Search Results (21)

Soil salinity and bacterial spot of tomato (BST), caused by Xanthomonas perforans, are major abiotic and biotic stresses limiting tomato production, particularly in Florida. While their individual effects are well documented, the impact of soil salinity on BST has not yet been investigated. This greenhouse study evaluated how increasing irrigation water salinity (electrical conductivity [EC] = 0.5, 3, 5, or 7 dS m⁻¹) affected tomato growth, physiology, BST severity, fruit quality, and transcriptomic responses. Salinity reduced plant growth and BST severity but did not directly affect X. perforans populations. Results indicated that reduced plant physiological activity (net CO₂ assimilation [A], transpiration [E], and stomatal conductance [g_s]) contributes to lower disease levels. Increased salinity led to more solute concentrations, altered sugar metabolism, and improved perceived taste, as supported by taste panel, osmolality, and transcriptomic analyses. They also showed that transcriptional responses to salinity (EC = 7 dS m⁻¹) and X. perforans infection were strongly time-dependent. Salt-treated plants exhibited fewer differentially expressed genes following inoculation, whereas comparisons between EC 7-treated and control plants revealed extensive salinity-induced reprogramming. KEGG analysis indicated enrichment of photosynthesis, carbon metabolism, amino acid biosynthesis, and ribosome pathways, while defense-related pathways, including MAPK signaling and plant–pathogen interaction, were downregulated, suggesting that tomato prioritized adaptation to salinity over pathogen defense. Full article

Bacterial spot, caused by Xanthomonas species, is a destructive tomato disease that reduces yield and fruit quality worldwide. The tomato resistance gene Rx4 confers hypersensitive response and field resistance to race T3 of Xanthomonas euvesicatoria pv. perforans, but downstream components associated with Rx4-mediated field resistance remain unclear. Here, we compared the susceptible processing tomato line OH 88119 with its near-isogenic line Rx4-1806 after spray inoculation with the race T3 strain Xv829. Transcriptome profiling at 1, 6, and 72 h post-inoculation identified limited transcriptional differences at 1 and 6 h, but 2247 differentially expressed genes at 72 h, including 1712 genes downregulated in Rx4-1806. Enrichment analyses highlighted plant–pathogen interaction, plant hormone signal transduction, and MAPK signaling pathways. Among candidate defense-related genes, SlWRKY33 was downregulated in Rx4-1806 and selected for functional validation. CRISPR/Cas9-mediated knockout of SlWRKY33 enhanced resistance in both OH 88119 and Rx4-1806, whereas SlWRKY33 overexpression increased infected leaf area and bacterial population. Knockout of SlPUB23 enhanced resistance in Rx4-1806 but not in OH 88119. These results suggest that SlWRKY33 and SlPUB23 negatively regulate tomato field resistance to bacterial spot race T3, with SlPUB23 functioning in an Rx4-dependent manner. Full article

Bacterial spot of the pepper (BSP) and the tomato (BST) caused by multiple Xanthomonas spp. remains a major constraint to production of both crops worldwide. The widespread breakdown of dominant resistance genes, such as Bs2, due to the emergence of virulent races, like Xanthomonas euvesicatoria P6, has underscored the need for more durable, non-race-specific resistance. The recessive genes, bs5; bs6; and bs8, have emerged as promising alternatives, conferring broad-spectrum resistance without triggering a hypersensitive response. In this study, we systematically evaluated the individual and combinatorial effects of these three recessive resistance genes against three Xanthomonas species, X. euvesicatoria (Xe), X. hortorum pv. gardneri (Xhg), and X. perforans (Xp). Using near-isogenic lines (NILs) developed in the susceptible Early Calwonder (ECW) background, we assessed the in planta bacterial population growth and symptom development across a panel of eight genotypes carrying different gene combinations. Our results demonstrate that bs5, particularly when combined with either bs6 or bs8, significantly reduces bacterial growth and disease severity across all three Xanthomonas species. The triple-stacked line (ECW568 (i.e., bs5, bs6, and bs8)) consistently displayed the strongest suppression of pathogen proliferation and symptom development. By contrast, bs6 and bs8, alone or in combination, were largely ineffective. In some cases, combining bs6 with bs8 was less effective than bs8 alone. These findings reinforce the central role of bs5 in conferring quantitative resistance and highlight the additive benefit of pyramiding recessive resistance genes. Furthermore, we have demonstrated that these recessive resistance genes are effective in limiting the ability of the emerging pathogen, X. perforans, to grow in planta, and thus are predicted to offer a high level of resistance in the field. Our work provides key insights for breeding durable, broad-spectrum resistance into commercial pepper cultivars and offers a framework for integrated disease management strategies in the face of rapidly evolving bacterial pathogens Full article

