Bisdechlorogeodin from antarctic Pseudogymnoascus sp. LAMAI 2784 for citrus canker control.

AIMS: Citrus canker caused by Xanthomonas citri subsp. citri (X. citri) is a disease of economic importance. Control of this disease includes the use of metallic copper, which is harmful to the environment and human health. Previous studies showed that the crude extract from the fungus Pseudogymnoascus sp. LAMAI 2784 isolated from Antarctic soil had in vitro antibacterial action against X. citri. The aim of the present study was to expand the applications of this extract. METHODS AND RESULTS: In greenhouse assays, the crude extract was able to reduce bacterial infection on citrus leaves from 1.55 lesions/cm2 (untreated plants) to 0.04 lesions/cm2. Bisdechlorogeodin was identified as the main compound of the bioactive fraction produced by Pseudogymnoascus sp. LAMAI 2784, which inhibited bacterial growth in vitro (IC90 ≈ 156 µg ml-1) and permeated 80% of X. citri cells, indicating that the membrane is the primary target. CONCLUSION: The present results showed that the bioactive fraction of the extract is mainly composed of the compound bisdechlorogeodin, which is likely responsible for the biological activity against X. citri, and the main mechanism of action is the targeting of the cell membrane. This study indicates that bisdechlorogeodin has valuable potential for the control of X. citri.

Design and Synthesis of Mandelic Acid Derivatives for Suppression of Virulence via T3SS against Citrus Canker.

Citrus canker, a highly contagious bacterial disease caused by Xanthomonas citri subsp. citri (Xcc), poses a substantial threat to citrus crops, leading to serious reductions in fruit yield and economic losses. Most commonly used bactericides against Xcc lead to the rapid development of resistant subpopulations. Therefore, it is imperative to create novel drugs, such as type III secretion system (T3SS) inhibitors, that specifically target bacterial virulence factors rather than bacterial viability. In our study, we designed and synthesized a series of mandelic acid derivatives including 2-mercapto-1,3,4-thiazole. Seven substances were found to reduce the level of transcription of hpa1 without affecting bacterial viability. In vivo bioassays indicated that compound F9 significantly inhibited hypersensitive response and pathogenicity. RT-qPCR assays showed that compound F9 visibly suppressed the expression of Xcc T3SS-related genes as well as citrus canker susceptibility gene CsLOB1. Furthermore, the combination with compound F9 and quorum-quenching bacteria HN-8 can also obviously alleviate canker symptoms.

Design, Synthesis, Antibacterial Activity, and Mechanisms of Novel Benzofuran Derivatives Containing Disulfide Moieties.

The unsatisfactory effects of conventional bactericides and antimicrobial resistance have increased the challenges in managing plant diseases caused by bacterial pests. Here, we report the successful design and synthesis of benzofuran derivatives using benzofuran as the core skeleton and splicing the disulfide moieties commonly seen in natural substances with antibacterial properties. Most of our developed benzofurans displayed remarkable antibacterial activities to frequently encountered pathogens, including Xanthomonas oryzae pv oryzae (Xoo), Xanthomonas oryzae pv oryzicola (Xoc), and Xanthomonas axonopodis pv citri (Xac). With the assistance of the three-dimensional quantitative constitutive relationship (3D-QSAR) model, the optimal compound V40 was obtained, which has better in vitro antibacterial activity with EC50 values of 0.28, 0.56, and 10.43 µg/mL against Xoo, Xoc, and Xac, respectively, than those of positive control, TC (66.41, 78.49, and 120.36 µg/mL) and allicin (8.40, 28.22, and 88.04 µg/mL). Combining the results of proteomic analysis and enzyme activity assay allows the antibacterial mechanism of V40 to be preliminarily revealed, suggesting its potential as a versatile bactericide in combating bacterial pests in the future.

Antibacterial activity of Cymbopogon species essential oils against Xanthomonas citri and their use in post-harvest treatment for citrus canker management.

