Search

Peanut (Arachis hypogea L.) bacterial wilt (BW) is a devastating disease caused by Ralstonia solanacearum that results in severe yield and quality losses. Plant defensins are short cysteine-rich peptides with antimicrobial activity. The role of defensin genes (AhDef) in peanut is unclear. A genome-wide investigation of AhDef genes was undertaken, and 12 identified AhDef genes were classified into two groups containing the gamma-thionin domain formed by four disulfide pairs: Cys1-Cys8, Cys2-Cys5, Cys3-Cys6, and Cys4-Cys7. In silico analysis revealed that AhDef genes showed highly conserved architectural features and contained cis-elements associated with phytohormone signaling and defense responses. A highly resistant cultivar, H108 (R) and a susceptible accession, H107 (S) were tested by R. solanacearum inoculation. H108 (R) showed fewer symptoms than H107 (S) owing to inhibition of bacterial reproduction and spread in the vascular bundles of roots and stems. In a transcriptomic expression profile, AhDef genes, particularly AhDef1.6 and AhDef2.2, were up-regulated in H108 (R) compared with H107 (S) under R. solanacearum infection and phytohormone treatment. Subcellular localization showed that the AhDef1.6 and AhDef2.2 proteins were both expressed specifically on the plasma membrane. Overexpression of protein fusion AhDef2.2-YFP in Nicotiana benthamiana and peanut leaves increased resistance to R. solanacearum, suggesting its role in response to BW infection. AhDef2.2 may be valuable for peanut resistance breeding.

Potato plants and their tubers in Egypt are affected by one of the most renowned soil-borne pathogen, Ralstonia solanacearum, that caused brown rot in potato tubers and wilt in plants. There is no efficient therapeutic bactericide so; control of bacterial wilt is very rough. The study investigated three different concentrations of seven essential plant oils under in vitro and in vivo conditions as a result of their effects on Ralstonia solanacearum growth and their possibility use as potato seed pieces dressing for controlling bacterial wilt disease incidence. In vitro, anise oil at the three tested different concentrations (0.04, 0.07, and 0.14% vol/vol) was the most effective one inhibiting the growth of T4 and W9 isolates of Ralstonia solanacearum then pursued by thyme, lemongrass, and clove oils. On the other hand, rocket oil at the tested concentration was the least effective one followed by fennel oil. However, wheat germ oil was not completely effective. In vivo, experiment revealed that anise oil at the three concentrations significantly reduced disease incidence and severity in sponta and hermes potato cultivars and their effect was associated with increase of peroxidase, polyphenoloxidase, phenols and the foliar fresh weight of treated plants as well as the weight of tubers/plant followed by thyme and lemongrass oils compared to the infected untreated control. Morphological differences in bacterial cell structure have been observed using a transmission electron microscope (TEM). Anise oil at higher concentration caused of cell wall rupture and degraded cellular components.

Bacterial wilt is one of the main diseases of Solanum spp., which caused by Ralstonia solanacearum (RS), formerly known as Pseudomonas solanacearum. Different concentrations of chitosan nanoparticles have been evaluated as one of the alternative methods of disease management in vitro and in vivo to reduce the risks of pesticide residues. Results in vitro experiment indicated that RS5 isolate was the most virulence one compared to RS1 and RS3. Increasing concentration of nano-chitosan, lead to increase inhibition zone, and this was observed at higher concentrations (100 and 200 µg/ml). In vivo results showed the highest concentration of spraying chitosan nanoparticles increase percentage reduction of disease incidence and severity, in effected potato and tomato plants. Recorded data of disease incidence and severity in treated potato plants were 78.93 % and 71.85 %, while on tomato plants were 81.64 % and 77.63 %, respectively compared to untreated infected potato plants were recorded 15.38 %, 20.87 %, and tomato plants were 20.98 % and 28.64 %. Results also revealed that 100 µg/ml of chitosan nanoparticles the lowest treatments used as soil amended curative treatments led to incease percentage reduction of disease incidence and severity, respectively on potato and tomato plants, but less than preventive treatment. The results registered that on potato plant were 54.93 % and 52.65 %, whilst recorded on tomato plants were 59.93 % and 56.74 %. Transmission electron microscopy (TEM) micrpgraphs illustrated that morphological of healthy R. solanacearum cells were undesirably stained with uranyl. The electron-dense uranyl acetate dye was limited to the cell surface slightly than the cytoplasm, which designated the integrity of the cell film of healthy cells. While bacterial cells treated with nano-chitosan, showed modification in the external shape, such as lysis of the cell wall and loss of cell flagella. Also, the result of using Random amplified polymorphic DNA (RAPD)-PCR observed that differences in treated Ralstonia solanancearum genotype by nano-chitosan compared to the genotype of the same untreated isolate.

Blood disease in bananas caused by Ralstonia syzygii subsp. celebesensis is a bacterial wilt disease that causes major yield losses of banana in Indonesia and peninsular Malaysia. The disease has significantly increased its geographic distribution in the past decade. Diagnostic methods are an important component of disease management in vegetatively propagated crops such as banana to constrain incursions of plant pathogens. Therefore, the objectives of this study were (i) to design and rigorously validate a novel banana Blood disease (BBD) real-time PCR assay with a high level of specificity and sensitivity of detection and (ii) to validate published PCR-based diagnostic methods targeting the intergenic region in the megaplasmid (“121 assay” with primer set 121) or the phage tail protein-coding sequence in the bacterial chromosome (“Kubota assay” and “BDB2400 assay” with primer set BDB2400). Assay validation included 339 samples (174 Blood disease bacteria, 51 bacteria associated with banana plants, 51 members of the Ralstonia solanacearum species complex, and 63 samples from symptomatic and healthy plant material). Validation parameters were analytical specificity (inclusivity and exclusivity), selectivity, limit of detection, accuracy, and ruggedness. The 121 assay and our newly developed BBD real-time PCR assay detected all R. syzygii subsp. celebesensis strains with no cross-specificity during validation. Two different PCR assays using the primer set BDB2400 lacked specificity and selectivity. This study reveals that our novel BBD real-time PCR assay and the conventional PCR 121 assay are reliable methods for Blood disease diagnostics, as they comply with all tested validation parameters.

