Biocontrol of tomato Verticillium wilt disease by plant growth-promoting bacteria encapsulated in alginate extracted from brown seaweed.

The use of beneficial microorganisms and polysaccharides for the biocontrol of plant diseases currently represents a promising tool for the management of soil-borne pathogens. Despite advancements, enhancing the efficacy and sustainability of these biocontrol methods, particularly in complex soil environments, remains a challenge. Thus, we investigated the potential of four PGPR strains encapsulated in natural alginate extracted from a brown seaweed Bifurcaria bifurcata to evaluate its biocontrol capacities against Verticillium wilt of tomato, ensuring optimal performance through a synergistic effect and innovative bacterial release. Our research demonstrated that the application of PGPR and alginate reduced disease severity and mortality rate and increased the natural defenses of tomato. Results showed that supplying alginate or the PGPR consortium at the root level s stimulates phenylalanine ammonia-lyase activity (the key enzyme of the phenylpropanoid metabolism) and the accumulation of phenolic compounds and lignin in leaves and roots. Treatment with PGPR encapsulated in alginate beads showed the best biocontrol efficiency and was accompanied by a synergistic effect reflecting a rapid, intense, and systemic induction of defense mechanisms known for their effectiveness in inducing resistance in tomato. These promising results suggest that such bioformulations could lead to innovative agricultural practices for sustainable plant protection against pathogens.

The novel bacteriocin BacYB1 produced by Leuconostoc mesenteroides YB1: From recent analytical characterization to biocontrol Verticillium dahliae and Agrobacterium tumefaciens.

Biocontrol of phytopathogens involving the use of bioactive compounds produced by lactic acid bacteria (LAB), is a promising approach to manage many diseases in agriculture. In this study, a lactic acid bacterium designated YB1 was isolated from fermented olives and selected for its antagonistic activity against Verticillium dahliae (V. dahliae) and Agrobacterium tumefaciens (A. tumefaciens). Based on the 16S rRNA gene nucleotide sequence analysis (1565 pb, accession number: OR714267), the new isolate YB1 bacterium was assigned as Leuconostoc mesenteroides YB1 (OR714267) strain. This bacterium produces an active peptide "bacteriocin" called BacYB1, which was purified in four steps. Matrix-assisted lasers desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) based approach was performed to identify and characterize BacYB1. The exact mass was 5470.75 Da, and the analysis of the N-terminal sequence (VTRASGASTPPGTASPFKTL) of BacYB1 revealed no significant similarity to currently available antimicrobial peptides. The BacYB1 displayed a bactericidal mode of action against A. tumefaciens. The potentiel role of BacYB1 to supress the growth of A. tumefaciens was confirmed by live-dead cells viability assay. In pot experiments, the biocontrol efficacy of BacYB1 against V. dahliae wilt on young olive trees was studied. The percentage of dead plants (PDP) and the final mean symptomes severity (FMS) of plants articifialy infected by V. dahliae and treated with the pre-purified peptide BacYB1 (preventive and curative treatments) were significantly inferior to untreated plants. Biochemical analysis of leaves of the plants has shown that polyophenols contents were highly detected in plants infected by V. dahliae and the highest contents of chlorophyl a, b and total chlorophyll were recorded in plants treated with the combination of BacYB1 with the biofertilisant Humivital. BacYB1 presents a promising alternative for the control of Verticillium wilt and crown gall diseases.

Revealing the Complete Bispecific Phosphatase Genes (DUSPs) across the Genome and Investigating the Expression Patterns of GH_A11G3500 Resistance against Verticillium wilt.

