Plant Growth-promoting Properties Research Articles

Towards enhancing phytoremediation: The effect of syringic acid, a plant secondary metabolite, on the presence of phenoxy herbicide-tolerant endophytic bacteria.

Among emerging pollutants, residuals of phenoxy herbicides, including 2-chloro-4-methylphenoxy acid (MCPA), are frequently detected in non-targeted areas. MCPA can be removed from environmental matrices using biological remediation methods including endophyte-assisted phytoremediation. The interactions between selected plants excreting to the rhizosphere plant secondary metabolites (PSMs) and plant-associated bacteria (incl. endophytes) can speed up the removal of organics and increase the plants resistance to pollutants such as MCPA. The role of plant-associated bacteria in endophyte-assisted phytoremediation has been partially described, however neither MCPA-tolerant endophytic bacteria has been isolated nor characterized. So far, promising results were obtained by simultaneous cultivation of Cucurbita pepo (zucchini) and amendment of soil with structurally related PSM syringic acid (SA), which can substantially enhance removal of MCPA from soil. Hence, the main aim of this research was to study the effect of PSM (SA) on the presence of functional MCPA-tolerant endophytic bacteria using a culture-dependent and -independent approach. Comparison between the molecular and microbiological analysis revealed differences between applied methods. However, irrespectively of the genera identification methods, presence of phenolic compounds (MCPA or SA) favorized presence of potential MCPA-degraders. On the basis of MCPA tolerance tests of isolated bacteria, two Pseudomonas endophytic isolates from zucchini roots and three isolates from zucchini leaves i.e. Pseudomonas sp., Paenarthrobacter sp. and Acinetobacter sp. were selected for further screening of plant growth promoting properties (PGPP). MCPA-tolerant endophytic bacteria showed multiple PGPP. Therefore, these isolates can potentially contribute to an improved fitness of plants used for the purpose of enhancing phytoremediation of environments polluted with phenoxy herbicides.

Bioprospecting of Selected Trichoderma spp. for Its Plant Growth Promoting and Biocontrol Properties

Bioprospecting for Trichoderma strains from peat soil collected at MARDI Sessang Station, Saratok, Sarawak, revealed promising candidates as plant growth-promoting microbes (PGPM) and producers of phytohormones such as indole-3-acetic acid (IAA) and gibberellic acid (GA3). The study aimed to identify Trichoderma strains with dual functions in biocontrol and plant growth enhancement. A total of seventeen strains were isolated and screened for their biocontrol activity against significant plant pathogens—Ralstonia solanacearum and Colletotrichum gloeosporioides and also their potential to produce IAA and GA3. Among the isolates, one strain exhibited strong antagonistic activity against R. solanacearum, a pathogen responsible for bacterial wilt, suggesting its potential for biocontrol applications. Additionally, two strains showed significant inhibitory effects against C. gloeosporioides, the causative agent of anthracnose. Four strains demonstrated the ability to produce IAA, an essential auxin for root development and overall plant growth promotion and two strains were identified as GA3 producers, contributing to plant growth by promoting cell elongation and germination. This study highlights the potential of Trichoderma strains from peat soils in Sarawak as valuable resources for sustainable agriculture. The dual functionality of these strains as biocontrol agents and phytohormone producers makes them promising candidates for integrated pest management (IPM) and biofertilizer development. Future research should focus on field trials and further molecular characterization to fully explore the potential of these Trichoderma isolates in enhancing crop productivity.

Screening and assessment of PGP and biocontrol properties of Azotobacter species isolated from agriculture soils of North Karnataka

