity of two enzymes associated with defence against insects (polyphenoloxidase and peroxidase). Serenade treated plants grew faster and foliage from treated plants had significantly higher numbers of glandular trichomes and higher polyphenoloxidase and peroxidase activities than untreated plants. However, Serenade treatment did not affect the degree of induction of plant defences when damaged by BAW feeding and did not slow the growth rate of BAW relative to plants not treated with Serenade. Therefore, the biofungicide Serenade increased plant growth and altered the densities of trichomes and the activities of two defensive enzymes in plants, but it did not affect overall susceptibility of the plants to a generalist herbivore. [ABSTRACT FROM AUTHOR]

Abstract Background Oxidative stress mediated by reactive oxygen species (ROS) is a common denominator in arsenic toxicity. Arsenic stress in soil affects the water absorption, decrease stomatal conductance, reduction in osmotic, and leaf water potential, which restrict water uptake and osmotic stress in plants. Arsenic-induced osmotic stress triggers the overproduction of ROS, which causes a number of germination, physiological, biochemical, and antioxidant alterations. Antioxidants with potential to reduce ROS levels ameliorate the arsenic-induced lesions. Plant growth promoting rhizobacteria (PGPR) increase the total soluble sugars and proline, which scavenging OH radicals thereby prevent the oxidative damages cause by ROS. The main objective of this study was to evaluate the potential role of Arsenic resistant PGPR in growth of maize by mitigating arsenic stress. Methodology Arsenic tolerant PGPR strain MD3 (Pseudochrobactrum asaccharolyticum) was used to dismiss the ‘As’ induced oxidative stress in maize grown at concentrations of 50 and 100 mg/kg. Previously isolated arsenic tolerant bacterial strain MD3 “Pseudochrobactrum asaccharolyticum was used for this experiment. Further, growth promoting potential of MD3 was done by germination and physio-biochemical analysis of maize seeds. Experimental units were arranged in Completely Randomized Design (CRD). A total of 6 sets of treatments viz., control, arsenic treated (50 & 100 mg/kg), bacterial inoculated (MD3), and arsenic stress plus bacterial inoculated with three replicates were used for Petri plates and pot experiments. After treating with this MD3 strain, seeds of corn were grown in pots filled with or without 50 mg/kg and 100 mg/kg sodium arsenate. Results The plants under arsenic stress (100 mg/kg) decreased the osmotic potential (0.8 MPa) as compared to control indicated the osmotic stress, which caused the reduction in growth, physiological parameters, proline accumulation, alteration in antioxidant enzymes (Superoxide dismutase-SOD, catalase-CAT, peroxidase-POD), increased MDA content, and H2O2 in maize plants. As-tolerant Pseudochrobactrum asaccharolyticum improved the plant growth by reducing the oxidation stress and antioxidant enzymes by proline accumulation. PCA analysis revealed that all six treatments scattered differently across the PC1 and PC2, having 85.51% and 9.72% data variance, respectively. This indicating the efficiency of As-tolerant strains. The heatmap supported the As-tolerant strains were positively correlated with growth parameters and physiological activities of the maize plants. Conclusion This study concluded that Pseudochrobactrum asaccharolyticum reduced the ‘As’ toxicity in maize plant through the augmentation of the antioxidant defense system. Thus, MD3 (Pseudochrobactrum asaccharolyticum) strain can be considered as bio-fertilizer.

Phosphorus (P) is the second most important macro-element for plant growth, and its low availability in soil is a major obstacle to crop production. Inorganic phosphate (Pi) is the least available form in the soil, while organic phosphate (Po) is the most dominant one, up to 80% of which exists as inositol hexakisphosphate, also known as phytic acid (PA) that cannot be absorbed by plant roots unless hydrolyzed by microbial phytases. Similar to phosphate-solubilizing bacteria, many plant growth-promoting rhizobacteria (PGPR) can play a relevant role in phosphate turnover. In our study, we screened a series of PGPR strains for phytase activities using PA as a sole source of P. Three strains (named C2, N4, and S10) with relatively high phytase activities ranging from 42.84 to 100.55 Units g−1 were selected for barley growth assays. When barley plants grown in poor sandy soil and irrigated with a PA-containing solution were inoculated with each of these PGPR isolates, a significant growth enhancement was observed. This positive effect was well illustrated by an increase in root growth, plant height, and chlorophyll contents. In addition, the inoculated barley plants accumulated significantly higher Pi contents in leaves and roots compared to non-inoculated plants. Finally, the expression of a number of high-affinity Pi transporter genes (PHT1.1, PHT1.4, PHT1.8, and PHT1.6) in inoculated barley plants was downregulated especially in roots, compared to non-inoculated plants. This difference is most likely due to the bacterial phytases that change the P availability in the rhizosphere. In summary, these three strains can improve barley growth under phosphate-limited conditions and should be considered in developing eco-friendly biofertilizers as an alternative to conventional P fertilizers. [ABSTRACT FROM AUTHOR]

Aim Bacterial exopolysaccharides (EPS) possess numerous properties beneficial for the growth of microbes and plants under hostile conditions. The study aimed to develop a bioformulation with bacterial EPS to enhance the bioinoculant's shelf life and functional efficacy under salinity stress. Methods and results High EPS-producing and salt-tolerant bacterial strain (Bacillus haynessi SD2) exhibiting auxin-production, phosphate-solubilization, and biofilm-forming ability, was selected. EPS-based bioformulation of SD2 improved the growth of three legumes under salt stress, from which pigeonpea was selected for further experiments. SD2 improved the growth and lowered the accumulation of stress markers in plants under salt stress. Bioformulations with varying EPS concentrations (1% and 2%) were stored for 6 months at 4°C, 30°C, and 37°C to assess their shelf life and functional efficacy. The shelf life and efficacy of EPS-based bioformulation were sustained even after 6 months of storage at high temperature, enhancing pigeonpea growth under stress in both control and natural conditions. However, the efficacy of non EPS-based bioformulation declined following four months of storage. The bioformulation (with 1% EPS) modulated bacterial abundance in the plant's rhizosphere under stress conditions. Conclusion The study brings forth a new strategy for developing next-generation bioformulations with higher shelf life and efficacy for salinity stress management in pigeonpea. [ABSTRACT FROM AUTHOR]

The article presents a study which investigated the fluorescent Pseudomonads against coriander powdery mildew under in vitro conditions. Topics discussed include identification of fluorescent Pseudomonads, biochemical characterization of fluorescent Pseudomonads, and assessment of fluorescent Pseudomonads under in vitro condition.

