Broad-spectrum Antifungal Activity Research Articles

Clerodane Diterpenoids Identified from Polyalthia longifolia Showing Antifungal Activity against Plant Pathogens.

In the search for new natural resources showing plant disease control effects, we found that the methanol extract of Polyalthia longifolia suppressed fungal disease development in plants. To identify the bioactive substances, the methanol extract of P. longifolia was extracted by organic solvents, and consequently, four new 2-oxo-clerodane diterpenes (1-4), a new 4(3 → 2)-abeo-clerodane diterpene (5), together with ten known compounds (6-16) were isolated and identified from the extracts. Of the new compounds, compound 2 showed a broad spectrum of antifungal activity with moderated minimum inhibitory concentration (MIC) values in a range of 50-100 μg/mL against tested fungal pathogens. Considering with the known compounds, compound 6 showed the most potent antifungal activity with an MIC value in the range of 6.3-12.5 μg/mL. When compound 6 was evaluated for an in vivo antifungal activity against rice blast, tomato late blight, and pepper anthracnose, compound 6 reduced the plant disease by at least 60% compared to the untreated control at concentrations of 250 and 500 μg/mL. Together, our results suggested that the methanol extract of twigs and leaves of P. longifolia and its major compound 6 could be used as a source for the development of eco-friendly plant protection agents.

Identification and delineation of action mechanism of antifungal agents: Reveromycin E and its new derivative isolated from Streptomyces sp. JCK-6141

Streptomyces species have been used as biocontrol agents for the management of fungal postharvest diseases. Reveromycin E (RE) and its new derivative, reveromycin E 1-methyl ester (REME), were isolated from Streptomyces sp. JCK-6141. Both compounds displayed broad-spectrum and extensive antifungal activities at acidic condition, but their activities were dramatically reduced at neutral or base conditions. These compounds effectively suppressed the cherry tomato gray mold and mandarin blue mold caused by Botrytis cinerea and Penicillium italicum, respectively, at 10 and 50 mg L−1. In in vitro and in vivo assays, RE showed stronger antifungal activity than REME. Reveromycin was known as an isoleucine tRNA synthetase (IleRS) inhibitor. However, there is unconsolidated result in confirming binding site of reveromycin in previous studies. A computational study revealed that RE had a lower binding energy than REME and both compounds tend to bind catalytic domain rather than editing domains of IleRS. Our results indicated that Streptomyces sp. JCK-6141 producing reveromycins can be widely used as a new microbial fungicide for the control of postharvest diseases on fruit.

Isolation, characterization and identification of novel broad spectrum bacterial antagonist(s) to control Fusarium wilt of eggplant

Soil bacteria are now-a-days familiar for plant disease prevention in comparison to chemical control measures in an eco-friendly way. Antagonistic soil bacteria have created tremendous interests among scientists to be an alternative means of plant disease control. The aim of our study was to isolate soil bacteria with a multifaceted role, both in the aspects of plant nutrition and disease prevention. To achieve our goal, rhizobacteria from crop plants, cultivated in different regions of West Bengal were isolated and from a total of 250 isolates, only eight were primarily selected based on their initial growth suppression capabilities against the phytopathogen Fusarium oxysporum. Finally, the two bacterial isolates, NC1 and NC2, showed in vitro broad-spectrum antifungal activity against seven potent phytopathogenic fungi, i.e., Fusarium oxysporum, Alternaria alternata, Colletotrichum capsici, Macrophomina phaseolina, Sclerotium hydrophilum, Rhizoctonia solani and Penicillium digitatum, where they suppressed mycelial growth up to 69% over untreated control. The two potent antagonists were screened in vitro for their plant growth promoting (PGP) and antifungal properties where they showed their efficacy to produce many lytic enzymes, indole acetic acid (IAA) and ammonia. The isolates were detected as Gram-positive, endospore, and capsule forming rod-shaped bacteria. On the basis of morphological, physiological, biochemical and BLAST analysis of 16s rDNA sequences, NC1 and NC2 were identified as Bacillus amyloliquefaciens KY568716 and Bacillus velezensis KY568715. When applied on eggplant, both the isolates suppressed Fusarium wilt symptoms and enhanced plant growth significantly. The effects were observed up to 30 days after pathogen inoculation and both the isolates were effective in reducing Fusarium wilt disease symptoms by 57.23% and 64.19% respectively, as compared to pathogen treated plants. They also showed significant enhancement of all plant growth parameters such as root and shoot length, biomass and chlorophyll content. Thus, the two isolates can be used to develop an effective dual function bio-control agents to control plant diseases as well as promoting plant growth.