Plant growth-promoting rhizobacteria (PGPR) are recognized for their ability to produce phytohormones, root-stimulating compounds, anti-fungal compounds and other secondary metabolites, making them potential biocontrol agents in agriculture. In the present study, 85 Azotobacter isolates were isolated from the agricultural soils of Raichur and Chikkabalapura locations. The isolates were further accessed for morphological, biochemical and plant growth-promotion (PGP) properties. All the isolated strains showed brown to black colour colonies on the Waksmann 77 media plate. Similar biochemical results were obtained for all the Azotobacter isolates. The isolates such as Azt-85 recorded the highest N2 fixation (33.36 µgN/mL/Day), Azt-69 produced IAA (24.67 µg/mL), and Azt-51 produced GA (23.7 µg/25mL). The anti-fungal efficacy studies were conducted using the dual culture technique using the efficient PGPR Azotobacter isolates against fungal species (Fusarium oxysporum f. sp. lini, Fusarium oxysporum f. sp. ciceris and Aspergillus flavus). After the incubation period, the Azt-41 isolate showed the highest zone of inhibition (18 mm) against Fusarium oxysporum f. sp. lini. Similarly, Azotobacter isolates viz., Azt-25, 38 and 41 showed maximum growth inhibition (9 mm) against Fusarium oxysporum f. sp. ciceris. Similarly, the Azt-31 isolate recorded a moderate (13 mm) zone of inhibition against Aspergillus flavus. Integrating sustainable biocontrol strategies by injecting beneficial microbes like Azotobacter can enhance resilient food production systems and reduce reliance on chemical inputs through PGPR properties.

Whole-Genome Profiling of Endophytic Strain B.L.Ns.14 from Nigella sativa Reveals Potential for Agricultural Bioenhancement.

Endophytic microbes in medicinal plants often possess beneficial traits for plant health. This study focuses on the bacterial endophyte strain B.L.Ns.14, isolated from Nigella sativa leaves, which demonstrated multiple plant growth-promoting properties. In vitro tests showed that B.L.Ns.14 supports plant growth, colonization, and tolerance to abiotic stress. The strain also exhibited antifungal activity against phytopathogens such as Rhizoctonia solani, Colletotrichum acutatum, Verticillium dahliae, and Fusarium oxysporum f. sp. radicis-lycopersici. Whole-genome analysis, supported by ANI and dDDH values, identified B.L.Ns.14 as Bacillus halotolerans. Genome mining revealed 128 active carbohydrate enzymes (Cazymes) related to endophytism and biocontrol functions, along with genes involved in phosphate solubilization, siderophore and IAA production, biofilm formation, and motility. Furthermore, genes for osmolyte metabolism, Na+/H+ antiporters, and stress response proteins were also identified. The genome harbors 12 secondary metabolite biosynthetic gene clusters, including those for surfactin, plipastatin mojavensin, rhizocticin A, and bacilysin, known for their antagonistic effects against fungi. Additionally, B.L.Ns.14 promoted Arabidopsis thaliana growth under both normal and saline conditions, and enhanced Solanum lycopersicum growth via seed biopriming and root irrigation. These findings suggest that Bacillus halotolerans B.L.Ns.14 holds potential as a biocontrol and plant productivity agent, warranting further field testing.

Exploring the Plant Growth-Promotion Properties of Rhizospheric and Endophytic Bacteria Associated with Robinia pseudoacacia L. in Serpentine Soil.

Serpentine soils are characterized as a unique environment with low nutrient availability and high heavy metal concentrations, often hostile to many plant species. Even though these unfavorable conditions hinder the growth of various plants, particular vegetation with different adaptive mechanisms thrives undisturbed. One of the main contributors to serpentine adaptation represents serpentine bacteria with plant growth-promoting properties that assemble delicate interactions with serpentine plants. Robinia pseudoacacia L. is an invasive but adaptive species with phytoremediation potential and demonstrates extraordinary success in this environment. To explore more in-depth the role of plant growth-promoting serpentine bacteria, we isolated them and tested their various plant growth-promoting traits both from the rhizosphere and roots of R. pseudoacacia. Based on the demonstrated plant growth-promoting traits such as siderophore production, phosphate solubilization, nitrogen fixation, indole-3-acetic acid production, and ACC deaminase production, we sequenced overall 25 isolates, 14 from the rhizosphere and 11 from the roots. Although more efficient in exhibiting plant growthpromoting traits, rhizospheric bacteria showed a low rate of diversity in comparison to endophytic bacteria. The majority of the isolates from the rhizosphere belong to Pseudomonas, while isolates from the roots exhibited higher diversity with genera Pseudomonas, Bacillus, Staphylococcus, Lysinibacillus and Brevibacterium/Peribacillus/Bacillus. The capacity of the described bacteria to produce siderophores, solubilize phosphate, and fix nitrogen highlights their central role in enhancing nutrient availability and facilitating R. pseudoacacia adaptation to serpentine soils. The findings highlight the potential significance of serpentine bacteria, particularly Pseudomonas, in contributing to the resilience and growth of R. pseudoacacia in serpentine environments.