Citrus canker is a disease caused by the gram-negative bacterium Xanthomonas citri subp. citri (X. citri), which affects all commercially important varieties of citrus and can lead to significant losses. Fruit sanitization with products such as chlorine-based ones can reduce the spread of the disease. While effective, their use raises concerns about safety of the workers. This work proposes essential oils (EOs) as viable alternatives for fruit sanitization. EOs from Cymbopogon species were evaluated as to their antibacterial activity, their effect on the bacterial membrane, and their ability to sanitize citrus fruit. The in vitro assays revealed that the EOs from C. schoenanthus and C. citratus had a lower bactericidal concentration at 312 mg L-1, followed by 625 mg L-1 for C. martini and C. winterianus. Microscopy assay revealed that the bacterial cell membranes were disrupted after 15 min of contact with all EOs tested. Regarding the sanitizing potential, the EOs with higher proportions of geraniol were more effective in sanitizing acid limes. Fruit treated with C. shoenanthus and C. martini showed a reduction of ∼68% in the recovery of viable bacterial cells. Therefore, these EOs can be used as viable natural alternatives in citrus fruit disinfection.

Visible-light-driven water-soluble zinc oxide quantum dots for efficient control of citrus canker.

BACKGROUND: Citrus canker caused by Xanthomonas citri subsp. citri (Xcc) is a devastating bacterial disease that reduces citrus yield and quality, posing a serious threat to the citrus industry. Several conventional chemicals have been used to control citrus canker. However, this approach often leads to the excessive use of chemical agents, can exacerbate environmental pollution and promotes the development of resistant Xcc. Therefore, there is significant interest in the development of efficient and environmentally friendly technologies to control citrus canker. RESULTS: In this study, water-soluble ZnO quantum dots (ZnO QDs) were synthesised as an efficient nanopesticide against Xcc. The results showed that the antibacterial activity of ZnO QDs irradiated with visible light [half-maximal effective concentration (EC50) = 33.18 µg mL-1] was ~3.5 times higher than that of the dark-treated group (EC50 = 114.80 µg mL-1). ZnO QDs induced the generation of reactive oxygen species (•OH, •O- 2 and 1O2) under light irradiation, resulting in DNA damage, cytoplasmic destruction, and decreased catalase and superoxide dismutase activities. Transcription analysis showed downregulation of Xcc genes related to 'biofilms, virulence, adhesion' and 'DNA transfer' exposure to ZnO QDs. More importantly, ZnO QDs also promoted the growth of citrus. CONCLUSION: This research provides new insights into the photocatalytic antibacterial mechanisms of ZnO QDs and supports the development of more efficient and safer ZnO QDs-based nanopesticides to control citrus canker. © 2024 Society of Chemical Industry.

Design, synthesis, antibacterial evaluation of isopropylamine linked with different substituted phenol and piperazine novel derivatives.

BACKGROUND: Xanthomonas oryzae pv. oryzae (Xoo) is often considered one of the most destructive bacterial pathogens causing bacterial leaf blight (BLB), resulting in significant yield and cost losses in rice. In this study, a series of novel derivatives containing the isopropanolamine moiety linked to various substituted phenols and piperazines were designed, synthesized and screened. RESULTS: Antibacterial activity results showed that most compounds had good inhibitory effects on Xoo, among which compound W2 (EC50 = 2.74 µg mL-1) exhibited the most excellent inhibitory activity, and W2 also had a certain curative effect (35.89%) on rice compared to thiodiazole copper (TC) (21.57%). Scanning electron microscopy (SEM) results indicated that compound W2 could cause rupture of the Xoo cell membrane. Subsequently, proteomics and quantitative real-time polymerase chain reaction revealed that compound W2 affected the physiological processes of Xoo and may exert antibacterial activity by targeting the two-component system pathway. Interestingly, W2 upregulated Xoo's methyltransferase to impact on its pathogenicity. CONCLUSION: The present study offers a promising phenolic-piperazine-sopropanolamine compound as an innovative antibacterial strategy by specifically targeting the two-component system pathway and inducing upregulation of methyltransferase to effectively impact Xoo's pathogenicity. © 2024 Society of Chemical Industry.

