Systemic evaluation of novel acaricide hexythiazox for bioactivity improvement and risk reduction at the enantiomer level.

Traditional risk assessments of chiral pesticides mainly depend on racemic form, which is often incomprehensive. This study conducted systemic investigations on the bioactivity, toxicity, and ecotoxicological effects of hexythiazox (HTZ) at the enantiomer level. The elution order and absolute configuration of HTZ enantiomers were determined. (4R, 5R)-(+)-HTZ exhibited 708 and 1719 times higher bioactivity against Tetranychus cinnabarinus and Tetranychus urticae eggs than (4S, 5S)-(-)-HTZ, respectively. Molecular docking indicated greater interactions between (4R, 5R)-(+)-HTZ and chitin synthase leading to higher bioactivity of (4R, 5R)-(+)-HTZ. However, (4S, 5S)-(-)-HTZ induced greater changes in protein and malondialdehyde content, and antioxidant and detoxification enzyme activities than (4R, 5R)-(+)-HTZ in earthworms. Furthermore, integrated biomarker response results indicated (4S, 5S)-(-)-HTZ exhibited higher toxic effects on earthworms than (4R, 5R)-(+)-HTZ. Finally, significant differentially expressed genes (DEGs) were observed in earthworms after exposure to (4R, 5R)-(+)-HTZ and (4S, 5S)-(-)-HTZ, respectively. These DEGs were mainly enriched in glycolysis/gluconeogenesis and purine metabolism pathways in earthworms. Additionally, six metabolism pathways were also enriched, including pyruvate metabolism, fatty acid biosynthesis, oxidative phosphorylation, citric acid cycle, fatty acid degradation, and ATP-binding cassette transporters. These findings suggest that earthworms exhibited enantiomer-specific responses to (4R, 5R)-(+)-HTZ and (4S, 5S)-(-)-HTZ. This study provides systemic insight into the toxicity mechanism of HTZ at the enantiomer level and the potential to develop (4R, 5R)-(+)-HTZ as a high-efficiency and low-risk pesticide.

Corrigendum: Favorable physiological and morphological effects of molybdenum nanoparticles on tobacco (Nicotiana tabacum L.): root irrigation is superior to foliar spraying.

[This corrects the article DOI: 10.3389/fpls.2023.1220109.].

Favorable physiological and morphological effects of molybdenum nanoparticles on tobacco (Nicotiana tabacum L.): root irrigation is superior to foliar spraying.

Introduction: Nano fertilizers can provide efficient solutions to the increasing problem of nutrient deficiency caused by low availability. However, the most important prerequisite is to fully understand whether nanomaterials induce phytotoxicity in plants under a variety of different conditions. The mechanisms underlying interactions between molybdenum nanoparticles (Mo NPs) and plants with respect to their uptake and biological effects on crops are still not fully understood. Methods: In this study, the impacts of Mo NPs over a range of concentrations (0, 25, and 100 µg/mL) on tobacco (Nicotiana tabacum L.) seedling growth were comparatively evaluated under foliar applications and root irrigation. Results: The results indicated that more significant active biological effects were observed with root irrigation application of Mo NPs than with foliar spraying. The agronomic attributes, water content and sugar content of Mo NPs-exposed seedlings were positively affected, and morphologically, Mo NPs induced root cell lignification and more vascular bundles and vessels in tobacco tissues, especially when applied by means of root irrigation. Moreover, the photosynthetic rate was improved by 131.4% for root exposure to 100 µg/mL Mo NPs, mainly due to the increased chlorophyll content and stomatal conductance. A significant concentration-dependent increase in malonaldehyde (MDA) and defensive enzyme activity for the Mo NPs-treated tobacco seedlings were detected compared to the controls. Significantly improved absorption of Mo by exposed tobacco seedlings was confirmed with inductively coupled plasma mass spectrometry (ICP-MS) in tobacco tissues, regardless of application method. However, the accumulation of Mo in roots increased by 13.94 times, when roots were exposed to 100 mg/L Mo NPs, higher than that under treatment with foliar spray. Additionally, Mo NPs activated the expression of several genes related to photosynthesis and aquaporin processes. Discussion: The present investigations offer a better understanding of Mo NPs-plant interactions in terrestrial ecosystems and provide a new strategy for the application of Mo NPs as nano fertilizers in crop production.

