Alternative control of grape rots by essential oils of two Eucalyptus species

BACKGROUND

Essential oils (EOs) are volatile natural compounds produced by plant secondary metabolism, and some of them exhibit antimicrobial activity. The objective of the present study was to determine the chemical composition the EOs of Eucalyptus staigeriana and Eucalyptus globulus, and their effect in vitro and in vivo against Botrytis cinerea and Colletotrichum acutatum, the most important fungal rot diseases of grapes. Moreover, grapes collected from field experiments were used to evaluate the impact of the alternative control on the alcoholic fermentation and wine composition.

RESULTS

The major compound of E. staigeriana EO were citral 30.91% (19.74% geranial, 11.17% neral), 1.8-cineole (24.59%) and limonene (19.47%), while 1.8-cineole represented 68.26% of E. globulus EO. The two EOs showed in vitro antifungal activity against both pathogens. Eucalyptus staigeriana EO exhibited the highest activity inhibiting mycelial growth (MG) and conidial germination at 0.5 μL mL^-1 . Moreover, this EO was able to reduce the incidence and severity of grey rot caused by B. cinerea and the severity of ripe rot caused by C. acutatum The alternative control did not significantly influence alcoholic fermentation, the physicochemical characteristics, and the volatile composition of wines.

CONCLUSION

These results are promising and indicate that E. staigeriana EO might be further investigated as a natural alternative for the control of fungal rots on wine grapes. © 2019 Society of Chemical Industry.

Late-Stage C-H Functionalization of Nicotinamides for the Expedient Discovery of Novel Antifungal Leads

Encouraged by the successful flexible modifications of the succinate dehydrogenase inhibitors, antifungal activity guided by the divergent synthesis of nicotinamides of the prevalidated pharmacophore 2-(2-oxazolinyl)aniline was conducted. The work highlighted the first utilization of the late-stage C-H functionalization assisted by the innate pharmacophore for the discovery of promising agrochemicals. New synthetic methodology and antifungal exploration of alkoxylated nicotinamides were accomplished. Fifty-five functionalized nicotinamides of 7 types were rationally designed and efficiently prepared through C-H functionalization, which facilitated the acquirement of four N-para aryloxylated nicotinamides (E3, E13, E19, and E22) as potential antifungal candidates against Botrytis cinerea, with the EC₅₀ values lower than 5 mg/L. In vivo/vitro biotest, molecular docking, and structural analysis reconfirmed the novelty and practical potential of the antifungal candidates E3 and E19. This operationally simple platform will provide various "polar parts" and offer intriguing opportunities for the optimization of the carboxamide fungicides and structure-related pharmaceuticals.

The Arabidopsis Pleiotropic Drug Resistance Transporters PEN3 and PDR12 Mediate Camalexin Secretion for Resistance to Botrytis cinerea

Plant defense often depends on the synthesis and targeted delivery of antimicrobial metabolites at pathogen contact sites. The pleiotropic drug resistance (PDR) transporter PENETRATION3 (PEN3)/PDR8 in Arabidopsis (Arabidopsis thaliana) has been implicated in resistance to a variety of fungal pathogens. However, the antimicrobial metabolite(s) transported by PEN3 for extracellular defense remains unidentified. Here, we report that PEN3 functions redundantly with another PDR transporter (PDR12) to mediate the secretion of camalexin, the major phytoalexin in Arabidopsis. Consistent with this, the pen3 pdr12 double mutants exhibit dramatically enhanced susceptibility to the necrotrophic fungus Botrytis cinerea as well as severe hypersensitivity to exogenous camalexin. PEN3 and PDR12 are transcriptionally activated upon B. cinerea infection, and their expression is regulated by the mitogen-activated protein kinase 3 (MPK3) and MPK6, and their downstream WRKY33 transcription factor. Further genetic analysis indicated that PEN3 and PDR12 contribute to B. cinerea resistance through exporting not only camalexin but also other unidentified metabolite(s) derived from Trp metabolism, suggesting that PEN3 and PDR12 have multiple functions in Arabidopsis immunity via transport of distinct Trp metabolic products.

