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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.

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.

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.

Tomato is one of the world’s most commonly grown and consumed vegetables. However, it can be attacked by the Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis (Cmm), which causes bacterial canker on tomato plants, resulting in significant financial losses in field production and greenhouses worldwide. The current management strategies rely principally on the application of various chemical pesticides and antibiotics, which represent a real danger to the environment and human safety. Plant growth-promoting rhizobacteria (PGPR) have emerged as an attractive alternative to agrochemical crop protection methods. PGPR act through several mechanisms to support plant growth and performance, while also preventing pathogen infection. This review highlights the importance of bacterial canker disease and the pathogenicity of Cmm. We emphasize the application of PGPR as an ecological and cost-effective approach to the biocontrol of Cmm, specifying the complex modes of biocontrol agents (BCAs), and presenting their direct/indirect mechanisms of action that enable them to effectively protect tomato crops. Pseudomonas and Bacillus are considered to be the most interesting PGPR species for the biological control of Cmm worldwide. Improving plants’ innate defense mechanisms is one of the main biocontrol mechanisms of PGPR to manage bacterial canker and to limit its occurrence and gravity. Herein, we further discuss elicitors as a new management strategy to control Cmm, which are found to be highly effective in stimulating the plant immune system, decreasing disease severity, and minimizing pesticide use.

Plant nutrition through mineral fertilizers is commonly used in soilless culture systems. Our study aims to replace intensive mineral fertilizers with bio-fertilizers, at least partially. We supplemented 50% of the mineral fertilizers with Chlorella vulgaris microalgae, a mix of beneficial bacteria and mycorrhiza. In addition, we investigated how to enhance spinach quality by implementing a sustainable and eco-friendly production method. Our research focused on analyzing the parameters of leaf quality and nitrate accumulation of baby spinach grown in a floating culture system utilizing biofertilizers. When mycorrhiza, algae, and bacteria supplemented 50% of mineral fertilizers, 17.5%, 20%, and 21.9% fewer leaf yields than 100% mineral fertilizers (5270 g m−2) were achieved. However, biofertilizers improved the internal leaves’ quality of hydroponically grown baby spinach. The highest amount of total phenolic (356.88 mg gallic acid 100g−1), vitamin C (73.83 mg 100 g−1), total soluble solids (9.4%), phosphorus (0.68%), and iron (120.07 ppm) content were obtained by using mycorrhiza. Bacteria induced the lowest nitrate content (206 mg kg−1) in spinach leaves, while 100% mineral fertilizers showed the highest nitrate (623 mg kg−1) concentration. Moreover, bacteria provided the highest SPAD-chlorophyll (73.72) and titrable acidity (0.31%). The use of microalgae, Chlorella vulgaris, induced the highest amount of potassium (9.62%), calcium (1.64%), magnesium (0.58%), zinc (75.21 ppm), and manganese (64.33 mg kg−1). In conclusion, our findings demonstrate that the utilization of biofertilizers has the potential to significantly reduce the reliance on mineral fertilizers by up to 50%. Furthermore, an improvement in the quality of baby spinach, as evidenced by an increase in health-beneficial compounds, is possible. Thus, implementing biofertilizers in the cultivation of soilless baby spinach presents a promising approach to achieving both environmental sustainability and improved crop quality.

Rice production in the Central Plains of Thailand plays a key role in the country’s food security. However, the overuse of inputs coupled with the rising production costs are making it increasingly difficult for smallholder rice farming to remain economically and environmentally sustainable. Replicated production-scale field trials of Cost Reduction Operating Principles (CROP)—Thailand’s national package of best management practices for rice production—were established in tandem with laser land leveling (LLL), mechanical drum seeder, and the application of two biofertilizer products (i.e., PGPR II, that contains Azospirillum brasilense Sp. TS29 and Burkholderia vietnamiensis S45; and LDD #12, that contains Azotobacter tropicalis, Burkholderia unamae and Bacillus subtilis) and compared with farmer’s practices (FP). Performance indicators (PI) promoted by the Sustainable Rice Platform (SRP) were used to assess economic and environmental indicators. CROP + PGPR had significantly higher net income (79%) and nitrogen-use efficiency (57%) compared with FP. Pesticide use (28%), seed (60%), inorganic fertilizer N (41%) and total production costs (19%) were reduced in all CROP treatments compared with FP. These results demonstrate that the application of CROP, LLL, mechanical drum seeder, and biofertilizers can substantially improve the economic and environmental sustainability of rice production in the Central Plains of Thailand.

Combined stressors (high soil salinity and saline water irrigation) severely reduce plant growth and sugar beet yield. Seed inoculation with plant growth-promoting rhizobacteria (PGPR) and/or foliar spraying with silica nanoparticles (Si-NP) is deemed one of the most promising new strategies that have the potential to inhibit abiotic stress. Herein, sugar beet (Beta vulgaris) plants were treated with two PGPR (Pseudomonas koreensis MG209738 and Bacillus coagulans NCAIM B.01123) and/or Si-NP, during two successive seasons 2019/2020 and 2020/2021 to examine the vital role of PGPR, Si-NP, and their combination in improving growth characteristics, and production in sugar beet plants exposed to two watering treatments (fresh water and saline water) in salt-affected soil. The results revealed that combined stressors (high soil salinity and saline water irrigation) increased ion imbalance (K+/Na+ ratio; from 1.54 ± 0.11 to 1.00 ± 0.15) and declined the relative water content (RWC; from 86.76 ± 4.70 to 74.30 ± 3.20%), relative membrane stability index (RMSI), stomatal conductance (gs), and chlorophyll content, which negatively affected on the crop productivity. Nevertheless, the application of combined PGPR and Si-NP decreased oxidative stress indicators (hydrogen peroxide and lipid peroxidation) and sodium ions while increasing activities of superoxide dismutase (SOD; up to 1.9-folds), catalase (CAT; up to 1.4-folds), and peroxidase (POX; up to 2.5-folds) enzymes, and potassium ions resulting in physiological processes, root yield, and sugar yield compared to non-treated controls under combined stressors (high soil salinity and saline water irrigation). It is worth mentioning that the singular application of PGPR improved root length, diameter, and yield greater than Si-NP alone and it was comparable to the combined treatment (PGPR+Si-NP). It was concluded that the combined application of PGPR and Si-NP has valuable impacts on the growth and yield of sugar beet growing under combined stressors of high soil salinity and saline water irrigation.

