Xanthomonas Research Articles

Broad host range bacteriophages found in rhizosphere soil of a healthy tomato plant in Bulgaria

The urgent need of research of new approaches to control bacterial disease on economical important crops, focuses our attention on bacteriophages as alternative biocontrol agents. Thus, the purpose of this paper is to present the isolation and initial characterization of three bacteriophages (SfXv124t/1, 2 and 3) isolated from rhizosphere soil of a healthy tomato plant in Bulgaria that are capable to lyse three phytopathogenic bacteria. The initial characterization includes determination of: their host range, plaque morphology, optimal storage temperature of pure phage lysates, their sensitivity to UV light, thermal inactivation, optimal multiplicity of infection (MOI) and virion morphology. The obtained results showed that one of the phage isolates was capable to lyse wild strains from three phytopathogenic bacterial species: Xanthomonas vesicatoria, Xanthomonas euvesicatoria and Xanthomonas gardneri, and the two remaining phages were active against X. vesicatoria and X. euvesicatoria. On X. vesicatoria lawn, the phages produced the same plaque types that differed only in their size. Storage at 4 °C for 26 days did not lead to decrease in phage titer as opposed to storage at 28 °C followed by decrease to varying degree for all three phages. The results obtained after exposure of the phage lysates to sunlight (UVA + B) and UVC light in separate experiments showed that UVC had a potent phagocidal effect as after 50 min of exposure there were no viable phages in the samples. UVA an UVB had lethal effect for two of the phage isolates and absolutely no lethal effect for the third one as after 50 min of exposure to sunlight there was no decrease in the initial phage titer. Phage isolates were tested for their thermal inactivation after incubation of pure phage lysates at three different temperatures: 55 °C, 75 °C and 95 °C for a period of 10 and 30 min. The most lethal temperature turned out to be 95 °C as after 10 min there were no viable phages in the samples. Phage isolate SfXv124t/1 was the most susceptible as its titer decreased by 1 lg after 10 min of incubation at 55 °C and by another 1 lg after 30 min. The most thermally resistant isolate was SfXv124t/3 as its titer remained stable after 30 min of incubation at 55 °C and decreased only by lg after incubation at 75 °C for 10 min. The optimal MOI for SfXv124t/3 was 0,01 (tested range 0,01–100) with maximal phage titer, reported at the 24th hour of incubation. TEM micrographs of the same isolates reveals that it belongs to family Podoviridae.

Trends in Molecular Diagnosis and Diversity Studies for Phytosanitary Regulated Xanthomonas.

Bacteria in the genus Xanthomonas infect a wide range of crops and wild plants, with most species responsible for plant diseases that have a global economic and environmental impact on the seed, plant, and food trade. Infections by Xanthomonas spp. cause a wide variety of non-specific symptoms, making their identification difficult. The coexistence of phylogenetically close strains, but drastically different in their phenotype, poses an added challenge to diagnosis. Data on future climate change scenarios predict an increase in the severity of epidemics and a geographical expansion of pathogens, increasing pressure on plant health services. In this context, the effectiveness of integrated disease management strategies strongly depends on the availability of rapid, sensitive, and specific diagnostic methods. The accumulation of genomic information in recent years has facilitated the identification of new DNA markers, a cornerstone for the development of more sensitive and specific methods. Nevertheless, the challenges that the taxonomic complexity of this genus represents in terms of diagnosis together with the fact that within the same bacterial species, groups of strains may interact with distinct host species demonstrate that there is still a long way to go. In this review, we describe and discuss the current molecular-based methods for the diagnosis and detection of regulated Xanthomonas, taxonomic and diversity studies in Xanthomonas and genomic approaches for molecular diagnosis.

