Plant Growth Promotion Research Articles

Exploring microalgae and endophyte as biostimulants: Antioxidant and anti-inflammatory properties of Cannabis sativa L. sprouts under standard and enrichment conditions

Sprouts from germinated seeds of edible herbaceous plants are richer in bioactive compounds and micronutrients than mature plants. In recent years, the consumption of sprouted seeds in diets and the interest in exploring vegetable sprout's potential beneficial effects on human health has increased. In this work, the five-day-old sprouts of Cannabis sativa L. cultivar “Futura 75” were investigated and characterized. Hemp sprouts were obtained by germination tests under standard and enrichment conditions using the microalgal strain Chlorella sp. C2 and the bacterium Sphingomonas sp. Can_S11. The biochemical properties of hemp sprouts were analyzed for total polyphenol and flavonoid content and antioxidant activities (DPPH, ABTS, FRAP, ORAC, and Fe2+-chelating activity) by in vitro assays. A significant increase in phenolic compounds and greater antioxidant and anti-radical activities were observed for hemp sprouts obtained under enrichment conditions (dry microalgal biomass C2 and the bacterium Can_S11). Additionally, these sprouts and C. sativa seeds demonstrated enhanced protective effects on inflamed A549 cells, effectively mitigating the TNF-α induced changes and reducing the expression of IL-8 and COX-2. Overall, PGP (Plant Growth Promoting) microorganisms and microalgae represent a good strategy to promote the development of hemp sprouts and increase their phytochemical content, and antioxidant and anti-inflammatory activity.

Plant growth promotion of crops using phosphate solubilizing bacterial strains derived from insects

The aim of this study was to investigate insect derived bacteria for the ability to dissolve insoluble soil phosphate to release soluble phosphorus compounds, available to plants. Bacterial isolates were obtained from Diabrotica virgifera, Hermetia illucens, Oulema melanopus, and Ostrinia nubilalis. An in vitro evaluation of phosphate solubilization ability on Pikovskaya’s medium was done and the phosphate solubilizing index (PSI) was calculated for each isolate. Bacteria were tested in a greenhouse experiment on seeds of oats, wheat, triticale, barley and soybeans. After incubation, the weight and length of their aerial plant parts were measured. The highest increase in the weight of aerial parts was recorded for oats after using strain Om046 for inoculation (88.98%), then, wheat (Dv097, 31.43%), soybean (strain 96, 53.79%), and triticale (bacterial consortium, 36.9%). Bacteria used were identified as Lactococcus lactis (strains Om030 and Om046), Acinetobacter sp. (Dv123), Lactococcus garvieae (Dv097) and Rothia kristinae (strains 90 and 96). We showed that a successful application of insect derived bacteria for phosphate solubilization in soil, to promote plant growth, is possible. Innovative agriculture requires constant improvements in increasing crop growth. Thus, new sources of bacterial strains effectively promoting plant growth, are needed. We described a new source of plant growth-promoting bacteria that can be used in agriculture.

Insights on mining the pangenome of Sphingobacterium thalpophilum NMS02 S296 from the resistant banana cultivar Pisang lilin confirms the antifungal action against Fusarium oxysporum f. sp. cubense.

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), poses a significant global threat to banana cultivation. Conventional methods of disease management are increasingly challenged, thus making it necessary to explore alternative strategies. Bacterial endophytes, particularly from resistant genotypes, are gaining attention as potential biocontrol agents. Sphingobacterium thalpophilum, isolated from the resistant banana cultivar Pisang lilin (JALHSB010000001-JALHSB010000029), presents an intriguing prospect for combating Fusarium wilt. However, its underlying biocontrol mechanisms remain poorly understood. This study aimed to elucidate the antifungal efficacy of S. thalpophilum NMS02 S296 against Foc and explore its biocontrol mechanisms at the genomic level. Whole genome sequencing of S. thalpophilum NMS02 S296 was conducted using next-generation sequencing technologies and bioinformatics analyses were performed to identify genes associated with antifungal properties. In vitro assays were used to assess the inhibitory effects of the bacterial isolate on the mycelial growth of Foc. To explore the biomolecules responsible for the observed antagonistic activity, metabolites diffused into the agar at the zone of inhibition between Foc S16 and S. thalpophilum NMS02 S296 were extracted and identified. Whole genome sequencing revealed an array of genes encoding antifungal enzymes and secondary metabolites in S. thalpophilum NMS02 S296. In vitro experiments demonstrated significant inhibition of Foc mycelial growth by the bacterial endophyte. Comparative genomic analysis highlighted unique genomic features in S. thalpophilum linked to its biocontrol potential, setting it apart from other bacterial species. The study underscores the remarkable antifungal efficacy of S. thalpophilum NMS02 S296 against Fusarium wilt. The genetic basis for its biocontrol potential was elucidated through whole genome sequencing, shedding light on the mechanisms behind its antifungal activity. This study advanced our understanding of bacterial endophytes as biocontrol agents and offers a promising avenue for plant growth promotion towards sustainable strategies to mitigate Fusarium wilt in banana cultivation.

