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Gram-negative bacteria belonging to the Xanthomonas genus include plant pathogens representing a major challenge in the field of agriculture for a wide variety of economically important crops, such as tomato, pepper, and lettuce. Due to the massive usage of agrochemicals, Xanthomonas spp. are developing resistance to copper pesticides typically used to control microbial infections. An interesting alternative approach to control bacterial phytopathogens consists of using eco-friendly biocontrol agents, often beneficial microorganisms. Here, following the targeted, broad-spectrum screening of thousands of microorganisms isolated from different environmental locations, we isolated Bacillus velezensis strain 71 and Paenibacillus peoriae strain To99 displaying potent antagonistic activity against Xanthomonas spp. We found that oxydifficidin and polymyxin A secreted by B. velezensis 71 and P. peoriae To99, respectively, are mainly responsible for the anti-Xanthomonas activity. We further evaluated the performance of cell suspensions and cell-free supernatants of these isolates in controlling tomato bacterial spot disease in growth chamber and greenhouse conditions to validate the in vitro results. The overall results demonstrate the potential of treatments based on the secondary metabolites from both isolates and their cells as an alternative to copper-based chemicals to control leaf spot diseases caused by Xanthomonas spp. phytopathogens. [ABSTRACT FROM AUTHOR]

(1) Background: Ralstonia solanacearum causes tomato bacterial wilt disease, one of the most serious tomato diseases. As the combination of Trichoderma virens (Tvien6) and Bacillus velezensis (X5) was more effective at controlling tomato bacterial wilt disease than a single agent, we investigated the synergistic effect of Tvien6 and X5 in controlling this disease; (2) Methods: The disease incidence, plant heights and weights, relative chlorophyll content (SPAD values), defensive enzymes (PPO, POD, and SOD) activities, and metabolome were estimated among four treatment groups (BR treatment, X5 + R. solanacearum (RS-15); TR treatment, Tvien6+ RS-15; TBR treatment, Tvien6 + X5 + RS-15; and R treatment, RS-15); (3) Results: The R treatment group had the highest disease incidence and lowest plant heights, plant weights, SPAD values, defensive enzyme activities, and D-fructose and D-glucose contents; the TBR treatment group had the lowest disease incidence and highest plant heights, plant weights, SPAD values, defensive enzyme activities, and D-fructose and D-glucose contents; (4) Conclusions: The results revealed that Tvien6 and X5 can both individually promote tomato plant growth, increase leaf chlorophyll content, enhance defensive enzyme activities, and induce the accumulation of D-fructose and D-glucose; however, they were more effective when combined. [ABSTRACT FROM AUTHOR]

Tomato bacterial wilt (BW) caused by Ralstonia solanacearum seriously restricts tomato production and no effective control measures are available. A microbial restoration substrate (MRS) had been proved to be effective control of tomato BW in a greenhouse cultivation. In this study, MRS was combined with an avirulent Ralstonia solanacearum (aRS) strain to control the disease under an open field condition. In the two consecutive year (2017 and 2018) trials, the combined use of aRS and MRS resulted in better disease control compared with either aRS or MRS alone. Moreover, the combined treatment was more effective than expected and suggesting a synergistic control effect. Compared with control (CK, non-aRS or MRS), the application of aRS and MRS treatments alone or in combination could all promote plant growth, increase root activity and yield (e.g. the yield for the treatment of aRS + MRS increased by 463.64% in 2017). Soil nutrients, including soil organic carbon, total nitrogen, total phosphorus and total potassium contents were also significantly increased by the application of aRS and MRS treatments alone or in combination (P < 0.05). The application of MRS or in combination with aRS changed the soil from acidic to neutral, which is one of the key factors for controlling BW. The soil enzymatic activities were notably influenced by the combined use of aRS and MRS, which increased urease (87.37% in 2017 and 60.89% in 2018), catalase (93.67% in 2017 and 279.37% in 2018) and alkaline phosphatase activities (193.77% in 2017 and 455.73% in 2018). These results suggest that the combination of MRS and aRS could effectively control tomato BW and thus represents a promising new tool to control this disease. [ABSTRACT FROM AUTHOR]

