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Introduction: Bacterial spot, caused by diverse xanthomonads classified into four lineages within three species, poses a significant threat to global pepper and tomato production. In Taiwan, tomato bacterial spot xanthomonads phylogenetically related to an atypical Xanthomonas euvesicatoria pv. perforans (Xep) strain NI1 from Nigeria were found. Methods: To investigate the genetic structure of Taiwanese Xep strains and determine the phylogenetic position of the atypical strains, we completed high-quality, gap-free, circularized genomes of seven Taiwanese Xep strains and performed comparative genomic analyses with genomes of X. euvesicatoria pathovars. Average nucleotide identity, core genome analysis, and phylogenomic analysis were conducted. Results: Three sequenced strains were identified as typical Xep , while four clustered with the atypical strain NI1, forming a distinct genomovar within X. euvesicatoria, proposed as X. euvesicatoria genomovar taiwanensis (Xet). This new lineage likely originated in Taiwan and spread to Nigeria through global seed trade. At the genomovar level, chromosomes remained conserved among Taiwanese strains, while plasmids likely contributed to bacterial virulence, avirulence, and field fitness. Gap-free genomes revealed associations between the evolution of type III effectors, horizontal gene transfer events, plasmid diversity, and recombination. Discussion: This study highlights the critical roles of horizontal gene transfer and plasmids in shaping the genetic makeup, evolution, and environmental adaptation of plant pathogenic xanthomonads. The identification of a new genomovar, X. euvesicatoria genomovar taiwanensis , provides insights into the diversity and global spread of bacterial spot pathogens through seed trade. [ABSTRACT FROM AUTHOR]

The interaction of plant-growth promoting rhizobacteria (PGPR) and Arbuscular mycorrhizal fungi (AMF), used in biological control, could determine the outcome of the biocontrol of plant disease. The efficacy of AMF species (Funneliformi mosseae [Fm]) and PGPRs (Pseudomonas spp. V31Y4 and P. fluorescens WCS365) on pepper plant bacterial spot disease caused by Xanthomonas euvesicatoria (Xe) and host plant growth parameters were investigated. Bacteria biocontrol agents were suppressed significantly the disease severity, however Fm alone was not effective. Combination of Fm and WCS365 was the most successful treatment for disease suppression with a rate of 15% compared with the control. There was no significant difference among treatments with Xe induced defoliation. However, the number of leaves in plants inoculated with Fm and Xe decreased significantly compared with control plants. Nevertheless, single application of Fm and PGPRs significantly increased plant biomass, height and chlorophyll content, and the bacterial strains were more successful. The growth response (GR) value in plants ranged from 22 to 28.6% as a single or combination treatment without the disease pressure. However, under the disease pressure, this value changed from 3.6 to 20.9%. In disease-free conditions, V31Y4 treatment reduced Fm colonization, while WCS365 increased colonization. Conversely, under disease pressure, WCS365 treatment had no effect on Fm colonization while V31Y4 treatment increased it compared with the control. There was no significant relationship between phosphorus content and GR with disease severity.Finally, Fm application increased susceptibility to Xe in pepper plants, but the suitable PGPR and AMF combination treatment was more successful than single applications for disease suppression caused by Xe in pepper plants. [ABSTRACT FROM AUTHOR]

Bacterial leaf spot of pepper (BSP), primarily caused by Xanthomonas euvesicatoria (Xe), poses a significant challenge to pepper production worldwide. Despite its impact, the genetic diversity of this pathogen remains underexplored, which limits our understanding of its population structure. To bridge this knowledge gap, we conducted a comprehensive analysis using 103 Xe strains isolated from pepper in southwest Florida to characterize genomic and type III effector (T3E) variation in this population. Phylogenetic analysis of core genomes revealed a major distinct genetic lineage associated with amylolytic activity. This amylolytic lineage was represented in Xe strains globally. Molecular clock analysis dated the emergence of amylolytic strains in Xe to around 1972. Notably, non-amylolytic strains possessed a single base pair frameshift deletion in the amylase gene yet retained a conserved C-terminus. GUS assay revealed the expression of two open reading frames in non-amylolytic strains, one at the N-terminus and another that starts 136 base pairs upstream of the amylase gene. Analysis of T3Es in the Florida Xe population identified variation in 12 effectors, including two classes of mutations in avrBs2 that prevent AvrBs2 from triggering a hypersensitive response in Bs2-resistant pepper plants. Knowledge of T3E variation could be used for effector-targeted disease management. This study revealed previously undescribed population structure in this economically important pathogen. IMPORTANCE Bacterial leaf spot (BSP), a significant threat to pepper production globally, is primarily caused by Xanthomonas euvesicatoria (Xe). Limited genomic data has hindered detailed studies on its population diversity. This study analyzed the whole-genome sequences of 103 Xe strains from peppers in southwest Florida, along with additional global strains, to explore the pathogen's diversity. The study revealed two major distinct genetic groups based on their amylolytic activity, the ability to break down starch, with non-amylolytic strains having a mutation in the amylase gene. Additionally, two classes of mutations in the avrBs2 gene were found, leading to susceptibility in pepper plants with the Bs2 resistance gene, a commercially available resistance gene for BSP. These findings highlight the need to forecast the emergence of such strains, identify genetic factors for innovative disease management, and understand how this pathogen evolves and spreads. [ABSTRACT FROM AUTHOR]

Eggplant (Solanum melongena L.) is an important solanaceous vegetable and economic crop in the world. It is a very popular and nutrient rich vegetable, and it can be grown round the year in China. In September 2023, a suspected bacterial disease of the eggplant was found in the Greenhouse Eggplant Seedling Production Base in Tieling, Liaoning Province, China. The disease symptom was water-soaked tawny or light brown spots on eggplant seedling leaves, that gradually became black. Pathogenic bacteria were isolated from the infected leaf spots. Based on the phenotypic characteristics, bacteriological characteristics, physiological and biochemical tests and molecular biological identification, the bacteria isolates obtained in this study were identified as Xanthomonas euvesicatoria. Pathogenicity of these isolates was confirmed on ground tomato and pepper seedlings by artificial inoculation. To our knowledge, this is the first report of X. euvesicatoria causing bacterial spot of eggplant in China. [ABSTRACT FROM AUTHOR]

