Antifungal Activity of Volatile Compounds Produced by an Edible Mushroom Hypsizygus marmoreus against Phytopathogenic Fungi

Volatile compounds with antifungal activity produced by edible mushrooms have potential as biological control agents to combat fungal diseases and reduce fungicide use in agriculture. Here we investigated the antifungal activity of volatile compounds produced by the edible mushroom Hypsizygus marmoreus (TUFC 11906) against eight phytopathogenic fungi. The results showed that volatile compounds from the mycelia and culture filtrates (CFs) of H. marmoreus had antifungal activity against some phytopathogenic fungi. Among them, the mycelial growth and conidial germination of Alternaria brassicicola were significantly inhibited by 60 and 100%, respectively. Moreover, the volatile compounds from CFs inhibited the lesion formation of A. brassicicola on detached cabbage leaves by 94%. The volatile compounds had higher antifungal activity against A. brassicicola than other fungi. With the removal of the volatile compounds from conidia of A. brassicicola, the conidia began to germinate, which indicates fungistatic activity of the compounds. The volatile compounds were isolated from the CFs of H. marmoreus, and the major volatile compound with antifungal activity was estimated to be 2‐methylpropanoic acid 2,2‐dimethyl‐1‐(2‐hydroxy‐1‐methylethyl)propyl ester. As the volatile compound produced by H. marmoreus is a product of an edible mushroom and has fungistatic activity against some phytopathogenic fungi, especially A. brassicicola, it may be possible to use the compounds as a novel safe agent for protecting crops in the field and during storage.     

2,6‐Dimethoxy‐1,4‐Benzoquinone Enhances Resistance Against the Rice Blast Fungus Magnaporthe oryzae

We investigated the effect of 2,6‐dimethoxy‐1,4‐benzoquinone (DMBQ) on induced resistance to Magnaporthe oryzae in rice. DMBQ concentrations greater than 50 μg/ml inhibited spore germination and appressorium formation in M. oryzae. When rice leaves pretreated with 10 μg/ml DMBQ, which did not show antifungal activity against spore germination and appressorium formation of M. oryzae, were inoculated with M. oryzae spores 5 days after DMBQ pretreatment, blast lesion formation was inhibited compared with control leaves pretreated with distilled water. In addition, infection‐inhibiting activity against M. oryzae was significantly enhanced in rice leaf sheaths pretreated with 10 μg/ml DMBQ. H₂O₂ generation was observed in rice leaves pretreated with DMBQ, and PAL, POX, CHS and PR10a were significantly expressed in these leaves. These results suggested that DMBQ can protect rice from blast disease caused by M. oryzae.     

Molecular Phylogeny,Diversity, and Bioprospecting of Endophytic Fungi Associated with wild Ethnomedicinal North American Plant Echinacea purpurea (Asteraceae)

The endophytic fungal community associated with the ethnomedicinal plant Echinacea purpurea was investigated as well as its potential for providing antifungal compounds against plant pathogenic fungi. A total of 233 endophytic fungal isolates were obtained and classified into 42 different taxa of 16 genera, of which Alternaria alternata, Colletotrichum dematium, and Stagonosporopsis sp. 2 are the most frequent colonizers. The extracts of 29 endophytic fungi displayed activities against important phytopathogenic fungi. Eight antifungal extracts were selected for chemical analysis. Forty fatty acids were identified by gas chromatography‐flame‐ionization detection (GC‐FID) analysis. The compounds (–)‐5‐methylmellein and (–)‐(3R)‐8‐hydroxy‐6‐methoxy‐3,5‐dimethyl‐3,4‐dihydroisocoumarin were isolated from Biscogniauxia mediterraneaEPU38CA crude extract. (–)‐5‐Methylmellein showed weak activity against Phomopsis obscurans, P. viticola, and Fusarium oxysporum, and caused growth stimulation of C. fragariae, C. acutatum, C. gloeosporioides, and Botrytis cinerea. (–)‐(3R)‐8‐Hydroxy‐6‐methoxy‐3,5‐dimethyl‐3,4‐dihydroisocoumarin appeared slightly more active in the microtiter environment than 5‐methylmellein. Our results indicate that E. purpurea lives symbiotically with different endophytic fungi, which are able to produce bioactive fatty acids and aromatic compounds active against important phytopathogenic fungi. The detection of the different fatty acids and aromatic compounds produced by the endophytic community associated with wild E. purpurea suggests that it may have intrinsic mutualistic resistance against phytopathogen attacks in its natural environment.     