DUSPs, a diverse group of protein phosphatases, play a pivotal role in orchestrating cellular growth and development through intricate signaling pathways. Notably, they actively participate in the MAPK pathway, which governs crucial aspects of plant physiology, including growth regulation, disease resistance, pest resistance, and stress response. DUSP is a key enzyme, and it is the enzyme that limits the rate of cell metabolism. At present, complete understanding of the DUSP gene family in cotton and its specific roles in resistance to Verticillium wilt (VW) remains elusive. To address this knowledge gap, we conducted a comprehensive identification and analysis of four key cotton species: Gossypium arboreum, Gossypium barbadense, Gossypium hirsutum, and Gossypium raimondii. The results revealed the identification of a total of 120 DUSP genes in the four cotton varieties, which were categorized into six subgroups and randomly distributed at both ends of 26 chromosomes, predominantly localized within the nucleus. Our analysis demonstrated that closely related DUSP genes exhibited similarities in terms of the conserved motif composition and gene structure. A promoter analysis performed on the GhDUSP gene promoter revealed the presence of several cis-acting elements, which are associated with abiotic and biotic stress responses, as well as hormone signaling. A tissue expression pattern analysis demonstrated significant variations in GhDUSP gene expression under different stress conditions, with roots exhibiting the highest levels, followed by stems and leaves. In terms of tissue-specific detection, petals, leaves, stems, stamens, and receptacles exhibited higher expression levels of the GhDUSP gene. The gene expression analysis results for GhDUSPs under stress suggest that DUSP genes may have a crucial role in the cotton response to stress in cotton. Through Virus-Induced Gene Silencing (VIGS) experiments, the silencing of the target gene significantly reduced the resistance efficiency of disease-resistant varieties against Verticillium wilt (VW). Consequently, we conclude that GH_A11G3500-mediated bispecific phosphorylated genes may serve as key regulators in the resistance of G. hirsutum to Verticillium wilt (VW). This study presents a comprehensive structure designed to provide an in-depth understanding of the potential biological functions of cotton, providing a strong foundation for further research into molecular breeding and resistance to plant pathogens.

Application of garlic allelochemicals improves growth and induces defense responses in eggplant (Solanum melongena) against Verticillium dahliae.

Aqueous garlic extracts (AGE) and garlic allelochemical diallyl disulfide (DADS) have been recently reported to bear bioactive properties to stimulate plant growth and development and alter defense-related physiology. We, therefore, performed a bioassay to study these chemicals as possible biostimulants for defense against Verticillium dahliae in eggplant seedlings. AGE and DADS were applied as a foliar application to the eggplants and samples were collected before and after pathogen inoculation at various intervals to analyze the defense mechanism. The obtained data revealed that with the application of AGE and DADS, the seedlings showed responses including activation of antioxidant enzymes, an abundance of chlorophyll contents, alteration of photosynthesis system, and accumulation of plant hormones compared to the control plants. Furthermore, the microscopic analysis of the AGE or DADS treated plants showed high variability in pathogen density within the root crown at 28 days post-inoculation. The low abundance of reactive oxygen species was noticed in AGE or DADS treated plants, which indicates that the plants were able to successfully encounter pathogen attacks. The AGE and DADS treated plants exhibited a lower disease severity index (32.4% and 24.8% vs 87.1% in controls), indicating successful defense against Verticillium infection. Our results were therefore among the first to address the biostimulatory effects of AGE or DADS to induce resistance in eggplant seedlings against V. dahliae and may be used to establish preparation for garlic-derived bioactive compounds to improve growth and defense responses of eggplants under-protected horticultural situations such as glasshouse or plastic tunnels system.

Molecular evidence for the involvement of cotton GhGLP2, in enhanced resistance to Verticillium and Fusarium Wilts and oxidative stress.

Germin-like proteins (GLPs) are a diverse and ubiquitous family of plant glycoproteins belonging to the cupin super family; they play considerable roles in plant responses against various abiotic and biotic stresses. Here, we provide evidence that GLP2 protein from cotton (Gossypium hirsutum) functions in plant defense responses against Verticillium dahliae, Fusarium oxysporum and oxidative stress. Purified recombinant GhGLP2 exhibits superoxide dismutase (SOD) activity and inhibits spore germination of pathogens. Virus-induced silencing of GhGLP2 in cotton results in increased susceptibility to pathogens, plants exhibited severe wilt on leaves, enhanced vascular browning and suppressed callose deposition. Transgenic Arabidopsis (Arabidopsis thaliana) plants overexpressing GhGLP2 showed significant resistance to V. dahliae and F. oxysporum, with reduced mycelia growth, increased callose deposition and cell wall lignification at infection sites on leaves. The enhanced tolerance of GhGLP2-transgenic Arabidopsis to oxidative stress was investigated by methyl viologen and ammonium persulfate treatments, along with increased H2O2 production. Further, the expression of several defense-related genes (PDF1.2, LOX2, and VSP1) or oxidative stress-related genes (RbohD, RbohF) was triggered by GhGLP2. Thus, our results confirmed the involvement of GhGLP2 in plant defense response against Verticillium and Fusarium wilt pathogens and stress conditions.