A Novel Antifungal Actinomycete Streptomyces sp. Strain H3-2 Effectively Controls Banana Fusarium Wilt.

Banana Fusarium wilt disease caused by Fusarium oxyspoum f. sp. cubense (Foc) seriously threatens the banana industry. Foc tropical race 4 (Foc TR4) can infect almost all banana cultivars. Compared with traditional physical and chemical practices, biocontrol strategy using beneficial microbes is considered as an environmentally sound option to manage fungal disease. In this study, a strain, H3-2, isolated from a non-infected banana orchard, exhibited high antifungal activity against Foc TR4. According to its morphological, physiological, and biochemical characteristics, the strain H3-2 was identified as Streptomyces sp. and convinced by the polymorphic phylogenic analysis of 16S rRNA sequences. Extracts of the strain H3-2 suppressed the growth and spore germination of Foc TR4 in vitro by destroying cell membrane integrity and mycelial ultrastructure. Notably, the strain and its extracts showed broad-spectrum antifungal activity against the selected seven fungal phytopathogens. Fourteen chemical compounds in the extracts were identified by gas chromatography–mass spectrometer (GC-MS), primarily phenolic compounds. Additional pot inoculation experiment demonstrated that the fermentation broth of the strain H3-2 promoted the growth of banana seedlings by efficiently inhibiting the spread of banana Fusarium wilt disease. This study demonstrated the potential application of the novel Streptomyces sp. H3-2 for the management of banana Fusarium wilt.

Characterization and Antifungal Activity of Limonoid Constituents Isolated from Meliaceae Plants Melia dubia, Aphanamixis polystachya, and Swietenia macrophylla against Plant Pathogenic Fungi In Vitro

The plants of Meliaceae are native to tropical and subtropical regions as the Americas, west India, Southeast Asia, and Southern China. Many species of the genera Khaya, Swietenia, Aphanamixis, and Melia in this family are known as medicinal plants and have biological activities such as antiviral, antimicrobial, antifeeding, insecticidal, and cytotoxic properties. The objectives of this research are to characterize and evaluate the bioactive limonoids from several plants of Meliaceae against phytopathogenic fungi. During the search of antifungal compounds from the plants of Meliaceae, the three methanol extracts of Melia dubia, Aphanamixis polystachya, and Swietenia macrophylla were found to suppress the mycelial growth of several phytopathogenic fungi. Nine limonoids isolated from M. dubia (1–2), A. polystachya (3–5), and S. macrophylla (6–9) were evaluated, for the first time, their antifungal effectiveness against nine phytopathogenic fungi Fusarium oxysporum, Magnaporthe oryzae, Sclerotium rolfsii, Rhizoctonia solani, Alternaria spp., and Botrytis cinerea, and three oomycetes Phytophthora species. Limonoids 2, 3, 6, and 8 displayed a remarkable broad-spectrum antifungal activity against all the test fungi. Sclerotium rolfsii was highly sensitive to the four limonoids with IC50 values ranging from 79.4 to 128.0 µg/mL. Notably, chisocheton compound G (3) isolated from A. polystachya and khayanolide B (8) isolated from S. macrophylla were the most potent antifungal limonoids and exhibited a dose-dependent activity against Phytophthora species. Compounds 2 and 9 displayed moderate activity against M. oryzae. Our study results demonstrated the discovery of antifungal and lead compounds from the group of limonoids for application in the control of fungal plant diseases.

Irritable Bowel Syndrome Therapeutic Has Broad-Spectrum Antimicrobial Activity.