Impact of Plant Pathogen Infection on Salmonella enterica subsp. enterica Serotype Typhimurium Persistence in Tomato Plants

We investigated whether the co-occurrence of phytopathogens (Clavibacter michiganensis subsp. michiganensis [Cmm] and Xanthomonas gardneri [Xg]) frequently encountered in tomato production and Salmonella enterica subsp. enterica serotype Typhimurium (strain JSG626) affects the persistence of these pathogens in tomato plant tissues during the early stages of plant growth. Cmm increased the recovery of Salmonella Typhimurium (up to 1.8 log CFU per plant at 21 days postinoculation [DPI]) from coinoculated tomato plants compared with plants inoculated with Salmonella Typhimurium alone (P < 0.05). Xg had no effect on Salmonella Typhimurium persistence in the plants. Increased persistence of Salmonella Typhimurium was also observed when it was inoculated 7 days after Cmm inoculation of the same plant (P < 0.05). In contrast, Salmonella Typhimurium reduced the population of both Cmm and Xg (up to 1.5 log CFU per plant at 21 DPI; P < 0.05) in coinoculated plants compared with plants inoculated with Cmm or Xg alone. The Xg population increased (1.16 log CFU per plant at 21 DPI; P < 0.05) when Salmonella Typhimurium was inoculated 7 days after Xg inoculation compared with plants inoculated with Xg alone. Our findings indicate that the type of phytopathogen present in the phyllosphere and inoculation time influence the persistence of Salmonella Typhimurium JSG626 and its interactions with phytopathogens cocolonized in tomato plants. Salmonella reduced the phytopathogen load in plant tissues, and Cmm enhanced the recovery of Salmonella from the coinoculated plant tissues. However, further investigations are needed to understand the mechanisms behind these interactions.

Plant SWEETs: from sugar transport to plant-pathogen interaction and more unexpected physiological roles.

Sugars Will Eventually be Exported Transporters (SWEETs) have important roles in numerous physiological mechanisms where sugar efflux is critical, including phloem loading, nectar secretion, seed nutrient filling, among other less expected functions. They mediate low affinity and high capacity transport, and in angiosperms this family is composed by 20 paralogs on average. As SWEETs facilitate the efflux of sugars, they are highly susceptible to hijacking by pathogens, making them central players in plant–pathogen interaction. For instance, several species from the Xanthomonas genus are able to upregulate the transcription of SWEET transporters in rice (Oryza sativa), upon the secretion of transcription-activator-like effectors. Other pathogens, such as Botrytis cinerea or Erysiphe necator, are also capable of increasing SWEET expression. However, the opposite behavior has been observed in some cases, as overexpression of the tonoplast AtSWEET2 during Pythium irregulare infection restricted sugar availability to the pathogen, rendering plants more resistant. Therefore, a clear-cut role for SWEET transporters during plant–pathogen interactions has so far been difficult to define, as the metabolic signatures and their regulatory nodes, which decide the susceptibility or resistance responses, remain poorly understood. This fuels the still ongoing scientific question: what roles can SWEETs play during plant–pathogen interaction? Likewise, the roles of SWEET transporters in response to abiotic stresses are little understood. Here, in addition to their relevance in biotic stress, we also provide a small glimpse of SWEETs importance during plant abiotic stress, and briefly debate their importance in the particular case of grapevine (Vitis vinifera) due to its socioeconomic impact.

The HrpG/HrpX Regulon of Xanthomonads-An Insight to the Complexity of Regulation of Virulence Traits in Phytopathogenic Bacteria.

Bacteria of the genus Xanthomonas cause a wide variety of economically important diseases in most crops. The virulence of the majority of Xanthomonas spp. is dependent on secretion and translocation of effectors by the type 3 secretion system (T3SS) that is controlled by two master transcriptional regulators HrpG and HrpX. Since their discovery in the 1990s, the two regulators were the focal point of many studies aiming to decipher the regulatory network that controls pathogenicity in Xanthomonas bacteria. HrpG controls the expression of HrpX, which subsequently controls the expression of T3SS apparatus genes and effectors. The HrpG/HrpX regulon is activated in planta and subjected to tight metabolic and genetic regulation. In this review, we cover the advances made in understanding the regulatory networks that control and are controlled by the HrpG/HrpX regulon and their conservation between different Xanthomonas spp.