Verticillium dahliae VdTHI20, Involved in Pyrimidine Biosynthesis, Is Required for DNA Repair Functions and Pathogenicity.

Verticillium dahliae (V. dahliae) infects roots and colonizes the vascular vessels of host plants, significantly reducing the economic yield of cotton and other crops. In this study, the protein VdTHI20, which is involved in the thiamine biosynthesis pathway, was characterized by knocking out the corresponding VdTHI20 gene in V. dahliae via Agrobacterium tumefaciens-mediated transformation (ATMT). The deletion of VdTHI20 resulted in several phenotypic defects in vegetative growth and conidiation and in impaired virulence in tobacco seedlings. We show that VdTHI20 increases the tolerance of V. dahliae to UV damage. The impaired vegetative growth of ΔVdTHI20 mutant strains was restored by complementation with a functional copy of the VdTHI20 gene or by supplementation with additional thiamine. Furthermore, the root infection and colonization of the ΔVdTHI20 mutant strains were suppressed, as indicated by green fluorescent protein (GFP)-labelling under microscope observation. When the RNAi constructs of VdTHI20 were used to transform Nicotiana benthamiana, the transgenic lines expressing dsVdTHI20 showed elevated resistance to V. dahliae. Together, these results suggest that VdTHI20 plays a significant role in the pathogenicity of V. dahliae. In addition, the pathogenesis-related gene VdTHI20 exhibits potential for controlling V. dahliae in important crops.

A Cold-Adapted Chitinase-Producing Bacterium from Antarctica and Its Potential in Biocontrol of Plant Pathogenic Fungi.

To obtain chitinase-producing microorganisms with high chitinolytic activity at low temperature, samples collected from Fildes Peninsula in Antarctica were used as sources for bioprospecting of chitinolytic microorganisms. A cold-adapted strain, designated as GWSMS-1, was isolated from marine sediment and further characterized as Pseudomonas. To improve the chitinase production, one-factor-at-a-time and orthogonal test approaches were adopted to optimize the medium components and culture conditions. The results showed that the highest chitinolytic activity (6.36 times higher than that before optimization) was obtained with 95.41 U L-1 with 15 g L-1 of glucose, 1 g L-1 of peptone, 15 g L-1 of colloid chitin and 0.25 g L-1 of magnesium ions contained in the medium, cultivated under pH 7.0 and a temperature of 20 °C. To better understand the application potential of this strain, the enzymatic properties and the antifungal activity of the crude chitinase secreted by the strain were further investigated. The crude enzyme showed the maximum catalytic activity at 35 °C and pH 4.5, and it also exhibited excellent low-temperature activity, which still displayed more than 50% of its maximal activity at 0 °C. Furthermore, the crude chitinase showed significant inhibition of fungi Verticillium dahlia CICC 2534 and Fusarium oxysporum f. sp. cucumerinum CICC 2532, which can cause cotton wilt and cucumber blight, respectively, suggesting that strain GWSMS-1 could be a competitive candidate for biological control in agriculture, especially at low temperature.

Antagonistic activity and mechanism of an isolated Streptomyces corchorusii stain AUH-1 against phytopathogenic fungi.

The various diseases that occur during the growth of plants usually cause a significant reduction in production and quality of agricultural products. Actinomycetes, especially Streptomyces spp., become a valuable biological control resource due to their preponderant abilities to produce various secondary metabolites with novel structure and remarkable biological activity. The present work aimed to isolate an effective antagonistic actinomycete against various soilborne phytopathogenic fungi. By dual culture with Fusarium oxysporum f. sp. niveum, an antagonistic actinomycete named Streptomyces corchorusii stain AUH-1 was screened out from 26 soil samples. The in vitro bioassay results showed that S. corchorusii stain AUH-1 had a broad-spectrum antagonistic activity against a range of fungal plant pathogens, such as F. oxysporum f. sp. niveum, Phytophthora parasitica var. nicotianae, Rhizoctonia solani, P. capsica, Botryosphaeria dothidea, F. oxysporum f. sp. vasinfectum, Verticillium dahliae, and F. oxysporum f. sp. cucumerinum. According to the morphological observations in scanning electron microscopy (SEM) and fluorescence microscope (FM), it was found that the cell membranes of F. oxysporum f. sp. niveum were damaged when treated with the antifungal metabolite form S. corchorusii stain AUH-1. Meanwhile, the dropped ergosterol formation and increased malondialdehyde levels further confirmed that S. corchorusii strain AUH-1 exerted its antagonistic activity against F. oxysporum f. sp. niveum via damaging the structure and function of cell membranes. In conclusion, S. corchorusii strain AUH-1 showed a promising prospect for the development of biological agent, especially due to its broad-spectrum and effective antagonist on various soil-borne plant pathogens.