Comparative Study on the Fungicidal Activity of Metallic MgO Nanoparticles and Macroscale MgO Against Soilborne Fungal Phytopathogens.

Engineered nanoparticles have provided a basis for innovative agricultural applications, specifically in plant disease management. In this interdisciplinary study, by conducting comparison studies using macroscale magnesium oxide (mMgO), we evaluated the fungicidal activity of MgO nanoparticles (nMgO) against soilborne Phytophthora nicotianae and Thielaviopsis basicola for the first time under laboratory and greenhouse conditions. In vitro studies revealed that nMgO could inhibit fungal growth and spore germination and impede sporangium development more efficiently than could macroscale equivalents. Indispensably, direct contact interactions between nanoparticles and fungal cells or nanoparticle adsorption thereof were found, subsequently provoking cell morphological changes by scanning electron microscopy/energy-dispersive spectrometry (SEM/EDS) and transmission electron microscopy (TEM). In addition, the disturbance of the zeta potential and accumulation of various modes of oxidative stress in nMgO-exposed fungal cells accounted for the underlying antifungal mechanism. In the greenhouse, approximately 36.58 and 42.35% decreases in tobacco black shank and black root rot disease, respectively, could testify to the efficiency by which 500 µg/ml of nMgO suppressed fungal invasion through root irrigation (the final control efficiency reached 50.20 and 62.10%, respectively) when compared with that of untreated controls or mMgO. This study will extend our understanding of nanoparticles potentially being adopted as an effective strategy for preventing diversified fungal infections in agricultural fields.

Various antibacterial mechanisms of biosynthesized copper oxide nanoparticles against soilborne Ralstonia solanacearum.

The substantial antimicrobial efficacy of nanoparticles against phytopathogens has been extensively investigated for advanced agricultural applications. However, few reports have focused on soilborne pathogenic bacteria. The aim of this study was to obtain sustainably synthesized copper oxide nanoparticles (CuONPs) using papaya leaf extracts and investigate the bactericidal activity of these CuONPs against Ralstonia solanacearum, the cause of bacterial wilt, under laboratory and greenhouse conditions. The results showed that CuONPs possessed strong antibacterial activity and that all R. solanacearum were killed after exposure to 250 µg mL-1 CuONPs. CuONPs could interact with bacterial cells to prevent biofilm formation, reduce swarming motility and disturb ATP production. Ultrastructural observations by transmission electron microscopy (TEM) revealed that after interactions with CuONPs, bacterial cells suffered significantly from nanomechanical damage to the cytomembrane, accompanied by the absorption of multiple nanoparticles. In addition, molecular studies identified the downregulation mechanism of a series of genes involving pathogenesis and motility. The control efficiency of CuONPs in tobacco bacterial wilt disease management under greenhouse conditions was verified by root irrigation application, demonstrating that as-prepared CuONPs significantly reduced the disease occurrence and disease index. Our studies focused on developing biosynthesized nanoparticles as a biocompatible alternative for soilborne disease management.

MgONPs Can Boost Plant Growth: Evidence from Increased Seedling Growth, Morpho-Physiological Activities, and Mg Uptake in Tobacco (Nicotiana tabacum L.).