Wastewaters, as the major waste stream of the wine industry, are usually disposed in crude form due to the lack of sustainable treatments, which poses rising environmental threat. Considering biodegradability, nutrients content and other specific characteristics, winery wastewaters are suitable for utilization in xanthan production. In this study, the screening of local wild-type Xanthomonas euvesicatoria strains, isolated from pepper leaves, for xanthan production on medium containing wastewaters from rose wine industry, with initial sugar content of 25 g/L, was performed. Bioprocess success was estimated based on the quantity and quality of separated biopolymer. Additionally, composition of collected wastewaters was determined, and the obtained data indicate the importance of their proper management. The results of screening experiments suggest that applied X. euvesicatoria isolates have a statistically significant effect on xanthan concentration in cultivation medium, its molecular weight, as well as on apparent viscosity of xanthan aqueous solution. According to the obtained results, xanthan concentration varied from 4.0 g/L to 10.0 g/L, while the values of average molecular weight of xanthan and apparent viscosity of its solution ranged from 2.5 ∙ 105 g/mol to 8.5 ∙ 105 g/mol and from 40 mPa ∙ s to 60 mPa ∙ s, respectively. The results from this study suggest that X. euvesicatoria PL2 isolate showed the greatest potential for xanthan production on medium containing wastewaters from rose wine industry because of determined quantity of good-quality biopolymer. Further research is necessary in order to improve proposed bioprocess as sustainable biotechnological solution for winery wastewaters utilization. [ABSTRACT FROM AUTHOR]

Bacterial leaf blight (BLB) caused by Xanthomonas spp. is an important threat for eucalypt production. Planting of resistant genotypes is the best strategy for eucalypt BLB control. However, selection of resistant clones is challenging since the disease is caused by at least three Xanthomonas species that can be sympatric and cause a range of foliar symptoms. So far, standard area diagrams (SADs) to assess eucalypt BLB severity caused by different Xanthomonas species have not been reported. Here, SADs for eucalypt BLB severity assessment were developed. Plants of five eucalypt genotypes were individually inoculated with different Xanthomonas species and leaves exhibiting lesions varying in colour, shape, and size were digitally scanned for disease assessment. Among 150 scanned leaves, the actual leaf affected area ranged from 0.01% to 55%. Based on these minimum and maximum values and the frequency of severity distribution, the 10 leaves that best represented the distribution of affected leaf area were selected to assemble the SADs. Groups of experienced and inexperienced raters estimated BLB severity on a subset of 50 out of the 150 original leaves without and then with the use of the SADs. Correlation concordance analyses revealed that SADs provided a significant improvement in accuracy, precision and reliability of disease estimates by both rater groups, with higher gains observed for the inexperienced group. The SADs developed in this study will be useful for selection of eucalypt genotypes resistant to BLB under controlled conditions when knowledge on the Xanthomonas species composition is lacking or when local populations are comprised of several species. [ABSTRACT FROM AUTHOR]

It became necessary to employ safer and more efficient alternatives to plant pathogenic bacteria and land snails control due to the growing issues these snails and bacteria were causing on various crops. Green nanoparticles have been used because of their stability, low-cost feasibility and antimicrobial characteristics and snails. The current work intends to investigate the effectiveness of green synthetic silver and iron oxide nanoparticles of an aqueous extract of Acacia nilotica pods Ag-NPs (AEANP-AgNPs) and FeO-NPs (AEANP-FeONPs) against two identified plant pathogenic bacterial strains (Xanthomonas euvesicatoria and Pseudomonas syringae pv. tomato) and to land snails (Monacha cartusiana and Eobania vermiculata) collected from sandy loam soil. AEANP-AgNPs and AEANP-FeONPs were made and characterized using a TEM, Zeta potential, FTIR and EDX. Different concentrations of AEANP-AgNPs (1700, 3400, and 5100 ppm) and AEANP-FeONPs (2700, 5400, and 8100 ppm) were tested. The concentration (5100 ppm) of Ag-NPs was higher in the inhibition against P. syringae pv. tomato while (5400 ppm) and (8100 ppm) concentrations of FeO-NPs were equal to inhibition against X. euvesicatoria. In planta, the treated strain of X. euvesicatoria exhibited low severity while the treated strain of P. syringae pv. tomato didn't exhibit a significant difference severity. So, M. cartusiana snails were more sensitive to the toxic effect of Ag-NPs and FeO-NPs than adult snails, E. vermiculata. The mortality for adult snails was increased with increasing concentration of both nanoparticles. The LC50 concentrations of Ag-NPs for adult snails M. cartusiana and E. vermiculata were (1.885×103and 7.618×10³) and (4.066×10³ ppm and 10.776×10³ ppm) for FeO-NPs respectively. [ABSTRACT FROM AUTHOR]

IntroductionBacterial spot, caused by diverse xanthomonads classified into four lineages within three species, poses a significant threat to global pepper and tomato production. In Taiwan, tomato bacterial spot xanthomonads phylogenetically related to an atypical Xanthomonas euvesicatoria pv. perforans (Xep) strain NI1 from Nigeria were found.MethodsTo investigate the genetic structure of Taiwanese Xep strains and determine the phylogenetic position of the atypical strains, we completed high-quality, gap-free, circularized genomes of seven Taiwanese Xep strains and performed comparative genomic analyses with genomes of X. euvesicatoria pathovars. Average nucleotide identity, core genome analysis, and phylogenomic analysis were conducted.ResultsThree sequenced strains were identified as typical Xep, while four clustered with the atypical strain NI1, forming a distinct genomovar within X. euvesicatoria, proposed as X. euvesicatoria genomovar taiwanensis (Xet). This new lineage likely originated in Taiwan and spread to Nigeria through global seed trade. At the genomovar level, chromosomes remained conserved among Taiwanese strains, while plasmids likely contributed to bacterial virulence, avirulence, and field fitness. Gap-free genomes revealed associations between the evolution of type III effectors, horizontal gene transfer events, plasmid diversity, and recombination.DiscussionThis study highlights the critical roles of horizontal gene transfer and plasmids in shaping the genetic makeup, evolution, and environmental adaptation of plant pathogenic xanthomonads. The identification of a new genomovar, X. euvesicatoria genomovar taiwanensis, provides insights into the diversity and global spread of bacterial spot pathogens through seed trade.

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Outbreaks of bacterial leaf blight (BLB) frequently affect eucalypt plants under nursery and field conditions in several countries. Although research has been conducted to unveil the causal agent, different bacterial species have been associated with similar disease symptoms in different countries. In order to determine the causal agent of BLB in Brazil, a survey was conducted in nine states to recover bacterial isolates from eucalypt plants exhibiting typical BLB symptoms. A total of 41 yellow‐colony isolates with varying aggressiveness towards a susceptible eucalypt clone were obtained, with 16S rDNA sequences indicating that they belong to the Xanthomonas genus. Rep‐PCR analysis separated the Xanthomonas population affecting eucalypt into six distinct groups revealing its high genetic diversity. The same population formed three clusters together with reference strains of X. citri, X. euvesicatoria and X. phaseoli in a phylogenetic tree constructed with partial dnaK, fyuA, gyrB and rpoD gene sequences. Clustering in the phylogenetic tree was clearly related to grouping based on rep‐PCR. Genome sequence comparisons of representative eucalypt isolates with type strains of validly published Xanthomonas species confirmed that the population consisted of X. citri, X. euvesicatoria and X. phaseoli. Inoculation of tomato, common bean, castor bean and eucalypt plants showed that the representative eucalypt isolates can cause disease in these plant species. Based on the results, the transfer of Xanthomonas axonopodis pv. eucalyptorum to Xanthomonas citri is proposed. These results are relevant for eucalypt BLB management under nursery and field conditions, including selection and deployment of effective plant resistance. [ABSTRACT FROM AUTHOR]