Bacterial spot, caused by Xanthomonas perforans , is one of the major diseases in fresh market tomato production in Florida. It is reported that X. perforans has developed resistance to copper, an element of major bactericides used for management of this disease in Florida and worldwide. Continuous efforts are necessary for providing the tomato industry with new effective approaches to managing this important disease. A small molecule 3-indolylacetonitrile (IAN) that can inhibit biofilm formation has been reported to be effective against many medical bacterial pathogens. In this study, we evaluated the efficacy of IAN in planta for the control of bacterial leaf spot on tomato, the effectiveness of IAN when applied at different times from pathogen inoculation, how IAN efficacy compared to a copper bactericide (Kocide 3000), and if IAN could be applied as a tank mixture with copper bactericide. In vitro testing in liquid media was also completed to further investigate observations made in planta. Our results showed that IAN was effective in reducing disease severity of bacterial leaf spot on tomato between 0.5 and 1.0 mg/ml. However, phytotoxicity to tomato plants occurred when the concentration was higher than 1.0 mg/ml. IAN significantly (P < 0.05) reduced the disease when it was foliar applied during the period from 3 days prior to inoculation to 1 day after inoculation. When IAN was applied in combination with a copper bactericide Kocide 3000, additive effect was observed in reducing both disease severity and bacterial growth, compared to either IAN or copper alone, for both copper-sensitive and copper-resistant X. perforans strains. Results from this study indicated that IAN significantly reduced bacterial leaf spot on tomato and enhanced the efficacy of copper against X. perforans. Specifically, IAN significantly improved the control of bacterial leaf spot caused by a copper-resistant X. perforans strain. • 3-Indolylacetonitrile (IAN) reduced bacterial leaf spot on tomato in greenhouses. • Bacterial spot of tomato was further reduced by IAN in combination with Kocide 3000. • IAN increased efficacy of Kocide 3000 against copper-resistant X. perforans strains. • IAN inhibited in vitro bacterial growth of X. perforans in liquid media. [ABSTRACT FROM AUTHOR]

Bacterial spot caused by Xanthomonas perforans causes significant damage on tomato in Florida. Due to the presence of copper (Cu)-tolerant X. perforans strains, Cu bactericides are not effective in disease management. Hence, there is a critical need to find alternatives for Cu. Antibacterial activity of magnesium oxide (Nano-MgO), and other metal oxide nanoparticles, were evaluated against a Cu-tolerant and -sensitive X. perforans strain. In vitro experiments demonstrated high antibacterial activity of Nano-MgO against both strains compared with the commercial Cu. The minimum inhibitory concentration of Nano-MgO is 25 pg/ml and the minimum bactericidal concentration is 100 pg/ml against a Cu-tolerant X. perforans strain after 4 h of exposure. Structural changes in the bacterial membrane following exposure to Nano-MgO treatments compared with the controls were observed using transmission electron microscopy. In two greenhouse experiments with a Cu-tolerant sU'ain, bacterial spot severity was significantly reduced by Nano-MgO at 200 pg/ml compared with Cuethylene bis-dithiocarbamate (grower standard), and the unseated control (P = 0.05). In three field experiments, Nano-MgO at 200 pg/ml significantly reduced disease severity with no negative impact on yield compared with the untreated control. Inductively coupled plasma mass spectrometric analysis of the fruit confirmed that Nano-MgO application did not lead to the accumulation of Mg, Cu, Ca, K, Mn, P, and S. This study is the first to demonsPate the potential of Nano-MgO against bacterial spot of tomato. [ABSTRACT FROM AUTHOR]

Three crosses, Hawaii7981 × PI128216, Hawaii7981 × LA1589, and PI128216 × LA1589, were made to develop F2 populations for testing allelism among three genes Xv3, Rx4, and RxLA1589 conferring resistance to bacterial spot caused by Xanthomonas perforans race T3 in tomato. Each population consisted of 535–1 655 individuals. An infiltration method was used to inoculate the leaves of the parental and F2 plants as well as the susceptible control OH88119 for detecting hypersensitive resistance (HR). The results showed that all the tomato plants except OH88119 had HR to race T3, indicating that Xv3, Rx4, and RxLA1589 were allelic genes. Genomic DNA fragments of the Rx4 alleles from Hawaii7981, PI128216, and LA1589 were amplified using gene-specific primers and sequenced. No sequence variation was observed in the coding region of Rx4 in the three resistant lines. Based on the published map positions of these loci as well as the allelic tests and sequence data obtained in this study, we speculated that Xv3, Rx4, and RxLA1589 were the same gene. The results will provide useful information for understanding the mechanism of resistance to race T3 and developing resistant tomato varieties.