Potential of Trichoderma strains to positively modulate plant growth processes and bulb yield in Rabi onion

The use of beneficial microbes is hitherto known and constantly increasing in agriculture due to their positive impact on crop growth and yield, and their minimal negative impact on the environment. The objective of this study was to evaluate the impact of eight Trichoderma strains of diverse origin on crop growth and yield of onion under field conditions. The identity of the strains used in the current study was confirmed by ITS and Tef1 gene sequencing. Field experiments were conducted in the Rabi season for 2 years (2020–21, and 2022–23) to evaluate the effect of the application of eight different Trichoderma strains that were applied individually and separately as eight different treatments (T1–T8) in experimental plots. In the plant growth promotion assay conducted in vitro, all strains showed the ability to produce IAA (indole-3-acetic acid), with levels ranging from 23.52 μg/mL (T6) to 45.54 μg/mL (T3). Our results revealed that Trichoderma treated experimental plots displayed better growth indices (plant height, pseudostem diameter), RWC (Relative water content), leaf chlorophyll content, and yield-attributing features like biomass (bulb and root dry mass), bulb diameter, and harvested bulb yield compared to the untreated control plants. In terms of yield, the T2 strain exhibited the highest bulb yield consistently for both the years (2020–21 and 2022–23) followed by T3 being statistically at par with T5. Among all the evaluated Trichoderma strains, the strain T2 (OGRDT2) and T3 (GRDT1), taxonomically identified as Trichoderma longibrachiatum, registered bulb yield of 32.24 t/ha and 30.76 t/ha, respectively while T5 (GRDT3), identified as Trichoderma asperellum, registered 30.55 t/ha average yield for 2 years compared to 24.08 t/ha average yield recorded for untreated control plants with an increase of 34, 28 and 27%, respectively. Based on our findings, it is concluded that the T. longibrachiatum strains OGRDT2 (T2) and GRDT1 (T3), T. asperellum strain GRDT3 (T5) are the best inducers of the onion crop growth and yield in the Rabi season and would be explored further for its commercial application in onion farming.

Identification and Antagonistic Potential of Bacillus atrophaeus against Wheat Crown Rot Caused by Fusarium pseudograminearum

Fusarium pseudograminearum (Fpg) is a significant pathogen responsible for fusarium crown rot (FCR) in wheat (Triticum aestivum L.), a disease with devastating impacts on crop yield. The utilization of biocontrol bacteria to combat fungal diseases in plants is a cost-effective, eco-friendly, and sustainable strategy. In this trial, an endophytic bacterial species, designated as SW, was isolated from the roots of wheat. The strain exhibited potent antagonistic effects against Fpg and reduced the FCR disease severity index by 76.07 ± 0.33% in a greenhouse pot trial. Here, 106 colony-forming units (CFUs)/mL of the SW strain was determined to be the minimum dose required to exhibit the antagonism against Fpg. The strain was identified as Bacillus atrophaeus using genome sequencing and comparison with type strains in the NCBI database. Whole-genome sequencing analysis revealed that SW harbors genes for siderophores, antifungal metabolites, and antibiotics, which are key contributors to its antagonistic activity. Additionally, the strain’s ability to utilize various carbon and nitrogen sources, successfully colonize wheat root tissues as an endophyte, and form biofilms are critical attributes for promoting plant growth. In summary, these findings demonstrate the ability of Bacillus atrophaeus to control FCR disease in wheat in a sustainable agricultural setting.

Solubilization and enhanced degradation of benzene phenolic derivatives-Bisphenol A/Triclosan using a biosurfactant producing white rot fungus Hypocrea lixii S5 with plant growth promoting traits.