In order to screen out Actinomycetes which can significantly inhibit Xanthomonas oryzae pv. oryzae (Xoo), and X. oryzae pv. oryzicola (Xoc), this study collected soil from various plant rhizospheres and isolated 60 strains of Actinomycetes using the dilution-spread and streak-plate isolation methods. Through the co-culture and the oxford cup methods, one of the 60 strains of Actinomycetes, strain Sc-7, which has significant inhibitory effects against Xoo and Xoc was obtained. Based on morphological and microscopic observations, physiological and biochemical experiments, and polygenic cluster analysis, a phylogenetic evolutionary tree was constructed and this strain Sc-7 was identified as Streptomyces lavendulae. The potting experiment demonstrated that spraying 2-fold fermentation dilution of strain Sc-7 before pathogen inoculation had prevention control efficiency of 74.57% and 65.33% on rice BLB and BLS, respectively, and the lengths of the lesions were significantly shortened. The treatment with fermentation filtrate of strain Sc-7 made Xoc and Xoo cells extensively lysed, crumpled, and perforated, and increased cell membrane permeability and decreased extracellular polysaccharides. In addition, germination promotion assays demonstrated that different dilutions of strain Sc-7 fermentation broth could promote the growth of rice seed buds and roots. Compared with sterile water treatment, the treatments with fermentation at 10-fold and 50-fold dilutions increased the shoot length by 32.79% and 37.70% and root length by 75.00% and 97.00%, respectively. Tube-based seedling assays showed that 10-fold and 50-fold dilutions of strain Sc-7 fermentation increased plant height by 16.68% and 10.53%, respectively. Salt stress alleviation experiments exhibited that the treatment with 10-fold fermentation dilution of strain Sc-7 alleviated the rice symptoms caused by salt stress to a certain extent. The above results indicate that strain Sc-7 has the potential to promote plant growth and prevent diseases and is expected to be developed as a biopesticide and biofertilizer. [ABSTRACT FROM AUTHOR]

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Soil contamination with microplastics (MPs) is a persistent threat to crop production worldwide. With a wide range of MP types, including polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE), contaminating our environment, it is important to understand their impact on agricultural productivity. The present study was conducted to investigate the effects of different types of MPs (PS, PVC and PE) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and non-enzymatic), gene expression, proline metabolism, the AsA-GSH cycle and cellular fractionation and nutritional status, in different parts of rice (Oryza sativa L.) seedlings, which were also exposed to plant growth promoting rhizobacteria (PGPR), i.e. Bacillus mycoides PM35, i.e. 20 μL. The research outcomes indicated that the different types of MPs in the soil notably reduced plant growth and biomass, photosynthetic pigments and gas exchange attributes. However, MP stress also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolyte leakage (EL) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the fractionations of cellular components was observed. Although the application of B. mycoides PM35 showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased oxidative stress. In addition, the application of B. mycoides PM35 enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in O. sativa plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of MP contamination in agricultural soils. [ABSTRACT FROM AUTHOR]

Abstract Utilizing coastal land for agriculture presents challenges such as low water content, high soil salinity, and low organic compound content. To support plant growth under these conditions, biofertilizers composed of plant growth promoting Rhizobacteria (PGPR), especially those inhabiting coastal areas, are needed. The Parangkusumo sand dunes on the southern coast of Java, Indonesia, is a unique coastal ecosystem characterized by arid conditions, high temperatures, and high soil salinity. To date, no studies have reported the isolation of PGPR from this ecosystem. This study is the first to isolate and identify PGPR associated with Spinifex littoreus, a dominant plant species in the Parangkusumo sand dunes, which are adapted to the harsh condition of Parangkusumo sand dunes. Ten rhizobacterial isolates were obtained, with five identified as members of the Bacillaceae family. All isolates demonstrated phosphate solubilization activity, while seven exhibited cellulolytic activity. One isolate, Priestia aryabhattai strain 2, notably showed phosphate solubilization and nitrogen fixation activities. The findings of this PGPR activity screening offer valuable insights for developing biofertilizers tailored for coastal agricultural applications.

Potassium, a pivotal macronutrient essential for growth, development, and crop yield, serves as a critical determinant of soil productivity. Its depletion disrupts the equilibrium of soil nutrients, prompting an investigation into integrated potassium management strategies to address this challenge. A field experiment was conducted during the winter season of 2020 using a randomized complete block design, with eight treatments, each replicated three times in Chinese cabbage (Brassica rapa L. subsp. chinensis). These treatments comprised standard (100 %) and reduced (75 % and 50 %) rates of the recommended dose of potassium (RDK) via muriate of potash (MOP). Variations in the inclusion and exclusion of plant growth-promoting rhizobacteria (PGPR), farmyard manure (FYM) as 25 % of the potassium recommendation, and foliar spray of nano potash were systematically implemented. Findings unequivocally demonstrated that the treatmentT8, involving 100 % RDK +25 % K through FYM + PGPR + nano K fertilizer spray at 25 and 40 DAS, yielded significant improvements in both green fodder (64.0 t ha−1) and dry fodder (7.87 t ha−1).Moreover, T8 exhibited the highest values for total ash (8.75 %), total ash yield (68.9 ± 2.88 kg ha−1), ether extract (2.85 %), ether extract yield (22.4 ± 0.88 kg ha−1), crude protein (9.71 %), and total crude protein yield (76.4 ± 3.21 kg ha−1). Conversely, a marked reduction was observed in various fiber components and carbohydrate fractions upon application of the T8 treatment. The lowest values of yield, crude protein content, total ash ether extract were recorded in treatment T1 (control) applied with no potassium. This investigation underscores the inadequacy of the recommended potassium dose in achieving optimal productivity, necessitating a re-evaluation of potassium fertilization levels. The integrated approach involving FYM, PGPR, and nano potash, coupled with the recommended potassium dose through MOP, emerges as a promising avenue for augmenting both yield and quality parameters in Chinese cabbage.

Besides increasing plant growth, several Plant Growth Promoting Rhizobacteria (PGPR), can enhance tolerance to biotic and/or abiotic stresses of numerous plant species. While cultivated plants are frequently subject to combined stresses in the field, there is limited knowledge of the effect of PGPR on plants undergoing simultaneous stress conditions. Therefore, we tested the beneficial properties of the halotolerant PGPR Serratia sp. strain C2, previously shown to enhance salt stress tolerance in barley, on tomato plants exposed to salinity, to Potato Virus Y (PVY) infection, and both stresses simultaneously. In our experimental conditions, C2 inoculation improved tomato tolerance to salt stress and positively correlated with a 46–68 % decrease in the level of PVY RNA compared to non-inoculated tomato plants. Morphometric, physiological and biochemical analyses (e.g., chlorophyll, sugar and proline accumulation, oxidative stress status and NDVI) indicated that C2 treatments had beneficial effects on tomato growth under simple and combined stress conditions. This is the first report of a PGPR enhancing tolerance not only to individually induced salinity and PVY infection, but also to both stresses in combination. Moreover, the expression analysis of selected genes involved in stress responses and RNA silencing-mediated antiviral immunity suggests that C2 can interfere with distinct defence response pathways to enhance stress tolerance in tomato. These pioneering results support the perspective of using PGPR as multi-spectrum and multi-host biostimulants for improving plant growth and protection from biotic, abiotic, and combined stresses to promote sustainable crop production in the face of environmental changes.