Stimulatory Effects of Sublethal Doses of Carbendazim on the Virulence and Sclerotial Production of Botrytis cinerea

Stimulatory effects of low doses of fungicides on the virulence of phytopathogens have profound implications for applications of fungicides. The present study demonstrated that carbendazim sprayed at 0.001 to 0.03 μg/ml had stimulatory effects on the virulence of mycelia of Botrytis cinerea, and the maximum percent stimulations were 15.5 and 21.4% for isolates HB459 and HB536, respectively. Potato dextrose agar (PDA) amended with carbendazim at 0.01, 0.02, and 0.05 μg/ml inhibited mycelial growth of isolate HB536 by 0.8, 10.0, and 30.6%, respectively. However, after the inhibited mycelia were inoculated on cucumber leaves, virulence increased by 10.1, 12.9, and 10.8%, respectively. With respect to sclerotial production, carbendazim at 0.005 and 0.02 μg/ml in PDA significantly (P < 0.05) increased, while at 0.1 μg/ml significantly (P < 0.05) reduced the sclerotial number and weight of both isolates compared with nontreated controls. Conidia germination percentages slightly yet statistically significantly (P < 0.05) increased after being inoculated on PDA amended with carbendazim at 0.001 and 0.005 μg/ml. Carbendazim at 0.001∼0.02 μg/ml, either sprayed on cucumber leaves or cosuspended with conidia, exerted significantly (P < 0.05) stimulatory effects on the virulence of B. cinerea conidia. Mechanism studies showed that sublethal doses of carbendazim did not increase the expression levels of pathogenicity-related pectin methylesterase gene Bcpme1, endopolygalacturonase gene Bcpg2, cutinase gene CutA, xylanase gene Xyn11A, or NADPH oxidase gene BcnoxA.

Unveiling the Mechanisms for the Plant Volatile Organic Compound Linalool To Control Gray Mold on Strawberry Fruits

Fungal infections significantly alter the emissions of volatile organic compounds (VOCs) by plants, but the mechanisms for VOCs affecting fungal infections of plants remain largely unknown. Here, we found that infection by Botrytis cinerea upregulated linalool production by strawberries and fumigation with linalool was able to inhibit the infection of fruits by the fungus. Linalool treatment downregulated the expression of rate-limiting enzymes in the ergosterol biosynthesis pathway, and this reduced the ergosterol content in the fungi cell membrane and impaired membrane integrity. Linalool treatment also caused damage to mitochondrial membranes by collapsing mitochondrial membrane potential and also downregulated genes involved in adenosine triphosphate (ATP) production, resulting in a significant decrease in the ATP content. Linalool treatment increased the levels of reactive oxygen species (ROS), in response to which the treated fungal cells produced more of the ROS scavenger pyruvate. RNA-Seq and proteomic analysis data showed that linalool treatment slowed the rates of transcription and translation.

Synergistic Effect of Combined Application of a New Fungicide Fluopimomide with a Biocontrol Agent Bacillus methylotrophicus TA-1 for Management of Gray Mold in Tomato

Gray mold caused by Botrytis cinerea can be a severe disease of tomato infecting leaves and fruits of tomato plants. Chemical control is currently the most effective and reliable method; however, application of fungicides has many drawbacks. The combination of biological control agents with newly developed fungicides may be a practicable method to control B. cinerea. Fluopimomide is a newly developed fungicide with a novel mode of action. Bacillus methylotrophicus TA-1, isolated from rhizosphere soil of tomato, is a bacterial strain with a broad spectrum of antimicrobial activities. Little information is currently available about the effect of fluopimomide and its integrated effect on B. cinerea. Therefore, laboratory, pot, and field experiments were carried out to determine the effects of fluopimomide alone and in combination with B. methylotrophicus TA-1 against gray mold on tomato. The in vitro growth of B. methylotrophicus TA-1 was unaffected by 100 mg liter^-1 fluopimomide. Inhibition of B. cinerea mycelial growth was significantly increased under combined treatment of fluopimomide and B. methylotrophicus TA-1. In greenhouse experiments, efficacy against gray mold was significantly greater by an integration of fluopimomide and B. methylotrophicus TA-1 than by either alone; control efficacy of fluopimomide at 50 and 100 g ha^-1 in combination with B. methylotrophicus TA-1 at 10⁸ colony-forming units (cfu) ml^-1 reached 70.16 and 69.32%, respectively, compared with the untreated control. In both field trials during 2017 and 2018, control efficacy was significantly higher for the combination of fluopimomide at 50 and 100 g ha^-1 in combination with B. methylotrophicus TA-1 than for either treatment alone. The results from this study indicated that integration of the new fungicide fluopimomide with the biocontrol agent B. methylotrophicus TA-1 synergistically increased control efficacy of the fungicide against gray mold of tomato.

