Plant Growth-promoting Agents Research Articles

Effects of Klebsiella michiganensis LDS17 on Codonopsis pilosula growth, rhizosphere soil enzyme activities, and microflora, and genome-wide analysis of plant growth-promoting genes.

We comprehensively evaluated the plant growth-promoting characteristics and heavy metal (HM) resistance ability of the LDS17 strain, as well as the effects of strain LDS17 inoculation on the Codonopsis pilosula seedling growth and the soil qualities in the Codonopsis pilosula rhizosphere. We conducted whole-genome analysis and identified lots of genes and gene clusters contributing to plant-beneficial functions and HM resistance, which is critical for further elucidating the plant growth-promoting mechanism of strain LDS17 and expanding its application in the development of plant growth-promoting agents used in the environment under HM stress.

Pseudomonas sp. AMGC1 takes on rice blast: Broad-spectrum antimicrobial activity underpins plant growth and disease tolerance.

A diverse group of gram-negative bacteria called Pseudomonas have been extensively researched for their ability to promote plant growth and suppress pathogens. The aim of the study was to identify the strain AMGC1 as a biocontrol agent against rice blast disease and a plant growth-promoting agent. The activity of AMGC1 against phytopathogens and its plant growth promotion activity were tested in vitro. Molecular identification by 16S rRNA gene sequencing, detection of antifungal antibiotic genes, biochemical characterization and antibiotic resistance testing were performed. Moreover, an in-planta biocontrol experiment with a blast susceptible rice cultivar was conducted to assess the effectiveness in managing the disease. Thin-layer chromatography was used to verify the presence of antifungal compounds. The results showed that AMGC1 had strong antimicrobial activity and multiple plant growth promotion traits. The strain was identified as Pseudomonas sp. and it contained genes for phenazine-1-carboxamide, hydrogen cyanide, and 2-hexyl, 5-propyl resorcinol antifungals. In the in-planta suppression experiment, applying AMGC1 strain two days before pathogen inoculation reduced the disease severity by 28% and disease incidence by 29% compared to control. Applying AMGC1 two days after pathogen inoculation resulted in lower reductions in disease severity (17.10%) and disease incidence (18.5%). Two putative bioactive compounds, phenazine-1-carboxamide and 2-hexyl, 5-propyl resorcinol, were isolated and purified from the AMGC1 growth medium. AMGC1 showed varied carbohydrate utilization patterns and both resistance and susceptibility to different antibiotics. The strain had multiple features that enhance plant growth and resistance against various phytopathogens, making it a potential biocontrol agent for sustainable agriculture.

Novel report of Acinetobacter johnsonii as an indole-producing seed endophyte in Tamarindus indica L.

Plant-microbe associations have been regarded as an exciting topic of research due to their potential as environment friendly alternatives for stimulating crop growth and development. Seeds of Tamarindus indica L. have been chosen for the present study as seed endophytes prefer larger or nutritive cotyledon and hard seed coats for their colonization. The main objectives of our study were to isolate and identify the seed endophytes, their bioefficacy, and responsible chemical compounds. In a dose-dependent experiment, tamarind seed exudates (TSE) showed plant growth-promoting properties on Oryza sativa (53-81%), Daucus carota (10-31%), and Raphanus sativa (21-42%). Identification of the bacterial load in TSE through 16S rRNA sequencing revealed the existence of two bacterial species, Acinetobacter johnsonii and Niallia nealsonii. This is the first report of these two bacteria as seed endophytes of Tamarindus indica L. HRLC-MS analysis of TSE confirmed the presence of indole derivatives, primarily indole-3-lactic acid (ILA). The quantitative phytochemical estimation of bacterial culture filtrates revealed that indole-like substances were present in the extracts only in A. johnsonii at a concentration of 0.005mg/ml of indole acetic acid equivalent. Experimental results suggested that the stimulatory activity of TSE was caused by the presence of A. johnsonii, a potential plant growth-promoting bacteria that produced indole-like compounds. This study suggests tamarind seed exudates with its endophytic microbiota as a potent plant growth-promoting agent that may find use as a cheap and sustainable source of metabolites useful in the agro-industries.