Bacterial spot of tomato (BST), caused by Xanthomonas euvesicatoria pv. perforans (referred to as X. perforans thereafter), is widely distributed globally, including Florida, and reduces fruit quality and yield in tomato fields. Currently, copper-based bactericides are widely used for this disease control; however, the effectiveness of these treatments has diminished due to the emergence of copper-tolerant strains. Therefore, there is a need for novel chemical controls against BST. In this study, we investigated hexanoic acid (HA) as an alternative against copper-tolerant strains of X. perforans through laboratory, greenhouse, and field experiments. In vitro experiments demonstrated HA had a lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) compared to copper sulfate, with values of 512 and 1024 mg/L for HA versus 1024 and 2048 mg/L for copper sulfate. HA exhibited bactericidal activity within 1 h at 512 and 1024 mg/L. In greenhouse trials, HA applied at 512 and 1024 mg/L two days before inoculation significantly reduced disease severity compared to untreated controls and Kocide 3000 (copper hydroxide) + Penncozeb. However, field trials indicated that while HA reduced disease severity relative to the untreated control, it did not outperform the grower standard commercial bactericide ManKocide (copper hydroxide + mancozeb), nor did it improve total yield. Previous studies have shown the antimicrobial activity of HA against various other phytopathogens, but this study is the first to demonstrate the potential of hexanoic acid for controlling BST. Full article

The use of resistant varieties is an important strategy for managing tomato bacterial spot. The objective of this study was to evaluate the reaction of tomato genotypes to Xanthomonas euvesicatoria pv. perforans. The experiment was conducted in a randomized block design with 10 genotypes and four repetitions. The genotypes consisted of hybrids (UFU-1, UFU-2, UFU-3), wild resistant accession Solanum pennellii, commercial susceptible cultivar Santa Clara and homozygous lines (UFU-5, UFU-6, UFU-11, UFU-12, UFU-15). The UFU B8 isolate of X. euvesicatoria pv. perforans was used. The bacterial suspension was prepared and adjusted in a spectrophotometer OD₅₅₀ = 0.5 (1 × 10⁹ CFU mL⁻¹). Inoculation occurred 10 days after transplantation. Disease severity was assessed at 3, 6, 9, 12 and 15 days after inoculation, and the area under the disease progress curve (AUDPC) was calculated. There was a significant difference between the genotypes regarding the severity of the disease at 3, 6 and 12 days after inoculation. Lineages 5, 6 and 12, the hybrid UFU-1 and the wild accession S. pennellii showed the lowest severity of the disease, being promising for promoting genetic improvement programs aimed at resistance to the bacteria. Full article

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. Full article

As agricultural practices become more sustainable, adopting more sustainable practices will become even more relevant. Searching for alternatives to chemical compounds has been the focus of numerous studies, and bacteriocins are tools with intrinsic biotechnological potential for controlling plant diseases. We continued to explore the biotechnological activity of the bacteriocin Gluconacin from Gluconacetobacter diazotrophicus, PAL5 strain, by investigating this protein’s antagonism against important tomato phytopathogens and demonstrating its effectiveness in reducing bacterial spots caused by Xanthomonas perforans. In addition to this pathogen, the bacteriocin Gluconacin demonstrated bactericidal activity in vitro against Ralstonia solanacearum and Pseudomonas syringae pv. tomato, agents that cause bacterial wilt and bacterial spots, respectively. Bacterial spot control tests showed that Gluconacin reduced disease severity by more than 66%, highlighting the biotechnological value of this peptide in ecologically correct formulations. Full article