Structural insight into subunit F of respiratory chain complex I from Xanthomonas oryzae pv. oryzae inhibition by parthenolide.

BACKGROUND: Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious diseases of rice, and there is a lack of bactericides for controlling this disease. We previously found parthenolide (PTL) is a potential lead for developing bactericides against Xoo, and subunit F of respiratory chain complex I (NuoF) is an important target protein of PTL. However, the binding modes of PTL with NuoF need further elucidation. RESULTS: In this study, we obtained the crystal structure of Xoo NuoEF (complex of subunit E and F of respiratory chain complex I) with a resolution of 2.36 Å, which is the first report on the protein structure of NuoEF in plant-pathogenic bacteria. The possible binding sites of PTL with NuoF (Cys105 and Cys187) were predicted with molecular docking and mutated into alanine using a base mismatch method. The mutated proteins were expressed in Escherichia coli and purified with affinity chromatography. The binding abilities of PTL with mutated proteins were investigated via pull-down assay and BIAcore analysis, which revealed that double mutation of Cys105 and Cys187 in NuoF severely affected the binding ability of PTL with NuoF. In addition, the binding modes were further simulated with combined quantum mechanical/molecular mechanical calculations, and the results indicated that PTL may have a stronger binding with Cys105 than Cys187. CONCLUSION: NuoEF protein structure of Xoo was resolved, and Cys105 and Cys187 in NuoF are important binding sites of PTL. This study further clarified the action mechanism of PTL against Xoo, and will promote the innovation of bactericides targeting Xoo complex I. © 2024 Society of Chemical Industry.

Design, Synthesis and Bioactivity of Novel Pyrimidine Sulfonate Esters Containing Thioether Moiety.

Pesticides play an important role in crop disease and pest control. However, their irrational use leads to the emergence of drug resistance. Therefore, it is necessary to search for new pesticide-lead compounds with new structures. We designed and synthesized 33 novel pyrimidine derivatives containing sulfonate groups and evaluated their antibacterial and insecticidal activities. Results: Most of the synthesized compounds showed good antibacterial activity against Xanthomonas oryzae pv. Oryzae (Xoo), Xanthomonas axonopodis pv. Citri (Xac), Pseudomonas syringae pv. actinidiae (Psa) and Ralstonia solanacearum (Rs), and certain insecticidal activity. A5, A31 and A33 showed strong antibacterial activity against Xoo, with EC50 values of 4.24, 6.77 and 9.35 µg/mL, respectively. Compounds A1, A3, A5 and A33 showed remarkable activity against Xac (EC50 was 79.02, 82.28, 70.80 and 44.11 µg/mL, respectively). In addition, A5 could significantly improve the defense enzyme (superoxide dismutase, peroxidase, phenylalanine ammonia-lyase and catalase) activity of plants against pathogens and thus improve the disease resistance of plants. Moreover, a few compounds also showed good insecticidal activity against Plutella xylostella and Myzus persicae. The results of this study provide insight into the development of new broad-spectrum pesticides.

ERF Transcription Factor OsBIERF3 Positively Contributes to Immunity against Fungal and Bacterial Diseases but Negatively Regulates Cold Tolerance in Rice.

We previously showed that overexpression of the rice ERF transcription factor gene OsBIERF3 in tobacco increased resistance against different pathogens. Here, we report the function of OsBIERF3 in rice immunity and abiotic stress tolerance. Expression of OsBIERF3 was induced by Xanthomonas oryzae pv. oryzae, hormones (e.g., salicylic acid, methyl jasmonate, 1-aminocyclopropane-1-carboxylic acid, and abscisic acid), and abiotic stress (e.g., drought, salt and cold stress). OsBIERF3 has transcriptional activation activity that depends on its C-terminal region. The OsBIERF3-overexpressing (OsBIERF3-OE) plants exhibited increased resistance while OsBIERF3-suppressed (OsBIERF3-Ri) plants displayed decreased resistance to Magnaporthe oryzae and X. oryzae pv. oryzae. A set of genes including those for PRs and MAPK kinases were up-regulated in OsBIERF3-OE plants. Cell wall biosynthetic enzyme genes were up-regulated in OsBIERF3-OE plants but down-regulated in OsBIERF3-Ri plants; accordingly, cell walls became thicker in OsBIERF3-OE plants but thinner in OsBIERF3-Ri plants than WT plants. The OsBIERF3-OE plants attenuated while OsBIERF3-Ri plants enhanced cold tolerance, accompanied by altered expression of cold-responsive genes and proline accumulation. Exogenous abscisic acid and 1-aminocyclopropane-1-carboxylic acid, a precursor of ethylene biosynthesis, restored the attenuated cold tolerance in OsBIERF3-OE plants while exogenous AgNO3, an inhibitor of ethylene action, significantly suppressed the enhanced cold tolerance in OsBIERF3-Ri plants. These data demonstrate that OsBIERF3 positively contributes to immunity against M. oryzae and X. oryzae pv. oryzae but negatively regulates cold stress tolerance in rice.