Effects of SHAM on the Sensitivity of Sclerotinia sclerotiorum and Botrytis cinerea to QoI Fungicides

It is a common practice to add salicylhydroxamic acid (SHAM) into artificial medium in the in vitro sensitivity assay of fungal phytopathogens to the quinone outside inhibitor (QoI) fungicides. The rationale for adding SHAM is to inhibit fungal alternative oxidase, which is presumed to be inhibited by secondary metabolites of plants. Therefore, the ideal characteristics of SHAM should be almost nontoxic to phytopathogens and have no significant effect on control efficacy of fungicides. However, this study showed that the average effective concentration for 50% inhibition (EC₅₀) of mycelial growth values of SHAM were 97.5 and 401.4 μg/ml for Sclerotinia sclerotiorum and Botrytis cinerea, respectively. EC₅₀ values of the three QoI fungicides azoxystrobin, kresoxim-methyl, and trifloxystrobin in the presence of SHAM at 20 and 80 μg/ml for S. sclerotiorum and B. cinerea, respectively, declined by 52.7 to 78.1% compared with those without SHAM. For the dicarboximide fungicide dimethachlone, the average EC₅₀ values in the presence of SHAM declined by 18.2% (P = 0.008) for S. sclerotiorum and 35.9% (P = 0.012) for B. cinerea. Pot experiments showed that SHAM increased control efficacy of the three QoI fungicides against the two pathogens by 43 to 83%. For dimethachlone, SHAM increased control efficacy by 134% for S. sclerotiorum and 86% for B. cinerea. Biochemical studies showed that SHAM significantly inhibited peroxidase activity (P = 0.024) of B. cinerea and esterase activity (P = 0.015) of S. sclerotiorum. The strong inhibitions of SHAM per se on mycelial growth of B. cinerea and S. sclerotiorum and significant influences on the sensitivity of the two pathogens to both the QoI fungicides and dimethachlone as well as inhibitions on peroxidase and esterase indicate that SHAM should not be added in the in vitro assay of sensitivity to the QoI fungicides.

Synthesis, Fungicidal Activity and SAR of 2-Thiazolamide/Pyrazolamide-Cyclohexylsulfonamides against Botrytis cinerea

In order to explore more efficient sulfonamides against Botrytis cinereal, 36 novel cyclohexylsulfonamides were synthesized by N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDCI) and 1-hydroxybenzotriazole (HOBt) condensation reaction using chesulfamide as a lead compound, introducing thiazole and pyrazole active groups. Their structures were characterized by ¹H-NMR, ¹³C-NMR, mass spectrum (MS), and elemental analysis. Compound III -31 was further confirmed by X-ray single crystal diffraction. The in vitro and in vivo fungicidal activities against B. cinerea were evaluated by three bioassay methods. The results of mycelial growth demonstrated that median effective concentration (EC₅₀) values of nine compounds were close to boscalid (EC₅₀ = 1.72 µg/mL) and procymidone (EC₅₀ = 1.79 µg/mL) against B. cinerea (KZ-9). In the spore germination experiment, it was found that compounds III-19 and III-31 inhibited germination 93.89 and 98.00%, respectively; at 10 µg/mL, they approached boscalid (95.97%). In the tomato pot experiment, the control effects of two compounds (III-21 and III-27) were 89.80 and 87.90%, respectively, at 200 µg/mL which were significantly higher than boscalid (81.99%). The structure–activity relationship (SAR) was also discussed, which provided a valuable idea for developing new fungicides.

Curcumin Induces Oxidative Stress in Botrytis cinerea, Resulting in a Reduction in Gray Mold Decay in Kiwifruit

Curcumin exhibits efficient antimicrobial activity; nevertheless, its effect on the postharvest decay of fruit has not been examined. Here, effects of curcumin on the fruit gray mold of kiwifruit infected by Botrytis cinerea were analyzed. Results demonstrated that curcumin induced reactive oxygen species (ROS) production and triggered apoptosis in B. cinerea hyphae. Use of N-acetylcysteine, a ROS scavenger, partially ameliorated the inhibition of curcumin on B. cinerea. The NADPH oxidase inhibitor, diphenyleneiodonium chlorine, abrogated the ROS production induced by curcumin, suggesting that curcumin induces oxidative stress in B. cinerea via a NADPH-oxidase-dependent mechanism. Disease severity of gray mold in curcumin-treated kiwifruit was significantly reduced. The malondialdehyde content decreased while the antioxidant enzyme activity increased in kiwifruit with the application of increasing concentrations of curcumin. Collectively, these results indicate that curcumin can be used to control gray mold and elevate antioxidant activity in kiwifruit.