Bacterial wilt, caused by Ralstonia solanacearum, is a serious disease in pepper. However, the interaction between the pathogen and pepper remains largely unknown. This study aimed to gain insights into determinants of pepper susceptibility and R. solanacearum pathogenesis. We assembled the complete genome of R. solanacearum strain Rs-SY1 and identified 5,106 predicted genes, including 84 type III effectors (T3E). RNA-seq was used to identify differentially expressed genes (DEGs) in susceptible pepper CM334 at 1 and 5 days postinoculation (dpi) with R. solanacearum. Dual RNA-seq was used to simultaneously capture transcriptome changes in the host and pathogen at 3 and 7 dpi. A total of 1,400, 3,335, 2,878, and 4,484 DEGs of pepper (PDEGs) were identified in the CM334 hypocotyls at 1, 3, 5, and 7 dpi, respectively. Functional enrichment of the PDEGs suggests that inducing ethylene production, suppression of photosynthesis, downregulation of polysaccharide metabolism, and weakening of cell wall defenses may contribute to successful infection by R. solanacearum. When comparing in planta and nutrient agar growth of the R. solanacearum, 218 and 1,042 DEGs of R. solanacearum (RDEGs) were detected at 3 and 7 dpi, respectively. Additional analysis of the RDEGs suggested that enhanced starch and sucrose metabolism, and upregulation of virulence factors may promote R. solanacearum colonization. Strikingly, 26 R. solanacearum genes were found to have similar DEG patterns during a variety of host–R. solanacearum interactions. This study provides a foundation for a better understanding of the transcriptional changes during pepper–R. solanacearum interactions and will aid in the discovery of potential susceptibility and virulence factors.

Ralstonia causes wilt diseases by colonizing xylem vessels and disrupting water transport. The dogma is that bacterial biomass clogs vessels and reduces the flow of xylem sap due to Ralstonia abundance. However, the physiological mechanism of xylem disruption during bacterial wilt is untested. Using a tomato and Ralstonia pseudosolanacearum GMI1000 model, we visualized and quantified spatiotemporal dynamics of xylem disruption during bacterial wilt. First, we measured stomatal conductance of leaflets on mock-inoculated and wilt-symptomatic plants. Wilted leaflets had reduced stomatal conductance, as did turgid leaflets on the same petiole as wilted leaflets. Next, we used X-ray microcomputed tomography (X-ray microCT) and light microscopy to differentiate between mechanisms of xylem disruption: blockage by bacterial biomass, blockage by vascular tyloses, or sap displacement by gas embolisms. We imaged intact plant stems to quantify embolized vessels. Embolized vessels were rare, but infected plants with low bacterial populations had a nonsignificant trend of more vessel embolisms. To test whether vessels are clogged during bacterial wilt, we imaged excised stems after brief dehydration. Most vessels in mock-infected plants emptied their contents after excision, but nonconductive clogged vessels were abundant in infected plants by 2 days post infection. At wilt onset, when bacterial populations exceeded 5 × 108CFU/g stem tissue, approximately half of the vessels were clogged with electron-dense bacterial biomass. We found no evidence of tyloses in X-ray microCT reconstructions or from light microscopy of preserved stems. Therefore, bacterial blockage of vessels appears to be the principal cause of xylem disruption during Ralstonia wilt.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 “No Rights Reserved” license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law, 2022.

Tomato (Solanum lycopersicum L.) is one of the most important vegetables in Togo. Unfortunately, tomato is susceptible to many diseases, among which bacterial wilt caused by Ralstonia solanacearum causes major yield losses. In this study, incidence of bacterial wilt and its distribution was evaluated in the central region of Togo, the major tomato-producing area in the country. Overall, 16 localities were surveyed in four prefectures. In each locality, three fields were visited, the incidence of the disease was recorded, and diseased samples were collected for laboratory investigation. The results showed that bacterial wilt occurred in all of the fields visited, indicating a field incidence of 100%, whereas the plant incidence ranged from 10.00 ± 00 to 43.33 ± 3.33%, with an average of 20.94 ± 1.77%. The antibody-based ImmunoStrip test was positive for R. solanacearum in 100% of the visited fields. From 144 samples collected from fields, 45 R. solanacearum isolates were isolated on modified selective medium from South Africa. These survey results show that tomato bacterial wilt is a real threat to tomato production in the central region of Togo.

As tobacco bacterial wilt is a bacterial disease that is increasingly harmful to tobacco plants′ growth, it is of great significance to explore the changes in the soil microbial community structure and its biological regulation mechanism after tobacco plant suffers from bacterial wilt. Field experiments were conducted to investigate the differences of bacterial community structure among four treatments: ZCTR(conventional fertilization, rhizosphere soil of healthy tobacco plants), ZCSW(application of 1.2 t·hm-2 biochar, rhizosphere soil of healthy tobacco plants), QKTR(conventional fertilization, rhizosphere soil of bacterial wilt tobacco plants), and QKSW(application of 1.2 t·hm-2 biochar, rhizosphere soil of bacterial wilt tobacco plants). After the biochar application, the bacteria′s α diversity increased, albeit without a significant difference. The bacterial community richness and structure changed. Under the same fertilization conditions, the bacterial α diversity and community abundance of bacterial wilt tobacco plants in the rhizosphere soil were less than those of healthy soil. The bacterial α diversity and community richness of the rhizosphere soil of diseased tobacco plants without biochar were higher than that of healthy tobacco plants, the abundance of Gemmatimonadetes and Acidobacteria increased by 0.26 and 1.27 percent points, while the abundance of Proteobacteria and Actinobacteria decreased by 1.08 and 0.14 percent points. Compared with no biochar treatment, the plant height, leaf length, leaf width and stem girth of the biochar application treatment increased by 11.83%, 16.88%, 6.70% and 10.80%, respectively, and the disease index decreased. The incidence rate of the bacterial wilt was reduced by 9.1 percent points with the biochar application treatment compared with the no biochar treatment. Studies have shown that biochar application can alleviate the decline in bacterial abundance caused by bacterial wilt, reduce the relative abundance of pathogenic bacteria, and drive the increase in the relative abundance of functional growth-promoting bacteria(Gemmatimonadetes). This reduces the incidence of bacterial wilt and preliminarily clarifies the biochar′s mechanism on the micro-ecological regulation of bacterial wilt in tobacco-growing soil.