A multilocus sequence analysis (MLSA) was performed on five housekeeping genes (fusA, gapA, gltA, lacF and lepA) of 22 Xanthomonas euvesicatoria strains recently isolated from alfalfa, pepper and tomato plants in Iran. In addition, 161 strains isolated worldwide from pepper, poinsettia, rose and tomato plants were included in the analysis. All X. euvesicatoria pv. perforans isolates from tomato plants in Iran clustered in a monophyletic group, although five MLSA haplotypes were detected among them. The Iranian tomato strains presented 10 nucleotide differences in the lepA gene sequences compared to the known worldwide population of X. euvesicatoria pv. perforans. Statistical analyses revealed a recombination event that had occurred in the lepA gene of the strains isolated from tomato in Iran. BOX‐PCR analysis confirmed the inclusion of Iranian tomato strains within X. euvesicatoria pv. perforans. Furthermore, X. euvesicatoria pv. euvesicatoria strains isolated from pepper in Iran differed in one nucleotide in the lepA gene sequence from the known worldwide population of the pathovar, and clustered in a group containing strains isolated in Nigeria. The strains isolated from alfalfa in Iran clustered with the type strain of X. euvesicatoria pv. alfalfae. Altogether, the results reveal the existence of a phylogenetically novel population of X. euvesicatoria pv. perforans in Iran which needs further in‐depth analysis to pinpoint the epidemiological impact of these strains. [ABSTRACT FROM AUTHOR]

In this study, we aimed to identify potential biocontrol agents capable of suppressing tomato bacterial wilt caused by Ralstonia pseudosolanacearum . In total, 441 bacteria were isolated from the rhizosphere soil of tomato, Chinese chive, and Welsh onion. Based on the results of the in vitro antibacterial activity assay, 275 isolates were selected and further evaluated using a tomato seedling bioassay. Eighteen isolates that belonged to that the genera Ralstonia and Mitsuaria exhibited a relatively higher disease suppression (>50% reduction in disease severity) than the other isolates. The isolate TCR112 of Ralstonia and 10 isolates of Mitsuaria were assessed for their biocontrol effect in a series of pot experiments. Among the isolates, TCR112 (identified as Ralstonia sp.) and TWR114 (identified as Mitsuaria sp.), which showed a consistent disease suppression in pot experiments, were selected as final candidates for further evaluation under field conditions. The results showed that soil drenching at weekly intervals with isolates TCR112 and TWR114 reduced the wilt incidence in the first year by 57.2% and 85.8%, and in the second year by 57.2% and 35.3%, respectively, indicating that these isolates were promising biocontrol agents of tomato bacterial wilt. The isolates effectively reduced the pathogen population in the rhizosphere and crown of pot grown tomatoes. Monitoring the population dynamics of biocontrol isolates revealed that both isolates have stable rhizosphere and endophytic colonization capacities. Furthermore, the in vitro assay for siderophore, indole-3-acetic acid, protease, and polygalacturonase production revealed that TCR112 produces the former three substances and TWR114 produces the latter three substances. Altogether, the results suggest that both isolates suppress tomato bacterial wilt by preventing pathogen multiplication and infection via direct antagonism and/or indirect effects such as competing for nutrients and inducing resistance in tomato plants. Furthermore, this is the first study reporting the potential of Mitsuaria as a biocontrol agent against tomato bacterial wilt. [ABSTRACT FROM AUTHOR]

Bacterial spot, caused by Xanthomonas spp., is a widespread and damaging bacterial disease of tomato (Solatium lycopersicum). For disease management, growers rely on copper bactericides, which are often ineffective due to the presence of copper-tolerant Xanthomonas strains. This study evaluated the antibacterial activity of the new copper composites coreshell copper (CS-Cu), multivalent copper (MV-Cu), and fixed quaternary ammonium copper (FQ-Cu) as potential alternatives to commercially available micron-sized copper bactericides for controlling coppertolerant Xanthomonas perforans. In vitro, metallic copper from CS-Cu and FQ-Cu at 100 μg/ml killed the copper-tolerant X. perforans strain within 1 h of exposure. In contrast, none of the micron-sized copper rates (100 to 1,000 μg/ml) from Kocide 3000 significantly reduced copper-tolerant X. perforans populations after 48 h of exposure compared with the water control (P < 0.05). All copper-based treatments killed the copper-sensitive X. perforans strain within 1 h. Greenhouse studies demonstrated that all copper composites significantly reduced bacterial spot disease severity when compared with copper-mancozeb and water controls (P < 0.05). Although there was no significant impact on yield, copper composites significantly reduced disease severity when compared with water controls, using 80% less metallic copper in comparison with copper-mancozeb in field studies (P < 0.05). This study highlights the discovery that copper composites have the potential to manage copper-tolerant X. perforans and tomato bacterial spot. [ABSTRACT FROM AUTHOR]