The type VI secretion system of Xanthomonas phaseoli pv. manihotis is involved in virulence and in vitro motility

BackgroundThe type VI protein secretion system (T6SS) is important in diverse cellular processes in Gram-negative bacteria, including interactions with other bacteria and with eukaryotic hosts. In this study we analyze the evolution of the T6SS in the genus Xanthomonas and evaluate its importance of the T6SS for virulence and in vitro motility in Xanthomonas phaseoli pv. manihotis (Xpm), the causal agent of bacterial blight in cassava (Manihot esculenta). We delineate the organization of the T6SS gene clusters in Xanthomonas and then characterize proteins of this secretion system in Xpm strain CIO151.ResultsWe describe the presence of three different clusters in the genus Xanthomonas that vary in their organization and degree of synteny between species. Using a gene knockout strategy, we also found that vgrG and hcp are required for maximal aggressiveness of Xpm on cassava plants while clpV is important for both motility and maximal aggressiveness.ConclusionWe characterized the T6SS in 15 different strains in Xanthomonas and our phylogenetic analyses suggest that the T6SS might have been acquired by a very ancient event of horizontal gene transfer and maintained through evolution, hinting at their importance for the adaptation of Xanthomonas to their hosts. Finally, we demonstrated that the T6SS of Xpm is functional, and significantly contributes to virulence and motility. This is the first experimental study that demonstrates the role of the T6SS in the Xpm-cassava interaction and the T6SS organization in the genus Xanthomonas.

Ekonomski najznačajnije bakterioze pasulja

Beans are an important plant species that is grown in our agroecological conditions. One of the significant factors in the reduction and quality of yield are phytopathogenic bacteria that appear on leaves, stems, pods and seeds. Also, one of the reasons for the frequent incidence of the disease is the use of seeds that are not declared, and very often infected. In our conditions, depending on the environmental conditions, two species from the genus Xanthomonas and Pseudomonas predominantly appear. Species Xanthomonas axonopodis pv. phaseoli, the causal agent of common bacterial blight is affected by warmer and wet conditions, while the species Pseudomonas savastanoi pv. phaseolicola is affected by colder weather and humid conditions. Other bacteria that appear are of minor economic importance.

Occurrence of Bacterial Spot in Illinois Tomato Fields and Characteristics of the Causal Agents

Bacterial spot, caused by Xanthomonas spp., is one of the most important diseases of tomato in Illinois. Field surveys were conducted during 2017–19 to assess occurrence of bacterial spot in commercial tomato fields. Severity of foliage and fruit infection was recorded, and symptomatic samples were collected from three-to-five cultivars in three different farms in each of northern, central, and southern regions of Illinois. Severity of symptomatic foliage ranged from 0% to 91% (average 36.7%) and incidence of symptomatic fruit ranges from 0% to 30% (average 10.8%). During the surveys, 266 Xanthomonas isolates were collected and identified as Xanthomonas gardneri and X. perforans using Xanthomonas-specific hrp primers. Eighty-six percent of the isolates from the northern region were identified as X. gardneri, whereas 73% of the isolates from southern region were identified as X. perforans. Isolates from the central region were identified as X. perforans and X. gardneri 53% and 47% of the time, respectively. Multilocus sequence analysis using six housekeeping genes (fusA, gap-1, gltA, gyrB, lepA, and lacF) revealed the endemic population of X. gardneri and X. perforans. In addition to Xanthomonas, nine non-Xanthomonas bacterial genera were isolated from the samples, with most of the isolates classified as Microbacterium, Pantoea, and Pseudomonas.