Screening, Identification, and Characterization of Plant Growth-Promoting Rhizobacterium Strains from Alpine Grassland as Biocontrol Agents Against Fusarium oxysporum

Wilt and root rot diseases caused by Fusarium species can severely affect herbage plants, resulting in significant losses. Currently, the research and application of biological control methods targeting Fusarium-related diseases in herbage plants are limited. In this study, 11 plant growth-promoting rhizobacterium (PGPR) strains previously screened from alpine grassland were tested to assess their inhibitory effects on Fusarium oxysporum and their ability to produce siderophores, protease, cellulase, and amylase. Meanwhile, their plant growth-promoting properties, such as nitrogenase activity, phosphate dissolution, and IAA production, were determined. The results showed that the tested PGPR strains exhibited diverse functionalities. Nine PGPR strains demonstrated antagonistic effects on colony diameter against Fusarium oxysporum, with Bacillus subtilis gt11 showing the strongest inhibition, followed by Bacillus velezensis gt1 and Bacillus subtilis gtr1, with inhibition rates of 73.57%, 69.13%, and 67.94%, respectively. The test PGPR strains mainly comprised three genera: Pseudomonas, Bacillus, and Acinetobacter. Pseudomonas was the dominant genus. The PGPR strains displayed diverse inhibitory mechanisms. Bacillus velezensis gt1, Pseudomonas subtilis gt11, Bacillus subtilis gtr1, and Pseudomonas tritici gt6 exhibited high levels of siderophore, protease, cellulase, and amylase production, potentially inhibiting Fusarium oxysporum by degrading its cell wall through these enzyme activities. The majority of the tested PGPR strains have the characteristic of producing multiple enzymes. Considering the plant growth-promoting characteristics of nitrogenase activity (38.13–505.70 nmol C2H4/vial), phosphate solubilization (inorganophosphates ranging from 41.18 to 91.65 μg·mL−1; organophosphates ranging from 5.21 to 31.17 μg·mL−l), and IAA secretion (9.27–48.95 μg·mL−1), Bacillus subtilis gt11, Bacillus velezensis gt1, Acinetobacter calcoaceticus gt14, and Bacillus subtilis gtr1 show potential for development into biofertilizers or biocontrol agents.

Genomic profiling and assessment of the plant growth-enhancing traits in the novel actinomycete, Plantactinospora soli sp. nov.

Strain KLBMP 9567T, an isolate from weathered soil, was identified as a new actinobacterial species through a comprehensive polyphasic approach. Phylogenetic evaluations relying on 16S rRNA gene sequence placed KLBMP 9567T within the genus Plantactinospora, alongside its close relatives Plantactinospora veratri NEAU-FHS4T and Plantactinospora sonchi NEAU-QY2T, both sharing 98.6% sequence similarity. However, KLBMP 9567T demonstrated low digital DNA-DNA hybridization values with P. veratri NEAU-FHS4T and P. sonchi NEAU-QY2T, recorded at 48.5 and 29.1%, respectively. Meanwhile, the average nucleotide identity values were correspondingly recorded at 91.1 and 83.1%. The cell wall of KLBMP 9567T contained meso-diaminopimelic acid, with xylose, mannose, glucose and galactose as diagnostic sugars. The diagnostic dominant phospholipids included diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. Given phenotypic and genotypic data, KLBMP 9567T is recognized as a new species within the Plantactinospora genus, named Plantactinospora soli sp. nov., with the type strain KLBMP 9567T (= CGMCC 4.7773T = NBRC 115787T). Genome mining revealed genes associated with plant growth promotion, specifically those encoding enzymes for synthesizing plant hormones like indole acetic acid and gibberellic acid. Experimental validation demonstrated that KLBMP 9567T can produce significant quantities of indole acetic acid (20.6 mg l-1) and gibberellic acid (42.6 mg l-1). Moreover, co-culture with Arabidopsis showed marked growth enhancements: a 56.3% increase in lateral root proliferation, a 16.7% elongation in primary root length and a 44.8% boost in biomass accumulation. These findings underscore the strain's potent plant growth-promoting attributes, providing profound insights into the mechanisms by which KLBMP 9567T enhances plant growth.