In this study, we documented the impact of magnesium oxide nanoparticles (MgONPs) on the various morpho-physiological changes by root irrigation in tobacco plants in the matrix media, as well as the uptake and accumulation of the NPs over a range of concentrations (50⁻250 µg/mL). Our results showed that the seed germination rate was not affected following exposure to MgONPs for 5 days. Enhanced plant growth together with increased peroxidase activity (39.63 U mg-1 protein in the 250 µg/mL MgONPs treatment, 36.63 U mg-1 protein in the control), superoxide dismutase activity (30.15 U mg-1 protein compared to 26.95 U mg-1 protein in the control), and chlorophyll content (the chlorophyll a and b contents in 0 and 250 µg/mL of MgONPs were 0.21, 0.12 µg/g to 1.21, 0.67 µg/g, respectively) were observed after 30 days of MgONP treatment. However, the malondialdehyde, protein, and relative water contents did not differ significantly, indicating that the NPs in the test concentrations had no phytotoxicity and even promoted plant growth. Scanning electron microscopy and paraffin section observations indicated that the MgONPs did not affect the plant tissue structures and cells. In addition, an elevated Mg content was detected in the plant tissues exposed to MgONPs, suggesting that the Mg was taken up by the tobacco roots and translocated to the shoots and leaves, which were probably the most important tools to cause an increase in the chlorophyll content and stimulate growth. In particular, compared with the controls, a substantially higher Mg content was observed in the leaves (12.93 mg/g in the MgONPs treatment, 9.30 mg/g in the control) exposed to 250 µg/mL MgONPs, especially in the lower and middle leaves. This result confirmed that the contents of plant Mg-element in the old leaves were increased by MgONPs. In summary, this study investigated increased Mg uptake and growth stimulation, as well as the induction of various positive morpho-physiological changes to tobacco plants when exposed to MgONPs. Results elucidate the promotional impact of the NPs on plant health and their implications for agricultural safety and security.

Magnesium Oxide Nanoparticles: Effective Agricultural Antibacterial Agent Against Ralstonia solanacearum.

Magnesium (Mg) is an essential mineral element for plants and is nontoxic to organisms. In this study, we took advantage of nanotechnologies to systematically investigate the antibacterial mechanisms of magnesium oxide nanoparticles (MgONPs) against the phytopathogen Ralstonia solanacearum (R. solanacearum) in vitro and in vivo for the first time. R. solanacearum has contributed to catastrophic bacterial wilt, which has resulted in the world-wide reduction of tobacco production. The results demonstrated that MgONPs possessed statistically significant concentration-dependent antibacterial activity, and the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured as 200 and 250 µg/mL, respectively. Additional studies, aimed at understanding the toxicity mechanism of MgONPs, indicated that physical injury occurred to the cell membranes, along with decreased motility and biofilm formation ability of R. solanacearum, due to the direct attachment of MgONPs to the surfaces of the bacterial cells, which was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Reactive oxygen species (ROS) accumulation could also be an important reason for the antibacterial action, inducing DNA damage. The toxicity assessment assay under greenhouse conditions demonstrated that the MgONPs had exerted a large effect on tobacco bacterial wilt, reducing the bacterial wilt index. Altogether, the results suggest that the development of MgONPs as alternative antibacterial agents will become a new research subject.

Various Physiological Response to Graphene Oxide and Amine-Functionalized Graphene Oxide in Wheat (Triticum aestivum).

An increasing number of investigations have been performed on the phytotoxicity of carbon-based nanomaterials duo to their extensive use in various fields. In the present study, we investigated the phytotoxicity of unfunctionalized graphene oxide (GO) and amine-functionalized graphene oxide (G-NH2) on wheat (Triticum aestivum) in the concentration range from 125 to 2000 µg/mL after 9 days of hydroponic culture. Our results found that the incubation with both nanomaterials did not affect the final seed germination rate, despite some influence in the initial stage. Transmission electron microscopy (TEM) observations indicated that exposure to GO at a high concentration (above 1000 µg/mL) resulted in a severe loss of morphology of seedlings, and a decrease in root length, shoot length and relative biomass, along with obvious damage to plant tissue structures (root, stem and leaf) when compared with the control. GO induced increased damage to root cells, which were determined by electrolyte leakage. Conversely, the plant growth was enhanced under G-NH2 exposure, and the root and stem lengths were increased by 19.27% and 19.61% at 2000 µg/mL, respectively. The plant tissue structures were not affected, and neither GO nor G-NH2 were observed to accumulate in the wheat plant root cells. The present investigations provide important information for evaluation of the environmental safety of GO and better understanding plant-nanoparticle interactions.

Validation of reference genes for quantitative gene expression analysis in Ralstonia pseudosolanacearum CQPS-1 under environment stress.