Bioactive metabolites from tomato endophytic fungi with antibacterial activity against tomato bacterial spot disease

Endophytic fungi are potential antimicrobial agents that play an important role in improving plant growth. Endophytic fungi from healthy tomato plants have been evaluated for their potential antibacterial activity against Xanthomonas vesicatoria causing bacteria spot disease of tomato Thirty-eight different endophytic fungal isolates were isolated, and their extracts were screened for antibacterial activity using the well diffusion method. Three isolates showed strong antibacterial activity, which were molecularly identified as Diaporthe phaseolorum (USt1), Aspergillus fumigatus (USt2) and Aspergillus versicolor (USt3), respectively. Comparison of the components of the extracts between three isolates was made using a gas chromatography-mass spectrometry. Thirty eight compounds were found in A. fumigatus, thirty six compounds in D. phaseolorum and fourty two compounds were found in A. versicolor. The most prevalent compounds were acetol, hexanoic acid and acetic acid in all three fungi. Hexanoic acid (39.52%), acetic acid (8.95%) and acetol (8.10%), were found in A. fumigatus. However, the D. phaseolorum extract contained mainly hexanoic acid (42.35%) and acetic acid (11.89%) and acetol (9.52%), while A. versicolor contained hexanoic acid (34.44%), acetic acid (13.44%) and acetol (10.61%). Our results suggest that the three active endophytic fungi isolates provide a basis for the identification of new bioactive compounds, and for the effective biocontrol of bacterial spot of tomato.

Transmission of Xanthomonas gardneri to tomato seedlings during transportation and transplanting

Xanthomonas gardneri is the common causal agent of bacterial spot affecting field tomatoes in Ontario, Canada but spread during seedling transportation and transplanting is poorly understood. Spread during transportation and irrigation was determined by placing symptomatic seedlings at the top of a simulated plug trailer with healthy seedlings 30.5, 61.0, 91.5, and 122 cm below to assess pathogen movement with different irrigation treatments. The incidence of seedlings with symptoms 14 days after irrigation in the top to bottom (3.9%) and bottom to top (5.4%) treatments was greater than the dip treatment (0.4%). Symptoms were found at all distances below the inoculation point. A second set of experiments looked at spread in a transplanter by placing wet or dry symptomatic seedlings through the transplanter prior to healthy seedlings. Epiphytic X. gardneri was found on healthy seedlings from all diseased treatments 14 days after treatment, indicating transmission of X. gardneri during transplanting. A third set of experiments assessed the impact of transplanter transmission in the field by monitoring symptom appearance in initially healthy seedlings planted in rows with either machine-transplanted diseased plants or hand-planted diseased plants. There was no difference in the time to symptom appearance, except for one plant position which was not in the direction of transplanting. Thus, factors other than contaminated transplanters may be more important in X. gardneri transmission under field conditions. Best management practices for bacterial spot in field tomatoes should consider irrigation practices in plug trailers, while the contribution of contaminated transplanters to epidemics is likely limited.

PATHOLOGICAL, BIOCHEMICAL AND MOLECULAR CHARACTERIZATION OF THE SEED-BORNE BACTERIA "PANTOEA SPP., XANTHOMONAS SPP. AND PSEUDOMONAS SPP." FROM SOLANACEOUS PLANTS IN EGYPT

The seed-borne bacterial diseases of family solanaceae cause significant economic losses worldwide. In the present study, fourteen bacterial isolates were recovered from seeds of different varieties of tomato, eggplant, black nightshade and tobacco. The seed samples were collected from different locations in Egypt. Isolated bacteria were identified based on morphological, physiological and biochemical tests as well as colonial morphology aspects on the differential medium, yeast extract dextrose calcium carbonate (YDC) besides the selective media (PA 20, King's B and Tween B). Pathogenicity of the isolated bacteria was assessed for causing graywall, bacterial speck and bacterial spot symptoms on tomato seedlings. Disease symptoms were recognized on leaves and stems of the inoculated seedlings. Re-isolation from collected seeds of the inoculated tomato plants was performed. Results indicated that Pantoea spp. was an endophytic bacteria, Pseudomonas spp. was an epiphytic bacteria, while Xanthomonas spp. was both epiphytic and endophytic bacteria. Furthermore, cellular fatty acids composition were identified and quantified to give a profile for tested bacterial isolates. Moreover, the bacterial isolates were identified at the molecular level via PCR reactions utilizing the 16S rRNA gene. Partial DNA sequences were analyzed using BLAST tool revealed that the inferred 16S rRNA partial sequences of the 7 isolates showed similarity to Pantoea ananatis (3 isolates), Pseudomonas syringae pv. tomato (2 isolates) and Xanthomonas vesicatoria (2 isolates). To the best of our knowledge the bacterium associated with the graywall seems to be first report of P. ananatis isolated from tomato fruits and black nightshade seeds in Egypt.