BackgroundPlant growth promoting rhizobacteria (PGPR), such as Bradyrhizobium japonicum IRAT FA3, are able to improve seed germination and plant growth under various biotic and abiotic stress conditions, including high salinity stress. PGPR can affect plants' responses to stress via multiple pathways which are often interconnected but were previously thought to be distinct. Although the overall impacts of PGPR on plant growth and stress tolerance have been well documented, the underlying mechanisms are not fully elucidated. This work contributes to understanding how PGPR promote abiotic stress by revealing major plant pathways triggered by B. japonicum under salt stress.ResultsThe plant growth-promoting rhizobacterial (PGPR) strain Bradyrhizobium japonicum IRAT FA3 reduced the levels of sodium in Arabidopsis thaliana by 37.7%. B. japonicum primed plants as it stimulated an increase in jasmonates (JA) and modulated hydrogen peroxide production shortly after inoculation. B. japonicum-primed plants displayed enhanced shoot biomass, reduced lipid peroxidation and limited sodium accumulation under salt stress conditions. Q(RT)-PCR analysis of JA and abiotic stress-related gene expression in Arabidopsis plants pretreated with B. japonicum and followed by six hours of salt stress revealed differential gene expression compared to non-inoculated plants. Response to Desiccation (RD) gene RD20 and reactive oxygen species scavenging genes CAT3 and MDAR2 were up-regulated in shoots while CAT3 and RD22 were increased in roots by B. japonicum, suggesting roles for these genes in B. japonicum-mediated salt tolerance. B. japonicum also influenced reductions of RD22, MSD1, DHAR and MYC2 in shoots and DHAR, ADC2, RD20, RD29B, GTR1, ANAC055, VSP1 and VSP2 gene expression in roots under salt stress.ConclusionOur data showed that MYC2 and JAR1 are required for B. japonicum-induced shoot growth in both salt stressed and non-stressed plants. The observed microbially influenced reactions to salinity stress in inoculated plants underscore the complexity of the B. japonicum jasmonic acid-mediated plant response salt tolerance.

The objective of the study was to investigate the effects of sole applications of biofertilizers and phosphorus as well as their integrated use in lentil. The field experiment was conducted to study the effect of phosphorus (0, 15, 20 and 25 kg P2O5 ha−1) and biofertilizer inoculation treatments [uninoculated control, Mesorhizobium, Mesorhizobium + RB-1 (Pseudomonas argentinensis) and Mesorhizobium + RB-2 (Bacillus aryabhattai)] on nutrient uptake, nutrient use efficiency and residual nutrient status of soil after the harvest of chickpea. Mesorhizobium + RB-1 recorded the highest uptake of nitrogen (73.7, 59.0 and 132.7 kg ha−1 in grain, straw and total, respectively), phosphorus (8.29, 11.34 and 19.63 kg ha−1 in grain, straw and total) and potassium (23.48, 43.36 and 66.84 kg ha−1 in grain, straw and total) as well as partial factor productivity (113.1 kg grain kg−1 P2O5). Application of 25 kg P2O5 ha−1 recorded the highest phosphorus concentration (0.39% in grain and 0.26% in straw), phosphorus uptake (8.35, 12.32 and 20.67 kg ha−1 in grain, straw and total, respectively) and phosphorus status in soil after crop harvest (18.7 and 16.7 kg P ha−1 in 0–15 and 15–30 cm soil layers, respectively). Partial factor productivity was recorded the highest with the application of 15 kg P2O5 ha−1 (132.2 kg grain kg−1 P2O5). It can be concluded that dual applications of biofertilizers [Mesorhizobium + RB-1 (Pseudomonas argentinensis)] and 25 kg P2O5 ha−1 improve nutrient uptake by the crop and build up of nutrients in the soil after the harvest of the crop. [ABSTRACT FROM AUTHOR]

Microorganisms are cost-effective and eco-friendly alternative methods for removing heavy metals (HM) from contaminated agricultural soils. Therefore, this study aims to identify and characterize HM-tolerant (HMT) plant growth-promoting rhizobacteria (PGPR) isolated from industry-contaminated soils to determine their impact as bioremediators on HM-stressed pepper plants. Four isolates [Pseudomonas azotoformans (Pa), Serratia rubidaea (Sr), Paenibacillus pabuli (Pp) and Bacillus velezensis (Bv)] were identified based on their remarkable levels of HM tolerance in vitro. Field studies were conducted to evaluate the growth promotion and tolerance to HM toxicity of pepper plants grown in HM-polluted soils. Plants exposed to HM stress showed improved growth, physio-biochemistry, and antioxidant defense system components when treated with any of the individual isolates, in contrast to the control group that did not receive PGPR. The combined treatment of the tested HMT PGPR was, however, relatively superior to other treatments. Compared to no or single PGPR treatment, the consortia (Pa+Sr+Pp+Bv) increased the photosynthetic pigment contents, relative water content, and membrane stability index but lowered the electrolyte leakage and contents of malondialdehyde and hydrogen peroxide by suppressing the (non) enzymatic antioxidants in plant tissues. In pepper, Cd, Cu, Pb, and Ni contents decreased by 88.0-88.5, 63.8-66.5, 66.2-67.0, and 90.2-90.9% in leaves, and 87.2-88.1, 69.4-70.0%, 80.0-81.3, and 92.3%% in fruits, respectively. Thus, these PGPR are highly effective at immobilizing HM and reducing translocation in planta. These findings indicate that the application of HMT PGPR could be a promising "bioremediation" strategy to enhance growth and productivity of crops cultivated in soils contaminated with HM for sustainable agricultural practices. [ABSTRACT FROM AUTHOR]

Plant growth-promoting rhizobacteria (PGPR) colonize plant roots, establish a mutualistic relationship with the plants and help them grow better. This study reports novel findings on the plant growth-promoting effects of the PGPR Bacillus aryabhattai. Soil was collected from a soybean field, PGPR were isolated, identified, and characterized for their ability to promote plant growth and development. The bacterium was isolated from the soybean rhizosphere and identified as B. aryabhattai strain SRB02 via 16s rRNA sequencing. As shown by SEM, the bacterium successfully colonized rice and soybean roots within 2 days and significantly promoted the growth of the GA-deficient rice cultivar Waito-C within 10 days, as well as the growth of soybean plants with at least six times longer shoots, roots, higher chlorophyll content, fresh, and dry weight after 10 days of inoculation. ICP analysis showed up to a 100% increase in the quantity of 18 different amino acids in the SRB02-treated soybean plants. Furthermore, the 2-DE gel assay indicated the presence of several differentially expressed proteins in soybean leaves after 24 hrs of SRB02 application. MALDI-TOF-MS identified bconglycinin and glycinin along with several other proteins that were traced back to their respective genes. Analysis of bacterial culture filtrates via GCMS recorded significantly higher quantities of butanoic acid which was approximately 42% of all the metabolites found in the filtrates. The application of 100 ppm butanoic acid had significantly positive effects on plant growth via chlorophyll maintenance. These results establish the suitability of B. aryabhattai as a promising PGPR for field application in various crops. [ABSTRACT FROM AUTHOR]