Pseudoxanthomonas sp. JBR18, a halotolerant endophytic bacterium, improves the salt tolerance of Arabidopsis seedlings

Salinization of land is globally increasing due to climate change, and salinity stress is an important abiotic stressor that adversely affects agricultural productivity. In this study, we assessed a halotolerant endophytic bacterium, Pseudoxanthomonas sp. JBR18, for its potential as a plant growth-promoting agent with multiple beneficial properties. The strain exhibited tolerance to sodium chloride concentration of up to 7.5 % in the R2A medium. In vitro evaluation revealed that strain JBR18 possessed proteolytic, protease (EC 3.4), and cellulase (EC 3.2.1.4) activities, as well as the ability to produce indole-acetic acid, proline, and exopolysaccharides. Compared with the controls, co-cultivation of Arabidopsis seedlings with the strain JBR18 improved plant growth, rosette size, shoot and root fresh weight, and chlorophyll content under salinity stress. Moreover, JBR18-inoculated seedlings showed lower levels of malondialdehyde, reactive oxygen species, and Na+ uptake into plant cells under salt stress but higher levels of K+. Additionally, seedlings inoculated with JBR18 exhibited a delayed response time and quantity of salt-responsive genes RD29A, RD29B, RD20, RD22, and KIN1 under salt stress. These multiple effects suggest that Pseudoxanthomonas sp. JBR18 is a promising candidate for mitigating the negative impacts of salinity stress on plant growth. Our findings may assist in future efforts to develop eco-friendly strategies for managing abiotic stress and enhancing plant tolerance to salt stress.

Biological control of damping-off and plant growth promotion in soybean using Trichoderma virens

Rhizoctonia solani is soil borne pathogen that causes damping-off in legumes including soybean. To reduce disease infection of R. solani in soybean, seven isolates of Trichoderma virens were used as seed treatments. Soil was artificially infected using R. solani grown in organic media. Agronomic parameters and total phenolics were recorded at vegetative phase. Treatments with T. virens T.v6, T.v4, T.v7, and T.v3 showed lower disease incidence (22% to 34%) than that of the control (46%). T. virens T.v6 induced higher shoot and root length compared to plants grown in sterile soil. Phenolic in T. virens T.v7 treated plants showed the highest content (2.69 mg GAE/g) and the increase of this content was 13.7% compared to the control. Higher number of normal seedling growth and lower disease incidence than the control were observed in these treated plants. Another treatment with T. virens T.v6 showed lower amount of phenolic content (2.53 mg GAE/g) and lower increase of this content (7.2%) than those of T. virens T.v7 treated plants. However, the T. virens T.v6 treated plants performed higher normal seedling growth, lower disease incidence than the control. T. virens T.v6 and T.v7 were promising for plant growth promotion and biological control agents.

Candle soot colloids enhance tomato (Solanum lycopersicum) seed germination and seedling quality

The effect of candle soot colloids, a novel nanomaterial from candle combustion that we developed previously, on tomato (Solanum lycopersicum) seed germination and seedling vigor was investigated. Candle soot colloids were applied at different concentrations and hydrophobicities to tomato seeds and germination parameters and seedling vigor characteristics, such as length, fresh weight, dry weight, chlorophyll, and carotenoids, were measured. It was found that candle soot colloids significantly improved germination speed, seedling length, and seedling fresh weight compared to the control. The adherence of soot particles to the trichomes on the seed surface, which may help seeds retain moisture and stay hydrated, was observed. The chemical composition of the soot samples was analyzed using gas chromatography-time of flight mass spectrometry and two different chemical constituents in hydrophilic and hydrophobic soot samples that may affect seed germination were identified. A new potential use of candle soot colloids as plant growth-promoting agents and insights into the effects of nanomaterials on plant physiology and biochemistry were revealed by this study.