Xanthomonas euvesicatoria is a major cause of bacterial spot disease in various crops. The present study was focused on the pathosystem pepper (Capsicum annuum L.) - X. euvesicatoria 269p (wild strain). The infectious process was studied using several different modes of in vivo inoculation under controlled conditions. The spread of the pathogen in different parts of the plants was monitored by a new qPCR procedure developed for the detection of X. euvesicatoria, as well as by re-isolation of viable bacterial cells. Photosynthesis, the number of viable pathogens, oxidative stress markers, activities of the main antioxidant enzymes, and levels of non-enzymatic antioxidants in the novel single-leaf model system were studied. The most important observation is that the invasion of the pathogen causes local infection and the dissemination of bacteria to the healthy parts of the host is blocked. The plants limit bacterial colonization around the entry points. Oxidative burst and alterations in antioxidant defenses are detected in infectious leaf lesions. Localized ROS overproduction resembles a hypersensitive response, but several differences can be observed. We assumed that pepper plants are more likely to manifest an intermediate phenotype, similar to lesions simulating disease or leaf flecking. By localizing the infection, possibly involving oxidative stress, the plant survives. However, the same applies to bacteria. The pathogen multiplies at the infection spots and is transmitted to other plants. Our conclusion is that the intermediate phenotype in the studied pathosystem is an example of long and successful co-evolution for both species. [ABSTRACT FROM AUTHOR]

The valorization of industrial waste streams generated in vast quantities is becoming an increa-singly prominent priority in line with the principles of circular economy. One potential avenue for utilizing food industry waste streams lies in the production of microbial agents with biocontrol and PGP (plant-growth promotion) properties. Bacillus species, given their broad spectrum of bioactive metabolites, exhibit significant potential in the production of such bioagents. The aim of this study was to investigate the circular economy approach by utilizing whey from dairy industry, meat processing wastewater and digestate obtained from biogas production using solid meat industry effluents, as potential bases for media used to cultivate Bacillus sp. BioSol021 and to investigate their biocontrol activity against pepper black spot causal agent, Xanthomonas euvesicatoria, as well as their PGP effects in the pepper seed germination phase. The highest antimicrobial activity, tested using the disc diffusion method, was observed in the whey-based cultivation broth sample after 96 hours of cultivation. Pepper seeds treated with cultivation broth of Bacillus sp. BioSol021 based on meat industry wastewater exhibited the best results in terms of germination rate (80%), root length (10.40 mm) and shoot length (6.20 mm). The results of this study confirm the suitability of whey, meat industry waste-water, and biogas production digestate as the potential cultivation media components for producing Bacillus-based biocontrol and PGP agents for a more sustainable agricultural practice.

The present study was focused on the pathosystem pepper plants (Capsicum annuum L.)-phytopathogenic bacterium X. euvesicatoria (wild strain 269p)-bacteriophage BsXeu269p/3 and the possibility of bacteriophage-mediated biocontrol of the disease. Two new model systems were designed for the monitoring of the effect of the phage treatment on the infectious process in vivo. The spread of the bacteriophage and the pathogen was monitored by qPCR. A new pair of primers for phage detection via qPCR was designed, as well as probes for TaqMan qPCR. The epiphytic bacterial population and the potential bacteriolytic effect of BsXeu269p/3 in vivo was observed by SEM. An aerosol-mediated transmission model system demonstrated that treatment with BsXeu269p/3 reduced the amount of X. euvesicatoria on the leaf surface five-fold. The needle-pricking model system showed a significant reduction of the amount of the pathogen in infectious lesions treated with BsXeu269p/3 (av. 59.7%), compared to the untreated control. We found that the phage titer is 10-fold higher in the infection lesions but it was still discoverable even in the absence of the specific host in the leaves. This is the first report of in vivo assessment of the biocontrol potential of locally isolated phages against BS pathogen X. euvesicatoria in Bulgaria. [ABSTRACT FROM AUTHOR]

Intensive food production to feed the growing human population requires significant material and energy resources, simultaneously generating large amounts of waste, whose treatment adds an additional cost to the overall production process. Wastewaters arising from meat and dairy processing industries contain large amounts of organic and inorganic nutrients, which present a heavy environmental burden, but, on the other hand, could serve as nutrient sources for microbial growth. The aim of this study was to investigate the suitability of meat processing wastewater and whey from the dairy industry as media for the growth of biocontrol strain Bacillus velezensis IP22. Both waste-based media have contributed to antibacterial and antifungal activity to a similar degree, with highly comparable inhibition zone diameters against Xanthomonas campestris, Xanthomonas euvesicatoria and Aspergillus flavus. Furthermore, biocontrol activity of the cultivation broths obtained using the waste-based media was slightly lower compared to the nutrient broth medium, suggesting the possibility to replace the expensive chemically defined medium with a complex medium alternative. This approach based on circular economy principles promotes responsible resource utilization through the reuse of food industry effluents for the production of value value-added products, opening a chapter of possibilities to establish an industrial symbiosis network between companies in different industry branches.

The Gram-negative bacterial genus Xanthomonas includes numerous infra-specific taxa known as pathovars, which are defined primarily on host range and disease symptoms. With the advent of molecular sequence data, many pathovars have been transferred from X. campestris into other Xanthomonas species to better harmonise taxonomy and phylogeny. We performed whole-genome shotgun sequencing on pathotype strains of the following X. campestris pathovars: blepharidis, carissae, clerodendri, convolvuli, coriandri, daturae, euphorbiae, fici, heliotropii, ionidii, lawsoniae, mirabilis, obscurae, paulliniae, pennamericanum, spermacoces, uppalii, vernoniae, viegasii and zingibericola. These genomes showed more than 98% average nucleotide identity with the type-strain of X. euvesicatoria and less than 88% with the type-strain of X. campestris. We propose the transfer of these pathovars into X. euvesicatoria and present an emended species description for X. euvesicatoria.