Potential application of natural phenolic antimicrobials and edible film technology against bacterial plant pathogens

Abstract The aim of the present study is to use antimicrobial edible film technology and natural phenolic antimicrobials for inhibition of major bacterial plant pathogens such as Erwinia amylovora, Erwinia carotovora, Xanthomonas vesicatoria and Pseudomonas syringae. For this purpose phenolic acids (PAs) (gallic (GA), vanillic (VA), cinnamic acids (CA)), essential oils (EOs) (carvacrol (CAR), thymol (THY), eugenol (EUG) citral (CIT)), phenolic extracts (PEs) from clove (CE), oregano (OE), artichoke stem (ASE) and walnut shells (WSE) were evaluated as antimicrobial zein film components. Films containing PAs between 1 and 4 mg/cm2 inhibited all pathogens while EOs between 1 and 4 mg/cm2 and CE between 4 and 8 mg/cm2 inhibited pathogens except P. syringae. The most potent films were obtained by using GA against E. amylovora and P. syringae, VA against E. carotovora, and CA, THY or CAR against X. vesicatoria. The addition of phenolic compounds into films increased the porosity of films. The phenolic containing films also become more flexible and lost their brittleness. This study is important in that it prepared the basis of using edible antimicrobial coatings in outdoor applications on infected tree stems, soil surfaces and agronomy tools or in classical fruit and seedling coating applications to control bacterial contamination or spoilage.

In vitro antibacterial activity of Magnolia tamaulipana against tomato phytopathogenic bacteria

The tomato (Solanum lycopersicum Linnaeus) is one of the most important vegetable crops in the world. Still, there are phytopathogenic bacteria that cause a decrease in the yield or can kill the plant, like Pseudomonas syringae pv. tomato (Pst), Xanthomonas vesicatoria (Xv), Clavibacter michiganensis subsp. michiganensis (Cmm), Ralstonia solanacearum (Rs ) and Agrobacterium tumefeciens (At). Synthetic chemical fungicides are primarily used to control plant pathogenic bacteria, but their rapid growth makes them resistant to control. This research work is aimed at assessing the in vitro antibacterial activity of the ethanolic extract of Magnolia tamaulipana Vazquez leaves against Rs, Pst, Xv, Cmm, and At, as well as obtaining information about this plant species' chemical composition. The extract inhibited the growth of the five phytopathogenic bacteria that were tested. The growth inhibition rate ranged between 8.22 and 100%. The inhibitory concentration, IC&lt;sub&gt;50(90)&lt;/sub&gt;, required to inhibit 50 (90%) of Pst, Xv, Cmm, and At bacterial growth, was 34.71 (39.62), 23.09 (441.88), 64.75 (176.73) and 97.72 (535.48) ppm, respectively. The phytochemical analysis detected the presence of phenols, tannins, terpenes, saponins. M. tamaulipana ethanolic extract has antimicrobial properties and it must be considered a new control agent.

Genetic and structural determinants on iron assimilation pathways in the plant pathogen Xanthomonas citri subsp. citri and Xanthomonas sp.

Iron is a vital nutrient to bacteria, not only in the basal metabolism but also for virulent species in infection and pathogenicity at their hosts. Despite its relevance, the role of iron in Xanthomonas citri infection, the etiological agent of citrus canker disease, is poorly understood in contrast to other pathogens, including other members of the Xanthomonas genus. In this review, we present iron assimilation pathways in X. citri including the ones for siderophore production and siderophore-iron assimilation, proven to be key factors to virulence in many organisms like Escherichia coli and Xanthomonas campestris. Based on classical iron-related proteins previously characterized in E. coli, Pseudomonas aeruginosa, and also Xanthomonadaceae, we identified orthologs in X. citri and evaluated their sequences, structural characteristics such as functional motifs, and residues that support their putative functions. Among the identified proteins are TonB-dependent receptors, periplasmic-binding proteins, active transporters, efflux pumps, and cytoplasmic enzymes. The role of each protein for the bacterium was analyzed and complemented with proteomics data previously reported. The global view of different aspects of iron regulation and nutrition in X. citri virulence and pathogenesis may help guide future investigations aiming the development of new drug targets against this important phytopathogen.