Insights into Endophytic and Rhizospheric Bacteria of Five Sugar Beet Hybrids in Terms of Their Diversity, Plant-Growth Promoting, and Biocontrol Properties

Sugar beet is the most important crop for sugar production in temperate zones. The plant microbiome is considered an important factor in crop productivity and health. Here, we investigated the bacterial diversity of seeds, roots, and rhizosphere of five sugar beet hybrids named Eduarda (ED), Koala (KO), Tibor (T), Tajfun (TF), and Cercospora-resistant (C). A culture-independent next-generation sequencing approach was used for the further investigation of seed-borne endophytes. Hybrid-associated bacteria were evaluated for their plant growth–promoting (PGP) characteristics, antagonistic activity towards Cercospora beticola and several Fusarium strains in dual culture assays, and drought and salinity tolerance. High-throughput sequencing revealed that the Proteobacteria phylum was most dominant in the seeds of all hybrids, followed by Cyanobacteria and Actinobacteriota. The predominant genus in all hybrids was Pantoea, followed by Pseudomonas, Acinetobacter, Chalicogloea, Corynebacterium, Enterobacter, Enterococcus, Glutamicibacter, Kosakonia, and Marinilactibacillus. Unique genera in the hybrids were Pleurocapsa and Arthrobacter (T), Klebsiella (TF), Apibacter (ED), and Alloscardovia (KO). The genera that were most represented in one hybrid were Weissella and Staphylococcus (TF); Streptococcus (T); Gardnerella, Prevotella, and Rothia (KO); and Gilliamella, Lactobacillus, and Snodgrassella (ED). Thirty-two bacteria out of 156 isolates from the rhizosphere, roots, and seeds were selected with respect to various plant growth–promoting activities in vitro, i.e., nitrogen fixation, phosphate solubilization, siderophore production, indole-3-acetic acid production, 1-aminocyclopropane-1-carboxylic acid deaminase activity, hydrogen cyanide production, exoenzymatic activity (amylase, protease, lipase, cellulase, xylanase, mannanases, gelatinase, and pectinase), mitigation of environmental stresses, and antifungal activity. Mixta theicola KO3-44, Providencia vermicola ED3-10, Curtobacterium pusillum ED2-6, and Bacillus subtilis KO3-18 had the highest potential to promote plant growth due to their multiple abilities (nitrogen fixation, phosphate solubilization, production of siderophores, and IAA). The best antagonistic activity towards phytopathogenic fungi was found for Bacillus velezensis C3-19, Paenibacillus polymyxa C3-36 and Bacillus halotolerans C3-16/2.1. Only four isolates B. velezensis T2-23, B. subtilis T3-4, B. velezensis ED2-2, and Bacillus halotolerans C3-16/2.1 all showed enzymatic activity, with the exception of xylanase production. B. halotolerans C3-16/2.1 exhibited the greatest tolerance to salinity, while two B. subtilis strains (C3-62 and TF2-1) grew successfully at the maximum concentration of PEG. The current study demonstrates that sugar beet–associated bacteria have a wide range of beneficial traits and are therefore highly promising for the formulation of biological control and PGP agents.

Serendipita indica as a Plant Growth Promoter and Biocontrol Agent against Black Rot Disease in Cabbage Grown in a Phytotron

Serendipita indica, a mutualistic root endophytic fungus, has gained attention for its potential to enhance plant health and resistance to various stresses. This study investigated the impact of S. indica (strain DSM 11827) on plant growth promotion and the management of black rot disease. This is a devastating bacterial ailment caused by Xanthomonas campestris pv. campestris, which affects cruciferous crops worldwide. The experiment was conducted under sterile conditions in a phytotron for 10 weeks. It involved the substrate and seed inoculation of S. indica in a cabbage crop. The findings suggested that S. indica establishes mutualistic relationships with cruciferous plants, positively influencing their growth while simultaneously reducing their susceptibility to black rot disease. Plant morphological and physiological parameters were enhanced by S. indica application. Additionally, bio stress markers were also enhanced in response to black rot disease. Moreover, disease severity was reduced by 27.9% and 18.8% in the substrate and seeds treated with S. indica, respectively. However, our findings did not report any antagonistic effect between S. indica and two pathogens, i.e., Xanthomonas campestris pv. campestris and Alternaria brassicicola under the in vitro test, suggesting that the suppression of black rot disease in cabbage seedlings was induced indirectly by S. indica. This study, therefore, underscores the promising prospect of utilizing S. indica to promote crop productivity and combat the destructive impact of black rot disease in cruciferous plants, contributing to more sustainable and resilient agriculture.