Identification and genomic insights into Bacillus siamensis strains with host colonization potential and activity against tomato bacterial wilt.

Bacterial wilt (BW), caused by Ralstonia solanacearum species complex (RSSC), is considered as one of the most destructive plant diseases worldwide. In this study, two strains of Bacillus siamensis, BB605-1 and BB653, were screened and identified from endophytes in healthy tomato and mangrove plants, respectively. Both strains demonstrated antagonistic activities against all 16 RSSC strains, representing eight sequevars from various hosts. The growth of RSSC was suppressed by the crude antimicrobial extracts produced by two strains. The pot inoculation experiment revealed the control efficiencies of two strains against tomato bacterial wilt as 59.63% and 63.98%, respectively. After imparting rifampicin resistance to the strains and applying them to tomato plants, both strains successfully established stable colonization in the rhizosphere, roots, stems, and leaves of tomato plants. Additionally, our study demonstrated that both strains exhibited significant plant growth-promoting properties. Complete genome sequencing revealed genome size of 3.868 M bp with 3594 protein-coding genes for BB605-1, and 3.857 M bp with 3600 protein-coding genes for BB653. Genome analysis of both strains identified seven secondary metabolite clusters with known antimicrobial properties and predicted three unknown compounds with potentially novel properties. Genome mining revealed several key genes associated with plant growth regulation, colonization, and biofilm formation, and we also detected these corresponding substances. These findings provide a compelling case for the application of B. siamensis in agricultural practices. The isolates' multiple capacities to colonize, enhance plant growth, and exert antagonistic effects against BW positions them as highly promising candidates for an integrated biological solution. © 2024 Society of Chemical Industry.

The Potential of Biocrust-Forming Cyanobacteria to Enhance Seedling Growth of Native Semi-arid Plants Through Seed Biopriming

AbstractIn drylands, extreme environmental conditions pose a challenge for restoration, especially on a large scale. Direct seeding is the most cost-effective approach to restore large areas, but it requires improvements to enhance seedling survival and establishment. For this purpose, biopriming seeds with cyanobacteria is promising due to their plant growth-promoting properties. We evaluated the effect of seed biopriming with native biocrust-forming cyanobacteria on seed germination and radicle length of four native plant species, two perennials (Macrochloa tenacissima and Thymus hyemalis) and two annuals (Plantago ovata and Stipa capensis), chosen for their ubiquity in Mediterranean drylands. Treatments included seed biopriming with cyanobacteria inoculants (biomass + exudate), seed priming only with the cyanobacterial exudate, and controls (BG11 culture medium and distilled water). Biopriming effect was assessed individually for four native biocrust-forming cyanobacteria species: Nostoc commune, Tolypothrix distorta, Trichocoleus desertorum, and Leptolyngbya frigida. Seed biopriming showed no effect on germination with similar rates among treatments (on average, 45 ± 12.6% for M. tenacissima, 38.8 ± 12.4% for T. hyemalis, 91.7 ± 9.8% for P. ovata and 77.6 ± 10.8% for S. capensis). However, biopriming significantly affected radicle length of annual plants. Radicles were significantly increased in P. ovata when treated with cyanobacterial exudates (15–30% increase over control), and in S. capensis when treated with cyanobacterial biomass + exudate (26–42% increase over control). These results indicate that the effect of seed biopriming is species specific, but selecting the appropriate plant species and biopriming treatment can enhance plant survival and establishment in drylands, making restoration efforts more successful.

Pseudomonas putida triggers phosphorus bioavailability and P-transporters under different phosphate regimes to enhance maize growth