General plant diseases as well as soil‐borne pathogens severely reduce agricultural yield. The rhizosphere (the region of the soil that includes and surrounds the roots) is an important niche for microbial diversity in particular phytobeneficial bacteria including plant growth‐promoting rhizobacteria (PGPR) which have been used for a very long time to combat plant diseases. Pathogen control and crop productivity can both be improved through the use of PGPR several mechanisms, including iron‐based nutrition, antibiotics, volatile substances, enzymes, biofilm, allelochemicals, and so on. Their modes of action and molecular mechanisms have improved our comprehension of how they are used to control crop disease. Therefore, there is a lot of literal information available regarding PGPR, but this review stands out since it starts with the fundamentals: the concept of the rhizosphere and the colonization process of the latter, particularly because it covers the most mechanisms. A broad figure is used to present the study's findings. The advantages of using PGPR as bioinoculants in sustainable agriculture are also mentioned. [ABSTRACT FROM AUTHOR]

Nitrogen (N) deficiency limits crop productivity. In this study, rhizoengineering with biofilm producing rhizobacteria (BPR) contributing to productivity, physiology, and bioactive contents in tomato was examined under N-deficient field conditions. Here, different BPR including Leclercia adecarboxylata ESK12, Enterobacter ludwigii ESK17, Glutamicibacter arilaitensis ESM4, E. cloacae ESM12, Bacillus subtilis ESM14, Pseudomonas putida ESM17 and Exiguobacterium acetylicum ESM24 were used for the rhizoengineering of tomato plants. Rhizoengineered plants showed significant increase in growth attributes (15.73%–150.13 %) compared to the control plants. However, production of hydrogen peroxide (21.49–59.38 %), electrolyte leakage (19.5–38.07 %) and malondialdehyde accumulation (36.27–46.31 %) were increased remarkably more in the control plants than the rhizoengineered plants, thus N deficiency induced the oxidative stress. Compared to the control, photosynthetic rate, leaf temperature, stomatal conductance, intrinsic and instantaneous water use efficiency, relative water content, proline and catalase activity were incredibly enhanced in the rhizoengineered plants, suggesting both non-enzymatic and enzymatic antioxidant systems might protect tomato plants from oxidative stress under N-deficient field conditions. Yield (10.24–66.21 %), lycopene (4.8–7.94 times), flavonoids (52.32–110.46 %), phenolics (9.79–23.5 %), antioxidant activity (34.09–86.36 %) and certain minerals were significantly increased in the tomatoes from rhizoengineered plants. The principal component analysis (PCA) revealed that tomato plants treated with BPR induced distinct profiles compared to the control. Among all the applied BPR strains, ESM4 and ESM14 performed better in terms of biomass production, while ESK12 and ESK17 showed better results for reducing oxidative stress and increasing bioactive compounds in tomato, respectively. Thus, rhizoengineering with BPR can be utilized to mitigate the oxidative damage and increase the productivity and bioactive compounds in tomato under N-deficient field conditions.

Phosphorus (P) is the second most important macro-element for plant growth, and its low availability in soil is a major obstacle to crop production. Inorganic phosphate (Pi) is the least available form in the soil, while organic phosphate (Po) is the most dominant one, up to 80% of which exists as inositol hexakisphosphate, also known as phytic acid (PA) that cannot be absorbed by plant roots unless hydrolyzed by microbial phytases. Similar to phosphate-solubilizing bacteria, many plant growth-promoting rhizobacteria (PGPR) can play a relevant role in phosphate turnover. In our study, we screened a series of PGPR strains for phytase activities using PA as a sole source of P. Three strains (named C2, N4, and S10) with relatively high phytase activities ranging from 42.84 to 100.55 Units g−1 were selected for barley growth assays. When barley plants grown in poor sandy soil and irrigated with a PA-containing solution were inoculated with each of these PGPR isolates, a significant growth enhancement was observed. This positive effect was well illustrated by an increase in root growth, plant height, and chlorophyll contents. In addition, the inoculated barley plants accumulated significantly higher Pi contents in leaves and roots compared to non-inoculated plants. Finally, the expression of a number of high-affinity Pi transporter genes (PHT1.1, PHT1.4, PHT1.8, and PHT1.6) in inoculated barley plants was downregulated especially in roots, compared to non-inoculated plants. This difference is most likely due to the bacterial phytases that change the P availability in the rhizosphere. In summary, these three strains can improve barley growth under phosphate-limited conditions and should be considered in developing eco-friendly biofertilizers as an alternative to conventional P fertilizers.

The issue of arsenic (As) contamination in the environment has become a critical concern, impacting both human health and ecological equilibrium. Addressing this challenge requires a comprehensive strategy encompassing water treatment technologies, regulatory measures for industrial effluents, and the implementation of sustainable agricultural practices. In this study, diverse strategies were explored to enhance As accumulation in the presence of Acinetobacter bouvetii while safeguarding the host from the toxic effects of arsenate exposure. The sunflower seedlings associated with A. bouvetii demonstrated a favorable relative growth rate (RGR) and net assimilation rate (NAR) even less than 100 ppm of As stress. Remarkably, the NAR and RGR of A. bouvetii-associated seedlings outperformed those of control seedlings cultivated without A. bouvetii in As-free conditions. Additionally, a markedly greater buildup of bio-transformed As was observed in A. bouvetii-associated seedlings (P = 0.05). An intriguing observation was the normal levels of reactive oxygen species (ROS) in A. bouvetii-associated seedlings, along with elevated activities of key enzymatic antioxidants like catalases (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and peroxidases (POD), along with non-enzymatic antioxidants (phenols and flavonoids). This coordinated antioxidant defense system likely contributed to the improved survival and growth of the host plant species amidst As stress. A. bouvetii not only augmented the growth of the host plants but also facilitated the uptake of bio-transformed As in the contaminated medium. The rhizobacterium's modulation of various biochemical and physiological parameters indicates its role in ensuring the better survival and progression of the host plants under As stress.

Wheat (Triticum aestivum L.), a vital cereal, faces significant challenges from common root rot and spot blotch diseases caused by Bipolaris sorokiniana. This study aimed to explore the potential of plant growth promoting rhizobacteria (PGPR) to enhance wheat growth, reduce fertilizer input, and combat Bipolaris diseases. Two PGPR isolates, selected for their superior antagonistic properties, were identified as Stenotrophomonas koreensis RB11 and Bacillus amyloliquefaciens RB12. These PGPR strains displayed multiple plant growth promoting and biocontrol attributes, including phosphate solubilization, indole-3-acetic acid production, nitrogen fixation and antagonism against B. sorokiniana and other fungi. Wheat seed priming with the PGPR significantly improved germination, plant growth, nutrient content and biomass carbon accumulation in the rhizosphere soil. Importantly, the application of RB11 and RB12 allowed for a 25% and 50% reduction in nitrogen fertilizer usage, respectively, without compromising the yield. RB11 and RB12 also demonstrated potent inhibitory effects on B. sorokiniana conidial germination and significantly controlled common root rot and spot blotch in wheat, similar to those observed with the fungicide Protaf 250EC. Overall, this study underscores the multifaceted roles of S. koreensis RB11 and B. amyloliquefaciens RB12 in promoting wheat growth, reducing fertilizer inputs and effectively suppressing wheat pathogens. These findings contribute to the development of PGPR-based strategies for sustainable crop production and disease control.