Sweet pepper is an important vegetable in the world. Bacterial leaf spot, caused by the pathogen Xanthomonas perforans, is a limiting factor that significantly reduces the quality and yield of sweet peppers. The use of chemical fungicides is currently the main disease-control method for bacterial leaf spot disease. It is important to develop an eco-friendly biocontrol method by using antagonistic microorganisms. Bacillus amyloliquefaciens PMB04 has strong antagonistic effects against pathogens and can inhibit the occurrence of diseases. B. amyloliquefaciens PMB04 has the potential for the development of a disease-control product. Primarily, PMB04 contained a strong inhibitory effect against all isolated X. perforans strains. In the inoculation assay, the severity of bacterial leaf spot disease on sweet peppers was reduced by PMB04 bacterial suspensions. To increase the convenience of field applications in future prospects, the development of the PMB04 fermentation liquid was carried out using different ratios of brown sugar and yeast extract in a 30 L fermentation tank. The results exhibited that the fermentation liquid of the 3-1 and 2-1 formulas obtained the highest bacterial population in a 30 L fermentation tank. The fermentation liquid of the 0.5-0.5 formula was the most stable formula for two different conditions in terms of a consistent bacterial population and sporulation. In addition, the 200-fold dilution of the 3-1 and 0.5-0.5 fermentation liquids revealed the best control efficacy on bacterial leaf spot disease of sweet peppers. Additionally, the results of the 0.5-0.5 fermentation liquid (PMB4FL) with different dilution concentrations also demonstrated that the 200- and 500-fold dilutions had the best control efficacy. To understand the effect of commonly used copper-containing fungicides on sweet peppers on the application of microbial agent PMB4FL, the effects of copper hydroxide and tribasic copper sulfate on the growth of X. perforans strains and B. amyloliquefaciens PMB04 were assayed. The results exhibited that the above two fungicides did not have any inhibitory effect on the growth of PMB04 but had a strong inhibitory effect on the X. perforans strain. In the follow-up control experiment, the treatment of copper hydroxide had no synergistic effect with PMB4FL to control bacterial leaf spot disease. We concluded that the use of the PMB4FL fermentation liquid alone on the leaves could effectively control the occurrence of bacterial leaf spots in sweet pepper crops. Full article

Bacterial spot of tomato is among the most economically relevant diseases affecting tomato plants globally. In previous studies, non-formulated magnesium oxide nanoparticles (nano-MgOs) significantly reduced the disease severity in greenhouse and field conditions. However, the aggregation of nano-MgO in liquid suspension makes it challenging to use in field applications. Therefore, we formulated two novel MgO nanomaterials (SgMg #3 and SgMg #2.5) and one MgOH₂ nanomaterial (SgMc) and evaluated their physical characteristics, antibacterial properties, and disease reduction abilities. Among the three Mg nanomaterials, SgMc showed the highest efficacy against copper-tolerant strains of Xanthomonas perforans in vitro, and provided disease reduction in the greenhouse experiments compared with commercial Cu bactericide and an untreated control. However, SgMc was not consistently effective in field conditions. To determine the cause of its inconsistent efficacy in different environments, we monitored particle size, zeta potential, morphology, and crystallinity for all three formulated materials and nano-MgOs. The MgO particle size was determined by the scanning electron microscopy (SEM) and dynamic light scattering (DLS) techniques. An X-ray diffraction (XRD) study confirmed a change in the crystallinity of MgO from a periclase to an Mg(OH)₂ brucite crystal structure. As a result, the bactericidal activity correlated with the high crystallinity present in nano-MgOs and SgMc, while the inconsistent antimicrobial potency of SgMg #3 and SgMg #2.5 might have been related to loss of crystallinity. Future studies are needed to determine which specific variables impair the performance of these nanomaterials in the field compared to under greenhouse conditions. Although SgMc did not lead to significant disease severity reduction in the field, it still has the potential to act as an alternative to Cu against bacterial spot disease in tomato transplant production. Full article

