Bacillus species as versatile weapons for plant pathogens: a review

Plant pathogens are the main threat for profitable agricultural productivity. Currently, chemical-based pesticides are thought to be an effective and reliable agricultural management measure for controlling pests. Chemical pesticides are highly effective and convenient to use but they are a potential threat for the environment and all kinds of life on earth. Therefore, the use of biological control agents for the management of plant pathogens is considered as a safer and sustainable strategy for safe and profitable agricultural productivity. Bacillus-based biocontrol agents play a fundamental role in the field of biopesticides. Many Bacillus species have proved to be effective against a broad range of plant pathogens. They have been reported as plant growth promoter, systemic resistance inducer, and used for production of a broad range of antimicrobial compounds (lipopeptides, antibiotics and enzymes) and competitors for growth factors (space and nutrients) with other pathogenic microorganisms through colonization. The aim of this article is to present the biocontrol potential of Bacillus species in relation with their antagonizing attributes against plant pathogens. These attributes include production of lipopeptides, antibiotics and enzymes as well as plant growth promotion and systemic induced resistance

Pesticide Residues in Greenhouse Leafy Vegetables in Cold Seasons and Dietary Exposure Assessment for Consumers in Liaoning Province, Northeast China

Excessive pesticide application in greenhouses leads to elevated levels of pesticide residues, especially in cold seasons, thereby posing a potential dietary exposure risk to the residents’ health. This study aimed to investigate 65 pesticides in 469 leafy vegetable samples collected from greenhouses in Liaoning province between October 2018 and May 2020. Overall, the pesticide levels in 96.4% (452/469) of the samples were below the MRLs established by the Codex Alimentarius Commission. The detection rate of 65 pesticides ranged from 0.2% to 11.9%. Multiple pesticide contamination was common, with dimethomorph being the most recurrent contaminant. The dietary risk assessment study revealed obvious differences in chronic and acute exposure risk values. The chronic risk quotients (RQcs) for leafy vegetable samples were 0.001%–3.993%, indicating an acceptable public health risk for the residents. As two leafy vegetables highly consumed in cold seasons in northeast China, the acute risk quotients (RQas) of Chinese cabbage samples were significantly lower than 100%; however, pakchoi samples exhibited RQa values ranging from 0.159% to 580.529%, showing an unacceptable acute dietary risk. This highlights that, compared to the chronic dietary risks, the potential acute dietary risks induced by the pesticides are higher in greenhouse-grown leafy vegetables during cold seasons

Inhibitory Effects of Amorphigenin on the Mitochondrial Complex I of Culex pipiens pallens Coquillett (Diptera: Culicidae)

Previous studies in our laboratory found that the extract from seeds of Amorpha fruticosa in the Leguminosae family had lethal effects against mosquito larvae, and an insecticidal compound amorphigenin was isolated. In this study, the inhibitory effects of amorphigenin against the mitochondrial complex I of Culex pipiens pallens (Diptera: Culicidae) were investigated and compared with that of rotenone. The results showed that amorphigenin and rotenone can decrease the mitochondrial complex I activity both in vivo and in vitro as the in vivo IC50 values (the inhibitor concentrations leading to 50% of the enzyme activity lost) were determined to be 2.4329 and 2.5232 μmol/L, respectively, while the in vitro IC50 values were 2.8592 and 3.1375 μmol/L, respectively. Both amorphigenin and rotenone were shown to be reversible and mixed-I type inhibitors of the mitochondrial complex I of Cx. pipiens pallens, indicating that amorphigenin and rotenone inhibited the enzyme activity not only by binding with the free enzyme but also with the enzyme-substrate complex, and the values of KI and KIS for amorphigenin were determined to be 20.58 and 87.55 μM, respectively, while the values for rotenone were 14.04 and 69.23 μM, respectively

Toxicity of Amorphigenin from the Seeds of Amorpha fruticosa against the Larvae of Culex pipiens pallens (Diptera: Culicidae)