Glasshouse experiments were conducted to study infection and disease development in rockwool-grown rose plants inoculated with Ralstonia pseudosolanacearum. A R. pseudosolanacearum strain isolated from rose plants was more aggressive than strains from anthurium or curcuma. The three rose cultivars tested, Avalanche, Red Naomi, and Armando, differed in susceptibility. At 20°C, the rose strain caused hardly any symptoms over a 6-week period, whereas at 28°C typical wilt symptoms were observed within 2 weeks after stem inoculation of Armando, the most susceptible cultivar. Inoculating roots with the rose strain resulted only in weak atypical symptoms. Nevertheless, inoculating roots of cv. Armando at a relatively low inoculum dose of 104 cfu/ml led to high densities in the base of stems in one out of two experiments. R. pseudosolanacearum occasionally spread from stem inoculated plants with symptoms in rockwool slabs. This limited spread resulted in a low infection incidence, and only of plants directly adjacent to the plants with symptoms.

Bacterial wilt caused by Ralstonia solanacearum is a serious soilborne disease that results in severe losses to tobacco (Nicotiana tabacum) production in China. In this study, a novel RPA-LFD assay for the rapid visual detection of R. solanacearum was established using recombinase polymerase amplification (RPA) and lateral-flow dipstick (LFD). The RPA-LFD assay was performed at 37°C in 30 min without complex equipment. Targeting the sequence of the RipTALI-9 gene, we designed RPA primers (Rs-rpa-F/R) and an LF probe (Rs-LF-probe) that showed high specificity to R. solanacearum. The sensitivity of RPA-LFD assay to R. solanacearum was the same as that in conventional PCR at 1 pg genomic DNA, 103 CFU/g artificially inoculated tobacco stems, and 104 CFU/g artificially inoculated soil. The RPA-LFD assay could also detect R. solanacearum from plant and soil samples collected from naturally infested tobacco fields. These results suggest that the RPA-LFD assay developed in this study is a rapid, accurate molecular diagnostic tool with high sensitivity for the detection of R. solanacearum.

Strains of Erwinia tracheiphila, causal agent of bacterial wilt of cucurbits, are divided into distinct clades. Et-melo clade strains wilt Cucumis spp. but not Cucurbita spp., thus exhibiting host specificity, whereas Et-C1 clade strains wilt Cucurbita spp. more rapidly than Cucumis melo, thus exhibiting a host preference. This study investigated the contribution of the effector proteins Eop1 and DspE to E. tracheiphila pathogenicity and host adaptation. Loss of eop1 did not enable Et-melo strains to infect squash (Cucurbita pepo) or an Et-C1 strain to induce a more rapid wilt of muskmelon (Cucumis melo), indicating that Eop1 did not function in host specificity or preference as in the related pathogen E. amylovora. However, overexpression of eop1 from Et-melo strain MDCuke but not from Et-C1 strain BHKY increased the virulence of a BHKY eop1 deletion mutant on muskmelon, demonstrating that the Eop1 variants in the two clades are distinct in their virulence functions. Loss of dspE from Et-melo strains reduced but did not eliminate virulence on hosts muskmelon and cucumber, whereas loss of dspE from an Et-C1 strain eliminated pathogenicity on hosts squash, muskmelon, and cucumber. Thus, the centrality of DspE to virulence differs in the two clades. Et-melo mutants lacking the chaperone DspF exhibited similar virulence to mutants lacking DspE, indicating that DspF is the sole chaperone for DspE in E. tracheiphila, unlike in E. amylovora. Collectively, these results provide the first functional evaluation of effectors in E. tracheiphila and demonstrate clade-specific differences in the roles of Eop1 and DspE. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Ralstonia solanacearum species complex (RSSC) contains a group of destructive plant pathogenic bacteria, causing bacterial wilt of >200 species of crops and trees, such as Casuarina equisetifolia, worldwide. RSSC can survive in the soil environment for a long time and start infection after activation by host plants. This study conducted a transcriptome analysis on the expression pattern of the pathogenicity-related genes of a new isolated RSSC strain YQ (Ralstonia pseudosolanacearum phylotype I-16) in response to C. equisetifolia cladophyll (a branch of a stem that resembles and functions as a leaf) and root debris under in vitro culture. The cladophyll debris induced more genes up-regulated than the root debris, including pathogenicity-related genes involved in motility, effectors, type III secretion systems, quorum sensing, and plant cell wall degradation. Besides, many differentially expressed genes were related to transcriptional regulator such as cyclic dimeric guanosine monophosphate. Moreover, the cultures with cladophyll debris induced a faster wilting in bioassays, and the cell swimming was enhanced by cladophyll exudate. C. equisetifolia cladophylls could activate the expression of pathogenicity-related genes of strain YQ and accelerate infection. Our findings suggest that litterfall management in C. equisetifolia forests, or even other plantations, should receive attention to prevent the induction of bacterial wilt disease caused by RSSC.