Expression and characterization of two chitinases with synergistic effect and antifungal activity from Xenorhabdus nematophila.

Xenorhabdus nematophila HB310 secreted the insecticidal protein toxin complex. Two chitinase genes, chi60 and chi70, were found in X. nematophila toxin complex locus. In order to clarify the function of two chitinases, chi60 and chi70 genes were cloned and expressed in Escherichia coli Transetta (DE3). As a result, we found that the Chi60 and Chi70 belonged to glycoside hydrolases (GH) family 18 with a molecular mass of 65 kDa and 78 kDa, respectively. When colloidal chitin was treated as the substrate, Chi60 and Chi70 were proved to have the highest enzymatic activity at pH 6.0 and 50 °C. Chi60 and Chi70 had obvious growth inhibition effect against the second larvae of Helicoverpa armigera with growth inhibiting rate of 81.99% and 90.51%. Chi70 had synergistic effect with the insecticidal toxicity of Bt Cry 1Ac, but the Chi60 had no synergistic effect with Bt Cry 1Ac. Chi60 and Chi70 showed antifungal activity against Alternaria brassicicola, Verticillium dahliae and Coniothyrium diplodiella. The results increased our understanding of the chitinases produced by X. nematophila and laid a foundation for further studies on the mechanism of the chitinases.

Antifungal effects of actinomycin D on Verticillium dahliae via a membrane-splitting mechanism.

Antifungal bioassays led to the isolation of actinomycins D and A1 from Streptomyces luteus TRM45540 collected from Norpo in Xinjiang, and these compounds were identified by nuclear magnetic resonance spectroscopy. The antifungal activity of actinomycin D was higher than that of actinomycin A1. Actinomycin D clearly inhibited the spore germination, hyphal growth and biomass accumulation of Verticillium dahliae in a dose-dependent manner. Flow cytometric analysis with propidium iodide, total ergosterol measurement, cell leakage and scanning electron microscopy experiments demonstrated that the plasma membrane of this fungus was damaged by actinomycin D, resulting in swollen cells and cellular content leakage. Transmission electron microscopy revealed that parts of the plasma membrane infolded after being treated with actinomycin D. The antifungal activity of actinomycin D damaged the fungal plasma membrane of V. dahliae via a membrane-splitting mechanism, which provided new insights into the functional mechanism of actinomycin D.

GhHB12, a HD-ZIP I Transcription Factor, Negatively Regulates the Cotton Resistance to Verticillium dahliae.

The homeodomain-leucine zipper (HD-ZIP) is a plant-specific transcription factor family that plays important roles in plant developmental processes in response to multiple stressors. We previously isolated a cotton HD-ZIP class I transcription factor gene, GhHB12, which is regulated by the circadian clock and photoperiodism. Furthermore, it regulates cotton architecture, phase transition, and photoperiod sensitivity. Here we report that GhHB12 was induced by methyl jasmonate (MeJA) and Verticillium dahliae infection. Additionally, stress-responsive elements were found in the GhHB12 promoter. Promoter fusion analysis showed that GhHB12 was predominantly expressed in primary roots and that it was induced by mechanical damage. Overexpression of GhHB12 increased susceptibility of the cotton plant to the fungal pathogens Botrytis cinerea and V. dahliae, which was coupled with suppression of the jasmonic acid (JA)-response genes GhJAZ2 and GhPR3. Our results suggest that GhHB12, a cotton stress-responsive HD-ZIP I transcription factor, negatively regulates cotton resistance to V. dahliae by suppressing JA-response genes.