β-Carbonic anhydrase (βCA) is very important for plant growth and development, but its function in immunity has also been examined. In this study, we found that the expression level of Solanum lycopersicum βCA1 (SlβCA1) was significantly upregulated in plants treated with Xanthomonas euvesicatoria 85-10. The protein was localized in the nucleus, cell membrane and chloroplast. Using tomato plants silenced with SlβCA1, we demonstrated that SlβCA1 plays an active role in plant disease resistance. Moreover, we found that the elicitor PopW upregulated the expression of SlβCA1, while the microbe-associated molecular pattern response induced by PopW was inhibited in TRV-SlβCA1. The interaction between PopW and SlβCA1 was confirmed. Here, we found that SlβCA1 was positively regulated during PopW-induced resistance to Xanthomonas euvesicatoria 85-10. These data indicate the importance of SlβCA1 in plant basic immunity and its recognition by the Harpin protein PopW as a new target for elicitor recognition. [ABSTRACT FROM AUTHOR]

Bacterial spot caused by Xanthomonas euvesicatoria is a major disease of pepper (Capsicum annuum L.) in warm and humid production environments. Use of genetically resistant cultivars is an effective approach to manage bacterial spot. Two recessive resistance genes, bs5 and bs6, confer non-race-specific resistance against bacterial spot. The objective of our study was to map these two loci in the pepper genome. We used a genotyping-by-sequencing approach to initially map the position of the two resistances. Segregating populations for bs5 and bs6 were developed by crossing susceptible Early CalWonder (ECW) with near-isogenic lines ECW50R (bs5 introgression) or ECW60R (bs6 introgression). Following fine-mapping, bs5 was delimited to a -535 Kbp interval on chromosome 3, and bs6 to a -666 Kbp interval in chromosome 6. We identified 14 and 8 candidate resistance genes for bs5 and bs6, respectively, based on predicted protein coding polymorphisms between ECW and the corresponding resistant parent. This research enhances marker-assisted selection of bs5 and bs6 in breeding programs and is a crucial step towards elucidating the molecular mechanisms underlying the resistances. [ABSTRACT FROM AUTHOR]

As available tools for crop disease management are scarce, new, effective, and eco-friendly solutions are needed. So, this study aimed at assessing the antibacterial activity of a dried leaf Eucalyptus globulus Labill. aqueous extract (DLE) against Pseudomonas syringae pv. tomato (Pst), Xanthomonas euvesicatoria (Xeu), and Clavibacter michiganensis michiganensis (Cmm). For this, the inhibitory activity of different concentrations of DLE (0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 250 g L−1) was monitored against the type strains of Pst, Xeu, and Cmm through the obtention of their growth curves. After 48 h, results showed that the pathogen growth was strongly inhibited by DLE, with Xeu the most susceptible species (15 g L−1 MIC and IC50), followed by Pst (30 g L−1 MIC and IC50), and Cmm (45 and 35 g L−1 MIC and IC50, respectively). Additionally, using the resazurin assay, it was possible to verify that DLE considerably impaired cell viability by more than 86%, 85%, and 69% after Pst, Xeu, and Cmm were incubated with DLE concentrations equal to or higher than their MIC, respectively. However, only the treatment with DLE at 120 g L−1 did not induce any hypersensitive response in all pathogens when treated bacterial suspensions were infiltrated onto tobacco leaves. Overall, DLE can represent a great strategy for the prophylactic treatment of tomato-associated bacterial diseases or reduce the application of environmentally toxic approaches. [ABSTRACT FROM AUTHOR]

This study was carried out to determine the life span of Xanthomonas euvesicatoria (Xeu) in seeds, soil and plant residues and the first inoculum source that cause the onset of the disease. The study was carried out in the province of Tokat. Rifampicin-resistant Xeu isolate was inoculated into soil, seeds and plant residues. As a result of the studies, it was determined that Xeu remained viable in inoculated seeds until the 220th day (7 months), and lived in the soil for 105 days in summer and 14 days in winter. In plant residues, it was determined that the the life span in summer period was 60 days at 0 cm depth, 30 days at 20 cm depth; 30 days at 0 cm depth and 15 days at 20 cm depth in that of winter period. According to the results of this study, it was determined that the Xeu did not survive for a long time in plant residues and soil in Tokat province and thus was not carried to the next year, on the other hand the seed was the most important source of inoculum. [ABSTRACT FROM AUTHOR]

The Gram-negative bacterial genus Xanthomonas includes numerous infra-specific taxa known as pathovars, which are defined primarily on host range and disease symptoms. With the advent of molecular sequence data, many pathovars have been transferred from X. campestris into other Xanthomonas species to better harmonise taxonomy and phylogeny. We performed whole-genome shotgun sequencing on pathotype strains of the following X. campestris pathovars: blepharidis, carissae, clerodendri, convolvuli, coriandri, daturae, euphorbiae, fici, heliotropii, ionidii, lawsoniae, mirabilis, obscurae, paulliniae, pennamericanum, spermacoces, uppalii, vernoniae, viegasii and zingibericola. These genomes showed more than 98% average nucleotide identity with the type-strain of X. euvesicatoria and less than 88% with the type-strain of X. campestris. We propose the transfer of these pathovars into X. euvesicatoria and present an emended species description for X. euvesicatoria. [ABSTRACT FROM AUTHOR]

Bacterial spot caused by Xanthomonas euvesicatoria is a major disease of pepper (Capsicum annuum L.) in warm and humid production environments. Use of genetically resistant cultivars is an effective approach to manage bacterial spot. Two recessive resistance genes, bs5 and bs6, confer non-race-specific resistance against bacterial spot. The objective of our study was to map these two loci in the pepper genome. We used a genotyping-by-sequencing approach to initially map the position of the two resistances. Segregating populations for bs5 and bs6 were developed by crossing susceptible Early CalWonder (ECW) with near-isogenic lines ECW50R (bs5 introgression) or ECW60R (bs6 introgression). Following fine-mapping, bs5 was delimited to a ~535 Kbp interval on chromosome 3, and bs6 to a ~666 Kbp interval in chromosome 6. We identified 14 and 8 candidate resistance genes for bs5 and bs6, respectively, based on predicted protein coding polymorphisms between ECW and the corresponding resistant parent. This research enhances marker-assisted selection of bs5 and bs6 in breeding programs and is a crucial step towards elucidating the molecular mechanisms underlying the resistances.