Evaluating the potential of Bacillus licheniformis YZCUO202005 isolated from lichens in maize growth promotion and biocontrol

Lichens exist in an organismal organization of mycobiont, photobiont, and non-photoautotrophic bacteria. These organisms contribute to the growth of lichens even in poor nutrition substrates. However, studies on the isolation and application of non-photoautotrophic bacteria in plant growth and biocontrol are scanty. Therefore, a study was conducted to isolate and evaluate the potential of non-photoautotrophic bacteria from lichen tissues in maize plant growth promotion and biocontrol of plant pathogens (fungi and bacteria). Five bacterial strains were isolated and tested for their ability to produce indole-3-Acetic Acid (IAA). One bacterium named YZCUO202005 produced IAA, siderophores and biofilms, solubilized phosphate and potassium and exhibited extracellular enzymes (cellulases, proteases, amylase, and β −1,3-Glucanase). Based on the 16S rRNA sequence analysis results, YZCUO202005 was identified as Bacillus licheniformis. The strain inhibited the growth of five pathogenic fungi with an inhibition percent of between 58.7% and 71.7% and two pathogenic bacteria. Under greenhouse conditions, YZCUO202005 was tested for its abilities to enhance maize seed germination, and vegetative growth. Compared with the control treatment, the strain significantly enhanced the growth of stem length (i.e. 18 ± 0.64 cm, 78 ± 0.92 cm), leaf length (i.e. 10 ± 0.36 cm, 57 ± 1.42 cm), leaf chlorophyll levels (i.e., 13 ± 0.40, 40 ± 0.43 SPAD), and root length (i.e, 9.8 ± 2.25 cm, 22.5 ± 6.59 cm). Our results demonstrated that B. licheniformis YZCUO202005 from lichens has the potential to promote plant growth and reduce fungal and bacterial pathogens’ growth. Furthermore, the results suggest that lichens are naturally rich sources of plant growth promotion and biocontrol agents that would be used in agriculture.

Biocontrol property of Streptomyces parvulus VRR3 in green gram plant (Vigna radiata L.) against Fusarium solani in greenhouse

Actinomycetes are isolated from various habitats including, plants, rhizospheres of.plant roots, terrestrial environment, and marine sediments. These Actinomycetes produce various secondary metabolites with antifungal, antibacterial, anticancer and antidiabetic properties. In the present study, a total of 31 endophytic Actinomycetes strains were isolated from the root of Vigna radiata L. (green gram plant). The antagonistic property of all strains was tested in vitro against Fusarium solani. The mycelia growth inhibition varied between 10.5 ± 1.4 and 80.5 ± 4.2% by Actinomycetes, whereas, the crude extract showed 14.2 ± 1.1 and 78.4 ± 3.1% growth inhibition (p < 0.01). The selected twelve Actinomycetes produced extracellular lytic enzymes. The results revealed that Streptomyces parvulus produced protease (18 ± 2 U/mL), amylase (20 ± 1 U/mL), lipase (13 ± 1 U/mL) and cellulase (8 ± 0 U/mL) at high levels than other Actinomycetes (p < 0.01). In addition, the ability of the screened Actinomycetes to produce plant growth-promoting agents was analyzed. The results showed that S. parvulus and other strains produced Indole acetic acid (1.5 ± 0.3 to 34.1 ± 3.4 μg/mL), phosphate solubilisation ability (1.5–24.3 PO4−3 μg/mL). The thermostable and pH-stable secondary metabolite-producing organism was characterized as S. parvulus VRR3. The in vivo growth-promoting activity of the green gram plant was tested in the greenhouse. The results showed that the selected S. parvulus was able to improve the growth of green gram seedlings, showing enhanced shoot-, and root length (p < 0.01). In addition, the seedlings treated with S. parvulus showed a decreased incidence of Fusarium wilt disease symptoms, whereas the positive control developed >80% disease symptoms (p < 0.01). Hence, S. parvulus VRR3 has the potential to become an important biocontrol agent in modern agricultural practice.