Effect of Cultivation Time on Production of Antifungal Metabolite(s) by Streptomyces hygroscopicus in Laboratory‐Scale Bioreactor

Biological control agents offer one of the best alternatives to reduce the use of pesticides . Fungi from the genera Alternaria, Colletotrichum and Fusarium are listed among the most important storage pathogens of apple fruits. During storage, transport and marketing, pathogenic fungi can cause significant losses of apple fruits. This investigation studied the potential of Streptomyces hygroscopicus as a biocontrol agent against pathogenic fungi obtained from apple fruit samples expressing rot symptoms. Production of antifungal metabolites by S. hygroscopicus was carried out in 3‐l bench‐scale bioreactor (Biostat^® Aplus, Sartorius AG, Germany) during 7 days. Fermentation was carried out at 27°C with aeration rate of 0.5 vvm and agitation rate of 200 rpm. The aim was to analyse bioprocess parameters of batch biofungicide production in medium containing glucose as a carbon source and to examine at which stage of bioprocess production of antifungal metabolite(s) against six phytopathogenic fungi occurs. In vitro antifungal activity of the produced metabolites against six fungi of the genera Colletotrichum, Fusarium and Alternaria grown on potato dextrose agar were determined every 24 h using wells technique. Antifungal activity of cell‐free culture filtrate and filtrate treated with high temperature were tested. The filtrate treated with high temperature did not show any antifungal activity suggesting that active components are thermo unstable. Stationary phase of growth occurred between the third and fourth day of cultivation when production of secondary metabolites begins. Obtained results showed that maximal antifungal activity is achieved on fifth and sixth day of S. hygroscopicus cultivation under defined conditions (inhibition zone diameter higher than 30 mm for all test fungi).     

Heterologous expression and periplasmic secretion of an antifungal Bacillus amyloliquefaciensBLB369 endo‐β‐1,3‐1,4‐glucanase in Escherichia coli

The endo‐β‐1,3‐1,4‐glucanases are glycoside hydrolases involved in the enzymatic depolymerization of 1,3‐1,4 β‐glucans and showed an antifungal activity against some fungi. Bacillus amyloliquefaciensBLB369 has a high antagonistic activity against phytopathogenic fungi. Its glu369 full‐coding sequence of the endo‐β‐1,3‐1,4‐glucanase gene (732 bp) was sequenced, cloned and successfully expressed in Escherichia coli Top10. The encoded protein (243 amino acids) has a calculated molecular mass of 27.3 kDa. To simplify the purification procedure, the glu369 coding sequence was cloned into the vector pKJD4. The produced OmpA‐His‐Glu369 harboured OmpA signal sequence for E. coli periplasmic localization and followed by a 6His residues for its purification. The purified His‐tagged proteins revealed two bands on SDS‐PAGE analysis with molecular masses of about 30.5 (His‐Glu369) and 32.5 kDa (OmpA‐His‐Glu369). They had the ability to inhibit the growth of phytopathogenic fungus Alternaria alternata. These favourable properties make the endo‐β‐1,3‐1,4‐glucanase a good candidate for biotechnological applications.     