Drought is a major abiotic factor and affects cereal-based staple food production and reliability in developing countries such as Pakistan. To ensure a sustainable and consistent food supply, holistic production plans involving the integration of several drought mitigation approaches are required. Using a randomized complete block design strategy, we examined the drought-ameliorating characteristics of plant growth-promoting rhizobacteria (PGPR) and nanoparticles (NPs) exclusively or as a combined application (T4) through three stages (D1, D2, and D3) of wheat growth (T1, control). Our field research revealed that Azospirillum brasilense alone (T2) and zinc oxide NPs (T3) improved wheat plant water relations, chlorophyll, proline, phenolics and grain quality, yield, and their allied traits over the stressed treatments. Specifically, the best outcome was observed in the combined treatment of PGPR and ZnO NPs (T4). Interestingly, the combined treatment delivered effective drought mitigation through enhanced levels of antioxidants (15% APX, 27% POD, 35% CAT, 38% PPO and 44% SOD) over controls at the grain-filling stage (GFS, D3 × T1). The 40% improvements were recorded under the combined treatment at GFS over their respective controls. Their combined usage (PGPR and ZnO NPs) was concluded as an effective strategy for building wheat resilience under drought, especially in arid and semi-arid localities.

Various technologies, such as light-emitting diodes (LEDs) and beneficial plant micro-organisms, have been applied to enhance plant growth and development. We aimed to develop appropriate technology by incorporating the benefits of LED light, plant growth promoting rhizobacteria (PGPR), and arbuscular mycorrhiza fungi (AMF) into sweet girl cherry tomato (Solanum lycopersicum L.) seedling production. Our results demonstrated that incorporating red (R) and blue (B) LED lights, PGPR, and AMF positively affected tomato seedling growth. The optimal lighting conditions for tomato seedling growth were LEDs at 200 μmol/m2/s with a ratio of R60:B40 and 20 h/d exposure. The optimum LED-illuminated tomato seedlings significantly upregulated photosynthesis-related genes, including psbA, psbB, fdx, atpB, and rbcL. Plants inoculated with PGPR Bradyrhizobium sp. SUTN9-2, Bacillus velezensis SD10 and B. megaterium A20 had a high health index after inoculation. Furthermore, the optimized LED-illuminated tomato seedlings inoculated with SD10 had the highest health index. In addition, the optimum LED-illuminated tomato seedlings inoculated with SD10 and AMF had the highest biomass. Our experiment demonstrated that tomato seedlings produced under optimized LED lights inoculated with SD10 and AMF increased yield by about 16% under field conditions. Therefore, these results provided the optimum conditions for a high-quality tomato seedling production system.

Inoculation with plant growth promoting rhizobacteria (PGPR) might be a sustainable practice to increase nutrients use efficiency of crops. In order to elucidate the mechanisms underlying the beneficial interaction, an RNA-Seq transcriptional profiling of tomato leaves was performed after roots’ inoculation with Azospirillum baldaniorum (AB) or Paraburkholderia graminis (PG). Overall, 427 and 512 differentially expressed tomato genes were retrieved for AB and PB inoculation, respectively, and in both cases, the number of up-regulated genes exceeded the number of those down-regulated. Expression profiles suggest that the interactions between tomato seedlings and microorganisms are species-specific. The common activated pathways involved genes coding for proteins related to water and nutrients uptake, defense responses to biotic and abiotic stresses and hormonal regulation of fruit-set and ripening. While AB induced genes coding for MYB transcription factors known to be involved in response to biotic and abiotic stresses, PG upregulated 5 genes coding for putative late blight resistance protein homolog. Auxin responsive molecules and gibberellins involved in the fruit-set and early fruit growth in tomato were mainly induced by AB correlating to higher fruit number obtained in a previous field study. On the other hand, ERF transcription factors involved in ripening were induced mainly by PG treatment.

Considering the growth-promoting potential and other regulatory roles of bacteria, we investigated the possible mechanism of the role of Bacillus subtilis in conferring salt tolerance in soybean. Soybean (Glycine max cv. BARI Soybean-5) seeds were inoculated with B. subtilis, either through a presoaking with seeds or a direct application with pot soil. After 20 days of sowing, both the seed- and soil-inoculated plants were exposed to 50, 100, and 150 mM of NaCl for 30 days. A clear sign of oxidative stress was evident through a remarkable increase in lipid peroxidation, hydrogen peroxide, methylglyoxal, and electrolyte leakage in the salt treated plants. Moreover, the efficiency of the ascorbate (AsA)–glutathione (GSH) pathways was declined. Consequently, the plant growth, biomass accumulation, water relations, and content of the photosynthetic pigments were decreased. Salt stress also caused an increased Na+/K+ ratio and decreased Ca2+. On the contrary, the B. subtilis inoculated plants showed increased levels of AsA and GSH, their redox balance, and the activities of the AsA–GSH pathway enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, and peroxidase. The B. subtilis inoculated plants also enhanced the activities of glyoxalase enzymes, which mitigated methylglyoxal toxicity in coordination with ROS homeostasis. Besides this, the accumulation of K+ and Ca2+ was increased to maintain the ion homeostasis in the B. subtilis inoculated plants under salinity. Furthermore, the plant water status was uplifted in the salt treated soybean plants with B. subtilis inoculation. This investigation reveals the potential of B. subtilis in mitigating salt-induced oxidative stress in soybean plants through modulating the antioxidant defense and glyoxalase systems along with maintaining ion homeostasis and osmotic adjustments. In addition, it was evident that the soil inoculation performed better than the seed inoculation in mitigating salt-induced oxidative damages in soybean.

Agriculture has a lot of responsibility as the rise in the world’s population demands more food requirements. However, more than one type of biotic and abiotic stress continually impacts agricultural productivity. Drought stress is a major abiotic stress that significantly affects agricultural productivity every year as the plants undergo several morphological, biochemical, and physiological modifications, such as repressed root and shoot growth, reduced photosynthesis and transpiration rate, excessive production of reactive oxygen species (ROS), osmotic adjustments, and modified leaf senescence regulating and stress signaling pathways. Such modifications may permanently damage the plants; therefore, mitigation strategies must be developed. The use of drought resistant crop cultivars is more expensive and labor-intensive with few advantages. However, exploiting plant growth promoting rhizobacteria (PGPR) is a proven alternative with numerous direct and indirect advantages. The PGPR confers induced systemic tolerance (IST) mechanisms in plants in response to drought stress via multiple mechanisms, including the alteration of root architecture, maintenance of high relative water content, improvement of photosynthesis rate, production of phytohormones, exopolysaccharides, ACC deaminase, carotenoids and volatiles, induction of antioxidant defense system, and alteration in stress-responsive gene expression. The commercial application of PGPR as bioinoculants or biostimulants will remain contingent on more robust strain selection and performance under unfavorable environmental conditions. This review highlights the possible mechanisms of PGPR by activating the plant adaptive defense systems for enhancing drought tolerance and improving overall growth and yield.