Synthesis and In Vitro and In Vivo Biological Activity Evaluation and Quantitative Proteome Profiling of Oxadiazoles Bearing Flexible Heterocyclic Patterns

A novel series of simple 1,3,4-oxadiazoles that bear flexible heterocyclic patterns was prepared, and their biological activities in plant pathogenic bacteria, fungi, oomycetes, and Meloidogyne incognita in vitro and in vivo were screened to explore low-cost and versatile antimicrobial agents. Screening results showed that compounds, such as A₀, B₀, and C₄, were bioactive against Xanthomonas oryzae pv oryzae in vitro and in vivo, and such bioactivities were superior to those of commercial agents bismerthiazol and thiodiazole copper. Their antibacterial mechanisms were further investigated by quantitative proteomics and concentration-dependent scanning electron microscopy images. Antifungal results indicated that compound A₀ displayed a selective and better antifungal effect on Botrytis cinerea with inhibition rate of 96.8% at 50 μg/mL. Nematocidal bioassays suggested that compound D₁ had good in vitro nematocidal activity toward M. incognita at 24, 48, and 72 h, with the corresponding insecticidal efficiency of 48.7%, 64.1%, and 87.2% at 40 μg/mL. In vivo study further confirmed that compounds D₁ and F₂ showed nematocidal actions at 80 μg/mL with a disease index of 1.5. Given these advantages, this kind of molecular frameworks could be a suitable platform for exploring highly efficient agrochemicals.

Brassica meal-derived allyl-isothiocyanate postharvest application: influence on strawberry nutraceutical and biochemical parameters

BACKGROUND

The antimicrobial activity of allyl-isothiocyanate (AITC) on plant pathogens is well known and has already been demonstrated in the strawberry with respect to Botritis cinerea fungal infection using postharvest biofumigation. In the present study, vapours of 0.08 mg L^-1 of Brassica meal-derived AITC were applied to strawberry to assess its effect on fruit nutraceutical and biochemical parameters after 2 days of storage at 20 °C and 90% relative humidity.

RESULTS

Allyl-isothiocyanate showed no detrimental effect on final strawberry quality, anti-oxidant properties or ascorbic acid content. By contrast, an increased amount of asparagine and a higher ascorbate and glutathione redox potential were registered in the fruit soon after treatment. A reversible glutathione depletion action of AITC was also observed. Finally, total AITC residues in treated strawberry were quantified and a relatively high amount of AITC-adducts was found in fruit tissues.

CONCLUSION

The findings of the present study not only confirm the high potentiality of biofumigation with respect to extending the shelf-life of fruit, but also provide some insight regarding the mechanisms of action of AITC at the cellular level as a possible elicitor of fruit protective responses. Nevertheless, the nature of the AITC-adducts formed in fruit tissues needs further attention to enable a health and safety assessment of the final fruit. © 2019 Society of Chemical Industry.

Antimicrobial mechanism of reaction products of Morus notabilis (mulberry) polyphenol oxidases and chlorogenic acid

Herein, five polyphenol oxidases (PPOs) obtained from Morus notabilis (Mn) were characterized. Chlorogenic acid was the most readily oxidized substrate by these MnPPOs, and the products derived from the oxidation of chlorogenic acid by MnPPOs were tested for antimicrobial activity. The results showed that products of the five MnPPOs exhibited good inhibitory effects against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Sclerotinia sclerotiorum, and Botrytis cinerea. Because the products of MnPPO1 exhibited the strongest antimicrobial activity, the antimicrobial mechanism of these products was explored. The results showed that the products of MnPPO1 increased cell membrane permeability and chitinase and β-1,3-glucanase activities.

Global transcriptome analysis and differentially expressed genes in grapevine after application of the yeast-derived defense inducer cerevisane

BACKGROUND

Cerevisane, made up of cell wall derivatives from the Saccharomyces cerevisiae strain LAS117, is proposed as a resistance inducer in plants. The mode of action of cerevisane was investigated through transcriptome analysis (RNA-Seq) carried out on leaves of potted vines cv. Italia grown in the greenhouse and sprayed at 1-week intervals with cerevisane. Analyses were performed at three time points after one and three sprays as well as on vines challenged with artificial inoculation with Plasmopara viticola, Erysiphe necator and Botrytis cinerea.

RESULTS

Cerevisane proved effective against downy mildew and caused an increase in expression levels of several genes related to defense responses to fungal pathogens and other stresses and down-regulation of genes involved in several processes related to plant growth and development. Up-regulated genes included genes encoding (i) enzymes involved in hormone metabolism (i.e. salicylic acid, jasmonate, ethylene) and related plant responses, (ii) defense compounds (i.e. pathogenesis-related proteins, phenylalanine ammonia-lyase, stilbene synthases, lipoxygenase, leucine-rich repeat receptor-like protein kinases, non-specific plant lipid transfer proteins, serine-threonine protein kinases involved in signal transduction, superoxide dismutase and glutathione S-transferase involved in response to oxidative stress), (iii) secondary metabolites (i.e. phenylpropanoids, terpenoids, lignin), and (iv) photosynthetic processes (light harvesting chlorophyll A/B-binding proteins and components of the photosystems).