Bacteriophages have greatly engaged the attention of scientists worldwide due to the continuously increasing resistance of phytopathogenic bacteria to commercially used chemical pesticides. However, the knowledge regarding phages is still very insufficient and must be continuously expanded. This paper presents the results of the isolation, characterization, and evaluation of the potential of 11 phage isolates as natural predators of a severe phytopathogenic bacterium—Xanthomonas euvesicatoria. Phages were isolated from the rhizosphere of tomato plants with symptoms of bacterial spot. The plaque morphology of all isolates was determined on a X. euvesicatoria lawn via a plaque assay. Three of the isolates were attributed to the family Myoviridae based on TEM micrographs. All phages showed good long-term viability when stored at 4 °C and −20 °C. Three of the phage isolates possessed high stability at very low pH values. Fifty-five-day persistence in a soil sample without the presence of the specific host and a lack of lytic activity on beneficial rhizosphere bacteria were found for the phage isolate BsXeu269p/3. The complete genome of the same isolate was sequenced and analyzed, and, for the first time in this paper, we report a circular representation of a linear but circularly permuted phage genome among known X. euvesicatoria phage genomes. [ABSTRACT FROM AUTHOR]

Pepper (Capsicum annuum L.) carrying the gds (corresponding to bs5) gene can prevent the development of bacterial leaf spot disease without HR. However, little is known regarding the development of the resistance mechanism encoded by gds, especially its influence on the bacterium. Here, the effect of gds was compared with pattern-triggered immunity (PTI), another form of asymptomatic resistance, to reveal the interactions and differences between these two defense mechanisms. The level of resistance was examined by its effect on the bacterial growth and in planta expression of the stress and pathogenicity genes of Xanthomonas euvesicatoria. PTI, which was activated with a Pseudomonas syringae hrcC mutant pretreatment, inhibited the growth of Xanthomonas euvesicatoria to a greater extent than gds, and the effect was additive when PTI was activated in gds plants. The stronger influence of PTI was further supported by the expression pattern of the dpsA bacterial stress gene, which reached its highest expression level in PTI-induced plants. PTI inhibited the hrp/hrc expression, but unexpectedly, in gds plant leaves, the hrp/hrc genes were generally expressed at a higher level than in the susceptible one. These results imply that different mechanisms underlie the gds and PTI to perform the symptomless defense reaction. [ABSTRACT FROM AUTHOR]

Bacillus velezensis is a novel biocontrol species exhibiting several mechanisms in biological control of plant pathogens, including antibiosis, production of other types of antimicrobials, such as volatile organic compounds, direct competition for nutrients and growth space, and induction of plant immunity towards pathogens. The aim of this study was to assess the potential of Bacillus velezensis IP22, cultivated on the optimized medium with glycerol as carbon source, for in vitro suppression of phytopathogenic bacteria - Xanthomonas campestris and Xanthomonas euvesicatoria. Different potential biocontrol agents were investigated: the overall cultivation broth, containing cells of Bacillus velezensis IP22 and produced extracellular metabolites, and cell-free supernatant obtained by centrifugation of the cultivation broth (10000 rpm, 10 min), which contained only the produced extracellular compounds. Furthermore, supernatant samples were subjected to heat treatment to assess whether there were thermosensitive extracellular compounds present in the supernatant. Vacuum evaporation was performed to concentrate supernatant samples in order to compare the effect of higher concentration of extracellular compounds to pathogens' growth. The results have indicated average inhibition zone diameters of 66.00 mm for the cultivation broth samples, 25.67 mm for the supernatants, 10.00 mm for the heat treated supernatants and 43.50 mm for the concentrated supernatants. Further research should include optimization of the production processes aimed at maximization of Bacillus velezensis IP22 growth and/or biosynthesis of the antimicrobial metabolites, as well as their precise identification and characterization to better understand the mechanism(s) of biocontrol activity against phytopathogenic Xanthomonas spp.

The present study was focused on the pathosystem pepper plants (Capsicum annuum L.)-phytopathogenic bacterium X. euvesicatoria (wild strain 269p)-bacteriophage BsXeu269p/3 and the possibility of bacteriophage-mediated biocontrol of the disease. Two new model systems were designed for the monitoring of the effect of the phage treatment on the infectious process in vivo. The spread of the bacteriophage and the pathogen was monitored by qPCR. A new pair of primers for phage detection via qPCR was designed, as well as probes for TaqMan qPCR. The epiphytic bacterial population and the potential bacteriolytic effect of BsXeu269p/3 in vivo was observed by SEM. An aerosol-mediated transmission model system demonstrated that treatment with BsXeu269p/3 reduced the amount of X. euvesicatoria on the leaf surface five-fold. The needle-pricking model system showed a significant reduction of the amount of the pathogen in infectious lesions treated with BsXeu269p/3 (av. 59.7%), compared to the untreated control. We found that the phage titer is 10-fold higher in the infection lesions but it was still discoverable even in the absence of the specific host in the leaves. This is the first report of in vivo assessment of the biocontrol potential of locally isolated phages against BS pathogen X. euvesicatoria in Bulgaria.

Xanthomonas euvesicatoria pv. rosa strain Xer07 causes a leaf spot on a Rosa sp. and is closely related to X. euvesicatoria pv. euvesicatoria (Xee) and X. perforans (Xp), causal agents of bacterial spot of tomato. However, Xer07 is not pathogenic on tomato and elicits a hypersensitive reaction (HR). We compared the genomes of the three bacterial species to identify the factors that limit Xer07 on tomato. Comparison of pathogenicity associated factors including the type III secretion systems identified two genes, xopA and xer3856, in Xer07 that have lower sequence homology in tomato pathogens. xer3856 is a homolog of genes in X. citri (xac3856) and X. fuscans pv. aurantifolii, both of which have been reported to elicit HRs in tomato. When xer3856 was expressed in X. perforans and infiltrated in tomato leaflets, the transconjugant elicited an HR and significantly reduced bacterial populations compared to the wildtype X. perforans strain. When xer3856 was mutated in Xer07, the mutant strain still triggered an HR in tomato leaflets. The second gene identified codes for type III secreted effector XopA, which contains a harpin domain that is distinct from the xopA homologs in Xee and Xp. The Xer07-xopA, when expressed in X. perforans, did not elicit an HR in tomato leaflets, but significantly reduced bacterial populations. This indicates that xopA and xer3856 genes in combination with an additional factor(s) limit Xer07 in tomato. [ABSTRACT FROM AUTHOR]

As available tools for crop disease management are scarce, new, effective, and eco-friendly solutions are needed. So, this study aimed at assessing the antibacterial activity of a dried leaf Eucalyptus globulus Labill. aqueous extract (DLE) against Pseudomonas syringae pv. tomato (Pst), Xanthomonas euvesicatoria (Xeu), and Clavibacter michiganensis michiganensis (Cmm). For this, the inhibitory activity of different concentrations of DLE (0, 15, 30, 45, 60, 75, 90, 105, 120, 135, and 250 g L−1) was monitored against the type strains of Pst, Xeu, and Cmm through the obtention of their growth curves. After 48 h, results showed that the pathogen growth was strongly inhibited by DLE, with Xeu the most susceptible species (15 g L−1 MIC and IC50), followed by Pst (30 g L−1 MIC and IC50), and Cmm (45 and 35 g L−1 MIC and IC50, respectively). Additionally, using the resazurin assay, it was possible to verify that DLE considerably impaired cell viability by more than 86%, 85%, and 69% after Pst, Xeu, and Cmm were incubated with DLE concentrations equal to or higher than their MIC, respectively. However, only the treatment with DLE at 120 g L−1 did not induce any hypersensitive response in all pathogens when treated bacterial suspensions were infiltrated onto tobacco leaves. Overall, DLE can represent a great strategy for the prophylactic treatment of tomato-associated bacterial diseases or reduce the application of environmentally toxic approaches.