WIPK-NtLTP4 module improves the resistance to R. solanacearum via upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure in tobacco. Lipid transfer proteins (LTPs) are a class of small lipid binding proteins that play important roles in biotic and abiotic stresses. The previous study revealed that NtLTP4 positively regulates salt and drought stresses in Nicotiana tabacum. However, the role of NtLTP4 in biotic stress, especially regarding its function in disease resistance remains unclear. Here, the critical role of NtLTP4 in regulating resistance to Ralstonia solanacearum (R. solanacearum), a causal agent of bacterial wilt disease in tobacco, was reported. The NtLTP4-overexpressing lines markedly improved the resistance to R. solanacearum by upregulating the expression of defense-related genes, increasing the antioxidant enzyme activity, and promoting stomatal closure. Moreover, NtLTP4 interacted with wound-induced protein kinase (WIPK; a homolog of MAPK3 in tobacco) and acted in a genetically epistatic manner to WIPK in planta. WIPK could directly phosphorylate NtLTP4 to positively regulate its protein abundance. Taken together, these results broaden the knowledge about the functions of the WIPK-NtLTP4 module in disease resistance and may provide valuable information for improving tobacco plant tolerance to R. solanacearum.

Banana Xanthomonas Wilt (BXW), caused by Xanthomonas campestris pv. musacearum (Xcm), a devastating disease, causes up to 100% loss and affects all banana varieties. The disease is widespread in East and Central Africa region. Study objective was to evaluate the performance of single stem rouging options for rehabilitation of severely affected banana orchard. Five single stem rouging options were implemented in banana orchard with 80% BXW severity in Western Kenya. The options included rouging of infected banana plants; uprooting, cutting at the base, injecting 20 ml of glyphosate herbicide at the soil base of the pseudostem, uprooting the whole stool and control leaving the infected stools. Initial visual assesment before implementation of the orchard was over 80% infection. Later samples were collected for diagnosis of ten plants per treatment from different plant parts and were subjected to ELISA and PCR procedures for confirmion of the presence of Xcm. Rouging options was implemented for one year. During and after experimentation periodic visual assesment of BXW incidence and severity reduced. Results of ELISA assays and PCR results indicated Xanthomonas was present on banana plants. Rouging the infected banana stems by cutting at the base, uprooting and injection of herbicide reduced BXW incidence within six months. Xanthomonas, an inhibiting bacteria cannot surve without host and by killing the banana plant the Xanthomonas dies. Yields were recovered from the rehabilitated orchard within one year. Banana orchard highly infected with BXW was effectively rehabilitated.

Blood disease in bananas caused by Ralstonia syzygii subsp. celebesensis is a bacterial wilt causing significant crop losses in Indonesia and Malaysia. Disease symptoms include wilting of the plant and red-brown vascular staining, internal rot, and discoloration of green banana fruit. There is no known varietal resistance to this disease in the Musa genus, although variation in susceptibility has been observed, with the popular Indonesian cooking banana variety Kepok being highly susceptible. This study established the current geographic distribution of Blood disease in Indonesia and confirmed the pathogenicity of isolates by Koch’s postulates. The long-distance distribution of the disease followed an arbitrary pattern indicative of human-assisted movement of infected banana materials. In contrast, local or short-distance spread radiated from a single infection source, indicative of dispersal by insects and possibly contaminated tools, water, or soil. The rapid expansion of its geographical range makes Blood disease an emerging threat to banana production in Southeast Asia and beyond.

Thirteen-tomato genotypes were assembled from the USA, Taiwan and Ghana for screening for bacterial wilt resistance in two environments: in a screen house at Crops Research Institute, Kumasi, Ghana and in the field at a bacterial wilt hot spot at Bechem in the Brong-Ahafo region of Ghana. The bacterium, Ralstonia solanacearum was isolated using the serial dilution method on Nutrient Agar (NA) and aseptically cultured for inoculation. The bacterium was implicated as the causal organism of the bacterial wilt disease of tomato. A local check, Petofake and H7996 were used as susceptible and resistant checks respectively. Three genotypes, H7996, LA0442 and LA0443 demonstrated significant resistance stability in both experimental environments by recording significantly low wilt incidence and severity. H7996 was obtained from the World Vegetable Centre (WVC), Taiwan while the other two genotypes were collected from the University of California, Davis, USA. Apart from the highest yielding genotype LA 0442 that recorded 50.67 t/h, the rest recorded very low yields. The lowest yielding genotype AVTO 1713, recorded (12.67 t/h). Thus, the highest yielding genotype, LA 0442 over-yielded the lowest AVTO1713 by approximately 300%. It is instructive to note that LA0442, which was identified as a stable resistant genotype also recorded the highest yield. This result supports the potential of developing a resistant, high yielding variety using LA0442 as a parent. The future of the tomato industry in Ghana therefore looks promising.

Complex interactions based on host plant, rhizosphere microorganisms and soil microenvironment are presumed to be responsible for the suppressive properties of biochar against soil-borne diseases, although the underlying mechanisms are not well understood. This study is designed to evaluate the efficacy of biochar amendment for controlling tomato bacterial wilt caused by Ralstonia solanacearum, and to explore the interactions between biochar-induced changes in rhizosphere compound composition, the pathogen and tomato growth. The results showed that biochar amendment decreased disease incidence by 61–78% and simultaneously improved plant growth. The positive ‘biochar effect’ could be associated with enhanced microbial activity and alterations in the rhizosphere organic acid and amino acid composition. Specifically, elevated rhizosphere citric acid and lysine, but reduced salicylic acid, were induced by biochar which improved microbial activity and rendered the rhizosphere unsuitable for the development of R. solanacearum. In addition, nutrients which were either made more available by the stimulated microbial activity or supplied by the biochar could improve plant vigor and potentially enhance tomato resistance to diseases. Our findings highlight that biochar's ability to control tomato bacterial wilt could be associated with the alteration of the rhizosphere organic acid and amino acid composition, however, further research is required to verify these ‘biochar effects’ in field conditions.