Bacterial spot of tomato (BST) is a disease that severely afflicts tomato crops, especially in geographic areas such as the Southeastern U.S., where the environmental conditions favor rapid disease development. Farmers usually use chemical treatments such as copper–mancozeb mixtures and acibenzolar-S-methyl, among other methods, to manage BST. However, these chemical treatments generally fail to improve marketable yields, thus raising the question of whether the BST treatments are economical. We evaluated the efficacy and profitability of bactericide treatments consisting of copper-mancozeb, acibenzolar-S-methyl, and streptomycin, as well as three inoculation levels of Xanthomonas euvesicatoria pv. perforans, on the management of BST in Florida. Across three separate field trials, BST severity was inversely correlated with marketable tomato yields; however, bactericide treatments provided no statistical improvement in marketable yields. By accounting for yield and the BST treatment costs, our profitability analysis showed that the BST treatments did not pay off economically; the net returns of these treatments were statistically equivalent to the untreated controls. Full article

Bacterial spot of tomato continues to pose a significant problem to tomato production worldwide. In Florida, bacterial spot of tomato caused by Xanthomonas perforans is one of the most important diseases responsible for tomato yield loss. This disease is difficult to control, and new strategies are continually being investigated to combat the devastating effect of this disease. Recent efforts focusing on essential oils based on small molecules have spurred interests in the utilization of this class of chemicals for disease management. In this study, we evaluated the efficacy of eugenol for the management of bacterial spot of tomato caused by X. perforans. In the greenhouse experiments, eugenol applied as a foliar spray significantly (p < 0.5) reduced bacterial spot disease compared to the untreated control. In the field experiments, the area under the disease progress curve (AUDPC) was significantly (p < 0.5) lower in the plots treated with eugenol or eugenol combined with the surfactant Cohere than in the untreated control plots, and it was comparable to the copper-based treatments. To provide additional insights into the possible pathways of eugenol activities, we applied a liquid chromatography mass spectrometry (LC-MS)-based metabolomic study using a thermo Q-Exactive orbitrap mass spectrometer with Dionex ultra high-performance liquid chromatography (UHPLC) on X. perforans strain 91–118 treated with eugenol. Our results showed that eugenol affected metabolite production in multiple pathways critical to bacterial survival. For example, treatment of cells with eugenol resulted in the downregulation of the glutathione metabolism pathway and associated metabolites, except for 5-oxoproline, which accumulation is known to be toxic to living cells. While the peaks corresponding to the putatively identified sarmentosin showed the most significant impact and reduced in response to eugenol treatment, branched-chain amino acids, such as L-isoleucine, increased in production, suggesting that eugenol may not negatively affect the protein biosynthesis pathways. The results from our study demonstrated the efficacy of eugenol in the management of bacterial spot of tomato under greenhouse and field conditions and identified multiple pathways that are targeted. Full article