Abiotic stresses such as salt are typical negative factors that have a considerable impact on agricultural output around the world. The goal of this study was to investigate the effect of halotolerant plant-growth-promoting rhizobacteria (PGPR) on plant growth and soil function under salinity stress. The consortium of four PGPR (Pseudomonas putida, Alcaligenes sp., Klebsiella sp., and Pseudomonas cedrina) was tested for its effect on growth, chlorophyll content, oxidative stress, and root arbuscular mycorrhizal (AM) colonization of Medicago sativa in pots experiment under salt stress. The bacteria’s impact on soil enzyme activity was also investigated. Overall, in comparison to the non-inoculated control, inoculating M. sativa plants with the bacterial consortium allowed us to overcome the unfavorable effects of NaCl stress and enhanced plant growth, root AM colonization, and leaf chlorophyll content. It also reduced the levels of oxidative damage indicators such as malondialdehyde, hydrogen peroxide, and proline. Furthermore, the consortium had a beneficial effect on the activities of soil phosphatase, β-galactosidase, and arylamidase. The bacterial consortium has the potential to be employed as bio-inoculants for plants growing under salt stress.

Plant growth and crop productivity under unfavorable environmental challenges require a unique strategy to scavenge the severely negative impacts of these challenges such as soil salinity and water stress. Compost and plant growth-promoting rhizobacteria (PGPR) have many beneficial impacts, particularly in plants exposed to different types of stress. Therefore, a field experiment during two successive seasons was conducted to investigate the impact of compost and PGPR either separately or in a combination on exchangeable sodium percentage (ESP), soil enzymes (urease and dehydrogenase), wheat physiology, antioxidant defense system, growth, and productivity under deficient irrigation and soil salinity conditions. Our findings showed that exposure of wheat plants to deficit irrigation in salt-affected soil inhibited wheat growth and development, and eventually reduced crop productivity. However, these injurious impacts were diminished after soil amendment using the combined application of compost and PGPR. This combined application enhanced soil urease and dehydrogenase, ion selectivity, chlorophylls, carotenoids, stomatal conductance, and the relative water content (RWC) whilst reducing ESP, proline content, which eventually increased the yield-related traits of wheat plants under deficient irrigation conditions. Moreover, the coupled application of compost and PGPR reduced the uptake of Na and resulted in an increment in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) activities that lessened oxidative damage and improved the nutrient uptake (N, P, and K) of deficiently irrigated wheat plants under soil salinity. It was concluded that to protect wheat plants from environmental stressors, such as water stress and soil salinity, co-application of compost with PGPR was found to be effective.

Traditionally, medicinal plants have long been used as a natural therapy. Plant-derived extracts or phytochemicals have been exploited as food additives and for curing many health-related ailments. The secondary metabolites produced by many plants have become an integral part of human health and have strengthened the value of plant extracts as herbal medicines. To fulfil the demand of health care systems, food and pharmaceutical industries, interest in the cultivation of precious medicinal plants to harvest bio-active compounds has increased considerably worldwide. To achieve maximum biomass and yield, growers generally apply chemical fertilizers which have detrimental impacts on the growth, development and phytoconstituents of such therapeutically important plants. Application of beneficial rhizosphere microbiota is an alternative strategy to enhance the production of valuable medicinal plants under both conventional and stressed conditions due to its low cost, environmentally friendly behaviour and non-destructive impact on fertility of soil, plants and human health. The microbiological approach improves plant growth by various direct and indirect mechanisms involving the abatement of various abiotic stresses. Given the negative impacts of fertilizers and multiple benefits of microbiological resources, the role of plant growth promoting rhizobacteria (PGPR) in the production of biomass and their impact on the quality of bio-active compounds (phytochemicals) and mitigation of abiotic stress to herbal plants have been described in this review. The PGPR based enhancement in the herbal products has potential for use as a low cost phytomedicine which can be used to improve health care systems.

Biofortification has been widely used to increase mineral nutrients in staple foods, such as wheat (Triticum aestivum). In this study, a new approach has been used by analyzing the effect of inoculation with a plant growth-promoting rhizobacterium (PGPR), namely, Bacillus aryabhattai RSO25 and the addition of 1% (v/v) of organometallic Fe-containing polymeric nanoparticles (FeNPs) alone and in combination. Previously, the minimal inhibitory concentration of FeNPs for the bacterium was determined in order not to inhibit bacterial growth. All treatments had minor effects on seed germination and plant survival. Considering the physiology of plants, several photosynthetic parameters were significantly improved in individual treatments with FeNPs or the bacterium, particularly the efficiency of the photosystem II and the electron transport rate, which is indicative of a better photosynthetic performance. However, at the end of the experiment, a significant effect on final plant growth was not observed in shoots or in roots. When using FeNPs alone, earlier spike outgrow was observed and the final number of spikes increased by 20%. Concerning biofortification, FeNPs increased the concentration of Fe in spikes by 35%. In fact, the total amount of Fe per plant base rose to 215% with regard to the control. Besides, several side effects, such as increased Ca and decreased Na and Zn in spikes, were observed. Furthermore, the treatment with only bacteria decreased Na and Fe accumulation in grains, indicating its inconvenience. On its side, the combined treatment led to intermediate Fe accumulation in spikes, since an antagonist effect between RSO25 and FeNPs was observed. For this reason, the combined treatment was discouraged. In conclusion, of the three treatments tested, FeNPs alone is recommended for achieving efficient Fe biofortification in wheat.

Beneficial interactions between plants and some bacterial species have been long recognized, as they proved to exert various growth-promoting and health-protective activities on economically relevant crops. In this study, the growth promoting and antifungal activity of six bacterial strains, Paenarthrobacter ureafaciens, Beijerinckia fluminensis, Pseudomonas protegens, Arthrobacter sp., Arthrobacter defluii, and Arthrobacter nicotinovorans, were investigated. The tested strains resulted positive for some plant growth promoting (PGP) traits, such as indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase), siderophore production, and solubilization of phosphates. The effect of the selected bacteria on Arabidopsis thaliana seedlings growth was assessed using different morphological parameters. Bacterial activity against the phytopathogenic fungal species Aspergillus flavus, Fusarium proliferatum, and Fusarium verticillioides was also assessed, since these cause major yield losses in cereal crops and are well-known mycotoxin producers. Strains Pvr_9 (B. fluminensis) and PHA_1 (P. protegens) showed an important growth-promoting effect on A. thaliana coupled with a high antifungal activity on all the three fungal species. The analysis of bacterial broths through ultra performance liquid chromatography–mass spectrometry (UPLC–MS) and liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS/MS) confirmed the presence of potential PGP-compounds, among these are desferrioxamine B, aminochelin, asperchrome B, quinolobactin siderophores, and salicylic acid.