Characterization of a Novel Bacillus glycinifermentans Strain MGMM1 Based on Full Genome Analysis and Phenotypic Properties for Biotechnological Applications.

Bacillus species have gained much attention based on their phenotypic characteristics and their genetic architecture as biological control agents and plant growth-promotor with bioremediation potential. In this study, we analyzed the whole genome of a novel strain, Bacillus glycinifermentans MGMM1, isolated from the rhizosphere of a weed plant (Senna occidentalis) and assayed its phenotypic characteristics, as well as antifungal and biocontrol ability. The whole genome analysis of MGMM1 identified 4259 putative coding sequences, with an encoding density of 95.75% attributed to biological functions, including genes involved in stimulating plant growth, such as acetolactate synthase, alsS, and genes involved in the resistance to heavy metal antimony (arsB and arsC). AntiSMASH revealed the presence of biosynthetic gene clusters plipastatin, fengycin, laterocidine, geobacillin II, lichenysin, butirosin A and schizokinen. Tests in vitro confirmed that MGMM1 exhibited antifungal activity against Fusarium oxysporum f.sp. radicis-lycopersici (Forl) ZUM2407, Alternaria alternata, F. graminearum and F. spp. and produce protease, lipase amylase and cellulase. Bacillus glycinifermentans MGMM1 demonstrated proteolytic (4.82 ± 1.04 U/mL), amylolytic (0.84 ± 0.05 U/mL) and cellulosic (0.35 ± 0.02 U/mL) enzymatic activities, as well as indole-3-acetic acid production (48.96 ± 1.43 μg/mL). Moreover, the probiotic strain MGMM1 demonstrated a high biocontrol potential of inhibiting (up to 51.45 ± 8.08%) the development of tomato disease caused by Forl ZUM2407. These results suggest that B. glycinifermentans MGMM1 has significant potential as a biocontrol, plant growth-promoting agent in agriculture.

Arbuscular mycorrhizal fungi-mediated activation of plant defense responses in direct seeded rice (Oryza sativa L.) against root-knot nematode Meloidogyne graminicola.

Rhizosphere is the battlefield of beneficial and harmful (so called phytopathogens) microorganisms. Moreover, these microbial communities are struggling for their existence in the soil and playing key roles in plant growth, mineralization, nutrient cycling and ecosystem functioning. In the last few decades, some consistent pattern have been detected so far that link soil community composition and functions with plant growth and development; however, it has not been studied in detail. AM fungi are model organisms, besides potential role in nutrient cycling; they modulate biochemical pathways directly or indirectly which lead to better plant growth under biotic and abiotic stress conditions. In the present investigations, we have elucidated the AM fungi-mediated activation of plant defense responses against Meloidogyne graminicola causing root-knot disease in direct seeded rice (Oryza sativa L.). The study describes the multifarious effects of Funneliformis mosseae, Rhizophagus fasciculatus, and Rhizophagus intraradices inoculated individually or in combination under glasshouse conditions in rice plants. It was found that F. mosseae, R. fasciculatus and R. intraradices when applied individually or in combination modulated the biochemical and molecular mechanisms in the susceptible and resistant inbred lines of rice. AM inoculation significantly increased various plant growth attributes in plants with simultaneous decrease in the root-knot intensity. Among these, the combined application of F. mosseae, R. fasciculatus, and R. intraradices was found to enhance the accumulation and activities of biomolecules and enzymes related to defense priming as well as antioxidation in the susceptible and resistant inbred lines of rice pre-challenged with M. graminicola. The application of F. mosseae, R. fasciculatus and R. intraradices, induced the key genes involved in plant defense and signaling and it has been demonstrated for the first time. Results of the present investigation advocated that the application of F. mosseae, R. fasciculatus and R. intraradices, particularly a combination of all three, not only helped in the control of root-knot nematodes but also increased plant growth as well as enhances the gene expression in rice. Thus, it proved to be an excellent biocontrol as well as plant growth-promoting agent in rice even when the crop is under biotic stress of the root-knot nematode, M. graminicola.