Endocrine disrupting chemicals (EDCs) as benzene phenolic derivatives being hydrophobic partition to organic matter in sludge/soil sediments and show slow degradation rate owing to poor bioavailability to microbes. In the present study, the potential of a versatile white rot fungal isolate S5 identified as Hypocrea lixii was monitored to degrade bisphenol A (BPA)/triclosan (TCS) under shake flask conditions with concomitant production of lipopeptide biosurfactant (BS) and plant growth promotion. Sufficient growth of WRF for 5 days before supplementation of 50 ppm EDC (BPA/TCS) in set B showed an increase in degradation rates by 23% and 29% with corresponding increase in secretion of lignin-modifying enzymes compared to set A wherein almost 84% and 97% inhibition in fungal growth was observed when BPA/TCS were added at time of fungal inoculation. Further in set B, EDC concentration stimulated expression of laccase and lignin peroxidase (Lip) with 24.44 U/L of laccase and 281.69 U/L of Lip in 100 ppm BPA and 344 U/L Lip in 50 ppm TCS supplemented medium compared to their respective controls (without EDC). Biodegradation was also found to be correlated with lowering of surface tension from 57.02 mN/m (uninoculated control) to 44.16 mN/m in case of BPA and 38.49 mN/m in TCS, indicative of biosurfactant (BS) production. FTIR, GC-MS, and LC-ESI/MSMS confirmed the presence of surfactin lipopeptide isoforms. The WRF also displayed positive plant growth promoting traits as production of ammonia, indole acetic acid, siderophores, Zn solubilization, and 1-1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, reflecting its soil restoration ability. The combined traits of biosurfactant production, EDC degradation and plant growth promotion displayed by WRF will help in emulsifying the hydrophobic pollutants favoring their fast degradation along with restoration of contaminated soil in natural conditions.

Sodium alginate improves phytase stability and enhances soil phosphorous utilization

A plant growth-promoting endophytic strain Bacillus sp. WR11 produces high-level phytase. Phytase degrades phytate, which is the major form of organic phosphate in soils that cannot be readily utilized by plants. To strengthen the strain or its phytase for cost-efficient biodegradation of phytate, we compared the impacts of different chemical additives on phytase production and preservation. Phytate degradation ability in soils and growth promotion effect in wheat were evaluated. To ensure safe application, potential pathogenicity of the strain was also predicted. Phytase activity assay suggests that sodium alginate (SA) significantly improves phytase production to as higher as 2.21-fold, but has little influence on the growth of WR11 during liquid fermentation. During liquid storage of cell-free supernatant (CFS) at room temperature, SA maintains 68% phytase activity indicating significantly improved stability within four weeks. Determination of water-soluble P and phytate-P indicates Bacillus sp. WR11 and CFS effectively degrade 20.17–38.55% phytate in soils. Quantification of biomass, phosphorus and iron contents shows positive effect of WR11 and its CFS on wheat growth. Particularly, the degradation ability (63.2%) and growth promoting effect of CFS is much stronger in the presence of 0.8% SA. Genomic prediction demonstrates strain WR11 has a large number of genes in the databases of Pathogen-Host Interactions, Virulence Factors of pathogenic bacteria, Antibiotic Resistance Genes, and the Comprehensive Antibiotic Research Database, respectively. In conclusion, SA significantly improves phytase production and phytate degradation. Phytase accompanied with SA may be an alternative strategy for phytate degradation and plant growth promotion, when microorganisms have safety issues.

Microbiological mechanism of hydrogen fertilizer effect in soil.