Rice production in Ghana has become unsustainable due to the extremely nutrient-poor soils. It is caused by inadequate soil fertility management, including the inefficient application of fertilizers. A practical solution could be the biofertilizers, Azospirillum sp. B510. We performed field trials in Ghana and Japan to compare the effects of B510 colonization on selected Ghanaian rice varieties grown. The B510 inoculation significantly enhanced the rice cultivars’ growth and yield. The phenotypic characteristics observed in rice varieties Exbaika, Ex-Boako, AgraRice, and Amankwatia were mainly short length and high tillering capacity. These features are attributed to the host plant (cv. Nipponbare), from which the strain B510 was isolated. Furthermore, Azospirillum species has been identified as the dominant colonizing bacterium of rice rhizosphere across a diverse range of agroecologies in all major rice-growing regions in Ghana. Our results suggest that the utilization of B510 as a bio-fertilizer presents a promising way to improve rice growth, enhance soil fertility, and sustain rice productivity in Ghana.

Phytoremediation, a method of phytomanagement using the plant holobiont to clean up polluted soils, is particularly effective for degrading organic pollutants. However, the respective contributions of host plants and their associated microbiota within the holobiont to the efficiency of phytoremediation is poorly understood. The identification of plant-associated bacteria capable of efficiently utilizing these compounds as a carbon source while stimulating plant-growth is a keystone for phytomanagement engineering. In this study, we sampled the rhizosphere and the surrounding bulk soil of Salixpurpurea and Eleocharis obusta from the site of a former petrochemical plant in Varennes, QC, Canada. Our objectives were to: (i) isolate and identify indigenous bacteria inhabiting these biotopes; (ii) assess the ability of isolated bacteria to utilize alkanes and polycyclic aromatic hydrocarbons (PAHS) as the sole carbon source, and (iii) determine the plant growth-promoting (PGP) potential of the isolates using five key traits. A total of 438 morphologically different bacterial isolates were obtained, purified, preserved and identified through PCR and 16S rRNA gene sequencing. Identified isolates represent 62 genera. Approximately, 32% of bacterial isolates were able to utilize all five different hydrocarbons compounds. Additionally, 5% of tested isolates belonging to genera Pseudomonas, Acinetobacter, Serratia, Klebsiella, Microbacterium, Bacillus and Stenotrophomonas possessed all five of the tested PGP functional traits. This culture collection of diverse, petroleum-hydrocarbon degrading bacteria, with multiple PGP traits, represents a valuable resource for future use in environmental bio- and phyto-technology applications.

Soils and plant root rhizospheres have diverse microorganism profiles. Components of this naturally occurring microbiome, arbuscular mycorrhizal (AM) fungi and plant growth promoting rhizobacteria (PGPR), may be beneficial to plant growth. Supplementary application to host plants of AM fungi and PGPR either as single species or multiple species inoculants has the potential to enhance this symbiotic relationship further. Single species interactions have been described; the nature of multi-species tripartite relationships between AM fungi, PGPR and the host plant require further scrutiny. The impact of select Bacilli spp. rhizobacteria and the AM fungus Rhizophagus intraradices as both single and combined inoculations (PGPR[i] and AMF[i]) within field extracted arable soils of two tillage treatments, conventional soil inversion (CT) and zero tillage (ZT) at winter wheat growth stages GS30 and GS39 have been conducted. The naturally occurring soil borne species (PGPR[s] and AMF[s]) have been determined by qPCR analysis. Significant differences (p < 0.05) were evident between inocula treatments and the method of seedbed preparation. A positive impact on wheat plant growth was noted for B. amyloliquefaciens applied as both a single inoculant (PGPR[i]) and in combination with R. intraradices (PGPR[i] + AMF[i]); however, the two treatments did not differ significantly from each other. The findings are discussed in the context of the inocula applied and the naturally occurring soil borne PGPR[s] present in the field extracted soil under each method of tillage.

An increasing need for a more sustainable agriculturally-productive system is required in order to preserve soil fertility and reduce soil biodiversity loss. Microbial biostimulants are innovative technologies able to ensure agricultural yield with high nutritional values, overcoming the negative effects derived from environmental changes. The aim of this review was to provide an overview on the research related to plant growth promoting microorganisms (PGPMs) used alone, in consortium, or in combination with organic matrices such as plant biostimulants (PBs). Moreover, the effectiveness and the role of microbial biostimulants as a biological tool to improve fruit quality and limit soil degradation is discussed. Finally, the increased use of these products requires the achievement of an accurate selection of beneficial microorganisms and consortia, and the ability to prepare for future agriculture challenges. Hence, the implementation of the microorganism positive list provided by EU (2019/1009), is desirable.

The aim of this study was to assess the ability of Bacillus amyloliquefaciens, to augment plant growth and suppress gray mold and leaf spot in pepper plants. Morphological modifications in fungal pathogen hyphae that expanded toward the PGPR colonies were detected via scanning electron microscope. Furthermore, preliminary screening showed that PGPR could produce various hydrolytic enzymes in its media. Treatments with B. amyloliquefaciens suppressed Botrytis gray mold and Alternaria leaf spot diseases on pepper caused by Botrytis pelargonii and Alternaria alternata, respectively. The PGPR strain modulated plant physio-biochemical processes. The inoculation of pepper with PGPR decreased protein, amino acid, antioxidant, hydrogen peroxide, lipid peroxidation, and abscisic acid levels but increased salicylic acid and sugar levels compared to those of uninoculated plants, indicating a mitigation of the adverse effects of biotic stress. Moreover, gene expression studies confirmed physio-biochemical findings. PGPR inoculation led to increased expression of the CaXTH genes and decreased expression of CaAMP1, CaPR1, CaDEF1, CaWRKY2, CaBI-1, CaASRF1, CaSBP11, and CaBiP genes. Considering its beneficial effects, the inoculation of B. amyloliquefaciens can be proposed as an eco-friendly alternative to synthetic chemical fungicides.