Complete genome sequencing ofBacillus subtilis(CWTS 5), a siderophore-producing bacterium triggers antagonistic potential againstRalstonia solanacearum

The aims of this study were to explore the antagonistic potential of siderophore-producing Bacillus subtilis (CWTS 5) for the suppression of Ralstonia solanacearum and to explore the mechanisms of inhibition by FTIR, LC-MS, and whole genome analysis. A siderophore-producing B. subtilis (CWTS 5) possessing several plant growth-promoting properties such as IAA and ACC deaminase production, phosphate solubilization, and nitrogen fixation was assessed for its inhibitory effect against R. solanacearum, and its mechanisms were explored by in vitro and in vivo analyses. The active secondary metabolites in the siderophore extracts were identified as 2-deoxystreptamine, miserotoxin, fumitremorgin C, pipercide, pipernonaline, gingerone A, and deoxyvasicinone by LC-MS analysis. The Arnow's test and antiSMASH analysis confirmed the presence of catecholate siderophores, and the functional groups determined by FTIR spectroscopy confirmed the presence of secondary metabolites in the siderophore extract possessing antagonistic effect. The complete genome sequence of CWTS 5 revealed the gene clusters responsible for siderophore, antibiotics, secondary metabolite production, and antibacterial and antifungal metabolites. Furthermore, the evaluation of CWTS 5 against R. solanacearum in pot studies demonstrated 40.0% reduced disease severity index (DSI) by CWTS 5, methanolic extract (DSI-26.6%), ethyl acetate extract (DSI-20.0%), and increased plant growth such as root and shoot length, wet weight and dry weight of Solanum lycopersicum L. owing to its antagonistic potential. This genomic insight will support future studies on the application of B. subtilis as a plant growth promoter and biocontrol agent against R. solanacearum for bacterial wilt management. The results of this study revealed that B. subtilis (CWTS 5) possesses multiple mechanisms that control R. solanacearum, reduce disease incidence, and improve S. lycopersicum growth.

Plant Growth Promotion, Phytohormone Production and Genomics of the Rhizosphere-Associated Microalga, Micractinium rhizosphaerae sp. nov.

Microalgae are important members of the soil and plant microbiomes, playing key roles in the maintenance of soil and plant health as well as in the promotion of plant growth. However, not much is understood regarding the potential of different microalgae strains in augmenting plant growth, or the mechanisms involved in such activities. In this work, the functional and genomic characterization of strain NFX-FRZ, a eukaryotic microalga belonging to the Micractinium genus that was isolated from the rhizosphere of a plant growing in a natural environment in Portugal, is presented and analyzed. The results obtained demonstrate that strain NFX-FRZ (i) belongs to a novel species, termed Micractinium rhizosphaerae sp. nov.; (ii) can effectively bind to tomato plant tissues and promote its growth; (iii) can synthesize a wide range of plant growth-promoting compounds, including phytohormones such as indole-3-acetic acid, salicylic acid, jasmonic acid and abscisic acid; and (iv) contains multiple genes involved in phytohormone biosynthesis and signaling. This study provides new insights regarding the relevance of eukaryotic microalgae as plant growth-promoting agents and helps to build a foundation for future studies regarding the origin and evolution of phytohormone biosynthesis and signaling, as well as other plant colonization and plant growth-promoting mechanisms in soil/plant-associated Micractinium.

Evaluation of Soil Streptomyces spp. for the Biological Control of Fusarium Wilt Disease and Growth Promotion in Tomato and Banana

Fusarium oxysporum f. sp. lycopersici (Fol) and Fusarium oxysporum f. sp. cubense (Foc), are the causal agent of Fusarium wilt disease of tomato and banana, respectively, and cause significant yield losses worldwide. A cost-effective measure, such as biological control agents, was used as an alternative method to control these pathogens. Therefore, in this study, six isolates of the Streptomyces-like colony were isolated from soils and their antagonistic activity against phytopathogenic fungi and plant growth-promoting (PGP) activity were assessed. The results showed that these isolates could inhibit the mycelial growth of Fol and Foc. Among them, isolate STRM304 showed the highest percentage of mycelial growth reduction and broad-spectrum antagonistic activity against all tested fungi. In the pot experiment study, the culture filtrate of isolates STRM103 and STRM104 significantly decreased disease severity and symptoms in Fol inoculated plants. Similarly, the culture filtrate of the STRM304 isolate significantly reduced the severity of the disease and symptoms of the disease in Foc inoculated plants. The PGP activity test presents PGP activities, such as indole acetic acid production, phosphate solubilization, starch hydrolysis, lignin hydrolysis, and cellulase activity. Interestingly, the application of the culture filtrate from all isolates increased the percentage of tomato seed germination and stimulated the growth of tomato plants and banana seedlings, increasing the elongation of the shoot and the root and shoot and root weight compared to the control treatment. Therefore, the isolate STRM103 and STRM104, and STRM304 could be used as biocontrol and PGP agents for tomato and banana, respectively, in sustainable agriculture.