Otilonium bromide is a poorly absorbed oral medication used to control irritable bowel syndrome. It is thought to act as a muscle relaxant in the intestine. Here, we show that otilonium bromide has broad-spectrum antibacterial and antifungal activity, including against multidrug-resistant strains. Our results suggest otilonium bromide acts on enteric pathogens and may offer a new scaffold for poorly absorbed intestinal antimicrobial therapy.

Antimicrobial Activity of the Peptide LfcinB15 against Candida albicans.

Lactoferricin (Lfcin) is an amphipathic, cationic peptide derived from proteolytic cleavage of the N-lobe of lactoferrin (Lf). Lfcin and its derivatives possess broad-spectrum antibacterial and antifungal activities. However, unlike their antibacterial functions, the modes of action of Lfcin and its derivatives against pathogenic fungi are less well understood. In this study, the mechanisms of LfcinB15, a derivative of bovine Lfcin, against Candida albicans were, therefore, extensively investigated. LfcinB15 exhibited inhibitory activity against planktonic cells, biofilm cells, and clinical isolates of C. albicans and non-albicans Candida species. We further demonstrated that LfcinB15 is localized on the cell surface and vacuoles of C. albicans cells. Moreover, LfcinB15 uses several different methods to kill C. albicans, including disturbing the cell membrane, inducing reactive oxygen species (ROS) generation, and causing mitochondrial dysfunction. Finally, the Hog1 and Mkc1 mitogen-activated protein kinases were both activated in C. albicans cells in response to LfcinB15. These findings help us to obtain more insight into the complex mechanisms used by LfcinB15 and other Lfcin-derived peptides to fight fungal pathogens.

Preparation and Characterization of Liposomes Double-loaded with Amphotericin B and Amphotericin B/hydroxypropyl-beta-cyclodextrin Inclusion Complex.

Amphotericin B (AMB) is water-insoluble polyene, which has a broad spectrum of antifungal activity. The hydrophobic drug only exits in the phospholipid bilayer, leading to a low-drug liposomal loading capacity. This study is designed to prepare water-soluble inclusion complex (IC) between AMB and cyclodextrin (CD) to formulate liposomal vesicles, double-loaded with drug molecules in the phospholipid bilayer and AMB/CD IC in the aqueous core. Water-soluble AMB/CD IC was prepared by pH adjustment of the aqueous media and consequently characterized by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). Liposomes double-loaded with AMB were formulated by the thin-film hydration method and accordingly evaluated for vesicle size, polydispersity index, entrapment efficiency, zeta potential, and in vitro drug leakage. Hydroxypropyl β cyclodextrin (HP-β-CD) better solubilized AMB than both α-CD and β- CD e.g., the concentration of water-soluble AMB/HP-β-CD IC could reach 465 μg/mL. Both DSC and SEM data illustrated that the drug no longer existed in its crystalline form, in AMB/HP-β-CD IC. Liposomes double-loaded with hydrophilic AMB/HP-β-CD IC and hydrophobic AMB had a diameter of 270 nm, polydispersity index less than 0.27, and zeta potential ca.-42.8 mV. Moreover, liposomes double-loaded with AMB enhanced drug-liposomal loading capacity by 25%, less leaked drug in phosphate buffer pH 7.4 at 37°C in comparison to liposomes loaded with only hydrophobic AMB. Liposomes double-loaded with AMB and AMB/HP-β-CD IC increased drug-encapsulation ability and in vitro stability, suggesting potential drug delivery systems.