In the coming century, climate change and the increasing human population are likely leading agriculture to face multiple challenges. Agricultural production has to increase while preserving natural resources and protecting the environment. Drought is one of the major abiotic problems, which limits the growth and productivity of crops and impacts 1–3% of all land.To cope with unfavorable water-deficit conditions, plants use through sophisticated and complex mechanisms that help to perceive the stress signal and enable optimal crop yield are required. Among crop production, wheat is estimated to feed about one-fifth of humanity, but faces more and more drought stress periods, partially due to climate change. Plant growth promoting rhizobacteria are a promising and interesting way to develop productive and sustainable agriculture despite environmental stress. The current review focuses on drought stress effects on wheat and how plant growth-promoting rhizobacteria trigger drought stress tolerance of wheat by highlighting several mechanisms. These bacteria can lead to better growth and higher yield through the production of phytohormones, osmolytes, antioxidants, volatile compounds, exopolysaccharides and 1-aminocyclopropane-1-carboxylate deaminase. Based on the available literature, we provide a comprehensive review of mechanisms involved in drought resilience and how bacteria may alleviate this constraint

Drought is a major constraint in drylands for crop production. Plant associated microbes can help plants in acquisition of soil nutrients to enhance productivity in stressful conditions. The current study was designed to illuminate the effectiveness of desert rhizobacterial strains on growth and net-return of chickpeas grown in pots by using sandy loam soil of Thal Pakistan desert. A total of 125 rhizobacterial strains were isolated, out of which 72 strains were inoculated with chickpeas in the growth chamber for 75 days to screen most efficient isolates. Amongst all, six bacterial strains (two rhizobia and four plant growth promoting rhizobacterial strains) significantly enhanced nodulation and shoot-root length as compared to other treatments. These promising strains were morphologically and biochemically characterized and identified through 16sRNA sequencing. Then, eight consortia of the identified isolates were formulated to evaluate the growth and development of chickpea at three moisture levels (55%, 75% and 95% of field capacity) in a glass house experiment. The trend for best performing consortia in terms of growth and development of chickpea remained T2 at moisture level 1 > T7 at moisture level 2 > T4 at moisture level 3. The present study indicates the vital role of co-inoculated bacterial strains in growth enhancement of chickpea under low moisture availability. It is concluded from the results that the consortium T2 (Mesorhizobium ciceri RZ-11 + Bacillus subtilis RP-01 + Bacillus mojavensis RS-14) can perform best in drought conditions (55% field capacity) and T4 (Mesorhizobium ciceri RZ-11 + Enterobacter Cloacae RP-08 + Providencia vermicola RS-15) can be adopted in irrigated areas (95% field capacity) for maximum productivity of chickpea.

Arbuscular mycorrhizal (AM) fungi establish close interactions with host plants, an estimated 80% of vascular plant species. The host plant receives additional soil bound nutrients that would otherwise not be available. Other components of the microbiome, such as rhizobacteria, may influence interactions between AM fungi and the host plant. Within a commercial arable crop selected rhizobacteria in combination with AM fungi may benefit crop yields. The precise nature of interactions between rhizobacteria and AM fungi in a symbiotic relationship overall requires greater understanding. The present study aims to assess this relationship by quantifying: (1) AM fungal intracellular root structures (arbuscules) and soil glomalin as an indicator of AM fungal growth; and (2) root length and tiller number as a measure of crop growth, in response to inoculation with one of three species of Bacillus: B. amyloliquefaciences, B. pumilis, or B. subtilis. The influence of soil management, conventional (CT) or zero tillage (ZT) was a further variable evaluated. A significant (p < 0.0001) species-specific impact on the number of quantifiable AM fungal arbuscules was observed. The inoculation of winter wheat (Triticum aestivum) with B. amyloliquefaciences had a positive impact on AM fungal symbiosis, as indicated by an average of 3226 arbuscules per centimetre of root tissue. Bacillus subtilis increased root length significantly (p < 0.01) but decreased fungal symbiosis (p < 0.01). The inoculation of field soils altered the concentration of glomalin, an indicator of AM fungal growth, significantly (p < 0.00001) for each tillage treatment. The greatest increase was associated with B. amyloliquefaciences for both CT (p < 0.0001) and ZT (p < 0.00001). Bacillus subtilis reduced measured glomalin significantly in both tillage treatments (p < 0.0001 and p < 0.00001 for CT and ZT respectively). The interaction between rhizobacteria and AM fungi is variable, being beneficial or detrimental depending on species. This relationship was evident in both tillage treatments and has important implications for maximizing symbiosis in the crop plant-microbiome present in agricultural systems.

Modern agriculture increasingly demands an alternative to synthetic chemicals (fertilizers and pesticides) in order to respond to the changes in international law and regulations, but also consumers’ needs for food without potentially toxic residues. Microbial (arbuscular mycorrhizal and plant growth promoting rhizobacteria: Azotobacter, Azospirillum and Rizhobium spp.) and non-microbial (humic substances, silicon, animal- and vegetal-based protein hydrolysate and macro- and micro-algal extracts) biostimulants represent a sustainable and effective alternative or complement for their synthetic counterparts, bringing benefits to the environment, biodiversity, human health and economy. The Special Issue “Toward a sustainable agriculture through plant biostimulants: from experimental data to practical applications” compiles 34 original research articles, 4 review papers and 1 brief report covering the implications of microbial and non-microbial biostimulants for improving seedling growth and crop performance, nutrient use efficiency and quality of the produce as well as enhancing the tolerance/resistance to a wide range of abiotic stresses in particular salinity, drought, nutrient deficiency and high temperature. The present compilation of high standard scientific papers on principles and practices of plant biostimulants will foster knowledge transfer among researchers, fertilizer and biostimulant industries, stakeholders, extension specialists and farmers, and it will enable a better understanding of the physiological and molecular mechanisms and application procedure of biostimulants in different cropping systems.