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The limit values of resistance groups were established to Xanthomonas euvesicatoria and Xanthomonas vesicatoria by mean score - ms based on conducted statistical analysis of 155 selection lines of Bulgarian, introduced hybrids and pepper varieties: I- immune; R- resistant; MS- medium sensitive; S- sensitive; SS- strongly sensitive. The genetic diversity between the two bacteria suggest the use of separate resistant groups to determine the resistance. Data on the mean score of infestation on 116 pepper accessions to X. euvesicatoria and 155 (the previous 116 included) to X. vesicatoria were processed and the resistance groups were defined. Breeding pepper accessions with complex resistance requires the application of the established resistance groups to both pathogens. The limit values of the groups by ms based on the statistical analysis of the data on the resistance of pepper accessions to X. euvesicatoria and X. vesicatoria were specified. [ABSTRACT FROM AUTHOR]

Bacteriophages have greatly engaged the attention of scientists worldwide due to the continuously increasing resistance of phytopathogenic bacteria to commercially used chemical pesticides. However, the knowledge regarding phages is still very insufficient and must be continuously expanded. This paper presents the results of the isolation, characterization, and evaluation of the potential of 11 phage isolates as natural predators of a severe phytopathogenic bacterium—Xanthomonas euvesicatoria. Phages were isolated from the rhizosphere of tomato plants with symptoms of bacterial spot. The plaque morphology of all isolates was determined on a X. euvesicatoria lawn via a plaque assay. Three of the isolates were attributed to the family Myoviridae based on TEM micrographs. All phages showed good long-term viability when stored at 4 °C and −20 °C. Three of the phage isolates possessed high stability at very low pH values. Fifty-five-day persistence in a soil sample without the presence of the specific host and a lack of lytic activity on beneficial rhizosphere bacteria were found for the phage isolate BsXeu269p/3. The complete genome of the same isolate was sequenced and analyzed, and, for the first time in this paper, we report a circular representation of a linear but circularly permuted phage genome among known X. euvesicatoria phage genomes.

Pepper (Capsicum annuum L.) carrying the gds (corresponding to bs5) gene can prevent the development of bacterial leaf spot disease without HR. However, little is known regarding the development of the resistance mechanism encoded by gds, especially its influence on the bacterium. Here, the effect of gds was compared with pattern-triggered immunity (PTI), another form of asymptomatic resistance, to reveal the interactions and differences between these two defense mechanisms. The level of resistance was examined by its effect on the bacterial growth and in planta expression of the stress and pathogenicity genes of Xanthomonas euvesicatoria. PTI, which was activated with a Pseudomonas syringae hrcC mutant pretreatment, inhibited the growth of Xanthomonas euvesicatoria to a greater extent than gds, and the effect was additive when PTI was activated in gds plants. The stronger influence of PTI was further supported by the expression pattern of the dpsA bacterial stress gene, which reached its highest expression level in PTI-induced plants. PTI inhibited the hrp/hrc expression, but unexpectedly, in gds plant leaves, the hrp/hrc genes were generally expressed at a higher level than in the susceptible one. These results imply that different mechanisms underlie the gds and PTI to perform the symptomless defense reaction.

The global warming by increased CO2 will effect of plant pathogenic microorganisms and resistance of host plants, and it is expected to affect host-pathogen interactions. This study used Capsicum annuum L. and Xanthomonas euvesicatoria, a pathogenic bacteria of pepper, to investigate interactions between hosts and pathogens in a complex environment with increased cultivation temperature and drought stress. As a result, the bacterial spot disease of C. annuum L. caused by X. euvesicatoria was 35°C higher than 25°C. In addition, the effect on water potential on bacterial spot disease was much greater water potential -150 kPa than -30 kPa. The disease progress and severity higher than water potential -30 kPa. This result will useful for understanding interaction with red pepper and X. euvesicatoria under the complex environment with increased cultivation temperature and in water potential -150 kPa drought stress in the future.

Xanthomonas euvesicatoria (Xe) is a gram-negative phytopathogenic bacterium that causes bacterial spot disease in tomato/pepper leading to economic losses in plantations. DNA methyltransferases (MTases) are critical for the survival of prokaryotes; however, their functions in phytopathogenic bacteria remain unclear. In this study, we characterized the functions of two putative DNA MTases, XvDMT1 and XvDMT2, in Xe by generating XvDMT1- and XvDMT2-overexpressing strains, Xe(XvDMT1) and Xe(XvDMT2), respectively. Virulence of Xe(XvDMT2), but not Xe(XvDMT1), on tomato was dramatically reduced. To postulate the biological processes involving XvDMTs, we performed a label-free shotgun comparative proteomic analysis, and results suggest that XvDMT1 and XvDMT2 have distinct roles in Xe. We further characterized the functions of XvDMTs using diverse phenotypic assays. Notably, both Xe(XvDMT1) and Xe(XvDMT2) showed growth retardation in the presence of sucrose and fructose as the sole carbon source, with Xe(XvDMT2) being the most severely affected. In addition, biofilm formation and production of exopolysaccharides were declined in Xe(XvDMT2), but not Xe(XvDMT1). Xe(XvDMT2) was more tolerant to EtOH than Xe(XvDMT1), which had enhanced tolerance to sorbitol but decreased tolerance to polymyxin B. Using single-molecule real-time sequencing and methylation-sensitive restriction enzymes, we successfully predicted putative motifs methylated by XvDMT1 and XvDMT2, which are previously uncharacterized 6mA and 5mC DNA MTases, respectively. This study provided new insights into the biological functions of DNA MTases in prokaryotic organisms.