Highlights • Traditional and modern methods of diagnosing bacterial wilt disease of potato. • Evaluate the susceptibility of some Egyptian potato cultivars against to R. solanacearum. • Differentiate potato cultivars using molecular genetics methods such as SDS-PAGE profile by protein content., Bacterial wilt caused by Ralstonia solanacearum (Smith), is one of the chief severe diseases of potato in warm temperate regions, tropics and subtropics of the world. The study was conducted to isolate and identify bacterial pathogens and select the most resistant cultivars and avoid the decrease in the total value of Egyptian potato exports to the European Union (EU) due to the quarantine restrictions imposed by the EU on potato tubers exported from Egypt affected by bacterial wilt. The results of traditional identification through morphological and serological studies showed that the five isolates were isolated and identified as Ralstonia solanacearum. Furthermore, the results illustrated that RS5 isolate showed the lowest percentage of disease incidence reduction on the three tested potatoes cultivar Bellini, Spunta and Mondial recorded 9.64%, 15.41% and 34.12%, respectively. While, RS8 isolate exhibited the highest effective one the percentage of disease reduction on all tested potato cultivars. This isolate reduced disease incidence 60.60%, 63.21% and 71.66%, compering to the healthy control treatment. The result of molecular identification represent that the probe used in Taq-man (PCR) was of the type (B2) capable to detect only biovar 2 of R. solanacearum bacterial wilt. Furthermore, primer and probe are specific for detection of the race 3 biovar 2 strain. Positive results were obtained in all assays used including IFAS, protein content and SDS-PAGE with all five isolates. So the isolate (RS5) was the most virulence one, followed by RS1, RS3, RS2 and RS8, registered that the tested isolates were R. solanacearum race 3, biovar 2. Also, studies focused on the form of genetic distances and similarities based on pathogenic and plant growth parameters. The results illustrate that the highest genetic similarity (0.998) was found between Bellini and Spunta cultivars as the closest but the lowest value (0.946) was found between Mondial and Bellini as most distant. These results were similarity with genetic distances and SDS-PAGE profile of the three tested potato cultivars.

Bacterial wilt caused byR. solanacearumis a constraint that limits the production of solanaceous in Côte d'Ivoire. The genetic control, which is more widely used, comes up against the genetic and phenotypic variability of the strains. The objective of this study was to screen commercial and traditional varieties of Solanaceae against Ivorian strains of different phylotypes to assess their spectrum of resistance to the disease. The level of virulence of the five strains ofR. solanacearumwas evaluated in semi-controlled conditions against eight varieties of Solanaceae (pepper, eggplant and tomato). Four groups of strains were identified according to the level of virulence. Group 4, composed of strains (RUN 1794 and RUN 1854) of phylotype III and I, respectively, and originating from the localities of Kondoukro and Yamoussoukro, was very virulent. The resistant varieties were for the F1 kalenda eggplant, for the yellow chilli from Burkina and for the F1 Lindo tomato. These varieties could be used in the fight against bacterial wilt in Côte d'Ivoire.

Ralstonia solanacearum causes bacterial wilt disease in solanaceous crops. Identification of avirulence type III-secreted effectors recognized by specific disease resistance proteins in host plant species is an important step toward developing durable resistance in crops. In the present study, we show that R. solanacearum effector RipJ functions as an avirulence determinant in Solanum pimpinellifolium LA2093. In all, 10 candidate avirulence effectors were shortlisted based on the effector repertoire comparison between avirulent Pe_9 and virulent Pe_1 strains. Infection assays with transgenic strain Pe_1 individually carrying a candidate avirulence effector from Pe_9 revealed that only RipJ elicits strong bacterial wilt resistance in S. pimpinellifolium LA2093. Furthermore, we identified that several RipJ natural variants do not induce bacterial wilt resistance in S. pimpinellifolium LA2093. RipJ belongs to the YopJ family of acetyltransferases. Our sequence analysis indicated the presence of partially conserved putative catalytic residues. Interestingly, the conserved amino acid residues in the acetyltransferase catalytic triad are not required for effector-triggered immunity. In addition, we show that RipJ does not autoacetylate its lysine residues. Our study reports the identification of the first R. solanacearum avirulence protein that triggers bacterial wilt resistance in tomato. We expect that our discovery of RipJ as an avirulence protein will accelerate the development of bacterial wilt-resistant tomato varieties in the future. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

Background Understanding the specific inhibitory effects of different Brassica seed meals (BSMs) on soilborne pathogens is important for their application as biocontrol agents for controlling plant disease. In this study, the seed meals of Brassica napus L. (BnSM), Brassica campestris L. (BcSM), and Brassica juncea L. (BjSM), and the combined seed meal of BcSM and BjSM (CSM, 1:1), were selected for investigation. The inhibitory effects of these seed meals on the plant pathogen Ralstonia solanacearum (Smith) and tomato bacterial wilt, were assessed and compared. Results All the BSMs significantly inhibited the growth of R. solanacearum in vitro. Furthermore, the BSMs could effectively suppress R. solanacearum virulence traits, including motility, exopolysaccharide production, dehydrogenase activity, virulence-related gene expression, and colonization in the soil. Among them, BjSM showed the best inhibiting effects, and CSM displayed synergic toxicity against R. solanacearum. In addition, the predominant antibacterial compounds in BcSM and BjSM were identified as the volatile compounds, 3-butenyl isothiocyanate and allyl isothiocyanate, respectively. Finally, pot experiment verified that the control effects of BjSM and CSM on tomato wilt reached more than 90%. Conclusion This is the first study to report on the ability of different kinds of BSMs to suppress the virulence of R. solanacearum and biocontrol efficiencies against bacterial wilt in tomato plants. Furtherly, the main antibacterial compounds in the BSMs were identified. The results demonstrated that CSM may possess potential for controlling bacterial wilt caused by R. solanacearum. The results provide a fresh perspective for comprehending the mechanism underlying BSM suppression of pathogens and plant disease. This article is protected by copyright. All rights reserved.