Salinity is a major abiotic stress factor that affects crops and has an adverse effect on plant growth. In recent years, there has been increasing evidence that microbial volatile organic compounds (mVOC) play a significant role in microorganism–plant interactions. In the present study, we evaluated the impact of microbial volatile organic compounds (mVOC) emitted by Bacillus amyloliquefaciens GB03 on the biosynthesis of secondary metabolites and the antioxidant status in Mentha piperita L. grown under 0, 75 and 100 mM NaCl. Seedlings were exposed to mVOCs, avoiding physical contact with the bacteria, and an increase in NaCl levels produced a reduction in essential oil (EO) yield. Nevertheless, these undesirable effects were mitigated in seedlings treated with mVOCs, resulting in an approximately a six-fold increase with respect to plants not exposed to mVOCs, regardless of the severity of the salt stress. The main components of the EOs, menthone, menthol, and pulegone, showed the same tendency. Total phenolic compound (TPC) levels increased in salt-stressed plants but were higher in those exposed to mVOCs than in stressed plants without mVOC exposure. To evaluate the effect of mVOCs on the antioxidant status from salt-stressed plants, the membrane lipid peroxidation was analyzed. Peppermint seedlings cultivated under salt stress and treated with mVOC showed a reduction in malondialdehyde (MDA) levels, which is considered to be an indicator of lipid peroxidation and membrane damage, and had an increased antioxidant capacity in terms of DPPH (2,2-diphenyl−1-picrylhydrazyl) radical scavenging activity in relation to plants cultivated under salt stress but not treated with mVOCs. These results are important as they demonstrate the potential of mVOCs to diminish the adverse effects of salt stress.

The olive tree (Olea europaea L.) is an emblematic, long-living fruit tree species of profound economic and environmental importance. This study is a literature review of articles published during the last 10 years about the role of beneficial microbes [Arbuscular Mycorrhizal Fungi (AMF), Plant Growth Promoting Rhizobacteria (PGPR), Plant Growth Promoting Fungi (PGPF), and Endophytes] on olive tree plant growth and productivity, pathogen control, and alleviation from abiotic stress. The majority of the studies examined the AMF effect using mostly Rhizophagus irregularis and Glomus mosseae species. These AMF species stimulate the root growth improving the resistance of olive plants to environmental and transplantation stresses. Among the PGPR, the nitrogen-fixing bacteria Azospirillum sp. and potassium- and phosphorous-solubilizing Bacillus sp. species were studied extensively. These PGPR species were combined with proper cultural practices and improved considerably olive plant’s growth. The endophytic bacterial species Pseudomonas fluorescens and Bacillus sp., as well as the fungal species Trichoderma sp. were identified as the most effective biocontrol agents against olive tree diseases (e.g., Verticillium wilt, root rot, and anthracnose).

Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) are considered highly-efficient agents for conferring salt tolerance in host plants and improving soil fertility in rhizosphere. However, information about the inoculation of beneficial microbes on halophytes in arid and semi-arid regions remains inadequate. The objective of this study was to evaluate the influence of AMF (Glomus mosseae) inoculation, alone or in combination with PGPR (Bacillus amyloliquefaciens), on biomass accumulation, morphological characteristics, photosynthetic capacity, and rhizospheric soil enzyme activities of Elaeagnus angustifolia L., a typical halophyte in the northwest of China. The results indicate that, for one-year-old seedlings of Elaeagnus angustifolia L., AMF significantly promoted biomass accumulation in aboveground organs, increased the numbers of leaves and branches, and improved the leaf areas, stem diameters and plant height. AMF-mediated morphological characteristics of aboveground organs favored light interception and absorption and maximized the capacities for photosynthesis, transpiration, carbon dioxide assimilation and gas exchange of Elaeagnus angustifolia L. seedlings in saline soil. AMF also promoted root growth, modified root architecture, and enhanced soil enzyme activities. Elaeagnus angustifolia L. was more responsive to specific inoculation by AMF than by a combination of AMF and PGPR or by solely PGPR in saline soils. Therefore, we suggest that G. mosseae can be used in saline soil to enhance Elaeagnus angustifolia L. seedlings growth and improve soil nutrient uptake. This represents a biological technique to aid in restoration of saline-degraded areas.

Chilling stress limits processing tomato growth and yield, leading to high losses. An approach to increase the sustainability of crop production could involve the use of beneficial microorganisms. The objectives of this research were to investigate: (i) the efficacy of Funneliformis mosseae and Paraburkholderia graminis C4D1M in avoiding processing tomato damage during severe chilling stress; (ii) the synergic effect of the two microorganisms inoculated as a consortium; (iii) if the putative microorganism effects depended on the processing tomato genotype. To achieve these objectives, two experiments were carried out. In the first experiment, a modern genotype was assessed, while three genotypes were evaluated in the second experiment. At sowing, F. mosseae was mixed with peat. Nine days after sowing, P. graminis was inoculated close to the plant’s root collar. After 40 days of seed sowing, chilling treatment was performed at 1 °C for 24 h. F. mosseae mainly reduced the cell membrane injuries in term of electrolytic leakage and efficiency of photosystem II, after the chilling stress in both experiments. Conversely, in the second experiment, the consortium improved the seedling regrowth, increasing the efficiency of photosystem II. In addition, modern genotypes inoculated with microorganisms showed a better seedling regrowth.

Tomato is one of the world's most commonly grown and consumed vegetables. However, it can be attacked by the Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis ( Cmm ), which causes bacterial canker on tomato plants, resulting in significant financial losses in field production and greenhouses worldwide. The current management strategies rely principally on the application of various chemical pesticides and antibiotics, which represent a real danger to the environment and human safety. Plant growth-promoting rhizobacteria (PGPR) have emerged as an attractive alternative to agrochemical crop protection methods. PGPR act through several mechanisms to support plant growth and performance, while also preventing pathogen infection. This review highlights the importance of bacterial canker disease and the pathogenicity of Cmm . We emphasize the application of PGPR as an ecological and cost-effective approach to the biocontrol of Cmm , specifying the complex modes of biocontrol agents (BCAs), and presenting their direct/indirect mechanisms of action that enable them to effectively protect tomato crops. Pseudomonas and Bacillus are considered to be the most interesting PGPR species for the biological control of Cmm worldwide. Improving plants' innate defense mechanisms is one of the main biocontrol mechanisms of PGPR to manage bacterial canker and to limit its occurrence and gravity. Herein, we further discuss elicitors as a new management strategy to control Cmm , which are found to be highly effective in stimulating the plant immune system, decreasing disease severity, and minimizing pesticide use.