Acetochlor-tolerant growth-promoting bacteria were isolated and identified to develop a microbial agent and provide a feasible scheme along with a theoretical basis for this development. Highly acetochlor-tolerant bacteria were isolated from modified media with different acetochlor concentrations. The growth-promoting effect on maize was tested, and the feasibility was verified through germinationpromoting and potting experiments. Strains JL7 and JL16 showed a strong ability to induce high acetochlor tolerance and promote growth; moreover, the maximum acetochlor resistance for both strains was achieved at a concentration of 700 mg·L-1 . The phosphorus solubilization capacity of JL7 was 223.21 mg ·L-1, and the cumulative production of IAA was 82.40 mg ·L-1 . Strains JL7 and JL16 were identified as Enterbacter sp. and Acetobacter sp., respectively. The results of the germination promotion test showed that the germination rate increased by 9.42 and 3.84 percent points with the addition of strains JL7 and JL16 after 72 hours, respectively, compared with that of the CK. Furthermore, strain JL16 significantly promoted growth in terms of shoot and root lengths by 52.53% and 23.22%, respectively, compared with those of the CK. In the pot experiment, the addition of both JL7 and JL16 affected morphological indicators such as plant height, stem thickness, root diameter, and root length, all of which were promoted. Strains JL7 and JL16 were still tolerant to ethephon in the soil. Two acetochlor-tolerant strains showed a remarkable effect on promoting plant growth. The study provides a theoretical basis for microbial soil improvements by describing suitable strains and the development of innovative microbial fertilizers for future applications. [ABSTRACT FROM AUTHOR]

Phosphate solubilizing bacteria (PSB) are promising candidates for microbiological treatment to improve phosphorus-deficient or P-deficient soil. We have experimentally studied the growth promoting effects of PSBs on rice in P-deficient conditions. The 6 PSBs isolated from rhizosphere soil were identified by 16S rDNA sequencing as Enterobacter asburiae 30FPSSB1, E. mori NTTC11, Priestia aryabhattai KNB6, P. aryabhattai 49KNA2, P. megaterium 65KNA2, and Bacillus sp. 38DFWA. They exhibited plant growth promoting traits via phosphate solubilization and indole acetic acid (IAA) production respectively ranging within 32 - 42 mg/L and 5.3 - 340 μg/L. All the strains produced a large amount of siderophores, and some presented a broad range of antifungal activities reducing the growth of phytopathogens by 10 - 35 %. The effects of bacterial population on rice rhizosphere were evaluated on nutrient agar. Rhizobacterial treatments at high 105 - 108 CFU/mL concentrations inhibited plant growth in IAA dose dependent manner, but such effect diminished at low bacterial titers. The capacity of rhizobacteria to promote plant development under scarcity of P was investigated in pot experiments. Under axenic conditions, Bacillus and Priestia species promoted plant growth, whereas Enterobacter species suppressed it. Plants treated with Bacillus sp. 38DFWA, P. aryabhattai KNB6, and P. megaterium 65KNA2 had increased biomasses of shoots (by 33, 26 and 23 %, respectively) and roots (by 34, 48 and 48 %), which facilitated P availability and increased nutrient uptake in the plant tissues by 89, 96 and 143 %, when the inoculated plants were cultivated in insoluble P (tri-calcium phosphate, TCP) medium. In available P and TCP soil treatments, P. aryabhattai KNB6 and E. mori NTTC11 greatly increased rice plant biomass and gave the highest P accumulation in plant tissues. Interestingly, P. aryabhattai KNB6 strongly increased P uptake in plant tissue by 121 % and promoted rice growth by 22 % in P-deficient soil. This clearly demonstrates that P. aryabhattai KNB6 has great potential for use as a bio-inoculant, and is an attractive alternative to phosphate fertilizers. [ABSTRACT FROM AUTHOR]

Hydroponics is a contemporary agricultural system providing precise control over growing conditions, potentially enhancing productivity. Biofertilizers are environmentally friendly, next-generation fertilizers that augment product yield and quality in hydroponic cultivation. In this study, we investigated the effect of three bio-fertilizers in a hydroponic floating system, microalgae, plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF), combined with a 50% reduction in mineral fertilizer, on lettuce yield and quality parameters including antioxidants: vitamin C, total phenols and flavonoids. The treatments tested were: 100% mineral fertilizer (control 1), 50% mineral fertilizer (control 2), 50% mineral fertilizer with microalgae, 50% mineral fertilizer with PGPR and 50% mineral fertilizer with AMF. The research was conducted during the winter months within a controlled environment of a glasshouse in a Mediterranean climate. The PGPR comprised three distinct bacterial strains, while the AMF comprised nine different mycorrhizal species. The microalgae consisted of only a single species, Chlorella vulgaris. AMF inoculation occurred once during seed sowing, while the introduction of PGPR and microalgae occurred at 10-day intervals into the root medium. Our findings revealed that the treatment with PGPR resulted in the highest growth parameters, including the lettuce circumference, stem diameter and fresh leaf weight. The 100% mineral fertilizer and PGPR treatments also yielded the highest lettuce production. Meanwhile, the treatment with AMF showed the highest total phenol and flavonoid content, which was statistically similar to that of the PGPR treatment. Furthermore, the PGPR recorded the maximum range of essential nutrients, including nitrogen (N), potassium (K), iron (Fe), zinc (Zn) and copper (Cu). Thus, the inclusion of PGPR holds promise for optimizing the lettuce growth and nutrient content in hydroponic systems. In conclusion, PGPR has the potential to enhance nutrient availability in a floating hydroponic system, reducing the dependence on chemical fertilizers. This mitigates environmental pollution and fosters sustainable agriculture. [ABSTRACT FROM AUTHOR]

The third-most important food legume in terms of economic importance worldwide is the chickpea (Cicer arietinum L.). Its potential production is frequently constrained by numerous biotic stressors, such as the nematodes, insects Ascochyta blight, fusarsium wilt, and botrytis grey mould are the three major fungal diseases that cause significant economic losses, while Helicoverpa armigera, Aphis craccivora, cowpea weevil are the three major pre-harvest pest of chickpea. Several biological, chemical, cultural and, agronomical practices are used to control biotic stress, apart from that few modern biotechnological approaches also developed for high yielding and biotic stress resistant varieties. This paper aims to elaborate about different biotic stresses that affect Chickpea plant, their management strategies including traditional chemicals and adaptation of transgenic varieties with their limitations and also enlightened newer ray of hope i.e., plant growth promoting rhizobacteria that holds the ability to combat against biotic stress by mitigating stress ethylene level. [ABSTRACT FROM AUTHOR]