Xanthomonas euvesicatoria (Xe) is a gram-negative phytopathogenic bacterium that causes bacterial spot disease in tomato/pepper leading to economic losses in plantations. DNA methyltransferases (MTases) are critical for the survival of prokaryotes; however, their functions in phytopathogenic bacteria remain unclear. In this study, we characterized the functions of two putative DNA MTases, XvDMT1 and XvDMT2, in Xe by generating XvDMT1- and XvDMT2-overexpressing strains, Xe (XvDMT1) and Xe (XvDMT2), respectively. Virulence of Xe (XvDMT2), but not Xe (XvDMT1), on tomato was dramatically reduced. To postulate the biological processes involving XvDMTs, we performed a label-free shotgun comparative proteomic analysis, and results suggest that XvDMT1 and XvDMT2 have distinct roles in Xe. We further characterized the functions of XvDMTs using diverse phenotypic assays. Notably, both Xe (XvDMT1) and Xe (XvDMT2) showed growth retardation in the presence of sucrose and fructose as the sole carbon source, with Xe (XvDMT2) being the most severely affected. In addition, biofilm formation and production of exopolysaccharides were declined in Xe (XvDMT2), but not Xe (XvDMT1). Xe (XvDMT2) was more tolerant to EtOH than Xe (XvDMT1), which had enhanced tolerance to sorbitol but decreased tolerance to polymyxin B. Using single-molecule real-time sequencing and methylation-sensitive restriction enzymes, we successfully predicted putative motifs methylated by XvDMT1 and XvDMT2, which are previously uncharacterized 6mA and 5mC DNA MTases, respectively. This study provided new insights into the biological functions of DNA MTases in prokaryotic organisms. [ABSTRACT FROM AUTHOR]

The efficacy of a formulated product of tea tree oil (TTO) and a standard copper based bactericide in combinations with acibenzolar-S-methyl (ASM) for control of bacterial spot of pepper and bacterial speck of tomato was evaluated under controlled conditions. Treatments with copper hydroxide+ASM at both application rates and TTO+ASM showed the best efficacy in control of bacterial spot disease in pepper plants (with respective efficacy values 83.5%, 83.7 % and 86.9%). Similar efficacy was achieved by treatment with copper hydroxide alone (82.2%). On the other hand, the efficacy of TTO, applied alone, was significantly lower at both rates (63.8% and 71.5%) in bacterial spot control in pepper. The same treatments (copper hydroxide +ASM at both application rates and TTO+ASM) were most efficient in suppressing the causal agent of bacterial speck disease in tomato (87%, 82.3% and 81.6%). The efficacy of treatment with the standard bactericide copper hydroxide, applied alone, was significantly lower compared to its combination with ASM (79.1%). Similarly to the bacterial spot experiment, TTO treatments alone showed lower, although satisfactory efficacy at both application rates (66.1% and 68.9%). The results of this study showed that combination of the bioactive compound - ASM with either the standard copper hydroxide bactericide or TTO significantly improved their efficacy in both bacterial spot and speck disease control, and thus implied that combining different biorational compounds, such as essential oils and bioactive products, with standard copper treatments and their inclusion into integrated management programs are of essential importance for the control of bacterial diseases of pepper and tomato.

Xanthomonas euvesicatoria pv. rosa strain Xer07 causes a leaf spot on a Rosa sp. and is closely related to X. euvesicatoria pv. euvesicatoria (Xee) and X. perforans (Xp), causal agents of bacterial spot of tomato. However, Xer07 is not pathogenic on tomato and elicits a hypersensitive reaction (HR). We compared the genomes of the three bacterial species to identify the factors that limit Xer07 on tomato. Comparison of pathogenicity associated factors including the type III secretion systems identified two genes, xopA and xer3856, in Xer07 that have lower sequence homology in tomato pathogens. xer3856 is a homolog of genes in X. citri (xac3856) and X. fuscans pv. aurantifolii, both of which have been reported to elicit HRs in tomato. When xer3856 was expressed in X. perforans and infiltrated in tomato leaflets, the transconjugant elicited an HR and significantly reduced bacterial populations compared to the wildtype X. perforans strain. When xer3856 was mutated in Xer07, the mutant strain still triggered an HR in tomato leaflets. The second gene identified codes for type III secreted effector XopA, which contains a harpin domain that is distinct from the xopA homologs in Xee and Xp. The Xer07-xopA, when expressed in X. perforans, did not elicit an HR in tomato leaflets, but significantly reduced bacterial populations. This indicates that xopA and xer3856 genes in combination with an additional factor(s) limit Xer07 in tomato.

Pyraclostrobin is a broad-spectrum fungicide that inhibits mitochondrial respiration. However, it may also induce systemic resistance effective against bacterial and viral diseases. In this study, we evaluated whether pyraclostrobin enhanced resistance against the bacterial spot pathogen, Xanthomonas euvesicatora on pepper (Capsicum annuum). Although pyraclostrobin alone did not suppressed the in vitro growth of X. euvesicatoria, disease severity in pepper was significantly lower by 69% after treatments with pyraclostrobin alone. A combination of pyraclostrobin with streptomycin reduced disease by over 90% that of the control plants. The preventive control of the pyraclostrobin against bacterial spot was required application 1-3 days before pathogen inoculation. Our findings suggest that the fungicide pyraclostrobin can be used with a chemical pesticide to control bacterial leaf spot diseases in pepper.

Associating desirable agronomic characters of sweet peppers and resistance to bacterial spot (BS) has been challenging plant breeders, especially when seeking durable resistance. In this work, we select BS resistant progenies with desirable agronomic characteristics by mixed model. F2:3 plants derived from sixty F2 individuals from crosses between pure lines UENF 2285 (susceptible) × UENF 1381 (resistant) were phenotyped. For BS resistance assessment, 1320 seedlings were inoculated with Xanthomonas euvesicatoria in greenhouse. The progress of the disease on seedlings was evaluated by using a score scale, with values from one to five, for eleven consecutive days. With the values of the Area Under Disease Progress Curve (AUDPC), the components of variance were estimated, and the genetic values for resistance to bacterial spot predicted. Resistant seedlings were cultivated in the field for agronomic characters phenotyping. The average rank index was used to select promising offspring. The coefficient of additive genetic variation (12.97–32.57%) confirmed the existence of genetic variability in the population. The progeny-mean heritability was of high magnitude (80–97%), and narrow sense heritability had average magnitude (17–65%), which indicates desirable gains with the selection of individual plants. The accuracy of the selection was above 80% for all studied traits. The predicted genetic value for AUDPC was negative and the genetic gain was null; in contrast, for the IP variable and morphoagronomic characters, the predicted genetic gain was high. Thirty-three percent of promising segregation lines were selected, which should originate new pure line type sweet pepper cultivars resistant to BS. [ABSTRACT FROM AUTHOR]

Bacterial spot caused by Xanthomonas euvesicatoria is one of the most devastating pepper diseases in Serbia. Questionable seed quality, climatic conditions, and frequent irrigation during summer favour the disease occurrence and spread. The available management practices do not provide adequate disease control. Therefore, development of alternative and more sustainable disease management strategies is needed. Integration of classical and biological treatments could be an effective, environmentally safe option for reducing pepper bacterial spot severity. In order to develop an efficient integrated disease management program, we studied efficacy of biocontrol agents (bacteriophage strain KФ1 and two strains of Bacillus subtilis AAac and QST 713), systemic acquired resistance (SAR) inducer (acibenzolar-S-methyl - ASM), a commercial microbial fertilizer (Slavol), copper based compounds (copper hydroxide and copper oxychloride) in combination with or without mancozeb, and antibiotics (streptomycin sulphate and kasugamycin). They were applied as single treatments in two separate field experiments. Based on the single treatment efficacy, various combinations of the treatments were chosen for further testing in three separate field experiments. Additionally, we evaluated potential negative effect of ASM on pepper growth and yield in the growth chamber experiment. All the tested single treatments significantly reduced disease severity compared to the inoculated control (IC), except microbiological fertilizer and the antagonistic strain AAac. Integration of copper hydroxide, ASM and bacteriophages was the most efficient treatment, reducing the disease intensity by 96–98%. The results indicated that this combination may be an adequate alternative program for control of pepper bacterial spot. • Bacterial spot is one of the economically most important pepper diseases worldwide. • The currently available bactericides fail to provide satisfactory disease control. • Integration of copper hydroxide + ASM + bacteriophages was the most effective treatment. [ABSTRACT FROM AUTHOR]