Quantitative real-time reverse transcriptase PCR (qRT-PCR) has become the method choice for quantification of gene expression changes, however, the accuracy of the method depends on the stability of reference genes. Ralstonia pseudosolanacearum (R. pseudosolanacearum) is an important plant pathogen, infecting >450 plant species and causing bacterial wilt. In order to identify stable reference genes in R. pseudosolanacearum CQPS-1 under different environment stresses. We used five tools (△Ct method, GeNorm, NormFinder, BestKeeper, and RefFinder) to evaluate the stability of seven candidate reference genes including phosphoglycerate kinase (PGK), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), 16S ribosomal RNA (16S), cell division protein ftsZ (ftsZ), DNA gyrase subunit A (gyrA), Ribosomal protein L13 (rplM), and phosphoserine aminotransferase (serC) under biotic (growth phases) and abiotic stress (temperature, hydroxycoumarins, nutrition). Overall, gyrA and serC were the most stable genes under different growth phases, while serC, gyrA and ftsZ during temperature stress, gyrA, ftsZ and 16S under hydroxycoumarins stress, and serC and 16S under nutrition stress conditions. This study provides useful resources for normalizing expression changes of target genes in R. pseudosolanacearum subjected to environment stress.

Effects of Aphidius gifuensis on the feeding behavior and potato virus Y transmission ability of Myzus persicae.

The stylet penetration behavior of aphids when feeding on plants is associated with virus acquisition and inoculation. Aphidius gifuensis (Ashmead) is a primary endoparasitoid of Myzus persicae (Sulzer) which is the most efficient vector of plant viruses. Information about the effects of parasitoid on aphid and virus transmission can provide an essential foundation for designing effective biological control strategies. This study aimed to investigate the effects of A. gifuensis on the feeding behavior and potato virus Y (PVY) transmission ability of M. persicae. The results showed that after M. persicae was parasitized by A. gifuensis, the duration of the first probe significantly decreased. Additionally, A. gifuensis exerted remarkable effects on aphid feeding in phloem ingestion. The contribution of the E1 waveform to the phloem phase was significantly higher in all parasitized aphids than in the control group. Although the time of infestation increased for parasitized aphids, the total duration of phloem sap ingestion decreased. Interestingly, the percentage of time M. persicae spent in the xylem and phloem phases only changed significantly on day 5. The percent transmission of PVY by the aphids parasitized on day 5 was lower than that in the control, but no significant differences were detected. The significance of this work is the demonstration that A. gifuensis can impede the feeding behavior of M. persicae, which sheds light on the biological basis of A. gifuensis as a natural enemy, but unfortunately does not provide an immediate solution for disrupting the transmission of PVY.

Overexpression of NtWRKY50 Increases Resistance to Ralstonia solanacearum and Alters Salicylic Acid and Jasmonic Acid Production in Tobacco.

WRKY transcription factors (TFs) modulate plant responses to biotic and abiotic stresses. Here, we characterized a WRKY IIc TF, NtWRKY50, isolated from tobacco (Nicotiana tabacum) plants. The results showed that NtWRKY50 is a nuclear-localized protein and that its gene transcript is induced in tobacco when inoculated with the pathogenic bacterium Ralstonia solanacearum. Overexpression of NtWRKY50 enhanced bacterial resistance, which correlated with enhanced SA and JA/ET signaling genes. However, silencing of the NtWRKY50 gene had no obvious effects on plant disease resistance, implying functional redundancy of NtWRKY50 with other TFs. In addition, it was found that NtWRKY50 can be induced by various biotic or abiotic stresses, such as Potato virus Y, Rhizoctonia solani, Phytophthora parasitica, hydrogen peroxide, heat, cold, and wounding as well as the hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). Importantly, additional analysis suggests that NtWRKY50 overexpression markedly promotes SA levels but prevents pathogen-induced JA production. These data indicate that NtWRKY50 overexpression leads to altered SA and JA content, increased expression of defense-related genes and enhanced plant resistance to R. solanacearum. These probably due to increased activity of endogenous NtWRKY50 gene or could be gain-of-function phenotypes by altering the profile of genes affected by NtWRKY50.

Exposure to Umbelliferone Reduces Ralstonia solanacearum Biofilm Formation, Transcription of Type III Secretion System Regulators and Effectors and Virulence on Tobacco.