Fungal Competitors Affect Production of Antimicrobial Lipopeptides in Bacillus subtilis Strain B9-5.

Bacillus subtilis has shown success in antagonizing plant pathogens where strains of the bacterium produce antimicrobial cyclic lipopeptides (CLPs) in response to microbial competitors in their ecological niche. To gain insight into the inhibitory role of these CLPs, B. subtilis strain B9-5 was co-cultured with three pathogenic fungi. Inhibition of mycelial growth and spore germination was assessed and CLPs produced by B. subtilis B9-5 were quantified over the entire period of microbial interaction. B. subtilis B9-5 significantly inhibited mycelial growth and spore germination of Fusarium sambucinum and Verticillium dahliae, but not Rhizopus stolonifer. LC-MS analysis revealed that B. subtilis differentially produced fengycin and surfactin homologs depending on the competitor. CLP quantification suggested that the presence of Verticillium dahliae, a fungus highly sensitive to the compounds, caused an increase followed by a decrease in CLP production by the bacterium. In co-cultures with Fusarium sambucinum, a moderately sensitive fungus, CLP production increased more gradually, possibly because of its slower rate of spore germination. With co-cultures of the tolerant fungus Rhizopus stolonifer, B. subtilis produced high amounts of CLPs (per bacterial cell) for the duration of the interaction. Variations in CLP production could be explained, in part, by the pathogens' overall sensitivities to the bacterial lipopeptides and/or the relative growth rates between the plant pathogen and B. subtilis. CLP production varied substantially temporally depending on the targeted fungus, which provides valuable insight concerning the effectiveness of B. subtilis B9-5 protecting its ecological niche against the ingress of these pathogens.

A Phi-Class Glutathione S-Transferase Gene for Verticillium Wilt Resistance in Gossypium arboreum Identified in a Genome-Wide Association Study.

Verticillium wilt disease is one of the most destructive biotic stresses faced by cotton plants. Here, we performed a genome-wide association study (GWAS) in 215 Chinese Gossypium arboreum accessions inoculated as seedlings with Verticillium dahliae to identify candidate loci involved in wilt resistance. We identified 309 loci that had a significant association with Verticillium wilt resistance and - log(P) values >5.0; the highest signal appeared on Ca3 in a 74 kb haplotype block. Five genes were also located within this haplotype block. One of these genes, CG05, was positioned close to the most significant SNP Ca3_23037225 (14 kb); expression of the gene was induced by V. dahliae or by treatment with salicylic acid (SA). Therefore, we suggest that CG05 may respond to invasion by V. dahliae via an SA-related signaling pathway, and we designated this gene as GaGSTF9. We showed that GaGSTF9 was a positive regulator of Verticillium wilt through the use of virus-induced gene silencing (VIGS) and overexpression in Arabidopsis. In addition, the glutathione S-transferase (GST) mutant gstf9 of Arabidopsis was found to be more susceptible to Verticillium wilt than wild-type plants. The levels of endogenous SA and hydrogen peroxide had a significant effect on Arabidopsis plants that overexpressed GaGSTF9, indicating that GST may regulate reactive oxygen species content via catalytic reduction of the tripeptide glutathione (GSH), and then affect SA content. Our data demonstrated that GaGSTF9 was a key regulator mediating cotton responses to V. dahliae and a potential candidate gene for cotton genetic improvement.

Copper complexes of the 1,3,4-thiadiazole derivatives modulate antioxidant defense responses and resistance in tomato plants against fungal and bacterial diseases.