Metabolite Fingerprinting of Novel Streptomyces UK-238 from the Himalayan Forest

Aims: Characterization of antimicrobial metabolites of novel Streptomyces sp. UK-238. Background: Novel antimicrobial drug discovery is urgently needed due to emerging multi antimicrobial drug resistance among pathogens. Since many years, natural products have provided the basic skeletons for many therapeutic compounds including antibiotics. Bioprospection of un/under explored habitats and focussing on selective isolation of actinobacteria as a major reservoir of bio and chemodiversity has yielded good results. Objective: The main objectives of the study were the identification of UK-238 by 16S rDNA sequencing and antimicrobial metabolite fingerprinting of culture extracts. Methods: In the present study, a promising isolate, UK-238, has been screened for antimicrobial activity and metabolite fingerprinting from the Himalayan Thano Reserve forest. It was identified by 16S rDNA sequencing. Ethyl acetate extract was partially purified by column chromatography. The pooled active fractions were fingerprinted by GC-MS and compounds were tentatively identified by collated data analysis based on Similarity Index, observed Retention Index from Databases and calculated Retention Index. Results: UK-238 was identified as Streptomyces sp. with 98.4% similarity to S. niveiscabiei. It exhibited broad-spectrum antibacterial and antifungal activity. GC-MS analysis of active fractions of ethyl acetate extract showed the presence of eighteen novel antimicrobial compounds belonging to four major categories- alcohols, alkaloid, esters and peptide. Conclusion: The study confirms that bioprospection of underexplored habitats can elaborate novel bio and chemodiversity.

Structural studies on the O-specific polysaccharide of the lipopolysaccharide from Pseudomonas donghuensis strain SVBP6, with antifungal activity against the phytopathogenic fungus Macrophomina phaseolina

An O-specific polysaccharide (OPS) was isolated from the lipopolysaccharide (LPS) of Pseudomonas donghuensis SVBP6, a bacterium with a broad-spectrum antifungal activity in vitro, particularly that against Macrophomina phaseolina. This latter is one of the most virulent and dangerous pathogens of plants, including soybean which is an economically important crop in Argentina today. The OPS was studied by sugar analysis and spectroscopy (1D and 2D 1H and 13C NMR) showing the following trisaccharide repeating unit:→6)-ɑ-D-ManpNAc-(1 → 3)-β-l-Rhap-(1 → 4)-β-D-Glcp-(1→.The crude LPS, the purified LPS and the O-chain were assayed for their antifungal activity against M. phaseolina at 25, 50, 100, and 200 μg plug−1. The results showed that the crude LPS best inhibition was at 200 μg plug−1, able to inhibit the fungus growth by about 45%, while purified LPS and the corresponding OPS, in the same condition, reduced fungus growth by 65%, and 75%, respectively. Furthermore, the purified LPS and OPS significantly reduced the growth of M. phaseolina already at 100 μg plug−1 compared to the crude LPS. The structure of the O-chain is unique among the bacterial LPS and this is the first time that both the antifungal activity of a bacterial LPS and its corresponding O-chain were described.

Efficient preparation of the chiral intermediate of luliconazole with Lactobacillus kefir alcohol dehydrogenase through rational rearrangement of the substrate binding pocket

Abstract Luliconazole has been approved by the FDA for fungal infection therapy because of its broad-spectrum antifungal activity. However, low efficiency and harsh reaction conditions in the current synthesis of the luliconazole chiral intermediate (S)-2-chloro-1-(2,4-dichlorophenyl) ethanol ((S)-TCPE) limits its application. In the present study, a novel biocatalytic process for producing (S)-TCPE was developed. Based on a structural analysis at the atomic level on the wild-type (WT) Lactobacillus kefir ketoreductase (L. kefir KRED), a rational design of L. kefir KRED was performed with 2,2’,4’-trichloroacetophenone (TCAP) as the substrate. An enantioselective triple mutant A94S/S96E/E145A displaying a 117-fold increase in its relative activity compared to the WT was evolved, and the catalytic efficiency was raised to 5.17 s−1mM−1 from non-detectable. With 106 kg of wet cells of the triple variant loading, 275 kg TCAP was asymmetrically reduced with the yield of (S)-TCPE achieving 91% within 12 h, thus showing great potential for industrial applications. Furthermore, the molecular mechanism supporting the promotion of activity was revealed to be related to the rearrangement of the substrate binding pocket of the L. kefir KRED. By engineering an enzyme that serves as a biocatalyst for the efficient preparation of enantiomerically pure (S)-TCPE, the current study presents a reproducible strategy for the promotion of catalytic activity based on rational design.