In 2004, bacterial spot-causing xanthomonads (BSX) were reclassified into 4 species—Xanthomonas euvesicatoria, X. vesicatoria, X. perforans, and X. gardneri. Bacterial spot disease on pepper plant in Korea is known to be caused by both X. axonopodis pv. vesicatoria and X. vesicatoria. Here, we reidentified the pathogen causing bacterial spots on pepper plant based on the new classification. Accordingly, 72 pathogenic isolates were obtained from the lesions on pepper plants at 42 different locations. All isolates were negative for pectolytic activity. Five isolates were positive for amylolytic activity. All of the Korean pepper isolates had a 32 kDa-protein unique to X. euvesicatoria and had the same band pattern of the rpoB gene as that of X. euvesicatoria and X. perforans as indicated by PCR-restriction fragment length polymorphism analysis. A phylogenetic tree of 16S rDNA sequences showed that all of the Korean pepper plant isolates fit into the same group as did all the reference strains of X. euvesicatoria and X. perforans. A phylogenetic tree of the nucleotide sequences of 3 housekeeping genes—gapA, gyrB, and lepA showed that all of the Korean pepper plant isolates fit into the same group as did all of the references strains of X. euvesicatoria. Based on the phenotypic and genotypic characteristics, we identified the pathogen as X. euvesicatoria. Neither X. vesicatoria, the known pathogen of pepper bacterial spot, nor X. perforans, the known pathogen of tomato plant, was isolated. Thus, we suggest that the pathogen causing bacterial spot disease of pepper plants in Korea is X. euvesicatoria.

Pepper bacterial spot is one of the most severe plant diseases in terms of infection persistence and economic losses when it comes to fresh pepper fruits used in nutrition and industrial processing. In this study, Bacillus velezensis IP22 isolated from fresh cheese was used as a biocontrol agent of pepper bacterial spot, whose main causal agent is the cosmopolitan pathogen Xanthomonas euvesicatoria. After optimization of the cultivation medium composition aimed at maximizing of the antimicrobial activity against X. euvesicatoria and validation of the optimized medium at the scale of a laboratory bioreactor, in planta tests were performed. The results have showed significant suppression of bacterial spot symptoms in pepper plants by the produced biocontrol agent, as well as reduction of disease spreading on the healthy (uninoculated) pepper leaves. Furthermore, HPLC-MS (high pressure liquid chromatography–mass spectrometry) analysis was employed to examine antimicrobial metabolites produced by B. velezensis IP22, where lipopeptides were found with similar m/z values compared to lipopeptides from fengycin and locillomycin families. The bioprocess solution developed at the laboratory scale investigated in this study represents a promising strategy for production of pepper bacterial spot biocontrol agent based on B. velezensis IP22, a food isolate with a great perspective for application in plant protection.

Xanthomonas euvesicatoria phage KΦ1, a member of Myoviridae family, was isolated from the rhizosphere of pepper plants showing symptoms of bacterial spot. The phage strain expressed antibacterial activity to all X. euvesicatoria strains tested and did not lyse other Xanthomonas spp., nor other less related bacterial species. The genome of KΦ1 is double-stranded DNA of 46.077 bp including 66 open reading frames and an average GC content of 62.9%, representing the first complete genome sequence published for a phage infecting xanthomonads associated with pepper or tomato. The highest genome similarity was observed between phage KΦ1 and the Xanthomonas oryzae pv. oryzae specific phage OP2. On the other hand, when compared with other members of the genus Bcep78virus, the genome similarity was lower. Forty-four (67%) predicted KΦ1 proteins shared homology with Xanthomonas phage OP2, while 20 genes (30%) were unique to KΦ1. Phage KΦ1, which is chloroform resistant and stable in different media and in the pH range 5-11, showed a high titer storage ability for at least 2 years at +4°C. Copper-hydroxide and copper-oxychloride reduced phage activity proportionally to the used concentrations and the exposure time. UV light was detrimental to the phage strain, but skim milk plus sucrose formulation extended its survival in vitro. The phages survived for at least 7 days on the surface of pepper leaves in the greenhouse, showing the ability to persist on the plant tissue without the presence of the host bacterium. Results of three repeated experiments showed that foliar applications of the unformulated KΦ1 phage suspension effectively controlled pepper bacterial spot compared to the standard treatment and the untreated control. The integration of the phage KΦ1 and copper-hydroxide treatments resulted in an increased efficacy compared to the copper-hydroxide alone.

Xanthomonas, a complex group of pathogens, infects more than 400 plants, which is expanding to new hosts causing serious diseases. Genome-based studies are transforming our understanding on diversity and relationship of host-specific members, known as pathovars. In this study, we report complete genome sequence of a novel pathovar Xanthomonas axonopodis pv. commiphorae (Xcom) from India. It causes gumming disease of Commiphora wightii, a medicinally important plant. Genome-based phylogenetic and taxonomic investigation revealed that the pathovar belongs to Xanthomonas euvesicatoria and not X. axonopodis as reported earlier. Interestingly, it is a novel host and novel geographic origin for a X. euvesicatoria pathovar. A core-genome-based phylogenetic analysis resolved the pathovar complex of this species on the basis of their hosts. Interestingly, this pathovar harbors a unique 35-kb plasmid encoding type III effectors and toxin–antitoxin gene that is absent in other X. euvesicatoria pathovars and infects tomato, pepper, rose, onion, philodendron, alfalfa, and citrus plants. The pathovar contains two TAL (transcription activator-like) genes, one on plasmid and another on genomic region with an additional pseudo TAL gene flanked by IS elements in the plasmid. Further, Xcom has acquired a novel set of lipopolysaccharide biosynthesis genes after its divergence from the closely related pathovar that infects rose and supports the role of horizontal gene transfer in hypervariation at this locus in the species. Complete genome sequence of this variant pathovar has provided novel insights into evolution of an emerging pathovar in Xanthomonas and will be valuable resource in pathogenomics of X. euvesicatoria. [ABSTRACT FROM AUTHOR]