For a long time, intercropping and rotation of leguminous with non-leguminous crops is widely used to reduce the application of nitrogen fertilizer and increase yield in agroecosystems. At present, most researchers considered that this management measure is helpful for reducing fertilizer consumption and increasing its efficiency, as it can improve nutrient supply of legumestonon-legumes, the spatial nutrient utilization efficiency by enhancing soil spatial heterogeneity, and improve soil structure and disease resistance. However, current theories cannot fully explain the positive effect of crop rotation and inter-cropping systems involving legumes. A large amount of hydrogen (H2) can be produced as an obligatory by-product of nitrogenase responsible for nitrogen (N2) fixation in the root nodules of leguminous plants. Despite of substantial amounts of H2 enriched in the rhizosphere of legumes, only a minor proportion of H2 is found to leak to soil surface. Increasing evidence showed that most H2 released in soil is immediately depleted in the surrounding of N2-fixing nodules by H2-oxidizing bacteria (HOB) thriving in soil. HOB can use H2 as an electron donor to assimilate and fix CO2 through redox reactions to synthesize cellular substances and consequently promote plant growth. To date, however, little is known about the biological mechanism and ecological process behind the "hydrogen fertilizer effect". Therefore, we review the H2-induced plant growth-promoting effects and its microbiological mechanisms. Our aims were to explore a new way for enhancing agroecosystem production, and to provide scientific basis for future utilization of H2 in agricultural production practices.

Characterization of Sinorhizobium strains isolated from arid and semi-arid areas of Morocco promoting the growth of Vachellia gummifera

Vachellia gummifera is a nitrogen-fixing shrub endemic to Morocco, and represents a suitable candidate for reforestation programs in dry areas. In this study, we identified seven root microsymbionts of V. gummifera, and determined their phenotypic characteristics, Plant Growth-Promoting (PGP) activities and their symbiotic efficiency. The bacteria were isolated from root nodules of the plant grown in Moroccan forest soils located in arid and semi-arid regions. The 16S rRNA gene sequences analysis of seven isolates showed similarity values ranging from 99.85% to 99.92% with Sinorhizobium fredii USDA205T. The phenotypic analyses displayed that the strains use different carbohydrates, mainly mono and di-saccharides, as a sole carbon source, and 13 out of 15 amino acids tested as the sole nitrogen source. The strains have variable tolerance to heavy metals, but are sensitive to salinity and high temperature, as no one grew in the presence of 2% NaCl (w/v) or at 40 °C, respectively. On the other hand, the strains grew in a very high osmotic stress environment induced by PEG 6000 (20% w/v), and they all grow in a pH range between 6.5 and 9. The strains possess PGP activities, such as phosphate solubilization, siderophore, and indole acetic acid production. Inoculation under axenic conditions showed that the strains increased the aerial biomass of inoculated plants up to 217%, whereas the relative symbiotic efficiency percentages (74.87–140,3%) showed that most strains are very efficient. From all these results we concluded that our strains may be proposed as inoculum for large-scale applications, such as reforestation programs.

Use and impact of endophytic entomopathogenic fungi: Their potential in the context of agricultural sustainability

The use of entomopathogenic fungi (EF) as endophytes is an environmentally friendly alternative for sustainable food production, given that the current paradigm in crop protection is based on the use of organosynthetic pesticides, with more than two million tons per year worldwide. For these reasons, EF have the ability to live within plant tissues as endophytes acting as biopesticides. Under this scenario, this review analyzes and discusses the global status of the endophytic entomopathogenic fungi (EEF), their potential in plant protection against plant diseases and insect pests and as plant growth promoters. Successes and failures, and prospects for field application are examined. More than 7000 studies on EEF have been published, with important success cases. However, it is necessary to understand that the agricultural production is based on the use of external inputs, mainly pesticides. While progressive changes occur, it is fundamental to investigate the effect of these substances on the efficacy and persistence of EEF, without neglecting that the lack of knowledge of the effect of biotic and abiotic factors on EEF is an important cause of failures. Future studies should be focused on clarifying aspects such as: application strategies, endophytic persistence and transmission routes to improve the sustainability of agricultural production.

Responses of Water and Fertilizer Utilization Efficiency and Yield of Cotton to Foliar Biostimulant under Irrigation with Magnetic–Electric-Activated Water