Soil salinity is an important abiotic constraint that affects soil quality and crop productivity and has a direct impact on crop yields. Ensuring the sustainable use of saline soils while maintaining environmental integrity is of utmost importance. To achieve this, it is essential to explore and implement methods that can enhance productivity without causing harm to the ecosystem. In the current study, the effect of biochar, Simultaneous inoculation of biomes (Trichoderma harzanium and Pseudomonas fluorescence) and gypsum on soil properties and growth parameters of chickpea was investigated. Of all treatments, the combination of 75 percent GR + biochar@20t/ha and biome @2kg/ha had the greatest effect on lowering pH (9.32 to 7.61), EC (3.65 to 1.6 dSm-1) and SAR (24.22 to 5.9 Cmolc (+) kg-1). As a result, there was a notable improvement in the length of chickpea shoots and roots as well as the overall production of dry matter. [ABSTRACT FROM AUTHOR]

Biocontrol agents are microbiological-based alternatives to agrochemicals due to their effective and sustainable attributes in controlling phytopathogens. This research highlights the formulation of biocontrol agents using sugarcane-bagasse as a carrier matrix and the evaluation of the formulants in phytopathogen management. The isolated rhizospheric bacteria were screened for the antibiosis trait responsible for biocontrol activity using the agar streak method. Bacterial isolates with antibiosis potential were further identified phenotypically. The carrier was prepared by oven drying the sugarcane-bagasse at 90 °C for three days while grinding and sieving using a mesh sieve of 1.16 mm was done afterwards. For the biocontrol formulation, 200 mL of biocontrol inoculum was added to 20 g of sugarcane-bagasse for each organism to form the final products. Water and adhesion capacities were conducted on the three formulations and, the antagonistic potential of the formulants were evaluated using the maize growth profile after 21 days. A total of nine isolates were obtained; only three (3) showed antibiosis antagonistic activity and were further utilized for the formulations branded ZEEMYC (Mycobacterium spp.), ZEEPAS (Pseudomonas spp.), and ZEEBAC (Bacillus spp.), respectively. The water capacities of the three formulations were between 6.9 g and 9.9 g, respectively, while adhesion capacity was also observed. On day five (5), maize seeds planted in all pots sprouted, except diseased seeds without a biocontrol agent (DSs). On day 11, plant height, shoot length, and root length ranged between 36.5 cm and 39 cm, 31 cm and 34 cm, and 5 cm and 7 cm for plants with a biocontrol agent. Those of the control (healthy seeds without biocontrol) were 42 cm, 34.5 cm, and 7.5 cm, while barely visible growth was observed in the DSs. This study displays the potential of natural-based biocontrol agents in controlling the phytopathogen Aspergillus niger and contributes significantly to SDG 2. [ABSTRACT FROM AUTHOR]

Sorghum, a vital cereal crop with significant importance in traditional human health systems, faces severe challenges from biotic stresses. This study aimed to assess the morpho-physiological variations and plant growth promoting rhizobacteria (PGPR)-induced defense mechanisms in sorghum against Burkholderia sp. infection, a well-known cause of bacterial leaf stripe disease. Also, the alterations in the leaf protein band profile of sorghum exposed to Burkholderia infection were assessed via 2-D gel electrophoresis wherein the disappearance of protein bands in diseased leaf tissues was recorded. The selected PGPR, A. chroococcum Beijerinck 1901 (MCC 2351), B. megaterium (MCC 2336), and P. fluorescens (NAIMCC B-00,340), secreted hydrogen cyanide and ammonia, and produced lytic enzymes, cellulase and amylase. When tested in-planta, Burkholderia sp., applied as a foliar spray, more profoundly impacted the growth as compared to seed coat application, resulting in significant reductions in root dry biomass, whole plant length, and total chlorophyll content by 93.9, 73.4 and 53.8 %, respectively, compared to disease-free control. Visible symptoms of bacterial leaf stripe disease like brown discoloration and necrotic lesions were observed in infected sorghum plants. Furthermore, the level of phytochemicals, proline, and malondialdehyde and antioxidants, CAT and SOD, in foliage declined significantly by 46.4, 70.2, 20.7, and 16.9 %, respectively, following inoculation with Bacillus applied as a seed coat. Additionally, Burkholderia-infected plants exhibited cellular damage, mainly in leaf tissues, as revealed by SEM and CLSM. Interestingly, the PGPR inoculation substantially enhanced the measured growth parameters of sorghum while reducing the levels of phytochemicals and antioxidants. These findings suggest that A. chroococcum, B. megaterium, and P. fluorescens, possessing biocontrol activity, can be employed as a profitable, environment and pocket-friendly approach for managing plant diseases and promoting the production of sorghum under biotic stress, thereby sufficing the human food demands.

IntroductionDrought is assumed as one of the most severe abiotic stress factors limiting plant growth and crop production. Since in arid and semi-arid regions, some part of growth period of wheat is confronted with water limitation condition which can affect biochemical and physiological responses such as changes in photosynthetic efficiency of PSII, chlorophyll content, and stomatal conductance. Application of bio fertilizers and silicon is one of the most important strategies for alleviation of drought stress effects. Bio fertilizers (plant growth promoting rhizobacteria or PGPR and mycorrhiza) can improve plant performance under non-stress and stress conditions. Thererfore, it seems that application of nano silicon and bio-fertilizer can improve wheat yield under water limitation conditions.Materials and methodsIn order to study the effects of biofertilizers and nanosilicon on phosphorus uptake, grain yield, and some physiological traits of wheat (Triticum aestivum L.) under withholding irrigation conditions, a factorial experiment was carried out at the research farm faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili, with three replications during 2018-2019. The area is 38° 15′ N latitude, 48° 15′ E longitude, and 1350 m above mean sea level. Climatically, the area is situated in the semi-arid temperate zone with a cold winter and moderate summer. Factors were included irrigation in three levels (full irrigation as control; moderate water limitation or withholding irrigation at 50% of the heading stage; severe water limitation or withholding irrigation at 50% of the booting stage) based on codes 55 and 43 of the BBCH scale; foliar application of nano silicon (foliar application with water as control, 30 and 60 mg.L-1) and bio-fertilizer (no application as control, mycorrhiza application, both application of flavobacterium and pseudomonas, both application of flavobacterium and pseudomonas with mycorrhiza). Mycorrhiza fungi (mosseae) was purchased from the Zist Fanavar Turan Corporation and soils were treated based on method of Gianinazzi et al. (2001). Psedomunas and flovobacterium were isolated from the rhizospheres of wheat by Research Institute of Soil and Water, Tehran, Iran. For inoculation, seeds were coated with gum Arabic as an adhesive and rolled into the suspension of bacteria until uniformly coated. The strains and cell densities of microorganisms used as PGPR in this experiment were 1×108 colony forming units (CFU). In this study, electrical conductivity, stomatal conductance, leaf fluorescence parameters, phosphorus of root and grain, relative water content, electrolyte leakage, anthocyanins and grain yield of wheat were investigated. Analysis of variance and mean comparisons were performed using SAS ver 9.1 computer software packages. The main effects and interactions were tested using the least significant difference (LSD) test at the 0.05 probability level.Results and discussionThe results showed that application of both flavobacterium and pseudomonas with mycorrhiza and foliar application of 60 mg.L-1 nano silicon under severe water limitation increased 84.32%, 49% and 49.52% of electrolyte leakage, electrical conductivity and minimum fluorescence (F0) respectively, and decreased root and grain phosphorus by 30.67 and 36.05% compared to full irrigation. The highest RWC (92.26%), stomatal conductance (58.86 mmol.m-2.s), anthocyanin (0.0274 µmol.g-1FW), Fm (860), and Fv/Fm (0.909) were obtained at foliar application of 60 mg.L-1 nano silicon, both applications of flavobacterium and pseudomonas with mycorrhiza under normal irrigation. Also, the highest grain yield was obtained with both flavobacterium and pseudomonas with mycorrhiza and foliar application of 30 mg.l-1 nano silicon under normal irrigation. According to the results of this study both the application of biofertilizers and nanosilicon can improve wheat grain yield under water limitation conditions by improving the physiological traits and also the uptake of phosphorus from the soil.ConclusionGenerally, it seems that application of bio fertilizers and nano silicon can be recommended as the proper method for increasing the physiological trait grain yield of wheat under water limitation conditions.