Biological control of phytopathogen is a promising approach when compared to the use of chemical agents. In the present study, seven Streptomyces cultures showing promising anti biofilm activity against Ralstonia solanacearum was mixed individually with farmyard manure. All the Streptomyces fortified farmyard manure (SFYM) were screened for plant growth promotion and control of bacterial wilt caused by R. solanacearum on tomato. Further, the ability of SFYM on stimulating the production of defense-related enzymes in R. solanacearum-inoculated tomato plants was investigated. When compared to the control tomato plants, the SFYM-treated plants had longer shoot and root length along with higher fresh and dry weight. The maximum level of chlorophyll was observed in the plants treated with strain UP1A-1 (2.21 ± 0.18 mg g−1). Strain UP1A-1 also showed maximum of 96.8 ± 1.4% biocontrol efficacy in tomato plants challenged with R. solanacearum. In addition, the UP1A-1 treated tomato plants showed maximum accumulation of total phenolics (3.02 ± 0.09 mg g−1) after 6 days of pathogen inoculation (DPI). Similarly, tomato plants treated with UP1A-1 showed highest level of peroxides, polyphenol oxidase and phenylalanine ammonia lyase during 1–9 DPI. Findings of present study revealed that the Streptomyces culture UP1A-1 fortified farm yard manure could be applied as an eco-friendly alternative to synthetic agents for controlling bacterial wilt in tomato plants.

Turmeric (Curcuma longa L. (Zingiberaceae)) is a rich source of medicinally important chemical compounds obtained from both pseudostem (aboveground part) and rhizome (underground part). However, the availability of disease-free elite varieties of the plant is highly restricted. Leaf spot caused by Colletotrichum curcumae Butler & Bisby and bacterial wilt caused by Ralstonia pseudosolanacearum Safni have been reported as major diseases responsible for reduced rhizome productivity in the turmeric plant. Meristem culture is a well-known alternative for production of disease-free mother rhizome. The aim of this investigation was to eradicate bacterial and fungal disease instances through culturing of meristematic tissue pretreated with 1.44 to −2.88 μM GA (gibberellic acid) followed by detection of disease contamination using PCR amplification and chemical assay. Meristem (0.5 to 2.0 mm) was identified as a good material for initiating tissue culture, as it exhibited 100% survival rate and absence of R. pseudosolanacearum and C. curcumae when tested with SPA (sucrose peptone agar), TZC (Kelman’s tripheny tetrazolium chloride), and PDA (potato dextrose agar) selective media. Plantlets derived from meristematic tissues of size 2.0 mm were healthy and displayed rapid recovery and uniformity in size. Disease-free status of plantlets (derived from meristem culture) was confirmed by PCR products of specific primers, RP1F/RP1R and RP3F/RP3R for R. pseudosolanacearum and CCactF/CCactR and CChisF/CChisR for C. curcumae. Moreover, shoot elongation using supplemented GA in the culture medium was successfully induced for meristem cutting. All meristem cultures pretreated with GA were confirmed to be contamination-free through TZC, SPA, and PDA media as well as PCR amplification. Based on this study, the 1.0 to 2.0 mm in size of meristem cutting and pretreatment with 1.44 to 2.88 μM GA for shoot elongation were successfully identified in addition to confirming the disease-free status of the plantlets using chemical assay and PCR products.

Twelve F1 hybrids developed through line × tester design along with seven parents were evaluated for fruit yield, quality, incidence of bacterial wilt disease and anatomical features of root and stem to study the manifestation of heterobeltiosis, and to understand the implication of anatomical characters towards tolerance against bacterial wilt disease. Two hybrids (Utkal Deepti × CLN-2764A and Utkal Kumari × CLN-2777G) registering substantial tolerance against bacterial wilt exhibited marked heterobeltiosis for fruit yield per plant and other component traits. Hypocotyls of the highly tolerant hybrid did not show any bacterial colonization in xylem tissues under light microscope even at 8 days of inoculation with native bacterial isolate. The potted seedlings of tolerant hybrid showed mean disease index of 1.16 even at 20 days of inoculation with bacterial isolate which indicated promise for its utilization in bacterial wilt prone areas. Establishment of significant negative correlations between the incidence of bacterial wilt disease and the ratio of large vessels/small vessels in stem, diameter of large vessels in stem, and diameter of large vessels in roots suggested that these anatomical characters might be considered as important indices for selection of hybrid tolerant to bacterial wilt disease. Significant heterobeltiosis was also manifested for three anatomical traits. This study justified the scope of utilizing the anatomical features of stem and root in breeding tomato cultivars tolerant to bacterial wilt disease. Overwhelming response of non-additive genetic control for these anatomical traits also exposed the evidence of heterosis breeding for their improvement.

Bacterial wilt caused by Ralstonia solanacearum is a major constraint to production of potatoes (Solanum tuberosum L). To date, there are no known conventional bactericides which provide effective control of this soil borne pathogen. This study aimed at investigating the antibacterial activity of eugenol and thymol which are the major components of thyme and clove essential oils, respectively against R. solanacearum. The pathogen was isolated from potato tubers exhibiting bacterial wilt symptoms. The inhibitory effect of these compounds was assayed by disc diffusion and minimal inhibition concentration (MIC) methods. Combinational test was also performed using chequerboard assay. At a concentration of 100 mg mL-1, thymol and eugenol had inhibition zones of 27 and 17 mm, respectively. The MIC of eugenol and thymol were determined as 275 and 175 µg mL-1, respectively and both had bactericidal effect against R. solanacearum. Combinational test revealed an additive effect indicating that their combined use does not significantly enhance inhibition. Both compounds have a potential to be exploited as antibiotic for the management of bacterial wilt disease albeit thymol at a lower concentration. Exploitation of these volatile compounds in vivo however faces challenges which can be overcome through nanoencapsulation by an appropriate nanocarrier. Key words: Essential oils, inhibitory effect, combinational test, chequerboard assay, bactericidal effect.