Tomato ( Solanum lycopersicum) is the second most important vegetable crop in the world. Bacterial spot ( BS) of tomato, caused by four species of Xanthomonas: X. euvesicatoria, X. vesicatoria, X. perforans and X. gardneri, results in severe loss in yield and quality due to defoliation and formation of lesions on fruits, respectively. Currently management practices do not offer effective control under conditions of high disease pressure. Thus, developing BS resistance is a critical priority for tomato growers in order to minimize crop losses. Sixty-three advanced tomato breeding lines, heirlooms and wild tomato lines with diverse genetic backgrounds were screened under greenhouse and field conditions for BS resistance using X. perforans race T4, which was found to be a prevalent race in North Carolina. Race T4 isolate 9 was used to inoculate the plants by spraying, and disease severity was measured using the Horsfall-Barratt scale. Tomato lines 74L-1W(2008), NC2 CELBR, 081-12-1X-gsms, NC22L-1 (2008) and 52 LB-1 showed resistance to BS in the field and/or greenhouse trials. These lines were derived from S. pimpinellifolium L3707. Screening L3707 followed by development of a mapping population and mapping resistance genes might be useful for breeding resistance against BS in future breeding programmes. [ABSTRACT FROM AUTHOR]

A 2-year comprehensive field survey was conducted across major tomato-growing areas of Iran. Two hundred and thirty-four tomato fields and six tomato-producing greenhouses were surveyed for the potential presence of bacterial spot disease. Five hundred and ninety-six tomato samples with and without symptoms were analysed. While Xanthomonas spp. were found in association with tomato plants both with and without symptoms from five surveyed counties, the bacterial spot disease was observed only in plants from three of them. Only strains isolated from plants with symptoms induced disease symptoms on tomato, while those isolated from symptomless plants caused symptoms only on cabbage and common bean. None of the isolates caused disease symptoms on pepper and eggplant. Phylogenetic analysis showed that X. perforans is the causal agent of tomato bacterial spot in Iran, although X. campestris and X. axonopodis were also associated with symptomless tomato plants. All X. perforans isolates in this study were sensitive to streptomycin, copper sulphate and copper oxychloride at concentrations of 50 mg L−1, 200 mg L−1 and 0.8 g L−1, respectively. Unlike the type strain of X. perforans, isolates in this study did not produce bacteriocin against other Xanthomonas spp., nor were they detected using the usual species-specific primer pair Bs-XpF/Bs-XpR. This suggests an atypical nature of X. perforans strains in Iran, which leads to the hypothesis that X. perforans strains in Iran may have a separate origin to those causing disease epidemics elsewhere. The aggregated dispersal pattern of the diseased tomato fields signifies the seedborne introduction of the pathogen into the country. [ABSTRACT FROM AUTHOR]

Tomato bacterial spot is caused by Xanthomonas euvesicatoria, X. vesicatoria, X. perforans and X. gardneri. In order to determine the distribution, frequency of occurrence, and diversity of these species in the Brazilian commercial tomato fields, a survey was conducted between 2009 and 2012. In this period, 204 strains were obtained from 33 counties (22 with processing tomatoes and 11 with fresh-market tomatoes). Pathogenicity tests, BOX- PCR, PCR with species-specific primers, and sequence analysis of the avirulence gene avrXv3 were performed in order to identify the strains at species and race level. Xanthomonas perforans predominated among the strains (92%) and was present in most counties. In addition, this species was prevalent in most areas of both fresh-market tomatoes (63.6% of counties surveyed) and processing tomatoes (95.4% of counties surveyed). Fifteen strains (7.5%) were identified as X. gardneri, which was found mostly in fresh-market fields located at regions with altitude higher than 900 m, and only one strain of X. euvesicatoria (0.5%) was found in a processing tomato field. High genetic diversity was observed within X. perforans, with 137 BOX- PCR haplotypes. Race T3 prevailed (97.5%), but reported here for the first time is the occurrence of five strains identified as race T4 in fresh-market fields in the state of São Paulo. The race T4 phenotype of these strains resulted from the presence of an 859 bp insertion in the avirulence gene avrXv3. This insertion is related to amino acid sequences of a transposase found in X. gardneri, and to amino acid sequences of X. campestris. [ABSTRACT FROM AUTHOR]