The Antimicrobial Peptide Thanatin Reduces Fungal Infections in Arabidopsis

We explored the antifungal activity of thanatin, a 21 amino acid synthetic peptide from the hemipteran spined soldier bug Podisus maculiventris, against the mycotoxin‐producing plant pathogenic ascomycete Fusarium graminearum. In vitro germination assays showed complete inhibition of macroconidia germination and mycelia growth by >10 μm thanatin. Moreover, detached leaves of thanatin‐expressing Arabidopsis thaliana plants displayed enhanced resistance towards colonization with F. graminearum. Consistent with this, the plants showed also enhanced resistance of detached leaves to colonization with Botrytis cinerea. The results demonstrate a potential of thanatin for use in plant protection.     

Natural Product‐Based Fungicides Discovery: Design,Synthesis and Antifungal Activities of Some Sarisan Analogs Containing 1,3,4‐Oxadiazole Moieties

A series of sarisan analogs containing 1,3,4‐oxadiazole moieties were synthesized by iodine‐mediated oxidative cyclization and screened in vitro for their antifungal activities at 50 μg/mL against five phytopathogenic fungi such as Valsa mali, Curvularia lunata, Alternaria alternate, Fusarium solani and Fusarium graminearum. 1,3,4‐Oxadiazole derivatives 7e , 7p , 7r , 7t and 7u exhibited potent and a broad spectrum of antifungal activities against at least three phytopathogenic fungi at the concentration of 50 μg/mL. Especially, compound 7r displayed more potent antifungal activities against five phytopathogenic fungi than the positive control hymexazol. The EC₅₀ of 7r against V. mali, C. lunata and A. alternate were 12.6, 14.5 and 17.0 μg/mL, respectively. Additionally, some interesting results of structure‐activity relationships (SARs) were also observed.     

Antifungal properties of durancins isolated from Enterococcus durans A5‐11 and of its synthetic fragments

The aim of this work was to study the antifungal properties of durancins isolated from Enterococcus durans A5‐11 and of their chemically synthesized fragments. Enterococcus durans A5‐11 is a lactic acid bacteria strain isolated from traditional Mongolian airag cheese. This strain inhibits the growth of several fungi including Fusarium culmorum, Penicillium roqueforti and Debaryomyces hansenii. It produces two bacteriocins: durancin A5‐11a and durancin A5‐11b, which have similar antimicrobial properties. The whole durancins A5‐11a and A5‐11b, as well as their N‐ and C‐terminal fragments were synthesized, and their antifungal properties were studied. C‐terminal fragments of both durancins showed stronger antifungal activities than other tested peptides. Treatment of D. hansenii LMSA2.11.003 strain with 2 mmol l^?1 of the synthetic peptides led to the loss of the membrane integrity and to several changes in the ultra‐structure of the yeast cells. Chemically synthesized durancins and their synthetic fragments showed different antimicrobial properties from each other. N‐terminal peptides show activities against both bacterial and fungal strains tested. C‐terminal peptides have specific activities against tested fungal strain and do not show antibacterial activity. However, the C‐terminal fragment enhances the activity of the N‐terminal fragment in the whole bacteriocins against bacteria.

Significance and Impact of the Study

Antifungal properties of durancins isolated from Enterococcus durans A5‐11 and of their chemically synthesized fragments were determined. Treatment of D. hansenii LMSA2.11.003 strain with 2 mmol l^?1 of the synthetic peptides led to the loss of the membrane integrity and to several changes in the ultra‐structure of the yeast cells. This work contributes to improve understanding of molecular causes of antimicrobial activities of bacteriocins and their fragments. It may be proposed that the studied peptides affect all the yeast cellular and intramembranes including cytoplasmatic reticulum and nuclear and vacuolar membranes.     

Design,Synthesis, and Antifungal Activities of Novel 1,2,4‐Triazole Schiff Base Derivatives

With the aim to find new compounds with high antifungal activity, 21 4‐amino‐5‐substituted‐1,2,4‐triazole Schiff bases ( 2a  –  2g , 3a  –  3g , and 4a  –  4g ) were designed and synthesized. Their antifungal activities against Pythium solani, Gibberlla nicotiancola, Fusarium oxysporium f. sp. niveum, Gibberlla saubinetii, Alternaria iycopersici, Phytophthora capsici, Physalospora piricola, Cercospora arachidicola hori, and Fusarium oxysporium f. sp. cucumber were tested, parts of the compounds exhibited excellent antifungal activity. This research provides useful information for further study of antifungal agents.     

