Effect of Iron Availability on Induction of Systemic Resistance to Fusarium Wilt of Chickpea by Pseudomonas spp

Salicylic acid induced by Bacillus megaterium causing systemic resistance against collar rot in Capsicum chinense

KEY MESSAGE

Our findings suggest that the phytohormone salicylic acid, stimulated by Bacillus megaterium JPR68, plays a role in mitigating collar rot disease of Bhut Jolokia (Capsicum chinense Jacq.) Salicylic acid (SA) is a phytohormone that stimulates the plants immune response against various diseases. However, its function as a signaling molecule, particularly in relation to systemic acquired resistance (SAR) and induced systemic resistance (ISR), is still unclear. In this study, Bacillus megaterium JPR68 (BmJPR68) enhances the ISR of Capsicum chinense Jacq., resulting in elevated levels of SA within the plants. SA effectively inhibited the mycelial growth of Rhizoctonia solani and significantly reduced the necrosis, chlorosis, and collar rot in plants. The in vitro investigation revealed that the mycelial growth declined with increasing concentrations of SA and was completely inhibited at a concentration of 15 mM. The pathogenicity assay showed that leaves and fruits treated with SA impeded hyphal development and significantly retarded the growth of R. solani. In split root techniques, more SA was accumulated in the root tissues at the bacterized site compared to the non-bacterized side, although this accumulation reduced after 45 days. Additionally, the production of reactive oxygen species (ROS) was significantly diminished in plants treated with BmJPR68. SA production was assessed in both BmJPR68 and induced plants, indicating that the bacterial strain produced more SA compared to the induced plants. Fourier-transform infrared (FT-IR) analysis confirmed the presence of functional groups like O-H, N-H, S = O, C = C, C-N, and carboxylic/amine. The isoform of pathogenesis-related (PR) proteins was detected in the induced plants. This study provided valuable insights into SA induction using BmJPR68 to manage fungal disease in Capsicum chinense Jacq. during induced systemic resistance.

Progress in the Study of Natural Antimicrobial Active Substances in Pseudomonas aeruginosa

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in the prevention and treatment of infectious diseases caused by pathogens such as bacteria, fungi, and viruses. Microbial secondary metabolites have been recognized as important sources for new drug discovery and development, yielding a wide range of structurally novel and functionally diverse antimicrobial drugs for the treatment of a variety of diseases that are considered good producers of novel antimicrobial drugs. Bacteria produce a wide variety of antimicrobial compounds, and thus, antibiotics derived from natural products still dominate over purely synthetic antibiotics among the antimicrobial drugs developed and introduced over the last four decades. Among them, Pseudomonas aeruginosa secondary metabolites constitute a richly diverse source of antimicrobial substances with good antimicrobial activity. Therefore, they are regarded as an outstanding resource for finding novel bioactive compounds. The exploration of antimicrobial compounds among Pseudomonas aeruginosa metabolites plays an important role in drug development and biomedical research. Reports on the secondary metabolites of Pseudomonas aeruginosa, many of which are of pharmacological importance, hold great promise for the development of effective antimicrobial drugs against microbial infections by drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (2000-2024) on antimicrobial secondary metabolites from Pseudomonas aeruginosa.

Integration of Transcriptomics and WGCNA to Characterize Trichoderma harzianum-Induced Systemic Resistance in Astragalus mongholicus for Defense against Fusarium solani

Beneficial fungi of the genus Trichoderma are among the most widespread biocontrol agents that induce a plant's defense response against pathogens. Fusarium solani is one of the main pathogens that can negatively affect Astragalus mongholicus production and quality. To investigate the impact of Trichoderma harzianum on Astragalus mongholicus defense responses to Fusarium solani, A. mongholicus roots under T. harzianum + F. solani (T + F) treatment and F. solani (F) treatment were sampled and subjected to transcriptomic analysis. A differential expression analysis revealed that 6361 differentially expressed genes (DEGs) responded to T. harzianum induction. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the 6361 DEGs revealed that the genes significantly clustered into resistance-related pathways, such as the plant-pathogen interaction pathway, phenylpropanoid biosynthesis pathway, flavonoid biosynthesis pathway, isoflavonoid biosynthesis pathway, mitogen-activated protein kinase (MAPK) signaling pathway, and plant hormone signal transduction pathway. Pathway analysis revealed that the PR1, formononetin biosynthesis, biochanin A biosynthesis, and CHIB, ROS production, and HSP90 may be upregulated by T. harzianum and play important roles in disease resistance. Our study further revealed that the H2O2 content was significantly increased by T. harzianum induction. Formononetin and biochanin A had the potential to suppress F. solani. Weighted gene coexpression network analysis (WGCNA) revealed one module, including 58 DEGs associated with T. harzianum induction. One core hub gene, RPS25, was found to be upregulated by T. harzianum, SA (salicylic acid) and ETH (ethephon). Overall, our data indicate that T. harzianum can induce induced systemic resistance (ISR) and systemic acquired resistance (SAR) in A. mongholicus. The results of this study lay a foundation for a further understanding of the molecular mechanism by which T. harzianum induces resistance in A. mongholicus.