CONCLUSION

Cerevisane can be a useful tool in protection schedules against downy mildew on grapevine aimed at reducing the usage of synthetic fungicides and preventing fungicide resistance. The results provide the first basic knowledge on the mode of action of yeast-derived elicitors effective against P. viticola on grapevine. © 2019 Society of Chemical Industry.

Characterization of Botrytis cinerea From Commercial Cut Flower Roses

Botrytis cinerea Pers. infects cut flower roses (Rosa × hybrida L.) during greenhouse production and gray mold symptoms are often expressed in the postharvest environment, resulting in significant economic losses. Disease management is based on cultural practices and preventative chemical treatments; however, gray mold outbreaks continue to occur. Rose tissues from six commercial shipments from two greenhouses in Colombia were evaluated to determine the Botrytis species composition as well as identify other pathogens present, gray mold incidence and severity, and fungicide resistance profiles. Botrytis isolates (49 total) were grouped into six morphological phenotypes, and all were identified to be B. cinerea sensu stricto. Disease incidence was higher in the petals than in the stem, stamen, ovary, sepal, or leaf tissues. Other fungi were isolated infrequently and included Alternaria alternata, Cladosporium cladosporioides, Epicoccum nigrum, Penicillium citrinum, Aspergillus brasiliensis, and Diplodia sp. Fungicide resistance profiles were determined using previously established discriminatory doses. Isolates resistant to thiophanate-methyl, iprodione, boscalid, and cyprodinil were found frequently in all shipments and in both greenhouses. The frequency of resistance to penthiopyrad, fenhexamid, fluopyram, isofetamid, and fludioxonil varied between shipments and greenhouses. No resistance to pydiflumetofen was observed at the discriminatory doses tested. Isolates with resistance to multiple chemical classes were commonly found. These results indicate that fungicide resistance management practices may improve preharvest and postharvest gray mold control of cut flower roses.

Buckwheat Antifungal Protein with Biocontrol Potential To Inhibit Fungal ( Botrytis cinerea) Infection of Cherry Tomato

A 11 kDa antifungal protein FEAP was purified from buckwheat ( Fagopyrum esculentum) seed extract with a procedure involving (NH₄)₂SO₄ precipitation and chromatography on SP-Sepharose, Affi-gel blue gel, Mono S, and Superdex peptide. Its N-terminal sequence was AQXGAQGGGAT, resembling those of buckwheat peptides Fα-AMP1 and Fα-AMP2. FEAP exhibited thermostability (20-100 °C) and acid resistance (pH 1-5). Its antifungal activity was retained in the presence of 10-150 mmol/L of K⁺, Mn²⁺, or Fe³⁺ ions, 10-50 mmol/L of Ca²⁺ or Mg²⁺ ions, and 50% methanol, 50% ethanol, 50% isopropanol, or 50% chloroform. Its half-maximal inhibitory concentrations toward spore germination and mycelial growth in Botrytis cinerea were 79.9 and 236.7 μg/mL, respectively. Its antifungal activity was superior to the fungicide cymoxanil mancozeb (248.1 μg/mL). FEAP prevented B. cinerea from infecting excised leaves, intact leaves, and isolated fruits of cherry tomato. Its mechanism involved induction of an increase in cell membrane permeability and a decrease in mitochondrial membrane potential.

Combination of Suspension Array and Mycelial Growth Assay for Detecting Multiple-Fungicide Resistance in Botrytis cinerea in Hebei Province in China