Development of Real-Time and Colorimetric Loop Mediated Isothermal Amplification Assay for Detection of Xanthomonas gardneri

Xanthomonas gardneri is one of the causal agents of bacterial spot (BS), an economically important bacterial disease of tomato and pepper. Field-deployable and portable loop-mediated isothermal amplification (LAMP)-based instruments provide rapid and sensitive detection of plant pathogens. In order to rapidly and accurately identify and differentiate X. gardneri from other BS-causing Xanthomonas spp., we optimized a new real-time monitoring LAMP-based method targeting the X. gardneri-specific hrpB gene. Specificity and sensitivity of real-time and colorimetric LAMP assays were tested on the complex of bacterial strains pathogenic to tomato and pepper and on plants infected by the pathogen. The assay detection limit was 1 pg/μL of genomic DNA with an assay duration of only 30 min. The use of portable and handheld instruments allows for fast analysis, reducing the diagnosis time, and can contribute to proper disease management and control of X. gardneri. Due to the high efficiency of this method, we suggest its use as a standard diagnostic tool during phytosanitary controls.

Novel Xanthomonas Species From the Perennial Ryegrass Seed Microbiome - Assessing the Bioprotection Activity of Non-pathogenic Relatives of Pathogens.

The productivity of the Australian dairy industry is underpinned by pasture grasses, and importantly perennial ryegrass. The performance of these pasture grasses is supported by the fungal endophyte Epichloë spp. that has bioprotection activities, however, the broader microbiome is not well characterized. In this study, we characterized a novel bioprotectant Xanthomonas species isolated from perennial ryegrass (Lolium perenne L. cv. Alto). In vitro and in planta bioassays against key fungal pathogens of grasses (Sclerotium rolfsii, Drechslera brizae and Microdochium nivale) indicated strong bioprotection activities. A complete circular chromosome of ∼5.2 Mb was generated for three strains of the novel Xanthomonas sp. Based on the 16S ribosomal RNA gene, the strains were closely related to the plant pathogen Xanthomonas translucens, however, comparative genomics of 22 closely related xanthomonad strains indicated that these strains were a novel species. The comparative genomics analysis also identified two unique gene clusters associated with the production of bioprotectant secondary metabolites including one associated with a novel nonribosomal peptide synthetase and another with a siderophore. The analysis also identified genes associated with an endophytic lifestyle (e.g., Type VI secretion system), while no genes associated with pathogenicity were identified (e.g., Type III secretion system and effectors). Overall, these results indicate that these strains represent a novel, bioactive, non-pathogenic species of the genus Xanthomonas. Strain GW was the designated type strain of this novel Xanthomonas sp.

Citrus CsACD2 Is a Target of Candidatus Liberibacter Asiaticus in Huanglongbing Disease.

Citrus Huanglongbing (HLB), caused by Candidatus Liberibacter asiaticus (Las), is one of the most destructive citrus diseases worldwide, yet how Las causes HLB is poorly understood. Here we show that a Las-secreted protein, SDE15 (CLIBASIA_04025), suppresses plant immunity and promotes Las multiplication. Transgenic expression of SDE15 in Duncan grapefruit (Citrus × paradisi) suppresses the hypersensitive response induced by Xanthomonas citri ssp. citri (Xcc) and reduces the expression of immunity-related genes. SDE15 also suppresses the hypersensitive response triggered by the Xanthomonas vesicatoria effector protein AvrBsT in Nicotiana benthamiana, suggesting that it may be a broad-spectrum suppressor of plant immunity. SDE15 interacts with the citrus protein CsACD2, a homolog of Arabidopsis (Arabidopsis thaliana) ACCELERATED CELL DEATH 2 (ACD2). SDE15 suppression of plant immunity is dependent on CsACD2, and overexpression of CsACD2 in citrus suppresses plant immunity and promotes Las multiplication, phenocopying overexpression of SDE15. Identification of CsACD2 as a susceptibility target has implications in genome editing for novel plant resistance against devastating HLB.