Ralstonia solanacearum is one of the most devastating phytopathogens and causes bacterial wilt, which leads to severe economic loss due to its worldwide distribution and broad host range. Certain plant-derived compounds (PDCs) can impair bacterial virulence by suppressing pathogenic factors of R. solanacearum. However, the inhibitory mechanisms of PDCs in bacterial virulence remain largely unknown. In this study, we screened a library of coumarins and derivatives, natural PDCs with fused benzene and α-pyrone rings, for their effects on expression of the type III secretion system (T3SS) of R. solanacearum. Here, we show that umbelliferone (UM), a 7-hydroxycoumarin, suppressed T3SS regulator gene expression through HrpG-HrpB and PrhG-HrpB pathways. UM decreased gene expression of six type III effectors (RipX, RipD, RipP1, RipR, RipTAL, and RipW) of 10 representative effector genes but did not alter T2SS expression. In addition, biofilm formation of R. solanacearum was significantly reduced by UM, though swimming activity was not affected. We then observed that UM suppressed the wilting disease process by reducing colonization and proliferation in tobacco roots and stems. In summary, the findings reveal that UM may serve as a plant-derived inhibitor to manipulate R. solanacearum T3SS and biofilm formation, providing proof of concept that these key virulence factors are potential targets for the integrated control of bacterial wilt.

Graphene Oxide Induces Toxicity and Alters Energy Metabolism and Gene Expression in Ralstonia solanacearum.

Graphene oxide (GO) is a promising material for development as an antibacterial, phytoprotective agent due to its contact-based antibacterial activity induced by its physical and chemical properties. However, the mechanism underlying the antibacterial effect of GO has yet to be elucidated. In the current study, we investigated the effects of GO on the phytopathogen R. solanacearum at the molecular level with a specific focus on energy metabolism. Under controlled conditions, the bacteriostatic and bactericidal actions of GO were investigated with respect to concentration, treatment time and rotation speed. Transmission electron microscopy (TEM) and destabilization assays revealed that GO caused injury to bacterial cell membrane structures. Furthermore, adenosine triphosphate (ATP) levels decreased after exposure to sheets of GO, while malondialdehyde levels significantly increased, indicating the occurrence of lipid oxidation. A series of genes related to bacterial virulence, motility and oxidative stress were selected to evaluate the molecular mechanism underlying GO's effects on R. solanacearum. Using quantitative reverse transcription polymerase chain reaction (RT-qPCR), we showed that in the presence of GO, the expression levels of genes involved in virulence and motility were down regulated, with the exception of popA. The phcA, hrpB and flgG genes were significantly downregulated by 2.61-, 3.45- and 4.22-fold, respectively. Conversely, the expression levels of sodB, oxyR and dps, three important oxidative stress genes, were upregulated by 1.82-, 2.17-, and 3.79-fold, respectively. These findings confirmed that cell membrane damage and oxidative stress were responsible for the antibacterial actions of GO, in addition to disturbances to energy metabolism processes.

Resveratrol and Coumarin: Novel Agricultural Antibacterial Agent against Ralstonia solanacearum In Vitro and In Vivo.

Bacterial wilt is a destructive disease caused by the phytopathogen Ralstonia solanacearum (R. solanacearum), which is widely found in various tobacco-growing areas all over the world. Botanical bactericidal substances have gradually emerged as a hot topic in modern pesticide research. In this study, the antibacterial activities of two phytochemicals (resveratrol and coumarin) against R. solanacearum and their in vivo and in vitro efficacy for controlling tobacco bacterial wilt were evaluated. We rule out significant biological effects of both phytochemicals using transmission electron microscope (TEM) and fluorescence microscope, which suppressed the growth of R. solanacearum. Furthermore, we demonstrated that the toxicity mechanisms mainly involved damaging bacterial cell membrane and preventing swarming motility and biofilm formation. A further pot experiment demonstrated that coumarin and resveratrol significantly inhibited early adhesion and colonization of R. solanacearum in tobacco plants and the corresponding control efficacies were 68% and 85% after incubation for 13 days, respectively. The findings of this study suggest that both resveratrol and coumarin have potential as non-toxic antimicrobial strategies for controlling tobacco bacterial wilt disease.