Bacterial spot disease caused byXanthomonas campestrispv.vesicatoriais one of the most important destructive diseases of tomato in many parts of the agricultural world. Therefore, the present study aims to determine the effects ofBacillus subtilisCBR05 inoculation on bacterial spot disease severity and the induction of defence-related enzymes response in tomato. Tomato leaves were evaluated to determine the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO)) and the content of malondialdehyde (MDA). A reduction in bacterial spot severity was observed in plants inoculated withB. subtilis, compared with those of uninoculated controls. A significant increase in SOD, CAT, POD, and PPO activities was observed in plants treated withB. subtilisafter 24 h inoculation compared with non-inoculated pathogen control and mock-inoculated controls. Moreover, the MDA content was induced by pathogen infection, and its amount inB. subtilisinoculated plants was significantly lower than that in pathogen control. Our results suggest that early increases in antioxidant enzymes and the reduction in MDA content withB. subtilisinoculation may play a pivotal role in mitigating oxidative stress, thereby induced systemic resistance against bacterial spot disease in tomato. [ABSTRACT FROM PUBLISHER]

Acibenzolar-S-methyl (ASM) is a plant activator that triggers systemic acquired resistance that is labeled for use in Brazil for managing tomato bacterial spot. The aim of this study was to define the optimum relationship between interval and number of applications of ASM for the most efficacious control of bacterial spot on processing tomato. Four intervals between applications (4, 7, 10, and 14 days) and four application frequencies (4, 6, 8, and 10 applications) were evaluated in five trials performed between 2010 and 2011 in Brasília, Distrito Federal, and in Morrinhos, in the state of Goiás. Copper hydroxide (CH) was applied after ASM applications to complete 13 applications per growing season. Two check treatments were added: standard CH weekly applications and untreated. The following variables were evaluated: severity of bacterial spot, yield, percentage of ripe and rotten fruit, soluble solids content, and the benefit/cost ratio. Disease severity varied between treatments in three trials and yield varied in two trials. A greater number of applications resulted in a reduction of bacterial spot, and the ideal interval between applications was between 8 to 10 days. However, there was a reduction in yield with 10 ASM applications. The temporal effect of ASM applications on bacterial spot severity was evaluated under greenhouse conditions. Reduction in disease severity was observed up to 6 days following ASM application. Additionally, the weekly treatment of seven applications of ASM followed by six applications of CH was compared with a standard program of CH under commercial production conditions in Itaberaí, Goiás, where bacterial spot occurred naturally. The program with ASM and CH resulted in significantly less foliar disease severity than the standard program, which did not result in yield gains. In addition, no differences were detected between the two programs for soluble solids content, industrial yield, plant height, and percentage of ripe and rotten fruit. [ABSTRACT FROM AUTHOR]

Bacterial wilt is a serious soilborne disease of Solanaceae crops which is caused by Ralstonia solanacearum. The important role of biochar in enhancing disease resistance in plants has been verified; however, the underlying mechanism remains not fully understood. In this study, two different biochars, made from peanut shell (BC1) and wheat straw (BC2), were added to Ralstonia solanacearum-infected soil to explore the interrelation among biochar, tomato bacterial wilt, and soil microbial properties. The results showed that both BC1 and BC2 treatments significantly reduced the disease index of bacterial wilt by 28.6% and 65.7%, respectively. The populations of R. solanacearum in soil were also significantly decreased by biochar application. Ralstonia solanacearum infection significantly reduced the densities of soil bacteria and actinomycetes and increased the ratio of soil fungi/bacteria in the soil. By contrast, BC1 and BC2 addition to pathogen-infected soil significantly increased the densities of soil bacteria and actinomycetes but decreased the density of fungi and the ratios of soil fungi/bacteria and fungi/actinomycetes. Biochar treatments also increased soil neutral phosphatase and urease activity. Furthermore, higher metabolic capabilities of microorganisms by biochar application were found at 96 and 144 h in Biolog EcoPlates. These results suggest that both peanut and wheat biochar amendments were effective in inhibiting tomato bacterial wilt caused by R. solanacearum. The results suggest a relationship between the disease resistance of the plants and the changes in soil microbial population densities and activity. [ABSTRACT FROM AUTHOR]