UHPLC‐HRMS/MS Based Profiling of Algerian Lichens and Their Antimicrobial Activities

Lichens are complex symbiotic organisms able to produce a vast array of compounds. The Algerian lichen diversity has only prompted little interest even given the 1085 species listed. Herein, the chemodiversity of four Algerian lichens including Cladonia rangiformis, Ramalina farinaceae, R. fastigiata, and Roccella phycopsis was investigated. A dereplication strategy, using ultra high performance liquid chromatography‐high resolution‐electrospray ionization‐mass spectrometry (UHPLC‐HRMS/MS), was carried out for a comprehensive characterization of their substances including phenolics, depsides, depsidones, depsones, dibenzofurans, and aliphatic acids. Some known compounds were identified for the first time in some species. Additionally, the lichenic extracts were evaluated for their antifungal and antimicrobial activities on human pathogenic strains (Candida albicans, C. glabrata, Aspergillus fumigatus, Staphylococcus aureus, and Escherichia coli). Cyclohexane extracts were found particularly active against human pathogenic fungi with MIC₈₀ values ranging from 8 to 62.5 μg/mL, without cytotoxicity. This study highlights the therapeutic and prophylactic potential of lichenic extracts as antibacterial and antifungal agents.     

Characterisation of plant growth‐promoting rhizobacteria from rhizosphere soil of heat‐stressed and unstressed wheat and their use as bio‐inoculant

• High temperature induces several proteins in plants that enhance tolerance to high temperature shock. The fate of proteins synthesised in microbial cells or secreted into culture media by interacting microbes has not been fully elucidated. The present investigation aimed to characterise plant growth‐promoting rhizobacteria (PGPR) isolated from the rhizosphere of wheat genotypes (differing in tolerance to high temperature stress) and evaluate their performance as bioinoculant for use in wheat.
• Four bacterial strains, viz. Pseudomonas brassicacearum, Bacillus thuringiensis, Bacillus cereus strain W6 and Bacillus subtilis, were isolated from the rhizosphere of heat‐stressed and unstressed wheat genotypes. The wheat genotypes were exposed to high temperature stress at 45 °C for 10 days (3 h daily) at pre‐anthesis phase. Isolates were identified on the basis of morphology and biochemical characteristics, 16S rRNA gene sequencing and whole cell protein profiles. Results were further complemented by size exclusion chromatography (SEC) with fast protein liquid chromatography (FPLC) and SDS PAGE of 80% ammonium sulphate precipitates of the cell‐free supernatants.
• Isolates were positive for catalase, oxidases and antimicrobial activity . P. brassicacearum from the rhizosphere of the heat‐tolerant genotype was more efficient in phosphate solubilisation, bacteriocin production, antifungal and antibacterial activity against Helminthosporium sativum, Fusarium moniliforme and Klebsiella pneumonia, respectively. The inoculated seedlings had significantly higher root and shoot fresh weight, enhanced activity of antioxidant enzymes, proline and protein content. Total profiling of the culture with SDS‐PAGE indicated expression of new protein bands in 95 kDa in P. brassicacearum.
• Temperature‐induced changes in PGPR isolates are similar to those in the host plant. P. brassicacearum may be a good candidate for use in biofertiliser production for plants exposed to high temperature stress.