Optimization, characterization and antimicrobial activity of silver nanoparticles against plant bacterial pathogens phyto-synthesized by Mentha longifolia

The present study involves the Phyto-synthesis of the colloidal silver nanoparticles (AgNPs) and their applications to biologically control plant bacterial pathogens. The synthesis of AgNPs was monitored by measuring the absorbance and a characteristic surface plasmon resonance (SPR) band was observed at 450 nm. The different reaction conditions such as the temperature, incubation period, the concentration of the silver salt and the pH were optimized using the factorial design of the experiment for the better yield and the synthesis of AgNPs. The microscopic results showed that the AgNPs are anisotropic and nearly spherical and exist in the size range of ∼20–100 nm while the EDX analysis confirmed the presence of the elemental Ag. The x-ray diffraction pattern confirmed that the AgNPs are crystalline. The hydrodynamic diameter of AgNPs has measured in the range of ∼13–35 nm and the average size of a single particle was 15.55 nm. The ability of the AgNPs to biologically control the plant bacterial pathogens was measured in terms of antibacterial activity against gram-negative pathogenic bacterial strains; Pectobacterium carotovorum, Xanthomonas oryzae, Xanthomonas vesicatoria and Ralstonia solanacearum and potential antimicrobial activity were observed between 2–12 μg ml−1. The biocompatibility studies revealed that the AgNPs are highly biocompatible (LD100 208 μg ml−1) against RBCs. These findings endorse the applications of AgNPs to biological control the plant bacterial pathogens and the consumption of the plants treated with NPs is biocompatible for the humans.

Systemic Acquired Resistance Induced by Compatible and Incompatible Tomato Mosaic Viruses Effectively Controls Bacterial Spot and Speck Diseases in Tomato

Tomato plants (Solanum lycopersicum L.) cv. Moperou, which possess gene Tm-2 for resistance against tomato mosaic virus (ToMV), were pre-inoculated with compatible pathotype P2 or incompatible pathotype P0 strains of ToMV and subsequently challenge infected with Pseudomonas syringae pv. tomato and Xanthomonas vesicatoria. It was found that both types of virus strains, compatible and incompatible, induced systemic acquired resistance (SAR), which protected plants from subsequent pathogen infection. The percentage of protection of the compatible ToMV pathotype P2 strain was 100% against both bacterial infections, while that of the incompatible ToMV pathotype P0 strain varied from 26 to 77% within the timeline and depended on the pathogen races. The SAR induced by ToMV was confirmed by the increased antioxidant defense and hydrogen peroxide content in the leaves of tomato plants inoculated with compatible and incompatible ToMV strains.

The genetic arms race between plant and Xanthomonas: lessons learned from TALE biology.

The pathogenic bacterial genus Xanthomonas infects a wide variety of host plants and causes devastating diseases in many crops. Transcription activator-like effectors (TALEs) are important virulence factors secreted by Xanthomonas with the ability to directly bind to the promoters of target genes in plant hosts and activate their expression, which often facilitates the proliferation of pathogens. Understanding how plants cope with TALEs will provide mechanistic insights into crop breeding for Xanthomonas defense. Over the past 30 years, numerous studies have revealed the modes of action of TALEs in plant cells and plant defense strategies to overcome TALE attack. Based on these findings, new technologies were adopted for disease management to optimize crop production. In this article, we will review the most recent advances in the evolutionary arms race between plant resistance and TALEs from Xanthomonas, with a specific focus on TALE applications in the development of novel breeding strategies for durable and broad-spectrum resistance.