The larvicidal activity of the crude petroleum ether, ethyl acetate, acetone, chloroform and ethanol extracts of Amorpha fruticosa seeds was individually assayed for toxicity against the early fourth-instar larva of the mosquito, Culex pipiens pallens after 24 h exposure. Of the tested extracts, the ethanol one exhibited the highest larvicidal activity (LC50 = 22.69 mg/L). Amorphigenin (8'-hydroxyrotenone), a rotenoid compound which exhibits a strong larvicidal activity with LC50 and LC90 values of 4.29 and 11.27 mg/L, respectively, was isolated from the ethanol extract by column chromatograpy. Its structure was elucidated by 1H-NMR, UV and IR spectral data. Furthermore, investigation of amorphigenin’s effects on mitochondrial complex I activity and protein synthesis in C. pipiens pallens larvae reveals that amorphigenin decreases mitochondrial complex I activities to 65.73% at 10.45 μmol/L, compared to the control, when NADH were used as the substrate. Meanwhile, amorphigenin at 10.45 μmol/L also caused a 1.98-fold decrease in protein content, compared to the control larvae treated with acetone only

ANN and RSM based modelling for optimization of cell dry mass of Bacillus sp. strain B67 and its antifungal activity against Botrytis cinerea

The present study was conducted to present the comparative modelling, predictive and generalization abilities of response surface methodology (RSM) and artificial neural network (ANN) for optimization of fermenting medium. Cell dry mass and inhibition zone of strain B67 against Botrytis cinerea were used as response variables. The response variables were optimized and modelled as a function of five independent variables (pH, gelatine percentage, incubation period, agitation speed, and temperature) using response surface methodology and artificial neural network. The results of both approaches were compared for their modelling abilities in terms of root-mean-squared error (RMSE), mean absolute error (MAD), chi-square, and correlation coefficient, computed from experimental and predicted data. ANN models were proved to be superior to RSM with lower RMSE, MAD, and chi-square and higher values for correlation coefficient, coefficient of determination, and predictive coefficient of determination. The optimum fermenting conditions predicted were pH 6.65, gelatine 3.30%, incubation period 35 h, agitation speed 163 rpm, and incubation temperature 33.64 °C, with 15.00 g/L and 31.64 mm cell dry mass and inhibition zone, respectively. The predictive models were validated experimentally and were found in agreement with experimentally obtained values

Synthesis of 2-Acyloxycyclohexylsulfonamides and Evaluation on Their Fungicidal Activity

Eighteen N-substituted phenyl-2-acyloxycyclohexylsulfonamides (III) were designed and synthesized by the reaction of N-substituted phenyl-2-hydroxyl- cycloalkylsulfonamides (I, R1) with acyl chloride (II, R2) in dichloromethane under the catalysis of TMEDA and molecular sieve. High fungicidal active compound N-(2,4,5-trichlorophenyl)-2-(2-ethoxyacetoxy) cyclohexylsulfonamide (III-18) was screened out. Mycelia growth assay against the Botrytis cinerea exhibited that EC50 and EC80 of compound III-18 were 4.17 and 17.15 μg mL−1 respectively, which was better than the commercial fungicide procymidone (EC50 = 4.46 μg mL−1 and EC80 = 35.02 μg mL−1). For in vivo activity against B. cinerea in living leaf of cucumber, the control effect of compound III-18 was better than the fungicide cyprodinil. In addition, this new compound had broader fungicidal spectra than chlorothalonil

Synthesis, Fungicidal Activity and Mode of Action of 4-Phenyl-6-trifluoromethyl-2-aminopyrimidines against Botrytis cinerea

Anilinopyrimidines are the main chemical agents for management of Botrytis cinerea. However, the drug resistance in fungi against this kind of compounds is very serious. To explore new potential fungicides against B. cinerea, a series of 4-phenyl-6-trifluoromethyl-2-amino-pyrimidine compounds (compounds III-1 to III-22) were synthesized, and their structures were confirmed by 1H-NMR, IR and MS. Most of these compounds possessed excellent fungicidal activity. The compounds III-3 and III-13 showed higher fungicidal activity than the positive control pyrimethanil on fructose gelatin agar (FGA), and compound III-3 on potato dextrose agar (PDA) indicated high activity compared to the positive control cyprodinil. In vivo greenhouse results indicated that the activity of compounds III-3, III-8, and III-11 was significantly higher than that of the fungicide pyrimethanil. Scanning electron micrography (SEM) and transmission electron micrography (TEM) were applied to illustrate the mechanism of title compounds against B. cinerea. The title compounds, especially those containing a fluorine atom at the ortho-position on the benzene ring, could maintain the antifungal activity against B. cinerea, but their mechanism of action is different from that of cyprodinil. The present study lays a good foundation for us to find more efficient reagents against B. cinerea