3-Phenyllactic acid production by Lactobacillus crustorum strains isolated from naturally fermented vegetables

3-Phenyllactic acid (3-PLA) is a bioactive compound with broad-spectrum antibacterial and antifungal activity and several desirable pharmacological properties. In this study, 351 lactic acid bacterial strains isolated from naturally fermented Chinese vegetable samples were analyzed for their 3-PLA-producing ability, and three strains showing the greatest 3-PLA-producing ability were selected for further optimizing the fermentation conditions to enhance their 3-PLA yields. The results showed that all the strains were able to produce 3-PLA in MRS broth, but there were considerable variations in their 3-PLA-producing ability among the strains and among the species. Lactobacillus crustorum showed significantly higher 3-PLA-producing ability than the other species. In particular, L. crustorum NWAFU 1078 produced up to 45.2 mmol/L 3-PLA with a 73% substrate conversion rate under the optimized fermentation conditions that the culture was inoculated into MRS broth supplemented with 60 mmol/L phenylpyruvic acid as a substrate, 5.0% CaCO3 as a neutralizer and incubated for 48 h at 30 °C. This study indicates the possibility of the biotransformation of phenylpyruvic acid by L. crustorum NWAFU 1078 for highly efficient 3-PLA production.

Separation of Heat-Stable Antifungal Factor From Lysobacter enzymogenes Fermentation Broth via Photodegradation and Macroporous Resin Adsorption.

Heat-stable antifungal factor (HSAF) is produced by the fermentation of Lysobacter enzymogenes, which is known for its broad-spectrum antifungal activity and novel mode of action. However, studies on the separation of HSAF have rarely been reported. Herein, alteramide B (the main byproduct) was removed firstly from the fermentation broth by photodegradation to improve the purity of HSAF. Then, the separation of HSAF via adsorption by macroporous adsorption resins (MARs) was evaluated and NKA resin showed highest static adsorption and desorption performances. After optimizing the static and dynamic adsorption characteristics, the content of HSAF in the purified product increased from 8.67 ± 0.32% (ethyl acetate extraction) to 31.07 ± 1.12% by 3.58-fold. These results suggest that the developed strategy via photodegradation and macroporous resin adsorption is an effective process for the separation of HSAF, and it is also a promising method for the large-scale preparation of HSAF for agricultural applications.

Photostable 1-Trifluoromethyl Cinnamyl Alcohol Derivatives Designed as Potential Fungicides and Bactericides.

In the current work, a series of 1-trifluoromethyl cinnamyl alcohol derivatives were designed and synthesized and their antifungal activities were evaluated. The bioassay result showed that most compounds exhibited excellent antifungal activity in vitro at 10 μg mL-1. Next, photostable and easily synthesized compound 2 with broad-spectrum antifungal activity in vitro was selected as a potential candidate to evaluate its antibacterial and antifungal activities. The EC50 values of compound 2 against eight fungal plant pathogens in vitro ranged from 3.806 to 17.981 μg mL-1; at the same time, compound 2 could effectively control Podosphaera xanthii, Odium heveae Steinm, Puccinia striiformis West, and Puccinia sorghi in pot experiments. In addition, compound 2 exhibited excellent antibacterial activities in vitro and in vivo against Xanthomonas oryzae pv. oryzae. Furthermore, the absorption and translocation of compound 2 in wheat plants were determined by the high-performance liquid chromatography method. The result showed that compound 2 could be translocated acropetally as well as basipetally in wheat plants. Finally, it was found that compound 2 had no cross-resistance with carbendazim, azoxystrobin, and boscalid.

Advances in the biosynthesis of natamycin and its regulatory mechanisms

Natamycin is a polyene macrolide antibiotics with strong and broad spectrum antifungal activity. It not only effectively inhibits the growth and reproduction of fungi, but also prevents the formation of some mycotoxins. Consequently, it has been approved for use as an antifungal food preservative in most countries, and is also widely used in agriculture and healthcare. Streptomyces natalensis and Streptomyces chatanoogensis are the main producers of natamycin. This review summarizes the biosynthesis and regulatory mechanism of natamycin, as well as the strategies for improving natamycin production. Moreover, the future perspectives on natamycin research are discussed.