The metallic complexes µ-chloro-µ-[2,5-bis (2-pyridyl)-1,3,4-thiadiazole] aqua chlorocopper (II) dichlorocopper (II) (abbreviated 2PTH-Cu2-Cl4); aquabis [2,5-bis (2-pyridyl)-1,3,4-thiadiazole-κ2N2,N3] (trifluoromethane-sulfonato-κO) copper(II) trifluoro metrhanesulfonate (2PTH-Cu-tF) and bis[(2,5-bis(pyridine-2-yl)-1,3,4-thiadiazole-di-azido copper(II)] (2PTH-Cu-Az) were compared for their antimicrobial activities in vitro, and their aptitude to control Verticillium wilt and crown gall diseases development of tomato in the greenhouse. Results showed that the complex 2PTH-Cu-Az inhibited drastically the growth of V. dahliae in vitro. 2PTH-Cu2-Cl4 and 2PTH-Cu-tF did not display any noticeable antimicrobial activity in vitro against all of the pathogens tested. However, in planta evaluation revealed that the three complexes protected tomato against crown gall similarly. They also reduced Verticillium wilt disease severity, although the complex 2PTH-Cu-Az was the most efficient. When compared to other complexes, 2PTH-Cu-Az triggered only a weak oxidative burst as revealed by H2O2 measurement and the activity of ascorbate peroxidase and catalase. These results suggest that the superiority of 2PTH-Cu-Az against V. dahliae rely on its direct antifungal activity and its ability to modulate H2O2 accumulation.

The two-component response regulator VdSkn7 plays key roles in microsclerotial development, stress resistance and virulence of Verticillium dahliae.

The fungus Verticillium dahliae causes vascular wilt disease on various plant species resulting in devastating yield losses worldwide. The capacity of V. dahliae to colonize in host plant xylem and disseminate by microsclerotia has led to studies to evaluate genes associated with pathogenesis and microsclerotia formation. Here, we identified and characterized a V. dahliae homolog to Skn7, a two-component stress response regulator of Saccharomyces cerevisiae. Results showed that melanized microsclerotia formation and conidiation were significantly inhibited in the VdSkn7 deletion mutants. VdSkn7-deficient mutants displayed severe growth defect under heat shock, cell wall perturbing agents and H2O2, and were significantly less virulent but were not sensitive to osmotic stresses compared to the wild-type strain. Finally, we demonstrated that VdSkn7 is required for the plant penetration. Taken together, our study thus provides new evidence on the functional conservation and divergence of Skn7 orthologs among fungal organisms and indicates that VdSkn7 contributes to microsclerotial development, virulence and stress response of V. dahliae.

Effect of O-chitosan nanoparticles on the development and membrane permeability of Verticillium dahliae.

Verticillium dahliae, which causes wilting in over 300 woody and herbaceous plant species, is a representative of fungal plant diseases for which effective controls are still needed. In this study, the antifungal action of oleoyl-chitosan nanoparticles was investigated against V. dahliae. Media containing oleoyl-chitosan nanoparticles dramatically decreased the mycelium growth. The highest antifungal indexes were observed on media amended with 2mg/mL nanoparticles. Optical microscopy showed that spore germination and hyphae morphology were affected. Scanning electron microscopy and transmission electron microscopy demonstrated degenerative alterations including crumpled hyphae and spores, thickened cell walls, disappeared membranous organelles, massive vacuolation of the cytoplasm, and cell wall-plasmalemma separation. Fluorescence microscopy showed that nanoparticles were internalized by fungal cells. The sharp increase in the release of intracellular components and decrease of total cellular protein concentration demonstrated damaged cell membranes. Overall, the results indicate that oleoyl-chitosan nanoparticles have the potential to control phytopathogens in agriculture.

Small RNAs regulate the biocontrol property of fluorescent Pseudomonas strain Psd.

The production of biocontrol factors by Pseudomonads is reported to be controlled at the post-transcriptional level by the GacS/GacA signal transduction pathway. This involves RNA-binding translational repressor proteins, RsmA and RsmE, and the small regulatory RNAs (sRNAs) RsmX, RsmY, and RsmZ. While the former represses genes involved in secondary metabolite production, the latter relieves this repression at the end of exponential growth. We have studied the fluorescent Pseudomonas strain Psd, possessing good biocontrol potential, and confirmed the presence of rsmY and rsmZ by PCR amplification. Gene constructs for all the three small RNAs (RsmX, RsmY and RsmZ) carried on broad host-range plasmid, pME6032 were mobilized into strain Psd. Expression analysis of gacA in the recombinant strains over-expressing rsmX (Psd-pME7320), rsmY (Psd-pME6359) and rsmZ (Psd-pME6918) revealed a significant upregulation of the response regulator. Besides, a remarkable down-regulation of rsmA was also reported in all the strains. The variant strains were found to produce comparatively higher levels of phenazines. Indole acetic acid levels were higher to some extent, and strain Psd-pME6918 also showed elevated production of HCN. The tomato seedlings infected with Fusarium oxysporum and Verticillium dahliae in the presence of culture filtrate of the recombinant strains showed better plant protection response in comparison to the wild-type strain Psd. These results suggest that small RNAs are important determinants in regulation of the biocontrol property of strain Psd.