The decline of available phosphorus in soil due to anthropogenic activities necessitates utilizing soil microorganisms that influence soil phosphorus levels. However, the specific mechanisms governing their interaction in Zea mays under diverse phosphate regimes remain largely unknown. The present study investigated the dynamics of phosphorus solubilization and the impact of organic acid supplementation in combination with the beneficial rhizobacterium Pseudomonas putida (RA) on maize growth under phosphorus-limiting and unavailable conditions. HPLC analysis revealed gluconic acid as the primary organic acid (OA) produced by P. putida across all three conditions (P-sufficient, P-limiting, and P-unavailable), with the highest production occurring under P-limiting conditions. The study evaluates the effects of RA, OA, and OA + RA on plant growth parameters under P-limiting and insufficient conditions, revealing significant alterations in growth and biochemical parameters (P = 0.05) compared to their respective untreated controls. Additionally, plants treated with organic acids and bacterial inoculation show increased phosphorus concentrations in both roots and shoots. Gene expression analysis of key phosphorus transporter genes (PHT1, PHO1, PTF, PHF1) further supports the role of organic acids and bacterial inoculation in enhancing phosphorus uptake. In conclusion, our study affirms that the secretion of gluconic acid by RA and its plant growth-promoting properties boost phosphorus uptake and maize growth by increasing phosphorus availability and influencing the expression of phosphorus transport-related genes.

Whole-Genome Sequencing And Characterization Of Two Bacillus velezensis Strains from Termitarium and A Comprehensive Comparative Genomic Analysis of Biosynthetic Gene Clusters.

The speciesBacillus velezensisis known for its biosynthetic potential and metabolic versatility in producing several secondary metabolites and promoting plant growth. In this study, we isolated twoB. velezensisstrains, WGTg-8 and WGTm-299, from the termite gut and termitarium, which exhibited antimicrobial activity against multiple clinical and phytopathogens. The whole genomes of these strains were sequenced using the Illumina platform and annotated. The genome mining of the draft genome sequences revealed 48 biological gene clusters (BGCs) responsible for synthesizing various secondary metabolites. The construction of the similarity network of the BGCs and the comparative analysis with the genetically related organisms are aided in the identification of metabolites produced by these strains. We identified biosynthetic gene clusters (BGCs) coding for macrolactin H, bacilysin, bacillibactin, amylocyclin, comX4, and LCI, found in both strains with 100% similarity. The difficidin, bacillaene, thusin_alpha, and cericidin BGCs are exclusively found in strain WGTg-8, while the colicin BGC is exclusively present in the WGTm-299 strain. The fengycin and surfactin gene clusters are present in both strains with 80% similarity. Furthermore, 28 putative NRPS BGCs, NRPS-T1PKS hybrid clusters, a T1PKS, and a bacteriocin BGC were identified with very low similarity (≤ 25%) or no similarity with known antibiotics. In addition, we found several genes coding for plant growth-promoting properties, including nitrogen metabolism, hormone synthesis, sulfur metabolism, phosphate metabolism, and a few other properties.

Antibacterial, Herbicidal, and Plant Growth-Promoting Properties of Streptomyces sp. STD57 from the Rhizosphere of Adenophora stricta.

Bacterial wilt triggered by the soil-borne pathogenic bacterium Ralstonia solanacearum is one of the most serious diseases in tomato plants, leading to huge economic losses worldwide. Biological control is considered an environmentally friendly and sustainable way to manage soil-borne diseases. In this study, Streptomyces sp. STD57 isolated from the rhizosphere of Adenophora stricta showed strong antibacterial activity against R. solanacearum. Pot experiments showed that strain STD57 exhibited a significant biocontrol effect (81.7%) on tomato bacterial wilt in the greenhouse environment. Furthermore, strain STD57 could inhibit the growth of weeds (Amaranthus retroflexus, Portulaca oleracea, and Echinochloa crusgalli) but promote the growth of crops (wheat, rice, and tomato). The plant growth-promoting substance was identified as indoleacetic acid (IAA) by high-pressure liquid chromatography-mass spectrometry and genome analysis. Coarse separation of the fermented extracts revealed that the antibacterial and herbicidal substances were mainly in the fermentation supernatant and belonged to different products. These findings suggested that strain STD57 may be a potential biocontrol and bioherbicide agent useful in agriculture.

Two Novel Bacterial Species, Rhodanobacter lycopersici sp. nov. and Rhodanobacter geophilus sp. nov., Isolated from the Rhizosphere of Solanum lycopersicum with Plant Growth-Promoting Traits.