Evaluation of exploitive potential for higher bioactivity and lower residue risk enantiomer of chiral fungicide pydiflumetofen.

Pydiflumetofen, as a new succinate dehydrogenase inhibitor (SDHI) chiral fungicide, has been used in crop production because of its broad-spectrum and high-efficiency antifungal activity. However, little is known about pydiflumetofen at the chiral level. The stereoselective bioactivity and degradation of pydiflumetofen enantiomers were therefore investigated. Pydiflumetofen presented effective bioactivity against the eight tested phytopathogens, and its enantiomers showed significant differences in activity. The bioactivity of R-pydiflumetofen was 9.0-958.8 times higher than that of the S enantiomer. Treatment with R-pydiflumetofen increased the cell membrane permeability of Sclerotinia sclerotiorum and decreased exopolysaccharide and oxalic acid production more than treatment with S-pydiflumetofen. Furthermore, R-pydflumetofen exhibited better inhibitory activity against the succinate dehydrogenase enzyme of S. sclerotiorum than S-pydiflumetofen by 584-fold. According to homology modeling and molecular docking studies, the binding affinities of the R and S enantiomers were -7.0 and -5.3 kcal mol-1 , respectively. Additionally, the degradation half-lives of S- and R-pydiflumetofen in three vegetables (cucumber, eggplant, and cowpea) under field conditions were 2.56-3.12 days and 2.48-2.76 days, respectively, which reveals that R-pydiflumetofen degrades faster than S-pydiflumetofen. Based on the results obtained, R-pydiflumetofen not only exhibited a higher bactericidal activity, but also posed fewer residual risks in the environment. The mechanism of the stereoselective bioactivity was correlated with the stereoselective inhibition activity of the target enzyme and affected the cell membrane permeability and the production of exopolysaccharide and oxalic acid. This research could provide a foundation for the systematic evaluation of pydiflumetofen from an enantiomeric view. © 2021 Society of Chemical Industry.

Phytochemical analysis and antimicrobial activity of an endophytic Fusarium proliferatum (ACQR8), isolated from a folk medicinal plant Cissus quadrangularis L.

The endophytic fungi are an important source of bioactive natural products. This study includes evaluation of antimicrobial activity and phytochemical analysis of endophytic fungus ACQR8, recovered from the root tissues of a folk medicinal plant Cissus quadrangularis L., which was identified as Fusarium proliferatum by microscopic and molecular methods. The fungus showed broad spectrum antibacterial and antifungal activities against variety of important plant and human pathogens. To the best of our knowledge, this is the first study to record antifungal activity of any endophytic Fusarium sp. against phytopathogens Rhizoctonia solani, Fusarium oxysporum and the dermatophytes Trichophyton mentagrophyte and Microsporum gypseum. The minimum inhibitory concentration of the crude extract ranged from 40–120 µg/ml against pathogenic bacteria and 0.2–2.5 mg/ml against fungal pathogens. Besides, this study probably is also the first to document the phytochemical constituents of an endophytic Fusarium sp. Phytochemical testing and GC-MS (gas chromatography- mass spectrometry) analysis revealed the presence of fatty acids and its derivatives, phenolics, terpenoids and unsaturated alkenes in the crude extract which scientifically validates the highly promising antibacterial and antifungal activity exhibited by endophytic isolate ACQR8.

Design and synthesis of small molecular 2-aminobenzoxazoles as potential antifungal agents against phytopathogenic fungi.