Synthesis and fungicidal activity of tryptophan analogues - the unexpected calycanthaceous alkaloid derivatives.

A series of 21 N-protected tryptophan derivatives were synthesised from tryptophan in good yields. Their structures were characterised by IR, 1H NMR, 13C NMR, DEPT (90° and 135°) and MS analysis. The synthesised compounds were evaluated against a wide variety of plant pathogen fungi. Compounds a19 and a21 displayed activity against Fusarium oxysporum (F. oxysporum), and compound a21 showed high activity against F. oxysporum and Eggplant Verticillium, with EC50 values of 58.27 and 77.39 µg mL-1, respectively. Considering that the bioassay of the title compounds was evaluated, effects of the chain alkyl substituents may contribute to the significant variations in fungicidal potency. Their structure-antifungal activity relationships were also discussed. These results will pave the way for further design, structural modification and development of calycanthaceous alkaloids as antimicrobial agents.

The mononuclear nickel(II) complex bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ2 N2 ,N3 ]nickel(II) protects tomato from Verticillium dahliae by inhibiting fungal growth and activating plant defences.

BACKGROUND: The antifungal properties of the nickel(II) complex bis(azido-κN)bis[2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole-κ2 N2 ,N3 ]nickel(II) [NiL2 (N3 )2 ] and its parental ligand 2,5-bis(pyridin-2-yl)-1,3,4-thiadiazole were examined to evaluate their ability to protect tomato plants against Verticillium dahliae. Our main objectives were to determine their effects on the in vitro growth of the pathogen, and their aptitude for controlling verticillium wilt and activating plant defence responses in the greenhouse. RESULTS: NiL2 (N3 )2 exhibited in vitro an elevated inhibition of radial growth of three strains of the pathogen. According to the strain, the EC50 values ranged from 10 to 29 µg mL-1 for NiL2 (N3 )2 . In the greenhouse, it induced an elevated protection against V. dahliae when it was applied twice as foliar sprays at 50 µg mL-1 . It reduced the leaf alteration index by 85% and vessel browning by 96%. In addition, its protective ability was associated with the accumulation of H2 O2 and the activation of total phenolic content, as well as potentiation of the activity of peroxidase and polyphenol oxidase. CONCLUSION: These results demonstrated that the coordination of the ligand with Ni associated with the azide as a coligand resulted in an improvement in its biological activity by both inhibiting the growth of V. dahliae and activating plant defence responses. © 2016 Society of Chemical Industry.

Triterpene derivatives from Euphorbia enhance resistance against Verticillium wilt of tomato.

Oxidation of α-euphorbol and 31-norlanostenol, two triterpenic compounds isolated from the latex of Euphorbia resinifera and Euphorbia officinarum respectively, yielded four products named 3ß-tosyloxy-4α,14α-dimethyl-5α-cholesta-7,9-diene; 4α,14α-dimethyl-5α-cholesta-7,9-dien-3ß-ol; 24-methylen-elemo-lanosta-8,24-dien-3-one and elemo-lanost-8-en-3,11,24-trione. They were evaluated for protection of tomato plants against Verticillium dahliae in a greenhouse. The four semisynthesized products were phytotoxic at higher concentrations as they completely inhibited tomato germination at 100 and 500 µg/ml. However at lower concentrations (10 and 50 µg/ml) germination and root length were not affected. Disease resistance against Verticillium wilt was assessed in tomato plants derived from seeds that germinated in the presence of 10 and 50 µg/ml of the four products. All of them were able to reduce significantly disease severity, with 10 µg/ml being more effective than 50 µg/ml. Reduction of leaf alteration index and of stunting index ranged from 52 to 68% and from 43 to 67%, respectively, while vessel discoloration was reduced by at least 95%. The compounds were also able to elicit H2O2 accumulation before and after fungal inoculation and to significantly enhance peroxidase and polyphenol oxidase activities. These results suggest that the hemisynthetized triterpenes can be used as elicitors of disease resistance.