We introduce a novel method to detect and classify the severity of bacterial spot ( Xanthomonas spp.) in tomato ( Solanum lycopersicon ) fields. Visual spectrum images were used as inputs and they were taken at 85 days of the plantation. Two hybrids, Hypeel 108 and U2006, were planted and then inoculated separately with X. perforans and X. gardneri , respectively at 37 and 57 days. Ten (10) different plantation areas were then evaluated taking 18 image samples of each in sub-areas, which were analyzed by 7 experts to grade them and be used as comparison. Productivity was also measured in the areas in order to correlate those to the different severities of the disease in the experiment. Visual spectrum images were preprocessed to area size adjustment and brightness correction and then transformed to a CIELab color space for more stable chroma analysis. A clustering process was applied in the a channel in order to group regions related to healthy leaves, unhealthy ones, bare soil and other artifacts. Post-filtering was applied to channels L and b to evaluate regions with over and underexposition of light and reddish fruits being detected. All of the processed regions were then measured and compared using a novel Severity Index SI , which automatically grades, from 1.0 to 5.0, the presence and the severity of the disease. Sixteen classes of severity SC are also proposed, as equal intervals of SI index. Images were taken in a variety of conditions and results showed besides strong correlation with experts analysis, better explanation and smaller error when analyzing the productivity affected by the disease measurements. Results indicate potential for using this methodology for detecting and grading the severity of bacterial spot in tomato fields, with advantages such as capability of repeatable results with low variance, speed and direct field-based applicability. [ABSTRACT FROM AUTHOR]

Plants of Nicandra physaloides, Solanum americanum and Euphorbia heterophylla with leaf lesions have been found naturally grown among tomato plants in commercial fields in Brazil. Tomato bacterial spot was occurring in these fields. Xanthomonad-like isolates were obtained from affected weed leaf samples. These isolates were species identified using BOX-PCR and specific primers. Isolates from N. physaloides and S. americanum were identified as Xanthomonas perforans and that of E. heterophylla were identified as X. gardneri. Each of them was able to artificially infect and cause symptoms on the three weed species and tomato plants. [ABSTRACT FROM AUTHOR]

Field strains of tomato bacterial spot pathogen ( Xanthomonas euvesicatoria, X. vesicatoria, X. perforans, and X. gardneri) were characterized for sensitivity to copper and species composition. A total of 98 strains were isolated from symptomatic leaf and fruit samples collected from 18 tomato fields in Ontario. In greenhouse pathogenicity tests, most of the field strains caused severe (37 strains) to highly severe (23 strains) symptoms on 'Bonny Best' tomato plants, whereas 38 strains caused moderate symptoms. In MGY agar plates amended with various concentrations of copper sulfate, 11 strains were completely sensitive (no growth) and 87 strains were resistant (grew on 1.0 mmol/L or higher copper concentration). PCR analysis of the hrp gene cluster followed by restriction digestion with HaeIII and sequencing identified X. gardneri (35 strains) and X. perforans (26 strains) as predominant species and X. euvesicatoria and X. vesicatoria as less common species in Ontario tomato fields. Separation of field strains into various species was also confirmed with starch hydrolysis activity on agar medium. Moreover, 72 field strains produced shiny greenish-yellow colonies surrounded by a milky zone on xanthomonad differential (Xan-D) medium, and the colonies of 26 strains did not produce a milky zone. Thirty-four strains could not be clustered into any species and 25 of those strains were negative for the hrp gene PCR and also did not produce a milky zone around colonies on Xan-D medium. Our results suggest a widespread existence of copper-resistant strains and an increase in X. perforans strains of bacterial spot pathogen in Ontario. This information on copper resistance and species composition within bacterial spot pathogens in Ontario will be helpful for developing effective disease management strategies, making cultivar selection, and breeding new tomato cultivars. [ABSTRACT FROM AUTHOR]

Pseudomonas fluorescens J2 can produce 2,4-diacetylphloroglucinol (2,4-DAPG) as the main antibiotic compound and effectively inhibits the wilt pathogens Ralstonia solanacearum and Fusarium oxysporum . The phlF which negatively regulates the 2,4-DAPG synthesis in strain J2 was disrupted by homologous recombination to construct a mutant strain J2- phlF−. The mutant J2- phlF− produced much more 2,4-DAPG and showed higher inhibitory effect on R. solanacearum than the wild type strain J2 in vitro . The mutant J2- phlF− also showed more colonization of tomato roots and higher inhibition to R. solanacearum in soil than wild type strain J2. The biocontrol efficiency of mutant J2- phlF− was higher against tomato bacterial wilt than wild type strain J2, but the differences were not significant. However, the application of both strains with organic fertilizer improved the colonization and biocontrol efficiency against tomato bacterial wilt and mutant strain J2- phlF− showed higher biocontrol efficiency against tomato bacterial wilt than wild type strain J2. Both strains, J2 and J2- phlF−, could also promote the growth of tomato plants. [ABSTRACT FROM AUTHOR]