The potential of facultative predatory Actinomycetota spp. and prospects in agricultural sustainability.

Actinomycetota in the phylum of bacteria has been explored extensively as a source of antibiotics and secondary metabolites. In addition to acting as plant growth-promoting agents, they also possess the potential to control various plant pathogens; however, there are limited studies that report the facultative predatory ability of Actinomycetota spp. Furthermore, the mechanisms that underline predation are poorly understood. We assessed the diversity of strategies employed by predatory bacteria to attack and subsequently induce the cell lysing of their prey. We revisited the diversity and abundance of secondary metabolite molecules linked to the different predation strategies by bacteria species. We analyzed the pros and cons of the distinctive predation mechanisms and explored their potential for the development of new biocontrol agents. The facultative predatory behaviors diverge from group attack "wolfpack," cell-to-cell proximity "epibiotic," periplasmic penetration, and endobiotic invasion to degrade host-cellular content. The epibiotic represents the dominant facultative mode of predation, irrespective of the habitat origins. The wolfpack is the second-used approach among the Actinomycetota harboring predatory traits. The secondary molecules as chemical weapons engaged in the respective attacks were reviewed. We finally explored the use of predatory Actinomycetota as a new cost-effective and sustainable biocontrol agent against plant pathogens.

Isolation and &lt;i&gt;in vitro&lt;/i&gt; screening of plant growth promoting bacteria from rhizosphere and root tissues of potato tuber (&lt;i&gt;Solanum&lt;/i&gt; &lt;i&gt;tuberosum&lt;/i&gt; L.)

&lt;abstract&gt; &lt;p&gt;The accumulation of chemical fertilizers that harm the environment is one of the major Indonesian agricultural problems. However, it still has less effect on potato production and yield. The discovery and use of bacteria that have the potential as plant growth-promoting agents (PGPR) is a breakthrough that can help to increase growth to increase production, especially in potato plants. In this study, several bacteria successfully isolated from the rhizosphere and root tissue of potato plants (&lt;italic&gt;Solanum tuberosum&lt;/italic&gt; L.) were isolated from potato farms in Plaosan Village. Several in vitro screenings were carried out to assess the functional activity of plant growth promoters, including the IAA (indole-3-acetic acid) production test, siderophore production test, ACC (1-aminocyclopropane-1-carboxylate) deaminase production test and phosphate dissolution test. Based on the screening results, five isolates were considered as the best inoculants, there are R1.3, R2.2, JR2.1, E1.2 and E1.2.1. All R1.3, R2.2, E1.2 and E1.2.1 isolates were known to have the ability to produce phytohormones IAA, ACC deaminase, and siderophores. In contrast, JR2.1 isolate was not known to have the ability to fix nitrogen and produce IAA, ACC deaminase and siderophores. These isolates could be used as potential biofertilizer inoculants and provide a step towards sustainable agriculture.&lt;/p&gt; &lt;/abstract&gt;

Endophytic Diaporthe as Promising Leads for the Development of Biopesticides and Biofertilizers for a Sustainable Agriculture.