To provide a high-throughput, efficient, and accurate method to monitor multiple-fungicide resistance of Botrytis cinerea in the field, we used the suspension array, sequencing, and mycelial growth assay in our research. Discriminating-dose bioassays for detecting carbendazim, diethofencarb, boscalid, and iprodione resistance (Car^R, Die^R, Bos^R, and Ipr^R, respectively) were used to analyze 257 isolates collected from Hebei Province in China during 2016 and 2017. High resistance frequencies to carbendazim (100%), diethofencarb (92.08%), and iprodione (86.59%) were detected. Bos^R isolates accounted for 11.67% of the total. In addition, 103 isolates were randomly selected for phenotype and genotype detection. The high-throughput suspension array was utilized to detect eight genotypes simultaneously, including BenA-E198, BenA-198A, SdhB-H272, SdhB-272Y, BcOS1-I365, BcOS1-365S, erg27-F412, and erg27-412S, which were associated with resistance toward carbendazim or diethofencarb, boscalid, iprodione, and fenhexamid (Fen^R), respectively. Most of the benzimidazole-resistant isolates (81.55%) possessed the E198V mutation in the BenA gene. Ninety-three isolates with dual resistance to carbendazim and diethofencarb showed the E198V/K mutation. All Bos^R isolates carried the H272R mutation in the SdhB gene. The I365S and Q369P+N373S (66.99%) mutations in the BcOS1 gene were more frequently observed. No mutation was detected in the erg27 gene in Hebei isolates. There were 13 resistance profile phenotypes. Phenotypes with triple resistance were the most common (83.50%), and Car^RDie^RBos^SIpr^RFen^S was the major type. Car^R isolates that carried E198V/K/A were all highly resistant (HR) and only one F200Y mutant was moderately resistant (MR) to carbendazim. Isolates that possessed E198V/K were MR or HR to diethofencarb. Bos^R isolates that possessed H272R mutation were lowly resistant (LR). Ipr^R isolates were all LR or MR. The distribution of half maximal effective concentrations of Car^R isolates with E198V/K mutations and Ipr^R isolates with Q369P+N373S mutations significantly increased from 2016 to 2017. Combined with our observations, a combination method of the high-throughput suspension array and the mycelial growth assay was suggested to accurately monitor multiple resistance of B. cinerea in the field.

QSAR studies of phenylhydrazine-substituted tetronic acid derivatives based on the 1 H NMR and 13 C NMR chemical shifts

The quantitative structure-activity relationship models of 40 phenylhydrazine-substituted tetronic acid derivatives were established between the ¹ H nuclear magnetic resonance (NMR) and ¹³ C NMR chemical shifts and the antifungal activity against Fusarium graminearum, Botrytis cinerea, Rhizoctonia cerealis, and Colletotrichum capsici. The models were validated by R, R² , R_A² , variance inflation factor, F, and P values testing and residual analysis. It was concluded from the models that the ¹³ C NMR chemical shifts of C8, C10, C7, and the ¹ H NMR chemical shifts of Ha contributed positively to the activity against Fusarium graminearum, Botrytis cinerea, Colletotrichum capsici, and Rhizoctonia cerealis, respectively. The models indicated that decreasing the election cloud density of specific nucleuses in compounds, for example, by the substituting of electron withdrawing groups, would improve the antifungal activity. These models demonstrated the practical application meaning of chemical shifts in the quantitative structure-activity relationship study. Furthermore, a practical guide was provided for further structural optimization of the antifungal phenylhydrazine-substituted tetronic acid derivatives based on the ¹ H NMR and ¹³ C NMR chemical shifts.

Different Antifungal Activity of Anabaena sp., Ecklonia sp., and Jania sp. against Botrytis cinerea

Water extracts and polysaccharides from Anabaena sp., Ecklonia sp., and Jania sp. were tested for their activity against the fungal plant pathogen Botrytis cinerea. Water extracts at 2.5, 5.0, and 10.0 mg/mL inhibited B. cinerea growth in vitro. Antifungal activity of polysaccharides obtained by N-cetylpyridinium bromide precipitation in water extracts was evaluated in vitro and in vitro at 0.5, 2.0, and 3.5 mg/mL. These concentrations were tested against fungal colony growth, spore germination, colony forming units (CFUs), CFU growth, and on strawberry fruits against B. cinerea infection with pre- and post-harvest application. In in vitro experiments, polysaccharides from Anabaena sp. and from Ecklonia sp. inhibited B. cinerea colony growth, CFUs, and CFU growth, while those extracted from Jania sp. reduced only the pathogen spore germination. In in vitro experiments, all concentrations of polysaccharides from Anabaena sp., Ecklonia sp., and Jania sp. reduced both the strawberry fruits infected area and the pathogen sporulation in the pre-harvest treatment, suggesting that they might be good candidates as preventive products in crop protection.