Fabrication of Host-Guest Complexes between Adamantane-Functionalized 1,3,4-Oxadiazoles and ß-Cyclodextrin with Improved Control Efficiency against Intractable Plant Bacterial Diseases.

Supramolecular chemistry provides huge potentials and opportunities in agricultural pest management. In an attempt to develop highly bioactive, eco-friendly, and biocompatible supramolecular complexes for managing intractable plant bacterial diseases, herein, a type of interesting adamantane-functionalized 1,3,4-oxadiazole was rationally prepared to facilitate the formation of supramolecular complexes via ß-cyclodextrin-adamantane host-guest interactions. Initial antibacterial screening revealed that most of these adamantane-decorated 1,3,4-oxadiazoles were obviously bioactive against three typically destructive phytopathogens. The lowest EC50 values could reach 0.936 (III18), 0.889 (III18), and 2.10 (III19) µg/mL against the corresponding Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and Pseudomonas syringae pv. actinidiae (Psa). Next, the representative supramolecular binary complex III18@ß-CD (binding mode 1:1) was successfully fabricated and characterized by 1H nuclear magnetic resonance (NMR), isothermal titration calorimetry (ITC), high-resolution mass spectrometry (HRMS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). Eventually, correlative water solubility and foliar surface wettability were significantly improved after the formation of host-guest assemblies. In vivo antibacterial evaluation found that the achieved supramolecular complex could distinctly alleviate the disease symptoms and promote the control efficiencies against rice bacterial blight (from 34.6-35.7% (III18) to 40.3-43.6% (III18@ß-CD)) and kiwi canker diseases (from 41.0-42.3% (III18) to 53.9-68.0% (III18@ß-CD)) at 200 µg/mL (active ingredient). The current study can provide a feasible platform and insight for constructing biocompatible supramolecular assemblies for managing destructive bacterial infections in agriculture.

Copper Tolerance in Xanthomonas arboricola pv. pruni in South Carolina Peach Orchards.

Bacterial spot of peach, caused by Xanthomonas arboricola pv. pruni, causes yield loss every year in southeastern U.S. peach orchards. Management is mainly driven by season-long applications of copper-based products, site location, and choice of cultivar. Although tolerance to copper has not been reported in X. arboricola pv. pruni in the United States, adaptation of populations from frequent use is a concern. We collected X. arboricola pv. pruni from shoot cankers, leaves, and fruit of cultivar O'Henry over 2 years from three conventional farms and one organic farm in South Carolina, one orchard per farm. The four farms had been using copper extensively for years to control bacterial spot. X. arboricola pv. pruni was isolated from four canker types (bud canker, tip canker, nonconcentric canker, and concentric canker) in early spring (bud break), as well as from leaf and fruit tissues later in the season at the phenological stages of pit hardening and final swell. X. arboricola pv. pruni was most frequently isolated from cankers of the organic farm (24% of the cankers) and most isolates (45%) came from bud cankers. X. arboricola pv. pruni isolates were assessed for sensitivity to copper using minimal glucose yeast agar and nutrient agar amended with 38 µg/ml or 51 µg/ml of Cu2+. Two phenotypes of copper tolerance in X. arboricola pv. pruni were discovered: low copper tolerance (LCT; growth up to 38 µg/ml Cu2+) and high copper tolerance (HCT; growth up to 51 µg/ml Cu2+). A total of 26 (23 LCT and 3 HCT) out of 165 isolates in 2018 and 32 (20 LCT and 12 HCT) out of 133 isolates in 2019 were tolerant to copper. Peach leaves on potted trees were sprayed with copper rates typically applied at the stages of delayed dormancy (high rate; 2,397 µg/ml Cu2+), shuck split (medium rate; 599 µg/ml Cu2+), and during summer cover sprays (low rate; 120 µg/ml Cu2+), and subsequently inoculated with sensitive, LCT, and HCT strains. Results indicated that the low and medium rates of copper reduced bacterial spot incidence caused by the sensitive strain but not by the LCT and HCT strains. This study confirms existence of X. arboricola pv. pruni tolerance to copper in commercial peach orchards in the southeastern United States, and suggests its contribution to bacterial spot development under current management practices.