Plant pathogens are responsible for causing economic and production losses in several crops worldwide, thus reducing the quality and quantity of agricultural supplies. To reduce the usage of chemically synthesized pesticides, strategies and approaches using microorganisms are being used in plant disease management. Most of the studies concerning plant-growth promotion and biological agents to control plant diseases are mainly focused on bacteria. In addition, a great portion of registered and commercialized biopesticides are bacterial-based products. Despite fungal endophytes having been identified as promising candidates for their use in biological control, it is of the utmost importance to develop and improve the existing knowledge on this research field. The genus Diaporthe, encompasses plant pathogens, saprobes and endophytes that have been screened for secondary metabolite, mainly due to their production of polyketides and a variety of unique bioactive metabolites with agronomic importance. Some of these metabolites exhibit antifungal and antibacterial activity for controlling plant pathogens, and phytotoxic activity for the development of potential mycoherbicides. Moreover, species of Diaporthe are reported as promising agents in the development of biofertilizers. For this reason, in this review we summarize the potential of Diaporthe species to produce natural products with application in agriculture and describe the benefits of these fungi to promote their host plant's growth.

Characterization and antagonistic potentials of selected rhizosphere Trichoderma species against some Fusarium species.

Trichoderma fungi have been proved as efficient bioagents with great antifungal properties while many species in the plant’s rhizospheres have been characterized as plant growth-promoting agents. However, many rhizosphere Trichoderma are yet to be fully explored for plant disease management. In this study, Trichoderma species were isolated from the rhizosphere of maize, banana, and cassava, and their biocontrol potentials were screened against some Fusarium species from oak leaves (F2B and F3) and laboratory cultures (Fus 296 and Fus 294). The isolated rhizosphere Trichoderma were identified as Trichoderma virens 1 (TCIV), T. virens 2 (TCVII), T. virens 3 (TMSI), T. hazianum strain 1 (TCVI), T. harzianum strain 2 (TCVIII), T. erinaceum (TMZI), and T. koningiopsis (TMZII). The dual culture experiment recorded the highest percentage inhibition in TMZII against OakF2B (31.17%), TCVIII against Fus 294 (45.18%), TMZI against Fus 296 (47.37%), while TCIV was most effective against Oak F3 (44.15%). Among the Trichoderma culture filtrates evaluated, TCIV showed the highest percentage inhibition against Oak F3 (52.39%), Oak F2B (48.54%), Fus 294 (46.65%), and Fus 296 (44.48%). All the Trichoderma isolates demonstrated expressed varying levels of antagonism against the Fusarium pathogens in vitro.

Plant Growth Promoting Rhizobacteria for Biocontrol of Tomato Bacterial Wilt Caused by Ralstonia solanacearum

Bacterial wilt induced by Ralstonia solanacearum is one of the most damaging and widespread diseases of tomatoes in the world. Biological control with rhizobacteria is one of the efficient components of integrated pest management methods used to control the disease and enhance production. To this end, plant growth-promoting rhizobacteria (Bacillus isolate BDUA1, and Pseudomonas isolates BBDUA2 and BDUA3) isolated from the tomato rhizosphere were evaluated for their plant growth-promoting traits using standard methods, and selected isolates were also tested for their biocontrol efficacy on tomato bacterial wilt disease under greenhouse conditions. All isolates produced cellulase and lipase, and only BDUA1 and BDUA3 produced protease and amylase. Besides, BDUA1 and BDUA2 showed phosphate solubilization and production of indole-3-acetic acid, HCN, and siderophore, while BDUA3 solubilized phosphate and produced HCN and siderophore. Our results showed that BDUA1 and BDUA2 reduced bacterial wilt incidence on the Maya variety by 51.9% and 48.5%, respectively, and on the Melkesalsa variety by 51.8% and 48.5%, respectively. Treatment of the Melkesalsa variety with BDUA1 displayed the highest height (36.91 cm), followed by treatment with BDUA2 (31.74 cm) on the same variety. BDUA1 induced the highest effect on increasing the dry weight of shoots and roots by 4.16 g and 0.59 g in the Maya variety and in the Melkesalsa variety by 3.63 g and 0.48 g, respectively. Similarly, BDUA2 had the greatest effect on increasing the dry weight of shoots and roots by 3.8 g and 0.54 g of the Maya variety and on the Melkesalsa variety by 3.12 g and 0.41 g, respectively. The overall result showed that BDUA1 and BDUA2 could be used as promising plant growth promotion and biocontrol agents for the management of tomato bacterial wilt disease provided they were validated under field conditions.