     

Isolation and characterization of a proteinaceous antifungal compound from Lactobacillus plantarum YML007 and its application as a food preservative

Korean kimchi is known for its myriad of lactic acid bacteria (LAB) with diverse bioactive compounds. This study was undertaken to isolate an efficient antifungal LAB strain among the isolated kimchi LABs. One thousand and four hundred LABs isolated from different kimchi samples were initially screened against Aspergillus niger. The strain exhibiting the highest antifungal activity was identified as Lactobacillus plantarum YML007 by 16S rRNA sequencing and biochemical assays using API 50 CHL kit. Lact. plantarum YML007 was further screened against Aspergillus oryzae, Aspergillus flavus, Fusarium oxysporum and other pathogenic bacteria. The morphological changes during the inhibition were assessed by scanning electron microscopy. Preliminary studies on the antifungal compound demonstrated its proteinaceous nature with a molecular weight of 1256·617 Da, analysed by matrix‐assisted laser desorption ionization‐time‐of‐flight mass spectrometry (MALDI‐TOF). The biopreservative activity of Lact. plantarum YML007 was evaluated using dried soybeans. Spores of A. niger were observed in the negative control after 15 days of incubation. However, fungal growth was not observed in the soybeans treated with fivefold concentrated cell‐free supernatant of Lact. plantarum YML007. The broad activity of Lact. plantarum YML007 against various food spoilage moulds and bacteria suggests its scope as a food preservative.

Significance and Impact of the Study

After screening 1400 kimchi bacterial isolates, strain Lactobacillus plantarum YML007 was selected with strong antifungal activity against various foodborne pathogens. From the preliminary studies, it was found that the bioactive compound is a low molecular weight novel protein of 1256·617 Da. Biopreservative potential of Lact. plantarum YML007 was demonstrated on soybean grains, and the results point out YML007 as a potent biopreservative having broad antimicrobial activity against various foodborne pathogens.     

Antimycotic activities of Cinnamon-derived compounds against <Emphasis Type="Italic">Rhizoctonia solani</Emphasis> in vitro

In this study, the effects of medicinal plant extracts on the development of mycelium in the following phytopathogenic fungi were evaluated: Phytophthora capsici, Rhizoctonia solani, Fusarium solani, Colletotrichum gloeosprorioides, and Botrytis cinera. Of the 26 medicinal plants tested, six plant extracts showed antifungal activity against phytopathogenic fungi. The highest antifungal activity was exerted against R. solani by the n-hexane fraction of a Cinnamon (Cinnamomum cassia Blume) solvent extract. Therefore, the antifungal compound fractions I and II were purified from the n-hexane fraction by TLC on silica gel plates. When treated with solutions containing compound fractions I or II at a concentration of 2%, the mycelia growth rate of R. solani was reduced to 0.19 and 0.18, respectively. In addition, microscopic observation of the hyphal morphology of R. solani following treatment with compound fraction I revealed the presence of severely damaged hyphae. Specifically, the hyphal tips became swollen, collapsed or were completely destroyed in response to treatment with solution containing compound fraction I at concentration of 1%.     

Identification of a Vitis vinifera endo‐β‐1,3‐glucanase with antimicrobial activity against Plasmopara viticola

Inducible plant defences against pathogens are stimulated by infections and comprise several classes of pathogenesis‐related (PR) proteins. Endo‐β‐1,3‐glucanases (EGases) belong to the PR‐2 class and their expression is induced by many pathogenic fungi and oomycetes, suggesting that EGases play a role in the hydrolysis of pathogen cell walls. However, reports of a direct effect of EGases on cell walls of plant pathogens are scarce. Here, we characterized three EGases from Vitis vinifera whose expression is induced during infection by Plasmopara viticola, the causal agent of downy mildew. Recombinant proteins were expressed in Escherichia coli. The enzymatic characteristics of these three enzymes were measured in vitro and in planta. A functional assay performed in vitro on germinated P. viticola spores revealed a strong anti‐P. viticola activity for EGase3, which strikingly was that with the lowest in vitro catalytic efficiency. To our knowledge, this work shows, for the first time, the direct effect against downy mildew of EGases of the PR‐2 family from Vitis.     