Abstract Background The required amounts of chemical fertilizers (NPK) are determined by plant yield, and product quality is given less consideration. The use of PGPRs is an environmentally friendly approach that, in addition to increasing yield, also improves fruit quality. This study examined the role of specific Streptomyces strains in aiding cucumber plants to 1) use fewer NPK fertilizers in the same quantity 2) improve the quality of cucumber fruit, and 3) promote growth and defense system. Results In this study, the effect of 17 Streptomyces strains on the vegetative traits of cucumber seedlings of the Sultan cultivar was evaluated as the first test. Four strains of Streptomyces with the highest root and shoot dry weight were selected from the strains. This experiment was performed to determine the interaction effect of selected strains and different amounts of NPK on cucumber yield, quality, physiological and biochemical responses of plants. The first experiment’s results revealed that strains IC6, Y7, SS12, and SS14 increased significantly in all traits compared to the control, while the other strains dramatically improved several characteristics. Analysis of variance (ANOVA) revealed significant differences between the effect of strains, NPK concentrations, and their interactions on plant traits. The treatments containing 75% NPK + SS12, yielded the most fruit (40% more than the inoculated control). Antioxidant enzymes assay showed that SS12 substantially increased the activity of POX, PPO, and the expression of the genes related to these two enzymes. Hormone assay utilizing HPLC analysis revealed that various strains employ a specific mechanism to improve the immune system of plants. Conclusions Treatment with strain SS12 led to the production of cucumbers with the highest quality by reducing the amount of nitrate, and soluble sugars and increasing the amount of antioxidants and firmness compared to other treatments. A specific Streptomyces strain could reduce 25% of NPK fertilizer during the vegetative and reproductive growth period. Moreover, this strain protected plants against possible pathogens and adverse environmental factors through the ISR and SAR systems.

ABSTRACT Several strains in the Pseudomonas genus are categorized as plant growth-promoting rhizobacteria (PGPR). Although several of these strains are strong candidates for applications as biofertilizers or biopesticides, genome editing approaches are generally limited and require further development. Editing genomes in PGPR could enable more robust agricultural applications, persistence, and biosafety measures. In this study, we investigate the use of five phage-encoded recombinases to develop a recombineering workflow in three PGPR strains: Pseudomonas protegens Pf-5, Pseudomonas protegens CHA0, and Pseudomonas putida KT2440. Using point mutations in the rpoB gene, we reach maximum recombineering efficiencies of 1.5 × 10−4, 3 × 10−4, and 5 × 10−5, respectively, in these strains using λ-Red Beta recombinase from Escherichia coli. We further examine recombineering efficiencies across these strains as a function of selected mutation, editing template concentration, and phosphorothiolate bond protection. This work validates the use of these tools across several environmentally and biotechnologically relevant strains to expand the possibilities of genetic manipulation in the Pseudomonas genus. IMPORTANCE The Pseudomonas genus contains many members currently being investigated for applications in biodegradation, biopesticides, biocontrol, and synthetic biology. Though several strains have been identified with beneficial properties, chromosomal manipulations to further improve these strains for commercial applications have been limited due to the lack of efficient genetic tools that have been tested across this genus. Here, we test the recombineering efficiencies of five phage-derived recombinases across three biotechnologically relevant Pseudomonas strains: P. putida KT2440, P. protegens Pf-5, and P. protegens CHA0. These results demonstrate a method to generate targeted mutations quickly and efficiently across these strains, ideally introducing a method that can be implemented across the Pseudomonas genus and a strategy that may be applied to develop analogous systems in other nonmodel bacteria.

Water scarcity as well as soil degradation and environmental problems potentially caused by excessive application of chemical fertilizers are major challenges to agricultural production in semi-arid areas. It is crucial to explore a suitable and eco-friendly strategy to achieve sustainable production of maize with high crop water productivity and nitrogen use efficiency. Here, a two-year field experiment with three irrigation levels of W1 (220 mm), W2 (140 mm) and W3 (60 mm), and five fertilization types of no fertilizer (CK), chemical fertilizer (CF), bio-fertilizer combined with CF (CFB), organic fertilizer combined with 70% CF (CFO) and bio-fertilizer combined with CFO (CFOB) was conducted to investigate the effect on dry matter, N uptake and remobilization, grain yield, crop water productivity, nitrogen use efficiency and economic benefits of maize in 2021 and 2022. The results showed that the W2 and W3 decreased in the leaf area index, photosynthetic rate, dry matter accumulation, the maximum dry matter accumulation rate and actual crop evapotranspiration. Under W1 condition, the CFB improved the growth of maize, increased the dry matter and nitrogen accumulation and yield, with 8.1% and 7.4% higher than CF in 2021 and 2022, respectively. Under deficit irrigation (W2 and W3), CFOB significantly increased the leaf area index, photosynthetic rate, dry matter accumulation at later growth stage, in addition, CFOB increased the post-silking N uptake and the percentage in total N content, finally improved the grain yield with 23.8% and 22.8% under W2, 22.5% and 25.7% under W3 higher than that of the CF in 2021 and 2022, respectively. Irrigation and fertilizer showed a coupling effect on grain yield, crop water productivity, agronomy efficiency and nitrogen use efficiency. Overall, the CFOB under moderate deficit (W2) exhibited the highest water productivity, nitrogen use efficiency and economic benefits, as well as maintained the high yield, could be a promising approach to sustainable development of local maize.