Bacterial Leaf Spot (BLS) is a serious bacterial disease of chilli (Capsicum spp.) caused by at least four different Xanthomonas biotypes: X. euvesicatoria pv. euvesicatoria, X. euvesicatoria pv. perforans, X. hortorum pv. gardneri, and X. vesicatoria. Symptoms include black lesions and yellow halos on the leaves and fruits, resulting in reports of up to 66% losses due to unsalable and damaged fruits. BLS pathogens are widely distributed in tropical and subtropical regions. Xanthomonas is able to survive in seeds and crop residues for short periods, leading to the infections in subsequent crops. The pathogen can be detected using several techniques, but largely via a combination of traditional and molecular approaches. Conventional detection is based on microscopic and culture observations, while a suite of Polymerase Chain Reaction (PCR) and Loop-Mediated Isothermal Amplification (LAMP) assays are available. Management of BLS is challenging due to the broad genetic diversity of the pathogens, a lack of resilient host resistance, and poor efficacy of chemical control. Some biological control agents have been reported, including bacteriophage deployment. Incorporating stable host resistance is a critical component in ongoing integrated management for BLS. This paper reviews the current status of BLS of chilli, including its distribution, pathogen profiles, diagnostic options, disease management, and the pursuit of plant resistance. Full article

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. Full article

P. aeruginosa strain FG106 was isolated from the rhizosphere of tomato plants and identified through morphological analysis, 16S rRNA gene sequencing, and whole-genome sequencing. In vitro and in vivo experiments demonstrated that this strain could control several pathogens on tomato, potato, taro, and strawberry. Volatile and non-volatile metabolites produced by the strain are known to adversely affect the tested pathogens. FG106 showed clear antagonism against Alternaria alternata, Botrytis cinerea, Clavibacter michiganensis subsp. michiganensis, Phytophthora colocasiae, P. infestans, Rhizoctonia solani, and Xanthomonas euvesicatoria pv. perforans. FG106 produced proteases and lipases while also inducing high phosphate solubilization, producing siderophores, ammonia, indole acetic acid (IAA), and hydrogen cyanide (HCN) and forming biofilms that promote plant growth and facilitate biocontrol. Genome mining approaches showed that this strain harbors genes related to biocontrol and growth promotion. These results suggest that this bacterial strain provides good protection against pathogens of several agriculturally important plants via direct and indirect modes of action and could thus be a valuable bio-control agent. Full article

Microbes are natural chemical factories and their metabolome comprise diverse arrays of chemicals. The genus Xanthomonas comprises some of the most important plant pathogens causing devastating yield losses globally and previous studies suggested that species in the genus are untapped chemical minefields. In this study, we applied an untargeted metabolomics approach to study the metabolome of a globally spread important xanthomonad, X. perforans. The pathogen is difficult to manage, but recent studies suggest that the small molecule carvacrol was efficient in disease control. Bacterial strains were treated with carvacrol, and samples were taken at time intervals (1 and 6 h). An untreated control was also included. There were five replicates for each sample and samples were prepared for metabolomics profiling using the standard procedure. Metabolomics profiling was carried out using a thermo Q-Exactive orbitrap mass spectrometer with Dionex ultra high-performance liquid chromatography (UHPLC) and an autosampler. Annotation of significant metabolites using the Metabolomics Standards Initiative level 2 identified an array of novel metabolites that were previously not reported in Xanthomonas perforans. These metabolites include methoxybrassinin and cyclobrassinone, which are known metabolites of brassicas; sarmentosin, a metabolite of the Passiflora-heliconiine butterfly system; and monatin, a naturally occurring sweetener found in Sclerochiton ilicifolius. To our knowledge, this is the first report of these metabolites in a microbial system. Other significant metabolites previously identified in non-Xanthomonas systems but reported in this study include maculosin; piperidine; β-carboline alkaloids, such as harman and derivatives; and several important medically relevant metabolites, such as valsartan, metharbital, pirbuterol, and ozagrel. This finding is consistent with convergent evolution found in reported biological systems. Analyses of the effect of carvacrol in time-series and associated pathways suggest that carvacrol has a global effect on the metabolome of X. perforans, showing marked changes in metabolites that are critical in energy biosynthesis and degradation pathways, amino acid pathways, nucleic acid pathways, as well as the newly identified metabolites whose pathways are unknown. This study provides the first insight into the X. perforans metabolome and additionally lays a metabolomics-guided foundation for characterization of novel metabolites and pathways in xanthomonad systems. Full article