The foliar application of biostimulants at specific concentrations under magnetic–electric water irrigation has a positive effect on water and fertilizer use efficiency and yield of cotton, which is crucial for green and sustainable agricultural development. As a new type of fertilizer, biostimulants have demonstrated remarkable effects in improving crop yield and quality by enhancing nutrient uptake, promoting plant growth, and increasing resilience to environmental stress. In this study, the effects of magnetic–electric-activated water irrigation and foliar biostimulant application on cotton growth and yield were investigated, with the aim of understanding the underlying mechanisms. The field experiment included various irrigation treatments (brackish water, fresh water, magnetic–electric brackish water, and magnetic–electric fresh water) and biostimulant concentrations (1600, 1200, 800, 400 times dilution, and no spraying). SEM analysis indicated that under magnetoelectric water irrigation, the foliar application of biostimulants enhances physiological growth of cotton, improving the water and nutrient uptake efficiency, and thereby increasing yield. Specifically, the effective boll number and single boll weight under magnetic–electric fresh water irrigation with an 800 times biostimulant concentration increased by 21.84–48.78% and 5.50–18.91%, respectively, compared to the no-spraying treatment. The seed cotton yield rose by 16.61–38.63%, water-use efficiency improved by 24.35%, the harvest index reached 0.33, and nitrogen absorption increased by 76.21%. Thus, integrating magnetic–electric water irrigation with foliar biostimulants offers a theoretical and technical foundation for advancing green, high-quality agriculture and sustainable production.

Impact of a Potent Strain of Plant Growth-Promoting Bacteria (PGPB), Bacillus subtilis S1 on Bacterial Community Composition, Enzymatic Activity, and Nitrogen Content in Cucumber Rhizosphere Soils.

Antagonistic bacterial strains from Bacillus spp. have been widely studied and utilized in the biocontrol of phytopathogens and the promotion of plant growth, but their impacts on the rhizosphere microecology when applied to crop plants are unclear. Herein, the effects of applying the antagonistic bacterium Bacillus subtilis S1 as a biofertilizer on the rhizosphere microecology of cucumbers were investigated. In a pot experiment on cucumber seedlings inoculated with S1, 3124 bacterial operational taxonomic units (OTUs) were obtained from the rhizosphere soils using high-throughput sequencing of 16S rRNA gene amplicons, and the most abundant phylum was Proteobacteria that accounted for 49.48% in the bacterial community. S1 treatment significantly reduced the abundances of soil bacterial taxa during a period of approximately 30days but did not affect bacterial diversity in the rhizosphere soils of cucumbers. The enzymatic activities of soil nitrite reductase (S-Nir) and dehydrogenase (S-DHA) were significantly increased after S1 fertilization. However, the activities of soil urease (S-UE), cellulase (S-CL), and sucrase (S-SC) were significantly reduced compared to the control group. Additionally, the ammonium- and nitrate-nitrogen contents of S1-treated soil samples were significantly lower than those of the control group. S1 fertilization reshaped the rhizosphere soil bacterial community of cucumber plants. The S-CL activity and nitrate-nitrogen content in rhizosphere soil affected by S1 inoculation play important roles in altering the abundance of rhizosphere soil microbiota.

Small Regulatory RNAs of the Rsm Clan in Pseudomonas.

Bacteria of the genus Pseudomonas are ubiquitous on Earth due to their great metabolic versatility and adaptation to fluctuating environments and different hosts. Some groups are important animal/human and plant pathogens, whereas others are studied for their biotechnological applications, including bioremediation, biological control of phytopathogens and plant growth promotion. Notably, their adaptability is mediated by various signal transduction systems, with the post-transcriptional Gac-Rsm cascade playing a key role. This pervasive Pseudomonas pathway controls major transitions at the population level, such as motile/sessile lifestyle, primary/secondary metabolism or replicative/infective behaviour. A hallmark of the Gac-Rsm cascade is the participation of small, regulatory, non-coding RNAs of the Rsm clan. These RNAs are synthetised in response to cell-density-dependent autoinducer signals channelled through the GacS/GacA two-component system, and they counteract, by molecular mimicry, the translational control that RNA-binding proteins of the RsmA family exert over hundreds of mRNAs. Rsm RNAs have been investigated in a few Pseudomonas model species, evidencing the presence of a variable number and families of genes depending on the taxonomic clade. However, the global picture of the distribution of these riboregulators at the genus level was unknown until now. We have undertaken a comprehensive survey and annotation of the vast array of gene sequences encoding members of the Rsm RNA clan in 245 complete genomes that cover 28 phylogenomic clades across the entire genus. The properties of the different families of rsm genes, their phylogenetic radiation, as well as the features of their promoters and adjacent regions, are discussed. The novel insights presented in our manuscript will significantly boost research on the biology of these prevalent RNAs in understudied species of the genus Pseudomonas and closely related genera.