In nature, plants interact with multiple organisms, below and aboveground. Although interactions of plants with single biotic stressors are well characterized, knowledge of how the immune system responds to multiple biotic stressors is lacking. It is known that the two most important pathways involved in the plant immune defenses are jasmonic acid (JA) and salicylic acid (SA). The crosstalk between these plant hormonal signaling pathways seems to fine-tune the plant responses to different stressors. In this study, we characterized maize (Zea mays) hormonal interactions under the attack of two economically important pests: the bacterial pathogen that causes Goss’s bacterial wilt and leaf blight (Clavibacter michiganensis subsp. nebraskensis), and the chewing insect, fall armyworm (Spodoptera frugiperda). Our results indicate that the Goss’s wilt-resistant maize plants when pretreated with bacteria became more vulnerable to the subsequent attack by the fall armyworm larvae. Furthermore, plant hormone analysis demonstrated that the antagonistic interactions of JA-Isoleucine (JA-Ile), biologically active form of JA, and SA in maize plants contributed to enhanced plant susceptibility to herbivory. Collectively, our results suggest that plant hormonal interactions may play a major role in maize defense against multiple biotic stressors. Furthermore, this study will improve our understanding and ability to predict plant-induced hormone responses in an economically important crop.

Bacterial wilt caused by Ralstonia solanacearum is the main bacterial disease in potato. Solanum commersonii Dun. (cmm; 2n = 2x = 24, 1 EBN) is a native species to southern Brazil, Uruguay and Argentina with desirable traits for introgressive hybridisation breeding into cultivated potato such as resistance to R. solanacearum. In Uruguay, successful crosses between cmm and Solanum tuberosum Group Tuberosum (tbr; 2n = 4x = 48, 4 EBN) have been carried out with this objective, resulting in backcross 1, 2 and 3 progenies. The aim of this study was to characterise one backcross 3 progeny (BC3) using cytogenetic, genetic, morphological and agronomic descriptors. Resistance to R. solanacearum showed transgressive segregation and an association with plant architecture. Fifty-two percent of individuals had chromosome numbers close to cultivated potato with no evidence of preferential loss of cmm chromosomes. All BC3 individuals showed male sterility, probably due to nuclear-cytoplasmic interactions. Although there was wide segregation in morphological traits, most individuals resembled the recurrent tbr parents. A few more backcrosses combined with screening for bacterial wilt resistance may be necessary to allow for further recombination and removal of undesirable traits from cmm. The presence of BC3 individuals with chromosome numbers close to 2n = 48, combining morphological traits from tbr with good levels of resistance, suggests the occurrence of introgression events. This points to S. commersonii as one of the most promising genetic resources for potato breeding from the Southern Atlantic region.

The soilborne pathogen Ralstonia solanacearum causes a lethal bacterial wilt disease of tomato and many other crops by infecting host roots, then colonizing the water-transporting xylem vessels. Tomato xylem sap is nutritionally limiting but it does contain some carbon sources, including sucrose, trehalose, and myo-inositol. Transcriptomic analyses revealed that R. solanacearum expresses distinct catabolic pathways at low cell density (LCD) and high cell density (HCD). To investigate the links between bacterial catabolism, infection stage, and virulence, we measured in planta fitness of bacterial mutants lacking specific carbon catabolic pathways expressed at either LCD or HCD. We hypothesized that early in disease, during root infection, the bacterium depends on carbon sources catabolized at LCD, while HCD carbon sources are only required later in disease during stem colonization. A R. solanacearum ΔiolG mutant unable to use the LCD-catabolized nutrient myo-inositol was defective in tomato root colonization, but after it reached the stem this strain colonized and caused symptoms as well as wild type. In contrast, R. solanacearum mutants unable to use the HCD-catabolized nutrients sucrose (ΔscrA), trehalose (ΔtreA), or both (ΔscrA/treA), infected roots as well as wild-type R. solanacearum but were defective in colonization and competitive fitness in midstems and had reduced virulence. Further, xylem sap from tomato plants colonized by ΔscrA, ΔtreA, or ΔscrA/treA R. solanacearum mutants contained twice as much sucrose as sap from plants colonized by wild-type R. solanacearum. Together, these findings suggest that quorum sensing specifically adapts R. solanacearum metabolism for success in the different nutritional environments of plant roots and xylem sap. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Ralstonia solanacearum causes bacterial wilt of tomato and limits the crop production, and antagonistic microorganisms use to suppress the disease, of which Trichoderma and Pseudomonas species are the most effective agents to control bacterial wilt. In the present study, attempt was made to isolate these two microorganisms to evaluate their effectiveness to control R. solanacearum, the causal agent of bacterial wilt disease of tomato under greenhouse conditions. Thus R. solanacearum, Pseudomonas and Trichoderma spp. were isolated from wilted and healthy tomato plants grown from farmer's field in Ziway and Meki, Oromia Ethiopia. The virulence of the pathogen and the antagonistic effect of the bacteria and fungi were evaluated against R. solanacearum in vitro and in vivo condition. Based on the in vitro results the best two isolates were selected to show their antagonistic effect under greenhouse condition in single and combined designs. The result showed the pathogenicity test of the isolates were evaluated under greenhouse condition, and isolate AAURS1 showed highest virulence (75%) followed by isolate APPRCRS2 with pathogenicity of 50%. With regard to antagonism test, isolates AAURB20 and AAUTR23 showed the highest inhibition against R. solanacearum with inhibition zone of 16 and 15 mm, respectively. Among the treatments co-inoculation was more effective and reduced disease incidence by 13.33% and increased the bio-control efficacy by 72.22% when compared with individual treatment and negative control. The isolates significantly increased the plant height and dry weight by 72.33 cm and 12.18 g, respectively. Thus, the combined use of the biocontrol agents significantly reduced the incidence of tomato bacterial wilt disease. However, their performance should be evaluated using other yield parameters under field conditions to produce healthy tomato seedling to minimize the use of chemicals and reduce environmental pollution. Key words: Biocontrol, Pseudomonas, Ralstonia solanacearum, Trichoderma.