Soil-borne plant pathogens cause heavy losses to all major crops, leading to reductions in both yield and quality. Soil solarisation and bio-fumigation offer disease management options that are safe and reduce the use of pesticides for soil-borne plant pathogens. Mustard plant releases antimicrobial hydrolysis products, notably isothiocyanates when used as a bio-fumigant. Bacterial spot of tomato caused by Xanthomonas campestris pv. vesicatoria (Xcv) can survive in soil and plant debris, which serve as a primary inoculum for infecting the next tomato crop. An experiment was carried out with the objective of evaluating effects of soil solarisation and the use of Ethiopian mustard (Brassica carinata A. Braun) as a bio-fumigant to control bacterial spot disease and on yield of tomato. The treatments consisted of six types of potted soil medium (solarised at Haramaya and Dire Dawa, bio-fumigated, biofumigated as well as solarised at Haramaya and Dire Dawa, and untreated control as non-solarised non-biofumigated pots). Treated tomato seeds were planted and fruit yields were compared among treatments. Potted soil was inoculated with the pathogen, Xcv, belonging to T2P2 race group. The total microbial and Xcv counts were done before as well as after setting up the experiment. The results revealed that solarisation reduced the population of Xcv from 10.68 to 8.79 CFU g-1, total bacterial population from 11.27 to 9.86 CFU g-1, and total actinomycete counts from 11.69 to 9.44 CFU g-1 while bio-fumigation had a non-significant effect on Xcv and total microbial counts. None of the treatments exhibited a significant effect on fungal counts. The fruit yield of tomato grown on biofumigated as well as solarised soil was the highest (91.18 t ha-1) as compared to the other treatments. It can, therefore, be concluded that solarisation and bio-fumigation cannot be used as a bio-rational option for effective management of Xcv on tomato but the two methods could be used to increase tomato yield in the presence of the pathogen. [ABSTRACT FROM AUTHOR]

Highlights: [•] Out of 150 only 13 isolates inhibited Ralstonia solanacearum in vitro condition. [•] Thirteen isolates identified as Pseudomonas spp. and Bacillus spp. Serratia marcescens. [•] Of 13 isolates 11 produced siderophore, nine solubilized phosphate and all produced indole acetic acid (IAA). [•] In ad planta Bacillus cereus and Pseudomonas putida reduced bacterial wilt in tomato genotypes. [ABSTRACT FROM AUTHOR]

Abstract: Pseudomonas syringae pv. tomato, the causal agent of tomato bacterial speck, is common in greenhouses and fields all over Italy. The antibacterial activity of ethanol extracts of Punica granatum (pomegranate) fruit peels on P. syringae pv. tomato was studied both in vitro and in vivo. The minimum in vitro inhibition value for peel extract of P. granatum on the P. syringae pv. tomato Pt 1301 strain (from Turkey) was obtained at a concentration of 0.5%. The in vivo antibacterial action of this natural substance lasted at least 15 days, permitting the replacement or reduction of the commonly used copper compounds. The active components of the pomegranate peel extracts were ellagic and gallic acids. [Copyright &y& Elsevier]

The major virulence strategy of phytopathogenic bacteria is to secrete effector proteins into the host cell to target the immune machinery. AvrPto and AvrPtoB are two such effectors from Pseudomonas syringae, which disable an overlapping range of kinases in Arabidopsis and Tomato. Both effectors target surface-localized receptor-kinases to avoid bacterial recognition. In turn, tomato has evolved an intracellular effector-recognition complex composed of the NB-LRR protein Prf and the Pto kinase. Structural analyses have shown that the most important interaction surface for AvrPto and AvrPtoB is the Pto P+1 loop. AvrPto is an inhibitor of Pto kinase activity, but paradoxically, this kinase activity is a prerequisite for defense activation by AvrPto. Here using biochemical approaches we show that disruption of Pto P+1 loop stimulates phosphorylation in trans, which is possible because the Pto/Prf complex is oligomeric. Both P+1 loop disruption and transphosphorylation are necessary for signalling. Thus, effector perturbation of one kinase molecule in the complex activates another. Hence, the Pto/Prf complex is a sophisticated molecular trap for effectors that target protein kinases, an essential aspect of the pathogen's virulence strategy. The data presented here give a clear view of why bacterial virulence and host recognition mechanisms are so often related and how the slowly evolving host is able to keep pace with the faster-evolving pathogen. [ABSTRACT FROM AUTHOR]