Two novel bacterial species were isolated from the rhizosphere of Solanum lycopersicum (tomato plant), both exhibiting plant growth-promoting properties. Two isolated strains, Rhodanobacter lycopersici sp. nov. Si-cT and Rhodanobacter geophilus sp. nov. S2-gT, were classified through a polyphasic approach, confirming their novel status within the Rhodanobacter genus. The strains demonstrated a remarkable tolerance to extreme pH conditions, with R. lycopersici Si-cT surviving in pH 3.0-13.0 and R. geophilus S2-gT tolerating pH 2.0-13.0. Additionally, both strains exhibited multiple plant growth-promoting traits, including indole-3-acetic acid and ammonia production, phosphate solubilization, and siderophore formation. These characteristics suggest that the two strains may play an important role in promoting plant growth, especially in soils with variable pH levels. However, since the direct impact on plant growth was not experimentally tested, the potential of these bacteria for agricultural applications remains to be confirmed through further research. This study expands our understanding of the diversity within the Rhodanobacter genus and provides insights into the potential use of these novel species in sustainable agriculture.

Suppression of Thielaviopsis ethacetica wilt and root rot, the emerging pathogen on bell pepper (Capsicum annuum), and plant growth promotion properties by the safety indigenous Streptomyces SBcT04

Thielaviopsis ethacetica is an emerging pathogen responsible for wilt and root rot in bell peppers, significantly impacting crop yield. Biological control of the fungal pathogen provides significant advantages as a safe and efficient alternative to excessive chemical fungicides for managing plant diseases. Studying the screened and selected potential actinomycete strain from the indigenous collection is a quick and efficient measure to protect the yield of local bell pepper crops. The research assessed the indigenous actinomycete's ability to inhibit plant pathogens and promote plant growth both in vitro and in vivo. The Streptomyces SBcT04 was the most effective against T. ethacetica TROC-2 pathogen in vitro. The inhibition percentage reached 89.15 ± 0.46 %. SBcT04 also effectively promoted plant growth properties in vitro. This strain fixed nitrogen and produced substantial amountsof indole-3-acetic acid (IAA), siderophores, and enzymes. Furthermore, the safety characteristics of SBcT04 for both the host plant (in vivo) and animals (in vitro) were confirmed. Streptomyces SBcT04 significantly processed pathogens, resulting in a reduction of approximately 40 % in disease severity. Additionally, SBcT04 significantly promoted the host plant's growth, even in the presence of T. ethacetica TROC-2 infection. The indigenous Streptomyces SBcT04 efficiently inhibited T. ethacetica and significantly enhanced bell pepper plant growth. These advantageous characteristics of SBcT04 indicate its potential to foster secure and sustainable local bell pepper agricultural output.

Unveiling Bacillus rugosus CRI: A multi-stress tolerant endophyte revolutionizing rice resilience

The application of endophytes to mitigate stress in plants, particularly drought and salinity stress, has gained considerable attention, yet their role in rice remains underexplored. This study aimed to investigate the isolation and characterization of multi-stress-tolerant endophytic isolates with multiple plant growth-promoting attributes, including biocontrol potential against plant pathogens, from surface-sterilized leaf, stem, and root samples of various rice cultivars in Kerala. A total of 20 bacterial endophytes were isolated from rice plants and assessed for their plant growth-promoting (PGP) capabilities, biocontrol potential, and resilience to drought and salinity stress. Of these, 7 endophytic isolates exhibited notable PGP traits, and 3 demonstrated antifungal activity against Rhizoctonia solani and Fusarium oxysporum. Notably, only 3 endophytic isolates showed significant tolerance to drought conditions (−1.0 MPa) and salinity (150 mM), alongside strong growth-promoting abilities. The selected isolates significantly increased seed germination and seedling vigour (p ≤ 0.05), highlighting their effectiveness. Among these, the isolate CRI, identified as Bacillus rugosus through morphological, biochemical, and molecular (16S rRNA) analysis, stood out for its remarkable performance. Under stress conditions, rice seedlings treated with the multi-stress-tolerant CRI showed significant improved biomass, resilience, and enhanced biochemical processes, including better photosynthetic pigment levels and maintained membrane integrity. Field emission scanning electron microscopy (FE-SEM) confirmed the presence of these bacteria within the rice roots, underscoring their potential as a novel approach for enhancing stress tolerance and promoting rice growth. This study represents the first discovery of Bacillus rugosus as a potent multi-stress-tolerant endophyte, with dual benefits of promoting plant growth and exhibiting biocontrol activity. These findings pave the way for innovative strategies aimed at enhancing crop resilience and productivity, particularly in the face of increasing abiotic stressors in agricultural systems.