Management of Rhizoctonia blight of groundnut using antagonistic effects of bioagents and organic amendments

Rhizoctonia blight disease caused by Rhizoctonia solani in groundnut crop is one of the most devastating diseases occurring worldwide. The disease affects the morphological and physiological parameters of the crop leading to reduction in pod yield as well as oil yield. The pathogen was isolated locally and identified as Rhizoctonia solani based on molecular characterization. The efficacy of different bioagents in reducing the radial growth of pathogen was tested in vitro and highest mycelia growth inhibition was recorded by Trichoderma asperellum (89.07 %). Among the fungicides tested, 100 % mycelial growth inhibition was observed by use of Carbendazim 50 WP, Tebuconazole 25.9 % EC, Hexaconazole 5 % suspension concentrate (SC) and Tebuconazole 50 % + Trifloxystrobin 25 % water-dispersible granule (WG). Among different organic substances tested in vitro, neem seed cake achieved maximum mycelial growth inhibition of 50.74 % and 54.08 % at 10 % and 20 % concentrations respectively. In the field experiment, treatment with application of neem seed cake to the soil at 500 kg/ha + application of mustard seed cake to the soil at 500 kg/ha + treatment of seeds with Tebuconazole at 1.5 g/kg of seed + treatment of seeds with T. asperellum at 10 g/kg of seed was found to be the best in enhancing plant health, growth promotion and oil yield. The combined treatment of bioagent, fungicide and organic amendment recorded maximum number of branches (14.00), number of leaves (668.33), plant dry weight (64.17 g), 100 pod weight (65.00 g) and oil yield (47.33 %) compared to the control and other treatments along with reduction of the disease (59.61 %). In the physiological parameters study, the same treatment also recorded maximum pigment contents viz. Chlorophyll a (1.843 mg/g), Chlorophyll b (0.555 mg/g), total chlorophyll (2.397 mg/g) and carotenoid content (0.084 mg/g) but with minimum phenol content (1.693 mg/g). Thus, it can be concluded that integration of selective inputs in the combined treatment of Neem seed cake, Mustard seed cake, Tebuconazole and T. asperellum could enhance the plant health, morphological growth and physiological parameters and increased the oil yield in groundnut along with reduction of the disease.

Profiling Metabolites with Antifungal Activities from Endophytic Plant-Beneficial Strains of Pseudomonas chlororaphis Isolated from Chamaecytisus albus (Hack.) Rothm.

Fungal phytopathogens represent a large and economically significant challenge to food production worldwide. Thus, the application of biocontrol agents can be an alternative. In the present study, we carried out biological, metabolomic, and genetic analyses of three endophytic isolates from nodules of Chamaecytisus albus, classified as Pseudomonas chlororaphis acting as antifungal agents. The efficiency of production of their diffusible and volatile antifungal compounds (VOCs) was verified in antagonistic assays with the use of soil-borne phytopathogens: B. cinerea, F. oxysporum, and S. sclerotiorum. Diffusible metabolites were identified using chromatographic and spectrometric analyses (HPTLC, GC-MS, and LC-MS/MS). The phzF, phzO, and prnC genes in the genomes of bacterial strains were confirmed by PCR. In turn, the plant growth promotion (PGP) properties (production of HCN, auxins, siderophores, and hydrolytic enzymes, phosphate solubilization) of pseudomonads were bioassayed. The data analysis showed that all tested strains have broad-range antifungal activity with varying degrees of antagonism. The most abundant bioactive compounds were phenazine derivatives: phenazine-1-carboxylic acid (PCA), 2-hydroxy-phenazine, and diketopiperazine derivatives as well as ortho-dialkyl-aromatic acids, pyrrolnitrin, siderophores, and HCN. The results indicate that the tested P. chlororaphis isolates exhibit characteristics of biocontrol organisms; therefore, they have potential to be used in sustainable agriculture and as commercial postharvest fungicides to be used in fruits and vegetables.