• Isolates TS4 and TS6 express efficient PGPR properties. • Both isolates effectively colonize tomato rhizosphere. • Nethouse studies on tomato also showed significant results. • Careful evaluation is necessary before developing PGPR isolates as bioinoculants. An acute and compelling need to replace chemical fertilizers has shifted our focus towards plant growth-promoting rhizobacteria (PGPR) that rapidly colonize the rhizosphere. In the present investigation, two isolates from tomato rhizosphere, TS4 and TS6, were screened for various PGPR properties. Both isolates expressed different properties such as enzyme production and hydrogen sulfide (H 2 S) production. Production of Indole-3-Acetic Acid (IAA) was 13.33 μg mL−1 for both TS4 and TS6. Ammonia excretion was 75.0 μg mL−1 for TS4 and 82.5 μg mL−1 for TS6. Both isolates tolerated salt stress up to 10% sodium chloride (NaCl), drought stress tolerated by isolate TS4 was up to -0.30 MPa and TS6 survived up to -0.49 MPa osmotic pressure. To assess the colonization potential of the isolates, their biofilm potential and chemotactic behavior towards the tomato root exudates were studied. Colonization of the tomato rhizosphere by TS4 and TS6 was observed quantitatively and found that root tips were more profusely colonized as compared to the root base. Nethouse studies to test their influence on tomato revealed a positive influence in some plant aspects. All the results led to the conclusion that isolates TS6 identified as Micrococcus luteus and TS4 belonging to genera Lactobacillus were efficient PGPR. This paper highlights the efficacy of PGPR as a component of sustainable agriculture for improved productivity. However, the need of risk assessment and rigorous surveillance of bacteria before developing them as a bioformulation is also emphasized. [ABSTRACT FROM AUTHOR]

Clonal plantation involves the rooting of cuttings from superior genotypes selected for their hybrid vigor and desired qualities. However, the cuttings of some Eucalyptus species and their hybrid genotypes present difficulties in their rooting capacity. Applying PGPR to cutting growth medium as a root stimulating agent has not been extensively studied for Eucalyptus tree species. We aimed to assess the rooting capacity of cuttings taken from two poor-rooting Eucalyptus hybrid clones of E. grandis × E. nitens through the application of PGPR in nursery trials. Seven rhizospheric bacterial species that demonstrated the ability to produce indole-3-acetic acid and to solubilise phosphate were used to prepare two rhizospheric consortium inoculums in which Pseudomonas-Bacillus strains and non-Pseudomonas-Bacillus were grouped. Inoculums were tested for their rooting stimulating capacity on cuttings of the hybrids GN 018B and GN 010 and compared to the nursery standard indole-3-butyric acid. A total of 320 cuttings were treated. Both hybrid clones demonstrated significant (p < 0.0001) genotype differences for all three growth responses, i.e., total, root, and shoot length. Cuttings of both hybrids demonstrated high survival rates and rooting percentage. Although several rooting architectural configurations were prevalent, the Pseudomonas-Bacillus consortium promoted adventitious root development and fibrosity in GN 018B hybrids. [ABSTRACT FROM AUTHOR]

Industrialization and urbanization are important for economic development which makes the human life easy by providing different job opportunities, increasing the production level of cheaper goods and standard of living. Despite its many positive effects, industrialization has had a negative impact on the natural ecosystem through environmental pollution. It is responsible for a greater input of potentially toxic and non-toxic substances into essential environmental components such as air, soil and water. Continuous industrialization has resulted in significant environmental problems due to the release of pollutants and extremely difficult treatment of contaminated areas. This review focuses on the recent literature dealing with the role of Plant Growth Promoting Microbes (PGPMs), i.e. bacteria and Arbuscular mycorrhizal Fungi (AMF) in the remediation of polluted sites.

Key points Application of the PGPR significantly increased the population of the Bacillus and Pseudomonas genus. Application of the PGPR induced the growth of other beneficial bacteria. The PGPR have potential role as a ripening enhancer.

Soil salinity is an important abiotic constraint that affects soil quality and crop productivity and has a direct impact on crop yields. Ensuring the sustainable use of saline soils while maintaining environmental integrity is of utmost importance. To achieve this, it is essential to explore and implement methods that can enhance productivity without causing harm to the ecosystem. In the current study, the effect of biochar, Simultaneous inoculation of biomes (Trichoderma harzanium and Pseudomonas fluorescence) and gypsum on soil properties and growth parameters of chickpea was investigated. Of all treatments, the combination of 75 percent GR + biochar@20t/ha and biome @2kg/ha had the greatest effect on lowering pH (9.32 to 7.61), EC (3.65 to 1.6 dSm-1) and SAR (24.22 to 5.9 Cmolc (+) kg-1). As a result, there was a notable improvement in the length of chickpea shoots and roots as well as the overall production of dry matter.

The third-most important food legume in terms of economic importance worldwide is the chickpea (Cicer arietinum L.). Its potential production is frequently constrained by numerous biotic stressors, such as the nematodes, insects Ascochyta blight, fusarsium wilt, and botrytis grey mould are the three major fungal diseases that cause significant economic losses, while Helicoverpa armigera, Aphis craccivora, cowpea weevil are the three major pre-harvest pest of chickpea. Several biological, chemical, cultural and, agronomical practices are used to control biotic stress, apart from that few modern biotechnological approaches also developed for high yielding and biotic stress resistant varieties. This paper aims to elaborate about different biotic stresses that affect Chickpea plant, their management strategies including traditional chemicals and adaptation of transgenic varieties with their limitations and also enlightened newer ray of hope i.e., plant growth promoting rhizobacteria that holds the ability to combat against biotic stress by mitigating stress ethylene level.

Agricultural areas exhibiting numerous abiotic stressors, such as elevated water stress, temperatures, and salinity, have grown as a result of climate change. As such, abiotic stresses are some of the most pressing issues in contemporary agricultural production. Understanding plant responses to abiotic stressors is important for global food security, climate change adaptation, and improving crop resilience for sustainable agriculture, Over the decades, explorations have been made concerning plant tolerance to these environmental stresses. Plant growth-promoting rhizobacteria (PGPR) and their phytohormones are some of the players involved in developing resistance to abiotic stress in plants. Several studies have investigated the part of phytohormones in the ability of plants to withstand and adapt to non-living environmental factors, but very few have focused on rhizobacterial hormonal signaling and crosstalk that mediate abiotic stress tolerance in plants. The main objective of this review is to evaluate the functions of PGPR phytohormones in plant abiotic stress tolerance and outline the current research on rhizobacterial hormonal communication and crosstalk that govern plant abiotic stress responses. The review also includes the gene networks and regulation under diverse abiotic stressors. The review is important for understanding plant responses to abiotic stresses using PGPR phytohormones and hormonal signaling. It is envisaged that PGPR offer a useful approach to increasing plant tolerance to various abiotic stresses. However, further studies can reveal the unclear patterns of hormonal interactions between plants and rhizobacteria that mediate abiotic stress tolerance. [ABSTRACT FROM AUTHOR]