Trichoderma based formulations control the wilt disease of chickpea (Cicer arietinum L.) caused by Fusarium oxysporum f. sp. ciceris, better when inoculated as consortia: findings from pot experiments under field conditions

Background

Commercial/chemical pesticides are available to control Fusarium wilt of chickpea, but these antifungals have numerous environmental and human health hazards. Amongst various organic alternatives, use of antagonistic fungi like Trichoderma, is the most promising option. Although, Trichoderma spp. are known to control Fusarium wilt in chickpea but there are no reports that indicate the biocontrol efficacy of indigenous Trichoderma spp. against the local pathogen, in relation to environmental conditions.

Methods

In the present study, biological control activity of Trichoderma species formulations viz., Trichoderma asperellum, Trichoderma harzianum (strain 1), and Trichoderma harzianum (strain 2), either singly or in the form of consortia, was investigated against Fusarium oxysporum f. sp. ciceris, the cause of Fusarium wilt in chickpea, in multiyear pot trials under open field conditions. The antagonistic effect of Trichoderma spp. was first evaluated in in vitro dual culture experiments. Then the effects of Trichoderma as well as F. oxysporum, were investigated on the morphological parameters, disease incidence (DI), and disease severity (DS) of chickpea plants grown in pots.

Results

In dual culture experiments, all the Trichoderma species effectively reduced the mycelial growth of F. oxysporum. T. asperellum, T. harzianum (strain 1), and T. harzianum(strain 2) declined the mycelial growth of F. oxysporumby 37.6%, 40%, and 42%. In open field pot trials, the infestation of F. oxysporum in chickpea plants significantly reduced the morphological growth of chickpea. However, the application of T. asperellum, T. harzianum (strain 1), and T. harzianum (strain 2), either singly or in the form of consortia, significantly overcome the deleterious effects of the pathogen, thereby resulted in lower DI (22.2% and 11.1%) and DS (86% and 92%), and ultimately improved the shoot length, shoot fresh weight and shoot dry weight by 69% and 72%, 67% and 73%, 68% and 75%, during the years 1 and 2, respectively, in comparison with infested control. The present study concludes the usefulness and efficacy of Trichoderma species in controlling wilt disease of chickpea plants under variable weather conditions.

Genomics Analysis Reveals the Potential Biocontrol Mechanism of Pseudomonas aeruginosa QY43 against Fusarium pseudograminearum

Fusarium crown rot (FCR) in wheat is a prevalent soil-borne disease worldwide and poses a significant threat to the production of wheat (Triticum aestivum) in China, with F. pseudograminearum being the dominant pathogen. Currently, there is a shortage of biocontrol resources to control FCR induced by F. pseudograminearum, along with biocontrol mechanisms. In this study, we have identified 37 strains of biocontrol bacteria displaying antagonistic effects against F. pseudograminearum from over 8000 single colonies isolated from soil samples with a high incidence of FCR. Among them, QY43 exhibited remarkable efficacy in controlling FCR. Further analysis identified the isolate QY43 as Pseudomonas aeruginosa, based on its colony morphology and molecular biology. In vitro, QY43 significantly inhibited the growth, conidial germination, and the pathogenicity of F. pseudograminearum. In addition, QY43 exhibited a broad spectrum of antagonistic activities against several plant pathogens. The genomics analysis revealed that there are genes encoding potential biocontrol factors in the genome of QY43. The experimental results confirmed that QY43 secretes biocontrol factor siderophores and pyocyanin. In summary, QY43 exhibits a broad spectrum of antagonistic activities and the capacity to produce diverse biocontrol factors, thereby showing substantial potential for biocontrol applications to plant disease.

Salicylic Acid Biosynthesis and Metabolism: A Divergent Pathway for Plants and Bacteria

Salicylic acid (SA) is an active secondary metabolite that occurs in bacteria, fungi, and plants. SA and its derivatives (collectively called salicylates) are synthesized from chorismate (derived from shikimate pathway). SA is considered an important phytohormone that regulates various aspects of plant growth, environmental stress, and defense responses against pathogens. Besides plants, a large number of bacterial species, such as Pseudomonas, Bacillus, Azospirillum, Salmonella, Achromobacter, Vibrio, Yersinia, and Mycobacteria, have been reported to synthesize salicylates through the NRPS/PKS biosynthetic gene clusters. This bacterial salicylate production is often linked to the biosynthesis of small ferric-ion-chelating molecules, salicyl-derived siderophores (known as catecholate) under iron-limited conditions. Although bacteria possess entirely different biosynthetic pathways from plants, they share one common biosynthetic enzyme, isochorismate synthase, which converts chorismate to isochorismate, a common precursor for synthesizing SA. Additionally, SA in plants and bacteria can undergo several modifications to carry out their specific functions. In this review, we will systematically focus on the plant and bacterial salicylate biosynthesis and its metabolism.