Adaptation and Promotion of in Vitro Growth by Pseudomonas Aeruginosa GU270941.1 A in the Presence of Cadmium

Cadmium (Cd) is one of the most toxic heavy metals. Its high mobility and bioaccumulation power in plant, animal and human tissues differentiate it from the rest of its group and motivate the interest of scientists to know its effects and interaction with plants and the environment. The aim of the present study was to isolate and evaluate the in vitro tolerance of rhizospheric bacteria associated with rice plants in cadmium-contaminated environments and to evaluate them in vitro capacity to tolerate cadmium and the production of compounds related to their ability to remediate and promote plant growth. Rhizospheric bacteria were isolated, tolerance was found up to 500 mg/L CdCl2 and the ability to produce siderophore and solubilize phosphate at this concentration of cadmium was observed in vitro. The morphospecies with the ability to tolerate cadmium up to 500 mg/L found corresponds to Pseudomonas aeruginosa GU270941.1, a species of rhizospheric bacteria that shows an alternative to reduce cadmium uptake by rice plants and promote the growth of these plants for their adaptation and tolerance to this metal.

Evaluation of 1021Bp, a close relative of Pseudomonas eucalypticola, for potential of plant growth promotion, fungal pathogen suppression and boxwood blight control

BackgroundPseudomonas eucalypticola, a new species of the P. fluorescens group that generates most Pseudomonas-based biocontrol agents, has not been found in any plants other than Eucalyptus dunnii leaves. Except for antagonism to the growth of a few fungi, its features in plant growth promotion and disease control have not been evaluated. Here, we identified a similar species of P. eucalypticola, 1021Bp, from endophyte cultures of healthy leaves of English boxwood (Buxus sempervirens ‘Suffruticosa’) and investigated its antifungal activity, plant growth promotion traits, and potential for boxwood blight control.ResultsColorimetric or plate assays showed the properties of 1021Bp in nitrogen fixation, phosphate solubilization, and production of indole-3-acetic acid (IAA) and siderophores, as well as the growth suppression of all five plant fungal pathogens, including causal agents of widespread plant diseases, gray mold, and anthracnose. Boxwood plant leaves received 87.4% and 65.8% protection from infection when sprayed with cell-free cultural supernatant (CFS) but not the resuspended bacterial cells at 108–9/mL of 1021Bp at one and seven days before inoculation (dbi) with boxwood blight pathogen, Calonectria pseudonaviculata, at 5 × 104 spores/mL. They also received similarly high protection with the 1021Bp cell culture without separation of cells and CFS at 14 dbi (67.5%), suggesting a key role of 1021Bp metabolites in disease control.ConclusionsGiven the features of plant growth and health and its similarity to P. eucalypticola with the P. fluorescens lineage, 1021Bp has great potential to be developed as a safe and environmentally friendly biofungicide and biofertilizer. However, its metabolites are the major contributors to 1021Bp activity for plant growth and health. Application with the bacterial cells alone, especially with nonionic surfactants, may result in poor performance unless survival conditions are present.

Mechanistic insights to Paenibacillus lentimorbus mediated biocontrol of Alternaria solani in Solanum lycopersicum L. through carbohydrate reallocation and sweet immunity suppression

Researchers envisaged that PGPR (plant growth promoting rhizobacteria) has vast possibilities as a bioinoculant that will lead to revolution. However, it's still very far from becoming commercially successful. Here, the information regarding the root colonization of PGPR in host plants and plant response towards PGPR is inadequate. It can provide valuable information for developing successful biofertilizers and biocontrol agents. PGPR (Paenibacillus lentimorbus NRRL B-30488 or CHM12) has been previously reported as a successful commercial biofertilizer and biocontrol agent. However, the exact mechanism of plant growth promotion and biocontrol is poorly studied. So, CHM12 was appraised for biotic stress amelioration of pathogen Alternaria solani in Tomato (Solanum lycopersicum L.) var. S-22 plants. PGPR CHM12 was assessed for various plant growth parameters such as proline, sugar content, etc. in pathogen A. solani (AS) challenged plants and compared with the CHM12 treated plants in a greenhouse study. Then, the metabolomics tool (GC-MS) was used to identify metabolites and their respective genes playing pivotal roles in colonization tactics availed by PGPR. Further, gene expression analysis was done to affirm the involvement of various genes related to metabolites providing biotic stress tolerance in Tomato plants. The current research discerned that PGPR CHM12 revealed significant differences in different plant growth parameters studied. There were 33 distinct metabolites identified, which stipulated the involvement of carbohydrate metabolism mainly in combating biotic stress in this study. Thus, our study reconfirmed very few reported previous results through gene expression analysis, suggesting the downregulation of carbohydrate metabolism genes in PGPR-treated plants. This downregulation of carbohydrate genes might be the critical factor for suppressing the plant's immune response to gaining entry inside the host plant. This also helps in retaining and reallocating carbohydrates in plant cells to reduce pathogen proliferation.