In order to discover novel antifungal agents, three series of simple 2-aminobenzoxazole derivatives were designed, synthesized and evaluated for their antifungal activities against eight phytopathogenic fungi. The in vitro antifungal results showed that most of the target compounds exhibited excellent and broad-spectrum antifungal activities to all the tested fungi. Particularly, the six compounds 3a, 3b, 3c, 3e, 3m and 3v displayed the most potent antifungal activity, with EC50 value of 1.48–16.6 µg/mL, which were much superior to the positive control hymexazol. The in vivo study further confirmed that compounds 3a, 3c, 3e and 3m displayed good preventative effect against Botrytis cinerea at the concentration of 100 µg/mL. The structure–activity relationships research provides significant reference for the further structural optimization of 2-aminobenzoxazole as potential fungicides.Graphic abstractForty-four 2-aminobenzoxazole derivatives were designed and synthesized as agricultural antifungal agents, the in vitro and in vivo antifungal experiments showed that compounds 3a, 3b, 3c, 3e, 3m and 3v exhibited excellent and broad-spectrum antifungal activities compare with the commercial fungicide hymexazol. Supplementary InformationThe online version contains supplementary material available at 10.1007/s11030-021-10213-7.

Biocontrol potential and mode of action of entomopathogenic bacteria Xenorhabdus budapestensis C72 against Bipolaris maydis

Southern corn leaf blight (SCLB) caused by Bipolaris maydis is an important foliar disease of maize. In this study, a nematode-symbiotic bacterium Xenorhabdus budapestensis strain C72 was identified with remarkable inhibiting effect on mycelial growth and spore germination of B. maydis. The in vitro assay revealed that C72 cell-free culture media (CFCM) with thermostability exhibited broad-spectrum antifungal activities against other several important plant pathogenic fungi. The early colonization of B. maydis were significantly impaired by CFCM treatment under phytotron condition. This antagonism is likely to be the main contributor to the highly efficient plant protection of 40% (v/v) CFCM treatment against B. maydis, and the relative control effect reached to 59.15% and 77.96% in greenhouse and field experiments, which was comparable to the effect of fungicides. Moreover, we found that extracellular enzymes secreted by symbiotic bacterium may be one of the reasons for the antifungal potential of C72. Beside direct antagonistic effects provided by the bacterium, defense related genes were induced in maize after CFCM treatment. In summary, this study reported the first systematic evaluation of the effect of X. budapestensis C72 in controlling SCLB and exploration of its mode of action, then indicating that entomopathogenic bacteria have the potential to become a new and efficient biological control resource for plant fungal disease management.

Synthesis, Antifungal Activity, and 3D-QSAR Study of Novel Nopol-Derived 1,3,4-Thiadiazole-Thiourea Compounds.

A series of novel nopol derivatives bearing the 1,3,4-thiadiazole-thiourea moiety were designed and synthesized by multi-step reactions in search of potent natural product-based antifungal agents. Their structures were confirmed by FT-IR, NMR, ESI-MS, and elemental analysis. Antifungal activity of the target compounds was preliminarily evaluated by in vitro methods against Fusarium oxysporum f. sp. cucumerinum, Cercospora arachidicola, Physalospora piricola, Alternaria solani, Gibberella zeae, Rhizoeotnia solani, Bipolaris maydis, and Colleterichum orbicalare at 50 µg/mL. All the target compounds exhibited better antifungal activity against P. piricola, C. arachidicola, and A. solani. Compound 6j (R = m, p-Cl Ph) showed the best broad-spectrum antifungal activity against all the tested fungi. Compounds 6c (R = m-Me Ph), 6q (R = i-Pr), and 6i (R = p-Cl Ph) had inhibition rates of 86.1%, 86.1%, and 80.2%, respectively, against P. piricola, much better than that of the positive control chlorothalonil. Moreover, compounds 6h (R = m-Cl Ph) and 6n (R = o-CF3 Ph) held inhibition rates of 80.6% and 79.0% against C. arachidicola and G. zeae, respectively, much better than that of the commercial fungicide chlorothalonil. In order to design more effective antifungal compounds against A. solani, analysis of the three-dimensional quantitative structure–activity relationship (3D-QSAR) was carried out using the CoMFA method, and a reasonable and effective 3D-QSAR model (r2 = 0.992, q2 = 0.753) has been established. Furthermore, some intriguing structure–activity relationships were found and are discussed by theoretical calculation.