Extract from Maize (Zea mays L.): Antibacterial Activity of DIMBOA and Its Derivatives against Ralstonia solanacearum.

Many cereals accumulate hydroxamic acids involved in defense of plant against various fungi, bacteria, and insects. 2,4-dihydroxy-7-methoxy-1,4-benzoxazine-3-one, commonly known as DIMBOA, is one of the principal cyclic hydroxamic acids in aqueous extracts of maize. The aim of this study was to evaluate the antibacterial activity of the isolated DIMBOA and its derivatives 2-benzoxazolinone (BOA), 6-chloro-2-benzoxazolinone (CDHB), and 2-mercaptobenzothiazole (MBT) against Ralstonia solanacearum. MBT showed the strongest antibacterial activity, followed by CDHB and DIMBOA, with minimum inhibitory concentrations (MICs) of 50, 100 and 200 mg/L, respectively, better than the BOA with 300 mg/L. These compounds also significantly affect bacterial growth, reduce biofilm formation, and inhibit swarming motility within 24 h. This paper is the first to report the anti-R. solanacearum activity of DIMBOA from Z. mays. The bioassay and pot experiment results suggested that DIMBOA and its derivatives exhibit potential as a new matrix structure of designing target bactericide or elicitor for controlling tobacco bacterial wilt. Further studies must evaluate the efficacy of DIMBOA and its derivatives in controlling bacterial wilt under natural field conditions where low inoculum concentrations exist.

Graphene Oxide-Silver Nanocomposite: Novel Agricultural Antifungal Agent against Fusarium graminearum for Crop Disease Prevention.

Nanoparticle-based antibacterial agents have emerged as an interdisciplinary field involving medicine, material science, biology, and chemistry because of their size-dependent qualities, high surface-to-volume ratio, and unique physiochemical properties. Some of them have shown great promise for their application in plant protection and nutrition. Here, GO-AgNPs nanocomposite was fabricated through interfacial electrostatic self-assembly and its antifungal activity against phytopathogen Fusarium graminearum was investigated in vitro and in vivo for the first time. The results demonstrated that the GO-AgNPs nanocomposite showed almost a 3- and 7-fold increase of inhibition efficiency over pure AgNPs and GO suspension, respectively. The spore germination inhibition was stimulated by a relatively low concentration of 4.68 µg/mL (minimum inhibition concentration (MIC)). The spores and hyphae were damaged, which might be caused by an antibacterial mechanism from the remarkable synergistic effect of GO-AgNPs, inducing physical injury and chemical reactive oxygen species generation. More importantly, the chemical reduction of GO mediated by fungal spores was possibly contributed to the high antimicrobial activity of GO-AgNPs. Furthermore, the GO-AgNPs nanocomposite showed a significant effect in controlling the leaf spot disease infected by F. graminearum in the detached leaf experiment. All the results from this research suggest that the GO-AgNPs nanocomposite developed in this work has the potential as a promising material for the development of novel antimicrobial agents against pathogenic fungi or bacteria.

Evaluation of the Antibacterial Effects and Mechanism of Action of Protocatechualdehyde against Ralstonia solanacearum.

Protocatechualdehyde (PCA) is an important plant-derived natural product that has been associated with a wide variety of biological activities and has been widely used in medicine as an antioxidant, anti-aging and an anti-inflammatory agent. However, fewer reports concerning its antibacterial effects on plant-pathogenic bacteria exist. Therefore, in this study, protocatechualdehyde was evaluated for its antibacterial activity against plant pathogens along with the mechanism of its antibacterial action. PCA at 40 µg/mL was highly active against R. solanacearum and significantly inhibited its growth. The minimum bactericidal concentration and minimum inhibitory concentration values for PCA were 40 µg/mL and 20 µg/mL, respectively. Further investigation of the mechanism of action of PCA via transmission electron microscopy and biological assays indicated that the destruction of the cell structure, the shapes and the inhibition of biofilm formation were important. In addition, the application of PCA effectively reduced the incidence of bacterial wilt on tobacco under greenhouse conditions, and the control efficiency was as high as 92.01% at nine days after inoculation. Taken together, these findings suggest that PCA exhibits strong antibacterial activity against R. solanacearum and has the potential to be applied as an effective antibacterial agent for controlling bacterial wilt caused by R. solanacearum.