Antifungal Monoterpene Derivatives from the Plant Endophytic Fungus Pestalotiopsis foedan

A new monoterpene lactone, (1R,4R,5R,8S)‐8‐hydroxy‐4,8‐dimethyl‐2‐oxabicyclo[3.3.1]nonan‐3‐one ( 1 ), along with one related known compound, (2R)‐2‐[(1R)‐4‐methylcyclohex‐3‐en‐1‐yl]propanoic acid ( 2 ), were isolated from the liquid culture of the plant endophytic fungus Pestalotiopsis foedan obtained from the branch of Bruguiera sexangula. The structure and absolute configuration of 1 were determined on the basis of extensive analysis of NMR spectra combined with computational methods via calculation of the optical rotation (OR) and ¹³C‐NMR. Both compounds exhibited strong antifungal activities against Botrytis cinerea and Phytophthora nicotianae with MIC values of 3.1 and 6.3 μg/ml, respectively, which are comparable to those of the known antifungal drug ketoconazole. Compound 2 also showed modest antifungal activity against Candida albicans with a MIC value of 50 μg/ml.     

Dissecting virulence function from recognition: cell death suppression in Nicotiana benthamiana by XopQ/HopQ1‐family effectors relies on EDS1‐dependent immunity

Many Gram‐negative plant pathogenic bacteria express effector proteins of the XopQ/HopQ1 family which are translocated into plant cells via the type III secretion system during infection. In Nicotiana benthamiana, recognition of XopQ/HopQ1 proteins induces an effector‐triggered immunity (ETI) reaction which is not associated with strong cell death but renders plants immune against Pseudomonas syringae and Xanthomonas campestris pv. vesicatoria strains. Additionally, XopQ suppresses cell death in N. benthamiana when transiently co‐expressed with cell death inducers. Here, we show that representative XopQ/HopQ1 proteins are recognized similarly, likely by a single resistance protein of the TIR‐NB‐LRR class. Extensive analysis of XopQ derivatives indicates the recognition of structural features. We performed Agrobacterium‐mediated protein expression experiments in wild‐type and EDS1‐deficient (eds1) N. benthamiana leaves, not recognizing XopQ/HopQ1. XopQ recognition limits multiplication of Agrobacterium and attenuates levels of transiently expressed proteins. Remarkably, XopQ fails to suppress cell death reactions induced by different effectors in eds1 plants. We conclude that XopQ‐mediated cell death suppression in N. benthamiana is due to the attenuation of Agrobacterium‐mediated protein expression rather than the cause of the genuine XopQ virulence activity. Thus, our study expands our understanding of XopQ recognition and function, and also challenges the commonly used co‐expression assays for elucidation of in planta effector activities, at least under conditions of ETI induction.     

2H‐Pyran‐2‐one and 2H‐Furan‐2‐one Derivatives from the Plant Endophytic Fungus Pestalotiopsis fici

Two new α‐pyrones (=2H‐pyran‐2‐ones), ficipyrones A and B ( 1 and 2 , resp.), and two new α‐furanones (=2H‐furan‐2‐ones), ficifuranones A and B ( 3 and 4 , resp.), together with three known metabolites, antibiotic F 0368 ( 5 ), hydroxyseiridin ( 6 ), and hydroxyisoseiridin ( 7 ), were isolated from solid cultures of the plant endophytic fungus Pestalotiopsis fici. Their structures were elucidated primarily by NMR spectroscopy, and the absolute configuration of 1 was deduced from the circular‐dichroism (CD) data. Compound 1 showed antifungal activity against the plant pathogen Gibberella zeae (CGMCC 3.2873) with an IC₅₀ value of 15.9 μM .     

2‐(Undecyloxy)‐ethanol is a major component of the male‐produced aggregation pheromone of Monochamus sutor