Production of salicylic acid; a potent pharmaceutically active agent and its future prospects

Salicylic acid is one of the potent pharmaceutical organic acids that have various applications in the medical field. It acts as a plant hormone and helps in plant's growth & defence against pathogens. Beyond its numerous functions in plants, SA has great pharmaceutical importance since it acts as an intermediate for the synthesis of various drugs and dyes e.g. aspirin. At the industrial scale, chemical methods are used for the synthesis of SA but presently, several other sources are available that have the capability to alternate the chemical process which will be a step forward toward green synthesis. Aim of this paper is to provide comprehensive knowledge of SA production and its biological application.

Bacillus strain selection with plant growth-promoting mechanisms as potential elicitors of systemic resistance to gray mold in pepper plants

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Bacillus licheniformis induced resistance against gray mold in pepper plants.

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Bacillus licheniformis and Bacillus pumilus inhibited the growth of Botrytis cinerea and Fusarium solani.

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Plant growth promoting mechanisms were confirmed by isolated Bacillus strains.

Certain soil bacteria produce beneficial effects on the growth and health of plants; hence, their use is steadily increasing. Five strains of Bacillus with plant growth-promoting potential were selected in this study, which produced indole-3-acetic acid levels below 50 µg.mL⁻¹. On the other hand, while only strains M8 and M15 dissolved phosphorus, the latter was the only strain that did not produce siderophores. Only strains M8 and M16 significantly inhibited the in vitro growth of Botrytis cinerea and Fusarium solani phytopathogens, whose inhibition ranges fluctuated between 60% and 63% for strains M8 and M16 against B. cinerea and between 40% and 53% for strains M8 and M16 against F. solani. Based on these results, the need to implement resistance induction against gray mold on pepper plants was determined using strains M8 and M16. In this case, strain M16 inhibited the propagation of the necrotic spot by approximately 70%, whereas strain M8 significantly reduced the superoxide dismutase activity in systemic leaves, which substantially increased in plants inoculated with strain M8 and infected with the pathogen. Accordingly, the use of native rhizobacteria may entail biotechnological progress for the integrated management of crops in agriculture industry.

Bacterial Metabolites Produced Under Iron Limitation Kill Pinewood Nematode and Attract Caenorhabditis elegans

Pine Wilt Disease (PWD) is caused by Bursaphelenchus xylophilus, the pinewood nematode, and affects several species of pine trees worldwide. The ecosystem of the Pinus pinaster trees was investigated as a source of bacteria producing metabolites affecting this ecosystem: P. pinaster trees as target-plant, nematode as disease effector and its insect-vector as shuttle. For example, metals and metal-carrying compounds contribute to the complex tree-ecosystems. This work aimed to detect novel secondary metabolites like metallophores and related molecules produced under iron limitation by PWD-associated bacteria and to test their activity on nematodes. After screening 357 bacterial strains from Portugal and United States, two promising metallophore-producing strains Erwinia sp. A41C3 and Rouxiella sp. Arv20#4.1 were chosen and investigated in more detail. The genomes of these strains were sequenced, analyzed, and used to detect genetic potential for secondary metabolite production. A combinatorial approach of liquid chromatography-coupled tandem mass spectrometry (LC-MS) linked to molecular networking was used to describe these compounds. Two major metabolites were detected by HPLC analyses and described. One HPLC fraction of strain Arv20#4.1 showed to be a hydroxamate-type siderophore with higher affinity for chelation of Cu. The HPLC fraction of strain A41C3 with highest metal affinity showed to be a catecholate-type siderophore with higher affinity for chelation of Fe. LC-MS allowed the identification of several desferrioxamines from strain Arv20#4.1, in special desferrioxamine E, but no hit was obtained in case of strain A41C3 which might indicate that it is something new. Bacteria and their culture supernatants showed ability to attract C. elegans. HPLC fractions of those supernatant-extracts of Erwinia strain A41C3, enriched with secondary metabolites such as siderophores, were able to kill pinewood nematode. These results suggest that metabolites secreted under iron limitation have potential to biocontrol B. xylophilus and for management of Pine Wilt Disease.