Bacterial endophyte Pseudomonas mosselii PR5 improves growth, nutrient accumulation, and yield of rice (Oryza sativa L.) through various application methods

BackgroundPseudomonas spp. have drawn considerable attention due to their rhizospheric abundance and exceptional plant growth-promoting attributes. However, more research is needed on the optimal application methods of Pseudomonas mosselii for rice growth, nutrient accumulation, and yield improvement. This research explored the application of the endophytic bacterium P. mosselii PR5 on rice cultivar BRRI dhan29 with four treatments: control, seedling priming, root drenching, and bacterial cell-free culture (CFC) foliar application.ResultsPR5 led to better rice growth, improved nutrient acquisition, and higher yields compared to the control, regardless of the application method used. The highest results in fresh weight of root (146.93 g/pot), shoot (758.98 g/pot), and flag leaf (7.88 g/pot), dry weight of root (42.16 g/pot), shoot (97.32 g/pot), and flag leaf (2.69 g/pot), and grains/panicle (224.67), were obtained from seedling priming treatment, whereas root drenching resulted in maximum plant height (105.67 cm), root length (49.0 cm), tillers/pot (23.7), and panicles/pot (17.67). In all three application methods, rice grain yield per pot was higher in PR5 inoculated treatments, compared to the control. The amount of P, Mg and Zn in the shoot and N, P, Ca, Mg and Si content in the flag leaf was significantly increased along with effective suppression of naturally occurring blast disease in bacterial CFC foliar application, validated by multivariate analysis.ConclusionOur results indicated that rice seedlings priming with PR5 improved rice growth, yield and nutrient uptake, whereas CFC foliar application significantly increased the concentration of most nutrients in the rice plant and suppressed the naturally occurring rice blast disease. This research highlights the significant potential of P. mosselii PR5 in enhancing rice growth, yield, and nutrient uptake, particularly through seedling priming and CFC foliar application methods.

Characterization of Trichoderma spp. and their antagonistic activity against soilborne fungi associated with chickpea wilt in Sinaloa, Mexico

Chickpea wilt, caused by a complex of soilborne fungi (Fusarium spp. Macrophomina phaseolina, Rhizoctonia solani, Sclerotium rolfsii, and Sclerotinia sclerotiorum), is the most important disease of chickpeas (Cicer arietinum) in Mexico. The aims of this study were to characterize Trichoderma isolates using a combination of phenotypic and molecular approaches and to evaluate their antagonistic activity against soilborne fungi associated with chickpea wilt. A total of 30 Trichoderma isolates were obtained from rhizospheric soil samples collected from chickpea fields in different locations of Sinaloa, Mexico. Dual confrontation assays showed the potential antagonistic effect of Trichoderma isolates against F. languescens, M. phaseolina, R. solani, S. rolfsii, and S. sclerotiorum. Five Trichoderma isolates (FAVF335, FAVF340, FAVF345, FAVF349, and FAVF351) exhibited mycelial growth inhibition of the five pathogens that ranged from 56 to 71%. These isolates were characterized using cultural, morphological, and molecular studies and tested in vivo for their ability to control soilborne pathogens in two chickpea cultivars (Blanco Sinaloa-92 and P2245) under greenhouse conditions. Phylogenetic analysis based on a combined ITS, EF-1α, and rpb2 sequence dataset identified T. afroharzianum (FAVF345, FAVF349, and FAVF351) and T. longibrachiatum (FAVF335 and FAVF340). Coating of chickpea seeds with T. longibrachiatum (FAVF335 and FAVF340) significantly reduced the disease severity and improved the plant growth-promoting attributes.