Aims To establish protocols for the simultaneous detection and identification of Xanthomonas species causing tomato bacterial spot. Methods and Results We verified the specificity and sensitivity of the previously reported sets of primers designed for strains of the four species of Brazilian tomato bacterial spot xanthomonads, consisting of 30 of Xanthomonas euvesicatoria, 30 of X. vesicatoria, 50 of X. perforans and 50 of X. gardneri. Furthermore, we tested a multiplex PCR protocol for the purpose of concurrent species identification. The possibility of direct detection of the pathogens in diseased leaf samples was also verified. The primers were highly specific, amplifying only target DNA. The sensitivity of the primers in conventional PCR was 50 pg μl−1 for purified DNA and ranged from 5 × 102 to 5 × 104 CFU ml−1 when bacterial suspensions were analysed. The multiplex PCR was suitable for the detection of all four species and showed similar sensitivity to conventional PCR when tested on purified DNA. When using bacterial suspensions, its sensitivity was similar to conventional PCR only when a biological amplification step (Bio- PCR) was included. Both methods were able to detect the pathogens in symptomatic tomato leaves. Conclusions Brazilian Xanthomonas strains causing tomato bacterial spot can be differentiated and identified at species level by a PCR-based method and by a multiplex PCR. Significance and Impact of the Study This protocol may be a feasible alternative tool for the identification and detection of these pathogens in plant material and may be used for routine diagnostic purposes in plant pathology laboratories. [ABSTRACT FROM AUTHOR]

Abstract: Pseudomonas syringae utilizes a type III secretion system (T3SS) encoded by the hrp/hrc genes to translocate virulence proteins called effectors into plant cells. To ensure that the T3SS functions at appropriate times during infection, hrp/hrc and effector gene expression is modulated by environmental conditions and a complex network of transcription factors. The sigma factor HrpL activates hrp/hrc and effector genes, while σ54 and enhancer binding proteins HrpR and HrpS regulate hrpL. To better understand how environmental conditions control the T3SS regulatory cascade in P. syringae pathovar tomato strain DC3000, we tested the effects of various growth media and carbon sources on expression of the hrpRS operon, hrpL, and the effector avrPto. Fructose optimally induced hrpRS expression, while most other carbon sources had only mild stimulatory effects. In contrast, hrpL and avrPto were highly induced by several sugars and organic acids, yet expression decreased as cultures reached higher cell densities. This cell density-dependent regulation was not due to alteration of the pH of the medium, although involvement of a quorum sensing signal was also not apparent. Our findings may explain conflicting results from previous studies and additionally indicate that culture conditions should be considered carefully when examining T3SS gene expression. [Copyright &y& Elsevier]

The in vitro efficacy of different aqueous extracts of vermicompost prepared from leaves of Azardirachta indica, Lantana camera, Parthenium hysrerophorous were tested for the management of the pathogen. Vermicompost was prepared by mixing the respective substrates with cow dung slurry (9:1 ratio w/w) independently. Among the three aqueous extracts, vermicomposted neem was found to be superior to that of vermicomposted Lantana and Parthenium in suppression of growth of Xcampestris. Based on the results of the in vitro studies field studies were taken up as a combination of seed treatment with vermiconipost extract and soil application of vermicompost. The seeds of tomato were soaked for one hrs in different aqueous extracts of vermicomposts before sowing. The seedlings were raised in separate nursery beds of size 1 m x 1 m to which vermicompost was applied at the rate of 5 tons ha-1. From the nursery beds seedlings were transplanted to plots and each plant received 250g of vermicompost (spot application) in two split doses. Since the aqueous extract of vermicomposted neem showed better suppression of the pathogen in in vitro studies, the same vermicompost was used for soil application. The results showed that the best treatment for suppression of bacterial spot in tomato was seed treatment (1 h) with 10% aqueous extract of vermicomposted neem coupled with application of vermicomposted neem to the soil both during sowing as well as on transplantation. This treatment reduced the incidence of bacterial spot by 98% and resulted in maximum yield of 15.4 t ha-1. Bioagent like aqueous extract of vermicomposted neeni along with the soil amendment with the same vermicompost is essential for the management of the pathogen in affected soils. Use of such alternate materials which are non-polluting, cost effective, non hazardous and do not disturb ecological balance can reduce the use of copper based bactericides, leading to elimination of copper entry into the soil system. [ABSTRACT FROM AUTHOR]