Combined stressors (high soil salinity and saline water irrigation) severely reduce plant growth and sugar beet yield. Seed inoculation with plant growth-promoting rhizobacteria (PGPR) and/or foliar spraying with silica nanoparticles (Si-NP) is deemed one of the most promising new strategies that have the potential to inhibit abiotic stress. Herein, sugar beet ( Beta vulgaris ) plants were treated with two PGPR ( Pseudomonas koreensis MG209738 and Bacillus coagulans NCAIM B.01123) and/or Si-NP, during two successive seasons 2019/2020 and 2020/2021 to examine the vital role of PGPR, Si-NP, and their combination in improving growth characteristics, and production in sugar beet plants exposed to two watering treatments (fresh water and saline water) in salt-affected soil. The results revealed that combined stressors (high soil salinity and saline water irrigation) increased ion imbalance (K + /Na + ratio; from 1.54 ± 0.11 to 1.00 ± 0.15) and declined the relative water content (RWC; from 86.76 ± 4.70 to 74.30 ± 3.20%), relative membrane stability index (RMSI), stomatal conductance ( gs ), and chlorophyll content, which negatively affected on the crop productivity. Nevertheless, the application of combined PGPR and Si-NP decreased oxidative stress indicators (hydrogen peroxide and lipid peroxidation) and sodium ions while increasing activities of superoxide dismutase (SOD; up to 1.9-folds), catalase (CAT; up to 1.4-folds), and peroxidase (POX; up to 2.5-folds) enzymes, and potassium ions resulting in physiological processes, root yield, and sugar yield compared to non-treated controls under combined stressors (high soil salinity and saline water irrigation). It is worth mentioning that the singular application of PGPR improved root length, diameter, and yield greater than Si-NP alone and it was comparable to the combined treatment (PGPR+Si-NP). It was concluded that the combined application of PGPR and Si-NP has valuable impacts on the growth and yield of sugar beet growing under combined stressors of high soil salinity and saline water irrigation.

Considering the growth-promoting potential and other regulatory roles of bacteria, we investigated the possible mechanism of the role of Bacillus subtilis in conferring salt tolerance in soybean. Soybean ( Glycine max cv. BARI Soybean-5) seeds were inoculated with B. subtilis , either through a presoaking with seeds or a direct application with pot soil. After 20 days of sowing, both the seed- and soil-inoculated plants were exposed to 50, 100, and 150 mM of NaCl for 30 days. A clear sign of oxidative stress was evident through a remarkable increase in lipid peroxidation, hydrogen peroxide, methylglyoxal, and electrolyte leakage in the salt treated plants. Moreover, the efficiency of the ascorbate (AsA)-glutathione (GSH) pathways was declined. Consequently, the plant growth, biomass accumulation, water relations, and content of the photosynthetic pigments were decreased. Salt stress also caused an increased Na + /K + ratio and decreased Ca 2+ . On the contrary, the B. subtilis inoculated plants showed increased levels of AsA and GSH, their redox balance, and the activities of the AsA-GSH pathway enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione S -transferase, and peroxidase. The B. subtilis inoculated plants also enhanced the activities of glyoxalase enzymes, which mitigated methylglyoxal toxicity in coordination with ROS homeostasis. Besides this, the accumulation of K + and Ca 2+ was increased to maintain the ion homeostasis in the B. subtilis inoculated plants under salinity. Furthermore, the plant water status was uplifted in the salt treated soybean plants with B. subtilis inoculation. This investigation reveals the potential of B. subtilis in mitigating salt-induced oxidative stress in soybean plants through modulating the antioxidant defense and glyoxalase systems along with maintaining ion homeostasis and osmotic adjustments. In addition, it was evident that the soil inoculation performed better than the seed inoculation in mitigating salt-induced oxidative damages in soybean.

Agriculture has a lot of responsibility as the rise in the world's population demands more food requirements. However, more than one type of biotic and abiotic stress continually impacts agricultural productivity. Drought stress is a major abiotic stress that significantly affects agricultural productivity every year as the plants undergo several morphological, biochemical, and physiological modifications, such as repressed root and shoot growth, reduced photosynthesis and transpiration rate, excessive production of reactive oxygen species (ROS), osmotic adjustments, and modified leaf senescence regulating and stress signaling pathways. Such modifications may permanently damage the plants; therefore, mitigation strategies must be developed. The use of drought resistant crop cultivars is more expensive and labor-intensive with few advantages. However, exploiting plant growth promoting rhizobacteria (PGPR) is a proven alternative with numerous direct and indirect advantages. The PGPR confers induced systemic tolerance (IST) mechanisms in plants in response to drought stress via multiple mechanisms, including the alteration of root architecture, maintenance of high relative water content, improvement of photosynthesis rate, production of phytohormones, exopolysaccharides, ACC deaminase, carotenoids and volatiles, induction of antioxidant defense system, and alteration in stress-responsive gene expression. The commercial application of PGPR as bioinoculants or biostimulants will remain contingent on more robust strain selection and performance under unfavorable environmental conditions. This review highlights the possible mechanisms of PGPR by activating the plant adaptive defense systems for enhancing drought tolerance and improving overall growth and yield.

Plant growth and crop productivity under unfavorable environmental challenges require a unique strategy to scavenge the severely negative impacts of these challenges such as soil salinity and water stress. Compost and plant growth-promoting rhizobacteria (PGPR) have many beneficial impacts, particularly in plants exposed to different types of stress. Therefore, a field experiment during two successive seasons was conducted to investigate the impact of compost and PGPR either separately or in a combination on exchangeable sodium percentage (ESP), soil enzymes (urease and dehydrogenase), wheat physiology, antioxidant defense system, growth, and productivity under deficient irrigation and soil salinity conditions. Our findings showed that exposure of wheat plants to deficit irrigation in salt-affected soil inhibited wheat growth and development, and eventually reduced crop productivity. However, these injurious impacts were diminished after soil amendment using the combined application of compost and PGPR. This combined application enhanced soil urease and dehydrogenase, ion selectivity, chlorophylls, carotenoids, stomatal conductance, and the relative water content (RWC) whilst reducing ESP, proline content, which eventually increased the yield-related traits of wheat plants under deficient irrigation conditions. Moreover, the coupled application of compost and PGPR reduced the uptake of Na and resulted in an increment in superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX) activities that lessened oxidative damage and improved the nutrient uptake (N, P, and K) of deficiently irrigated wheat plants under soil salinity. It was concluded that to protect wheat plants from environmental stressors, such as water stress and soil salinity, co-application of compost with PGPR was found to be effective.

Beneficial interactions between plants and some bacterial species have been long recognized, as they proved to exert various growth-promoting and health-protective activities on economically relevant crops. In this study, the growth promoting and antifungal activity of six bacterial strains, Paenarthrobacter ureafaciens , Beijerinckia fluminensis , Pseudomonas protegens , Arthrobacter sp., Arthrobacter defluii , and Arthrobacter nicotinovorans , were investigated. The tested strains resulted positive for some plant growth promoting (PGP) traits, such as indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate-deaminase (ACC-deaminase), siderophore production, and solubilization of phosphates. The effect of the selected bacteria on Arabidopsis thaliana seedlings growth was assessed using different morphological parameters. Bacterial activity against the phytopathogenic fungal species Aspergillus flavus , Fusarium proliferatum , and Fusarium verticillioides was also assessed, since these cause major yield losses in cereal crops and are well-known mycotoxin producers. Strains Pvr&#95;9 ( B. fluminensis ) and PHA&#95;1 ( P. protegens ) showed an important growth-promoting effect on A. thaliana coupled with a high antifungal activity on all the three fungal species. The analysis of bacterial broths through ultra performance liquid chromatography-mass spectrometry (UPLC-MS) and liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS) confirmed the presence of potential PGP-compounds, among these are desferrioxamine B, aminochelin, asperchrome B, quinolobactin siderophores, and salicylic acid.