The small white‐marmorated longicorn beetle, Monochamus sutor (L.) (Coleoptera: Cerambycidae), is widely distributed throughout Europe and Asia. It is a potential vector of the pine wood nematode, Bursaphelenchus xylophilus (Steiner et Buhrer) Nickle, the causal agent of the devastating pine wilt disease. Volatiles were collected from both male and female beetles after maturation feeding. In analyses of these collections using gas chromatography (GC) coupled to mass spectrometry, a single male‐specific compound was detected and identified as 2‐(undecyloxy)‐ethanol. In analyses by GC coupled to electroantennography the only consistent responses from both female and male antennae were to this compound. Trapping tests were carried out in Spain, Sweden, and China. 2‐(Undecyloxy)‐ethanol was attractive to both male and female M. sutor beetles. A blend of the bark beetle pheromones ipsenol, ipsdienol, and 2‐methyl‐3‐buten‐2‐ol was also attractive to both sexes in Spain and Sweden, and further increased the attractiveness of the 2‐(undecyloxy)‐ethanol. The host plant volatiles α‐pinene, 3‐carene, and ethanol were weakly attractive, if at all, in all three countries and did not significantly increase the attractiveness of the blend of 2‐(undecyloxy)‐ethanol and bark beetle pheromones. 2‐(Undecyloxy)‐ethanol is thus proposed to be the major, if not only, component of the male‐produced aggregation pheromone of M. sutor, and its role is discussed. This compound has been reported as a pheromone of several other Monochamus species and is another example of the parsimony that seems to exist among the pheromones of many of the Cerambycidae. Traps baited with 2‐(undecyloxy)‐ethanol and bark beetle pheromones should be useful for monitoring and control of pine wilt disease, should M. sutor be proven to be a vector of the nematode.     

Synthesis and Antifungal Activity of 2‐Hydroxy‐4,5‐methylenedioxyaryl Ketones as Analogues of Kakuol

In a study aiming to determine the structural elements essential to the antifungal activity of kakuol, we synthesized a series of 2‐hydroxy‐4,5‐methylenedioxyaryl ketones, and we assayed their in vitro antifungal activity. The most sensitive target organisms to the action of these class of compounds were Phytophthora infestans, Phytium ultimum, Cercospora beticola, Cladosporium cucumerinum, and Rhizoctonia solani. Most of the analogs showed a remarkable in vitro activity, and some of them appeared significantly more effective than the natural product. The biological activity was mainly affected by introducing structural modification on the carbonyl moiety of the natural‐product molecule. In particular, compound 5a , bearing a C?C bond conjugated to the C?O group, was found active with a MIC value of 10 μg ml^?1 against Cladosporium cucumerinum. The results suggest that 2‐hydroxy‐4,5‐methylenedioxyaryl ketones can be considered promising candidates in the development of new antifungal compounds.     

Bacterial iturins mediate biocontrol activity of Bacillus sp. against postharvest pear fruit‐rotting fungi

A potential antagonist, Bacillus sp. LYLB4 isolated from pear fruits, was tested for its antifungal activity against postharvest pear pathogens. LYLB4 had a remarkable antifungal effect on Botryosphaeria dothidea. Although it showed a weak inhibition effect on the growth of Rhizopus stolonifer on potato dextrose agar (PDA) plates, LYLB4 almost completely destroyed R. stolonifer during direct contact in potato dextrose broth (PDB). LYLB4 treatment was able to significantly reduce disease incidence (by 68.9% and 100%, respectively) and lesion diameter (by 68.7% and 100%, respectively) of ring rot caused by B. dothidea and soft rot caused by R. stolonifer in pears. LYLB4 also suppressed several other phytopathogens in vitro, suggesting a broad‐spectrum antagonistic activity against fungal pathogens. 16S rRNA and gyrA sequence analysis indicated that LYLB4 is closely related to B. velezensis. Genome mining indicated that LYLB4 had 11 secondary metabolites encoding clusters, but that the surfactin and fengycin gene clusters may not be functional because of a large deletion. Matrix‐assisted laser desorption ionization‐time of flight mass spectra (MALDI‐TOF‐MS) demonstrated that iturins were the major lipopeptides, and that C₁₆/C₁₇ Bacillomycin D synthesis was stimulated when LYLB4 was co‐cultured with B. dothidea compared to the control. Overall, these results demonstrate that the main biocontrol mechanism adopted by LYLB4 could be through the production of toxic metabolites and direct contact with pathogens.