Dual Mode of Action of Grape Cane Extracts against Botrytis cinerea

Crude extracts of Vitis vinifera canes represent a natural source of stilbene compounds with well characterized antifungals properties. In our trials, exogenous application of a stilbene extract (SE) obtained from grape canes on grapevine leaves reduces the necrotic lesions caused by Botrytis cinerea. The SE showed to possess a direct antifungal activity by inhibiting the mycelium growth. The activation of some grapevine defense mechanism was also investigated. H₂O₂ production and activation of mitogen-activated protein kinase (MAPK) phosphorylation cascades as well as accumulation of stilbenoid phytoalexins were explored on grapevine cell suspension. Moreover, the transcription of genes encoding for proteins affecting defense responses was analyzed on grapevine plants. The SE induced some grapevine defense mechanisms including MAPK activation, and the expression of pathogenesis-related (PR) genes and of a gene encoding the glutathione-S-transferase 1 ( GST1) . By contrast, treatment of grapevine leaves with SE negatively regulates de novo stilbene production.

atrB-Associated Fludioxonil Resistance in Botrytis fragariae Not Linked to Mutations in Transcription Factor mrr1

Resistance to fludioxonil in Botrytis cinerea and B. fragariae was previously found to be linked to either overexpression of the drug efflux pump atrB activated by mutations in transcription factor mrr1 or to mutations in the osmoregulation gene os1. In the present study, isolates of B. cinerea, Botrytis group S, or B. fragariae collected from strawberry fields in the United States were resistant to fludioxonil with half-maximal effective concentration values ranging from 0.04 to 0.43 µg/ml for B. cinerea, 0.03 to 1.03 µg/ml for Botrytis group S, and 0.28 to 3.48 µg/ml for B. fragariae. Analyses of mrr1 sequences revealed various mutations linked to fludioxonil resistance in B. cinerea and Botrytis group S isolates. However, no mutations in mrr1 correlated with atrB overexpression-mediated resistance in B. fragariae isolates. Neither nucleotide variations in the 1,370-bp upstream region of atrB nor increased atrB copy numbers could explain the atrB overexpression in these B. fragariae isolates. Mutations in os1 conferred resistance to iprodione in B. cinerea and Botrytis group S isolates; none correlated with resistance to fludioxonil in B. fragariae. In contrast to European isolates, U.S. B. fragariae isolates contained a 3-bp insertion in the coding region of os1. These isolates were more sensitive to osmotic stress but it is unclear whether the insertion is responsible for this phenotype. Our findings suggest that atrB overexpression-associated fludioxonil resistance is an across-species mechanism of resistance to fludioxonil that can be induced by mutations in mrr1 and other, still-unknown mechanisms.

l-Glutamate treatment enhances disease resistance of tomato fruit by inducing the expression of glutamate receptors and the accumulation of amino acids

Gray mold caused by Botrytis cinerea is the most important disease in postharvest tomato fruit. Inducing resistance to fungal pathogens in the harvested fruit and vegetable is a promising approach to control postharvest losses. In the present study, the effect of l-glutamate on induction of resistance to B. cinerea and the underlying mechanisms were investigated. The results indicated that l-glutamate at 100 ppm was effective in reducing the gray mold of tomatoes after inoculation of the pathogen. Gene expressions of nine glutamate receptors, four pathogenesis-related proteins and the content of amino acids were affected by l-glutamate treatment. Furthermore, the metabolites of l-glutamate, including GABA, Met, Lys and Arg, could also induce significant resistance against B. cinerea in tomato fruit. Our findings suggested that l-glutamate treatment may represent a promising method for managing postharvest decay of tomato fruit.

The Importance of Selecting Appropriate Rotation and Tank-Mix Partners for Novel SDHIs to Enhance Botrytis Fruit Rot Control in Strawberry

Botrytis fruit rot (BFR), caused by the necrotrophic fungus Botrytis cinerea, is the most important disease of strawberry and is mainly controlled by applications of fungicides from multiple chemical groups. To develop more effective and sustainable BFR management programs, field trials were conducted to evaluate the efficacy of fluopyram and penthiopyrad, two newly registered succinate dehydrogenase inhibitors (SDHIs), rotated or tank mixed with the multisites thiram and captan or the single-sites fludioxonil and fenhexamid. The treatments were applied at two different strawberry fields during the 2013-14 and 2014-15 seasons. Overall, tank mixtures of fluopyram and penthiopyrad increased yield and reduced BFR better than rotations with the same fungicides. The multisite thiram tank mixed with fluopyram reduced BFR incidence by 63 to 86% versus 56 to 84% when the two fungicides were rotated. Thiram tank mixed with penthiopyrad reduced BFR incidence by 55 to 72% versus 42 to 66% when rotated. Captan rotated or tank mixed with fluopyram had a positive effect on yield and BFR incidence, whereas the combination of captan with penthiopyrad had negative impacts. Similarly, the single-site fenhexamid had significant positive impacts when rotated or tank mixed with fluopyram but resulted in poor BFR control when combined with penthiopyrad. The rotation of fludioxonil with both SDHIs had a significant positive effect, although its combination with fluopyram was more effective. The multirotation consisting of both SDHIs and different multi- and single-site fungicides did not provide a greater efficacy than the dual rotation or tank-mixture programs. Our findings suggest more scrutiny is needed when recommending tank-mixture or rotation partners for new fungicides to ensure compatibility and enhanced BFR management. Future recommendations should emphasize the importance of such selections at an early stage for delaying fungicide resistance development and extending the lifespan of at-risk fungicides.