Tapping into haloalkaliphilic bacteria for sustainable agriculture in treated wastewater: insights into genomic fitness and environmental adaptation.

The increasing salinity and alkalinity of soils pose a global challenge, particularly in arid regions such as Tunisia, where about 50% of lands are sensitive to soil salinization. Anthropogenic activities, including the use of treated wastewater (TWW) for irrigation, exacerbate these issues. Haloalkaliphilic bacteria, adapted to TWW conditions and exhibiting plant-growth promotion (PGP) and biocontrol traits, could offer solutions. In this study, 24 haloalkaliphilic bacterial strains were isolated from rhizosphere sample of olive tree irrigated with TWW for more than 20years. The bacterial identification using 16S rRNA gene sequencing showed that the haloalkaliphilic isolates, capable of thriving in high salinity and alkaline pH, were primarily affiliated to Bacillota (Oceanobacillus and Staphylococcus). Notably, these strains exhibited biofertilization and enzyme production under both normal and saline conditions. Traits such as phosphate solubilization, and the production of exopolysaccharide, siderophore, ammonia, and hydrogen cyanide were observed. The strains also demonstrated enzymatic activities, including protease, amylase, and esterase. Four selected haloalkaliphilic PGPR strains displayed antifungal activity against Alternaria terricola, with three showing tolerances to heavy metals and pesticides. The strain Oceanobacillus picturea M4W.A2 was selected for genome sequencing. Phylogenomic analyses indicated that the extreme environmental conditions probably influenced the development of specific adaptations in M4W.A2 strain, differentiating it from other Oceanobacillus picturae strains. The presence of the key genes associated with plant growth promotion, osmotic and oxidative stress tolerance, antibiotic and heavy metals resistance hinted the functional capabilities might help the strain M4W.A2 to thrive in TWW-irrigated soils. By demonstrating this connection, we aim to improve our understanding of genomic fitness to stressed environments. Moreover, the identification of gene duplication and horizontal gene transfer events through mobile genetic elements allow the comprehension of these adaptation dynamics. This study reveals that haloalkaliphilc bacteria from TWW-irrigated rhizosphere exhibit plant-growth promotion and biocontrol traits, with genomic adaptations enabling their survival in high salinity and alkaline conditions, offering potential solutions for soil salinization issues.

Effects of long-term continuous cultivation on the structure and function of soil bacterial and fungal communities of Fritillaria Cirrhosa on the Qinghai-Tibetan Plateau.

Fritillaria cirrhosa, an endangered medicinal plant in the Qinghai-Tibet Plateau, is facing resource scarcity. Artificial cultivation has been employed to address this issue, but problems related to continuous cultivation hinder successful transplantation. Imbalanced microbial communities are considered a potential cause, yet the overall changes in the microbial community under continuous cropping systems remain poorly understood. Here, we investigated the effects of varying durations of continuous cropping on the bacterial and fungal communities, as well as enzymatic activities, in the rhizospheric soil of F. cirrhosa. Our findings revealed that continuous cropping of F. cirrhosa resulted in soil acidification, nutrient imbalances, and increased enzyme activity. Specifically, after 10 years of continuous cropping, there was a notable shift in the abundance and diversity (e.g., Chao1 index) of soil bacteria and fungi. Moreover, microbial composition analyses revealed a significant accumulation of harmful microorganisms associated with soil-borne diseases (e.g., Luteimonas, Parastagonospora, Pseudogymnoascus) in successively cropped soils, in contrast to the significant reduction of beneficial microorganisms (e.g., Sphingomonas, Lysobacter, Cladosporium) that promote plant growth and development and protect against diseases such as Fusarium sp.These changes led to decreased connectivity and stability within the soil microbial community. Structural equation modeling and redundancy analysis revealed that alkaline hydrolytic nitrogen and available phosphorus directly influenced soil pH, which was identified as the primary driver of soil microbial community changes and subsequently contributed to soil health deterioration. Overall, our results highlight that soil acidification and imbalanced rhizosphere microbial communities are the primary challenges associated with continuous cropping of F. cirrhosa. These findings establish a theoretical foundation for standardized cultivation practices of F. cirrhosa and the bioremediation of continuously cultivated soils.