New Insights into the Antibacterial Activity of Hydroxycoumarins against Ralstonia solanacearum.

Coumarins are important plant-derived natural products with wide-ranging bioactivities and extensive applications. In this study, we evaluated for the first time the antibacterial activity and mechanisms of action of coumarins against the phytopathogen Ralstonia solanacearum, and investigated the effect of functional group substitution. We first tested the antibacterial activity of 18 plant-derived coumarins with different substitution patterns, and found that daphnetin, esculetin, xanthotol, and umbelliferone significantly inhibited the growth of R. solanacearum. Daphnetin showed the strongest antibacterial activity, followed by esculetin and umbelliferone, with MICs of 64, 192, and 256 mg/L, respectively, better than the archetypal coumarin with 384 mg/L. We further demonstrated that the hydroxylation of coumarins at the C-6, C-7 or C-8 position significantly enhanced the antibacterial activity against R. solanacearum. Transmission electron microscope (TEM) and fluorescence microscopy images showed that hydroxycoumarins may interact with the pathogen by mechanically destroying the cell membrane and inhibiting biofilm formation. The antibiofilm effect of hydroxycoumarins may relate to the repression of flagellar genes fliA and flhC. These physiological changes in R. solanacearum caused by hydroxycoumarins can provide information for integral pathogen control. The present findings demonstrated that hydroxycoumarins have superior antibacterial activity against the phytopathogen R. solanacearum, and thus have the potential to be applied for controlling plant bacterial wilt.

Graphene oxide exhibits broad-spectrum antimicrobial activity against bacterial phytopathogens and fungal conidia by intertwining and membrane perturbation.

To understand the interaction mechanism between graphene oxide (GO) and typical phytopathogens, a particular investigation was conducted about the antimicrobial activity of GO against two bacterial pathogens (P. syringae and X. campestris pv. undulosa) and two fungal pathogens (F. graminearum and F. oxysporum). The results showed that GO had a powerful effect on the reproduction of all four pathogens (killed nearly 90% of the bacteria and repressed 80% macroconidia germination along with partial cell swelling and lysis at 500 µg mL(-1)). A mutual mechanism is proposed in this work that GO intertwinds the bacteria and fungal spores with a wide range of aggregated graphene oxide sheets, resulting in the local perturbation of their cell membrane and inducing the decrease of the bacterial membrane potential and the leakage of electrolytes of fungal spores. It is likely that GO interacts with the pathogens by mechanically wrapping and locally damaging the cell membrane and finally causing cell lysis, which may be one of the major toxicity actions of GO against phytopathogens. The antibacterial mode proposed in this study suggests that the GO may possess antibacterial activity against more multi-resistant bacterial and fungal phytopathogens, and provides useful information about the application of GO in resisting crop diseases.

Hierarchical nanogaps within bioscaffold arrays as a high-performance SERS substrate for animal virus biosensing.

A three-dimensional (3D) biomimetic SERS substrate with hierarchical nanogaps was formed on the bioscaffold arrays of cicada wings by one-step and reagents-free ion-sputtering techniques. This approach requires a minimal fabrication effort and cost and offers Ag nanoislands and Ag nanoflowers with four types of nanogaps (<10 nm) on the chitin nanopillars to generate a high density of hotspots (∼2000/µm2). The 3D biomimetic substrate shows a low detection limit to Rhodamine 6G (10(-13) M), high average enhancement factor (EF, 5.8×10(7)), excellent signal uniformity (5.4%), good stability, and suitability in biosensing. Furthermore, the finite-difference time-domain (FDTD) electric-field-distribution simulations illustrate that the 3D biomimetic SERS substrate provides the high-density hotspot area within a detection volumem, resulting in enormous SERS enhancement. In addition, the conspicuous far-field plasmon resonance peaks were not found to be a strong requirement for a high EF in 3D biomimetic substrates. Additionally, the novel substrate was applied in label-free animal viruses detection and differentiation with small amounts (1.0 µL) and low concentrations of analyte (1×10(3) PFU/mL), and it exhibited potential as an effective SERS platform for virus detection and sensing.