Fruit juice mediated multicomponent reaction for the synthesis of substituted isoxazoles and their in vitro bio-evaluation.

A simple, efficient and eco-friendly procedure for the synthesis of isoxazole derivatives (4a-4h) using one-pot three-component reaction between substituted aldehydes (1a), methyl acetoacetate (2a) and hydroxylamine hydrochloride (3a) has been achieved in presence of Cocos nucifera L. juice, Solanum lycopersicum L. juice and Citrus limetta juice respectively. The homogeneity of synthesized compounds was confirmed by melting point and thin layer chromatography. The synthesized compounds were characterized by using 1H NMR, FTIR and CHN analyses and evaluated for in vitro herbicidal activity against Raphanus sativus L. (Radish seeds). The compounds (4a-4h) were also screened for their fungicidal activity against Rhizoctonia solani and Colletotrichum gloeosporioides. Antibacterial activity was also tested against Erwinia carotovora and Xanthomonas citri. From bio-evaluation data, it was found that compound 4b was most active against Raphanus sativus L. (root) and Raphanus sativus L. (shoot) respectively. Compound 4b was also found most active against both the fungus viz. R. solani and C. gloeosporioides showing maximum percentage growth inhibition i.e. 90.00 against R. solani and 82.45 against C. gloeosporioides at 2000 µg/mL concentration. Compound 4 h has shown maximum inhibition zone i.e. 3.00-9.60 mm against Erwinia carotovora at 2000 µg/mL concentration. Maximum Xanthomonas citri growth was also inhibited by compound 4 h showing inhibition zone 1.00-5.00 mm at highest concentration.

Discovery of Novel Dihydrolipoamide S-Succinyltransferase Inhibitors Based on Fragment Virtual Screening.

A series of new oxadiazole sulfone derivatives containing an amide moiety was synthesized based on fragment virtual screening to screen high-efficiency antibacterial agents for rice bacterial diseases. All target compounds showed greater bactericidal activity than commercial bactericides. 3-(4-fluorophenyl)-N-((5-(methylsulfonyl)-1,3,4-oxadiazol-2-yl)methyl)acrylamide (10) showed excellent antibacterial activity against Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola, with EC50 values of 0.36 and 0.53 mg/L, respectively, which were superior to thiodiazole copper (113.38 and 131.54 mg/L) and bismerthiazol (83.07 and 105.90 mg/L). The protective activity of compound 10 against rice bacterial leaf blight and rice bacterial leaf streak was 43.2% and 53.6%, respectively, which was superior to that of JHXJZ (34.1% and 26.4%) and thiodiazole copper (33.0% and 30.2%). The curative activity of compound 10 against rice bacterial leaf blight and rice bacterial leaf streak was 44.5% and 51.7%, respectively, which was superior to that of JHXJZ (32.6% and 24.4%) and thiodiazole copper (27.1% and 28.6%). Moreover, compound 10 might inhibit the growth of Xanthomonas oryzae pv. oryzae and Xanthomonas oryzae pv. oryzicola by affecting the extracellular polysaccharides, destroying cell membranes, and inhibiting the enzyme activity of dihydrolipoamide S-succinyltransferase.