Efficacy of a pyrimidine derivative to control spot disease on Solanum melongena caused by Alternaria alternata

The pyrimidine derivative (4,6-dimethyl-N-phenyldiethyl pyrimidine, DPDP) was tested as a foliar spray fungicide at 50 mg l⁻¹ for protection of eggplant (Solanum melongena) from spot disease caused by Alternaria alternata. Varied concentrations of DPDP (10–50 mg l⁻¹) differentially inhibited mycelial growth, conidial count and conidial germination of A. alternata growth in vitro; the magnitude of inhibition increased with increasing concentration. In vivo, an experiment was conducted in pots using a complete block randomized design and repeated twice with three replications and four treatments (control, A. alternata alone, DPDP alone and combination of DPDP and A. alternata) for 5 weeks (1 plant in pot × 3 pots per set (3 replications per treatment) × 4 sets (4 treatments) × 5 weeks × 2 experimental repetitions = 120 pots). In this experiment, 10-day-old eggplant seedlings were transplanted in pots and then inoculated with A. alternata, DPDP or their combination 1 week later. Leaves of the A. alternata-infected eggplant suffered from chlorosis, necrosis and brown spots during the subsequent 5 weeks. Disease intensity was obvious in infected leaves but withdrawn by DPDP. There were relationships between incidence and severity, greater in plant leaves infected A. alternata alone and diminished with the presence of DPDP. Moreover, the infection resulted in reductions in growth, decreases in contents of anthocyanins, chlorophylls, carotenoids and thiols as well as inhibitions in activities of superoxide dismutase (SOD), glutathione peroxidase (GPX) and glutathione-S-transferase (GST). Nonetheless, the application of DPDP at 50 mg led to a recovery of the infected eggplant; the infection-induced deleterious effects were mostly reversed by DPDP. However, treatment with DPDP alone seemed with no significant impacts. Due to its safe use to host and the inhibition for the pathogen, DPDP could be suggested as an efficient fungicide for protection of eggplant to control A. alternata spot disease.

Genetic and functional diversity among the antagonistic potential fluorescent pseudomonads isolated from tea rhizosphere

Twenty-five fluorescent pseudomonads from rhizospheric soil of six tea gardens in four district of Upper Assam, India were isolated and screened for antagonistic activity against fungal pathogens such as Fusarium oxysporum f. sp. raphani (For), Fusarium oxysporum f. sp. ciceri (Foc), Fusarium semitectum (Fs), and Rhizoctonia solani (Rs); and bacterial pathogens-Staphylococcus aureus (Sa), Escherichia coli (Ec), and Klebsiella pneumoniae (Kp). Most of the isolates exhibited strong antagonistic activity against the fungal pathogens and gram-positive bacterium i.e. Staphylococcus aureus. Productions of siderophore, salicylic acid (SA), hydrogen cyanide (HCN), and cell wall-degrading enzyme (chitinase) were studied to observe the possible mechanisms of antagonistic activity of the isolates. Correlation between the antagonistic potentiality of some isolates and their levels of production of siderophore, salicylic acid, and hydrogen cyanide was observed. Out of the 25 isolates, antibiotic-coding genes, 2,4-diacetylphloroglucinol (DAPG) and pyoluteorin (PLT) were detected in the isolates, Pf12 and Pf373, respectively. Genetic diversity of these fluorescent pseudomonads were analyzed with reference to four strains of Pseudomonas fluorescens NICM 2099(T), P. aeruginosa MTCC 2582(T), P. aureofaciens NICM 2026(T), and P. syringae MTCC 673(T). 16S rDNA-RFLP analysis of these isolates using three tetra cutter restriction enzymes (HaeIII, AluI and MspI) revealed two distinct clusters. Cluster A comprised only two isolates Pf141 and 24-PfM3, and cluster B comprised 23 isolates along with four reference strains.

Influence of mineral amendment on disease suppressive activity of Pseudomonas fluorescens to Fusarium wilt of chickpea

Fusarium wilt caused by Fusarium oxysporum f. sp. ciceri causes considerable yield loss of chickpea. Pseudomonas fluorescens4-92 (Pf4-92) strain can suppress the disease. Amendment of zinc EDTA and copper EDTA could not suppress the disease significantly when used alone; however, they significantly suppressed the disease in presence of Pf4-92. In vitro observation showed that at 40, 30 and 20microgml(-1) concentrations of these minerals, i.e. Zn, Cu and Zn plus Cu, respectively, completely repressed the production of the phytotoxin, fusaric acid (FA). FA concentration (0.5microgml(-1)) has been shown to suppress the production of 2,4-diacetylphloroglucinol (DAPG) by Pf4-92, and DAPG, salicylic acid, pyochelin and pyoluteorin production was enhanced by these mineral amendments. In rockwool bioassays, Zn, Cu and Zn plus Cu amendments reduced FA production and enhanced DAPG production. This study demonstrates that Zn and Cu enhance biocontrol activity by reducing FA produced by the pathogen, F. oxysporum f. sp. ciceri.