Synthesis and antifungal activities of novel thiophene-based stilbene derivatives bearing an 1,3,4-oxadiazole unit

BACKGROUND

Natural stilbenes (especially resveratrol and its derivatives) are well-known phytoalexins that are active against many plant diseases. However, oxidative degradation and low bioavailability limit their exogenous application as fungicides on crops. In this study, a new class of resveratrol-inspired thiophene-based stilbene derivatives bearing an 1,3,4-oxadiazole unit was synthesized and the derivatives' antifungal activities against phytopathogenic fungi were investigated.

RESULTS

The results revealed that compounds 5h and 5j exhibited improved antifungal activity against Botrytis cinerea with median effective concentrations (EC₅₀ ) of 168.5 and 155.4 µg mL^-1 , respectively, which were superior to the EC₅₀ of resveratrol (263.1 µg mL^-1 ). Compound 5j was shown to effectively control disease development in B. cinerea-infected tomatoes in vivo. Notably, considerably abnormal mycelial morphology and increased cell membrane conductivity were observed in the presence of compound 5j.

CONCLUSION

A new class of thiophene-containing stilbene derivatives was designed and synthesized. Bioassay results showed that compound 5j exhibited promising antifungal activity, suggesting practical potential for fungal disease control. © 2018 Society of Chemical Industry.

Novel film-forming formulations of the biocontrol agent Candida sake CPA-1: biocontrol efficacy and performance at field conditions in organic wine grapes

BACKGROUND

The biocontrol agent (BCA) Candida sake CPA-1 has previously effectively reduced Botrytis bunch rot (BBR) and it was also suggested as a promising strategy to control sour rot in grapes under field conditions. However, biocontrol efficacy of solid formulations of CPA-1 has never been tested in field trials. The present study aims to confirm the efficacy against BBR and sour rot in grapes under field conditions of two novel formulations recently developed by the addition of biodegradable coatings using a fluidized-bed spray-drying system.

RESULTS

Novel film-forming formulations of the BCA C. sake CPA-1 controlled B. cinerea as well as liquid formulation. Sour rot control resulted better in the second season and severity reductions were more satisfactory than incidence control. Visual and cryoSEM observations revealed that film-forming treatments were uniformly distributed on plant surfaces. CPA-1 coating could be observed on grapes at harvest time.

CONCLUSION

The results of this work suggest that solid formulations would be a competitive alternative to conventional fungicides because they were easy to package and transport, and cell viability could be maintained for a long period of time. © 2018 Society of Chemical Industry.

Proteomic analysis of the inhibitory effect of oligochitosan on the fungal pathogen, Botrytis cinerea

BACKGROUND

The fungal pathogen Botrytis cinerea infects a broad range of horticultural plants worldwide, resulting in significant economic losses. A derivative of chitosan, oligochitosan, has been reported to be an eco-friendly alternative to synthetic fungicides.

RESULTS

Oligochitosan can greatly inhibit B. cinerea spore germination and induce protein carbonylation. To further investigate the molecular mechanism underlying the inhibitory effect, a comparative proteome analysis was conducted of oligochitosan-treated versus non-treated B. cinerea spores. The cellular proteins were obtained from B. cinerea spore samples and subjected to two-dimensional gel electrophoresis. In total, 21 differentially expressed proteins (DEPs) were identified. Three DEPs were up-regulated in the oligochitosan-treated versus the untreated spores, including scytalone dehydratase and a serine carboxypeptidase III precursor. By contrast, seven DEPs, including Hsp 88 and cell division cycle protein 48, were down-regulated by oligochitosan treatment. Notably, 10 DEPs, including phosphatidylserine decarboxylase proenzyme and ATP-dependent molecular chaperone HSC82, were only detected in the control spores, whereas one DEP, a non-annotated predicted protein, was only detected in the oligochitosan-treated spores.

CONCLUSION

Oligochitosan may affect the spore germination of B. cinerea by impairing protein function. These findings have practical implications with respect to the use of oligochitosan for controlling fungal pathogens. © 2018 Society of Chemical Industry.