Pseudomonas produce various metabolites displaying herbicide activity against broomrape

Pseudomonads are well-known for their plant growth-promoting properties and biocontrol capabilities against microbial pathogens. Recently, their potential to protect crops from parasitic plants has garnered attention. This study investigates the potential of different Pseudomonas strains to inhibit broomrape growth and to protect host plants against weed infestation. Four Pseudomonas strains, two P. fluorescens JV391D17 and JV391D10, one P. chlororaphis JV395B and one P. ogarae F113 were cultivated using various carbon sources, including fructose, pyruvate, fumarate, and malate, to enhance the diversity of potential Orobanche growth inhibition (OGI)-specialized metabolites produced by Pseudomonas strains. Both global and targeted metabolomic approaches were utilized to identify specific OGI metabolites. Both carbon sources and Pseudomonas genetic diversity significantly influenced the production of OGI metabolites. P. chlororaphis JV395B and P. ogarae F113 produced unique OGI metabolites belonging to different chemical families, such as hydroxyphenazines and phloroglucinol compounds, respectively. Additionally, metabolomic analyses identified an unannotated potential OGI ion, M375T65. This ion was produced by all Pseudomonas strains but was found to be over-accumulated in JV395B, which likely explains its superior OGI activity. Then, greenhouse experiments were performed to evaluate the biocontrol efficacy of selected strains: they showed the efficacy of these strains, particularly JV395B, in reducing broomrape infestation in rapeseed. These findings suggest that certain Pseudomonas strains, through their metabolite production, can offer a sustainable biocontrol strategy against parasitic plants. This biocontrol activity can be optimized by environmental factors, such as carbon amendments. Ultimately, this approach presents a promising alternative to chemical herbicides.

Isolation and characterization of salt-stress-tolerant rhizosphere soil bacteria and their effects on plant growth-promoting properties

PGPR has a higher potential impact on agricultural crops. It enhances plant growth and development in a variety of adverse environmental conditions, including biotic and abiotic stresses. The PGPR is commercially vital since it is more efficient, safe for the environment, and beneficial to the economy. Nowadays, salt stress has an impact on the agricultural ecosystem. Salt-tolerant PGPR can directly stimulate plant growth and development by producing a variety of metabolites and phytohormones. The current study looked at the isolation of salt-tolerant bacterial species and their ability to stimulate plant development. Four bacterial species were chosen for their better salt stress tolerance (0–5%). They were identified by 16S rRNA sequencing: Solibacillus silvestris BR1, Peribacillus frigoritolerans BR2, Paenibacillus taichungensis CR1, and Solibacillus isronensis CR2. These strains were positive production of indole acetic acid with varying incubation periods (19.66 ± 1.528 to 646.111 ± 8.058 µg/mL), salt stress (ranging from 29.556 ± 1.171 to 147.8111 ± 2.086 µg/mL), phosphate solubilization (0.145 ± 0.011 to 0.921 ± 0.007 µg/mL), ammonium production (0.299 ± 0.047 to 1.202 ± 0.142 µg/mL), HCN production (0.308 ± 0.051 to 4.269 ± 0.069 µg/mL), and siderophore production (0.190 ± 0.064 to 1.543 ± 0.108 µg/mL) for control strains were used without salt stress. The production level was expressed using a standard curve containing various standards.

Arsenic Stress Mitigation Using a Novel Plant Growth-Promoting Bacterial Strain Bacillus mycoides NR5 in Spinach Plant (Spinacia oleracea L.).

Present study aimed to identify arsenic (As)-resistant bacterial strains that can be used to mitigate arsenic stress. A bacterium Bacillus mycoides NR5 having As tolerance limit of 1100 mg L-1 was isolated from Nag River, Maharashtra, India. It was also equipped with plant growth-promoting (PGP) attributes like phosphate solubilization, siderophores, ammonia, and nitrate reduction, with added antibiotic tolerance. Furthermore, scanning electron microscopy (SEM) and transmission electron micrograph (TEM) suggested biosorption as possible mechanisms of arsenic tolerance. A strong peak in FTIR spectra at 3379.0 corresponding to amine in As-treated NR5 also indicated metal interaction with cell surface protein. Amplification of arsenic reductase gene in NR5 further suggested intracellular transformation of As speciation. Moreover, As tolerance capability of NR5 was shown in spinach plants in which the bacterium effectively mitigated 25 ppm As by producing defense-related proline molecules. Evidence from SEM, TEM, and FTIR, concluded biosorption possibly the primary mechanism of As tolerance in NR5 along with the transformation of arsenic. B. mycoides NR5 with PGP attributes, high As tolerance, and antibiotic resistance mediated enhanced As tolerance in spinach plants advocated that the strain can be a better choice for As bioremediation in contaminated agricultural soil and water.