Biosynthesis of silver nanoparticles from Mukia maderaspatana (L) and their biological activities.

Nanotechnology is a field of science that consists of atoms, molecules and supramolecular molecules that create nanoparticles ranging in size from 1-100nm. Silver nanoparticles are widely used that are considered as effective antimicrobial agents. In this paper, the antioxidant activity of biosynthesized SNPs were analyzed by the DPPPH activity, hydrogen peroxide activity, hydroxyl RSA, TAC, TFC; their results confirmed that the phenolic compounds of this plant peels extracts enhanced the antioxidant and antiglycation activity with respect to silver nanoparticles. Biosynthesized nanoparticles of this plant extracts also showed strong zone of inhibition against the different Xanthomas, Pseudomonas and E. coli. This study concluded that biosynthesized nanoparticles of Mukia maderaspatna (M.M) plant peels extracts have the great biological activities i.e. antiglycation, antioxidant and antibacterial. More research is needed to know the exact dose rate and to compare the different dose combination of the plant with the strong antibiotic agents against these bacteria.

Biological activity of chitosan inducing resistance efficiency of rice (Oryza sativa L.) after treatment with fungal based chitosan.

Reduced pathogen resistance and management of the left-over rice stubble are among the most important challenges faced in rice cultivation. A novel and eco-friendly strategy to synthesise 'Fungal Chitosan' (FC) from Aspergillus niger using rice straw could serve as a sustainable treatment approach to improve both disease resistance and yields, while also effectively managing the rice stubble waste. The FC treatment promoted germination as well as growth parameters in rice varieties, TN1 (high yielding-susceptible) and PTB33 (low yielding-resistant) better than a commercial chitosan (PC). Treatments of exogenously applied FC to plants produced direct toxicity to Xoo, and reduced the BLB disease index by 39.9% in TN1. The capability of FC to trigger a cascade of defense pathways was evident from the measurable changes in the kinetics of defense enzymes, peroxidase (POD) and polyphenol oxidase (PPO). FC treatment increased levels of POD in TN1 by 59.4%, which was 35.3% greater than that of untreated PTB33. Therefore, the study demonstrated the effectiveness of FC treatments for use in agriculture as a potential biostimulant as well as protective agent against bacterial leaf blight, BLB, of rice (Oryza sativa) that could be produced from stubble waste and improve rice stubble management strategies.

Evaluation of Pomelo Seed Extracts as Natural Antioxidant, Antibacterial, Herbicidal Agents, and Their Functional Components.

Pomelo seeds (PS) are important by-product of pomelo fruits (Citrus grandis Osbeck). The value-added utilization of PS remains highly challenged. This study aimed to investigate the utilization potential of PS as natural antioxidant, antibacterial, herbicidal agents, and their functional components. The ethanolic extract (EE) of PS and its four fractions as PEE (petroleum ether extract), AcOEtE (ethyl acetate extract), BTE (butanol extract), and WE (water extract), were prepared and biologically evaluated. BTE exhibited the best antioxidant activity among all these extracts, in both ABTS (2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt) and FRAP (ferric reducing antioxidant power) assays. AcOEtE was superior to other extracts in herbicidal assay against both Festuca elata Keng (IC50 of 0.48 mg mL-1 ) and Amaranthus retroflexus L. (IC50 of 0.94 mg mL-1 ). Meanwhile, both AcOEtE and BTE demonstrated inhibitory effects against Bacillus subtilis, Escherichia coli, and Xanthomonas citri subsp. citri, with MIC ranging 2.5-5.0 mg mL-1 . Furthermore, the primary chemical components involving naringin, deacetylnomilin, limonin, nomilin, and obacunone, were quantified in all these extracts. PCA (principal component analysis) suggested that naringin might highly contribute to the antioxidant activity of PS, and the herbicidal activity should be ascribed to limonoids. This study successfully identified AcOEtE and BTE as naturally occurring antioxidant, antibacterial, and herbicidal agents, showing application potential in food and cosmetics industries, and organic farming agriculture.