Phytoremediation, a method of phytomanagement using the plant holobiont to clean up polluted soils, is particularly effective for degrading organic pollutants. However, the respective contributions of host plants and their associated microbiota within the holobiont to the efficiency of phytoremediation is poorly understood. The identification of plant-associated bacteria capable of efficiently utilizing these compounds as a carbon source while stimulating plant-growth is a keystone for phytomanagement engineering. In this study, we sampled the rhizosphere and the surrounding bulk soil of Salix purpurea and Eleocharis obusta from the site of a former petrochemical plant in Varennes, QC, Canada. Our objectives were to: (i) isolate and identify indigenous bacteria inhabiting these biotopes; (ii) assess the ability of isolated bacteria to utilize alkanes and polycyclic aromatic hydrocarbons (PAHS) as the sole carbon source, and (iii) determine the plant growth-promoting (PGP) potential of the isolates using five key traits. A total of 438 morphologically different bacterial isolates were obtained, purified, preserved and identified through PCR and 16S rRNA gene sequencing. Identified isolates represent 62 genera. Approximately, 32% of bacterial isolates were able to utilize all five different hydrocarbons compounds. Additionally, 5% of tested isolates belonging to genera Pseudomonas , Acinetobacter , Serratia , Klebsiella , Microbacterium, Bacillus and Stenotrophomonas possessed all five of the tested PGP functional traits. This culture collection of diverse, petroleum-hydrocarbon degrading bacteria, with multiple PGP traits, represents a valuable resource for future use in environmental bio- and phyto-technology applications.

Rice production in Ghana has become unsustainable due to the extremely nutrient-poor soils. It is caused by inadequate soil fertility management, including the inefficient application of fertilizers. A practical solution could be the biofertilizers, Azospirillum sp. B510. We performed field trials in Ghana and Japan to compare the effects of B510 colonization on selected Ghanaian rice varieties grown. The B510 inoculation significantly enhanced the rice cultivars' growth and yield. The phenotypic characteristics observed in rice varieties Exbaika, Ex-Boako, AgraRice, and Amankwatia were mainly short length and high tillering capacity. These features are attributed to the host plant ( cv. Nipponbare), from which the strain B510 was isolated. Furthermore, Azospirillum species has been identified as the dominant colonizing bacterium of rice rhizosphere across a diverse range of agroecologies in all major rice-growing regions in Ghana. Our results suggest that the utilization of B510 as a bio-fertilizer presents a promising way to improve rice growth, enhance soil fertility, and sustain rice productivity in Ghana.

An increasing need for a more sustainable agriculturally-productive system is required in order to preserve soil fertility and reduce soil biodiversity loss. Microbial biostimulants are innovative technologies able to ensure agricultural yield with high nutritional values, overcoming the negative effects derived from environmental changes. The aim of this review was to provide an overview on the research related to plant growth promoting microorganisms (PGPMs) used alone, in consortium, or in combination with organic matrices such as plant biostimulants (PBs). Moreover, the effectiveness and the role of microbial biostimulants as a biological tool to improve fruit quality and limit soil degradation is discussed. Finally, the increased use of these products requires the achievement of an accurate selection of beneficial microorganisms and consortia, and the ability to prepare for future agriculture challenges. Hence, the implementation of the microorganism positive list provided by EU (2019/1009), is desirable.

Soils and plant root rhizospheres have diverse microorganism profiles. Components of this naturally occurring microbiome, arbuscular mycorrhizal (AM) fungi and plant growth promoting rhizobacteria (PGPR), may be beneficial to plant growth. Supplementary application to host plants of AM fungi and PGPR either as single species or multiple species inoculants has the potential to enhance this symbiotic relationship further. Single species interactions have been described; the nature of multi-species tripartite relationships between AM fungi, PGPR and the host plant require further scrutiny. The impact of select Bacilli spp. rhizobacteria and the AM fungus Rhizophagus intraradices as both single and combined inoculations (PGPR [i] and AMF [i] ) within field extracted arable soils of two tillage treatments, conventional soil inversion (CT) and zero tillage (ZT) at winter wheat growth stages GS30 and GS39 have been conducted. The naturally occurring soil borne species (PGPR [s] and AMF [s] ) have been determined by qPCR analysis. Significant differences ( p < 0.05) were evident between inocula treatments and the method of seedbed preparation. A positive impact on wheat plant growth was noted for B. amyloliquefaciens applied as both a single inoculant (PGPR [i] ) and in combination with R. intraradices (PGPR [i] + AMF [i] ); however, the two treatments did not differ significantly from each other. The findings are discussed in the context of the inocula applied and the naturally occurring soil borne PGPR [s] present in the field extracted soil under each method of tillage.

The aim of this study was to assess the ability of Bacillus amyloliquefaciens , to augment plant growth and suppress gray mold and leaf spot in pepper plants. Morphological modifications in fungal pathogen hyphae that expanded toward the PGPR colonies were detected via scanning electron microscope. Furthermore, preliminary screening showed that PGPR could produce various hydrolytic enzymes in its media. Treatments with B. amyloliquefaciens suppressed Botrytis gray mold and Alternaria leaf spot diseases on pepper caused by Botrytis pelargonii and Alternaria alternata , respectively. The PGPR strain modulated plant physio-biochemical processes. The inoculation of pepper with PGPR decreased protein, amino acid, antioxidant, hydrogen peroxide, lipid peroxidation, and abscisic acid levels but increased salicylic acid and sugar levels compared to those of uninoculated plants, indicating a mitigation of the adverse effects of biotic stress. Moreover, gene expression studies confirmed physio-biochemical findings. PGPR inoculation led to increased expression of the CaXTH genes and decreased expression of CaAMP1, CaPR1, CaDEF1, CaWRKY2, CaBI-1, CaASRF1, CaSBP11, and CaBiP genes. Considering its beneficial effects, the inoculation of B. amyloliquefaciens can be proposed as an eco-friendly alternative to synthetic chemical fungicides.