Development of specific and selective bactericide by introducing exogenous metabolite of pathogenic bacteria.

The widespread and repeated use of broad-spectrum bactericides has led to an increase in resistance. Developing novel broad-spectrum bactericides cannot solve the resistance problem, and may even aggravate it. The design of specific and selective bactericides has become urgent. A specific bactericidal design strategy was proposed by introducing exogenous metabolites in this study. This strategy was used to optimize two known antibacterial agents, luteolin (M) and Isoprothiolane (D), against Xoo. Based on the prodrug principles, target compound MB and DB were synthesized by combing M or D with exogenous metabolites, respectively. Bactericidal activity test results demonstrated that while the antibacterial ability of target compounds was significantly improved, their selectivity was also well enhanced by the introducing of exogenous metabolites. Comparing with the original compound, the antibacterial activity of target compound was significantly increased 92.0% and 74.5%, respectively. The optimized target compounds were more easily absorbed, and the drug application concentrations were much lower than those of the original agents, which would greatly reduce environmental pollution and relieve resistance risk. Our proposed strategy is of great significance for exploring the specific and selective bactericides against other pathogens.

Novel Thiochromanone Derivatives Containing a Sulfonyl Hydrazone Moiety: Design, Synthesis, and Bioactivity Evaluation.

A series of novel thiochromanone derivatives containing a sulfonyl hydrazone moiety were designed and synthesized. Their structures were determined by 1H-NMR, 13C-NMR, and HRMS. Bioassay results showed that most of the target compounds revealed moderate to good antibacterial activities against Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicolaby, and Xanthomonas axonopodis pv. citri. Compound 4i had the best inhibitory activity against Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicolaby, and Xanthomonas axonopodis pv. citri, with the EC50 values of 8.67, 12.65, and 10.62 µg/mL, which were superior to those of Bismerthiazol and Thiodiazole-copper. Meanwhile, bioassay results showed that all of the target compounds proved to have lower antifungal activities against Sclerotinia sclerotiorum, Fusarium oxysporum, Gibberella zeae, Rhizoctonia solani, Verticillium dahlia, and Botrytis cinerea than those of Carbendazim.

Design, Synthesis and Antibacterial Activity of Novel Pyrimidine-Containing 4H-Chromen-4-One Derivatives*.

A series of pyrimidine-containing 4H-chromen-4-one derivatives were designed and synthesized by combining bioactive substructures. Preliminary biological activity results showed that most of the compounds displayed significant inhibitory activities in vitro against Xanthomonas axonopodis pv. Citri (X. axonopodis), Xanthomonas oryzae pv. oryzae (X. oryzae) and Ralstonia solanacearum (R. solanacearum). In particular, compound 2-[(3-{[5,7-dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-1-benzopyran-3-yl]oxy}propyl)sulfanyl]-4-(4-methylphenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile (4c) demonstrated a good inhibitory effect against X. axonopodis and X. oryzae, with the half-maximal effective concentration (EC50 ) values of 15.5 and 14.9 µg/mL, respectively, and compound 2-[(3-{[5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-1-benzopyran-3-yl]oxy}propyl)sulfanyl]-4-(3-fluorophenyl)-6-oxo-1,6-dihydropyrimidine-5-carbonitrile (4h) showed the best antibacterial activity against R. solanacearum with an EC50 value of 14.7 µg/mL. These results were better than commercial reagents bismerthiazol (BT, 51.7, 70.1 and 52.7 µg/mL, respectively) and thiodiazole copper (TC, 77.9, 95.8 and 72.1 µg/mL, respectively). In vivo antibacterial activity results indicated that compound 4c displayed better curative (42.4 %) and protective (49.2 %) activities for rice bacterial leaf blight than BT (35.2, 39.1 %) and TC (30.8, 27.3 %). The mechanism of compound 4c against X. oryzae was analyzed through scanning electron microscopy (SEM). These results indicated that pyrimidine-containing 4H-chromen-4-one derivatives have important value in the research of new agrochemicals.