Clavibacter nebraskensis causes Goss’s bacterial wilt and leaf blight, a major disease of maize. Infected crop residue is the primary inoculum source and infection can occur via wounds or natural openings, such as stomata or hydathodes. The use of resistant hybrids is the primary control method for Goss’s wilt. In this study, colonization and movement patterns of C. nebraskensis during infection were examined using green fluorescent protein (GFP)-labeled bacterial strains. We successfully introduced a plasmid to C. nebraskensis via electroporation, which resulted in GFP accumulation. Fluorescence microscopy revealed that in the absence of wounding, bacteria colonize leaf tissue via entry through the hydathodes when guttation droplets are present. Stomatal penetration was not observed under natural conditions. Bacteria initially colonize the xylem and subsequently the mesophyll, which creates the freckles that are characteristic of the disease. Bacteria infiltrated into the mesophyll did not cause disease symptoms, could not enter the vasculature, and did not spread from the initial inoculation point. Bacteria were observed exuding through stomata onto the leaf surface, resulting in the characteristic sheen of diseased leaves. Resistant maize lines exhibited decreased bacterial spread in the vasculature and the mesophyll. These tools to examine C. nebraskensis movement offer opportunities and new insights into the pathogenesis process and can form the basis for improved Goss’s wilt management through host resistance.

Tomato (Solanum lycopersicum L.) a native of South America is a source of vitamins, minerals and antioxidant lycopene, and considered as protective food. In India, the crop is grown under the area of about 0.458 M ha with production of 7.277 M mt and productivity of 15.9 mt/ha. Biotic factors play a role in low productivity of the crops in India. Among various diseases, bacterial wilt disease incited by Ralstonia solanacearum (Smith) Yabuuchi et al. (1996) is a devastating bacterium causing damage to the crop ranging from 2 to 95% depending on the seasons and cultivars. In India, majority of the isolates of R. solanacearum infecting tomato crop belonged to biovar 3, race 1 and phylotype I. However, less than 10% isolates of the bacteria belonged to biovar 4 particularly in the states of Jharkhand and Himachal Pradesh. The genetic diversity of R. solanacearum has been studied by using methods such as random amplified polymorphic DNA (RAPD), PCR—RFLP (PCR—Restriction Length Fragment Polymorphism) of hrp gene, Repetitive element palindromic-polymerase chain reaction (Rep-PCR) and multilocus sequence typing (MLST). The genetic diversity was recorded in Indian R. solanacearum isolates irrespective of their occurrence in different agro-climatic conditions.

The infection of potato with Ralstonia solanacearum UW551 gives rise to bacterial wilt disease via colonization of roots. The type III secretion system (T3SS) is a determinant factor for the pathogenicity of R. solanacearum. To fully understand perturbations in potato by R. solanacearum type III effectors(T3Es), we used proteomics to measure differences in potato root protein abundance after inoculation with R. solanacearum UW551 and the T3SS mutant (UW551△HrcV). We identified 21 differentially accumulated proteins. Compared with inoculation with UW551△HrcV, 10 proteins showed significantly lower abundance in potato roots after inoculation with UW551, indicating that those proteins were significantly downregulated by T3Es during the invasion. To identify their functions in immunity, we silenced those genes in Nicotiana benthamiana and tested the resistance of the silenced plants to the pathogen. Results showed that miraculin, HBP2, and TOM20 contribute to immunity to R. solanacearum. In contrast, PP1 contributes to susceptibility. Notably, none of four downregulated proteins (HBP2, PP1, HSP22, and TOM20) were downregulated at the transcriptional level, suggesting that they were significantly downregulated at the posttranscriptional level. We further coexpressed those four proteins with 33 core T3Es. To our surprise, multiple effectors were able to significantly decrease the studied protein abundances. In conclusion, our data showed that T3Es of R. solanacearum could subvert potato root immune-related proteins in a redundant manner. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Bacterial wilt (BW), caused by Ralstonia solanacearum species complex (RSSC), leads to substantial potato yield losses in Rwanda. Studies were conducted to (i) determine the molecular diversity of RSSC strains associated with BW of potato, (ii) generate an RSSC distribution map for epidemiological inferences, and (iii) test the pathogenicity of predominant RSSC phylotypes on six commercial potato cultivars. In surveys conducted in 2018 and 2019, tubers from wilting potato plants were collected for pathogen isolation. DNA was extracted from 95 presumptive RSSC strain colonies. The pathogen was phylotyped by multiplex PCR and typed at sequevar level. Phylotype II sequevar 1 strains were then haplotyped using multilocus tandem repeat sequence typing (TRST) schemes. Pathogenicity of one phylotype II strain and two phylotype III strains were tested on cultivars Kinigi, Kirundo, Victoria, Kazeneza, Twihaze, and Cruza. Two RSSC phylotypes were identified, phylotype II (95.79%, n = 91) and phylotype III (4.21%, n = 4). This is the first report of phylotype III strains from Rwanda. Phylotype II strains were identified as sequevar 1 and distributed across potato growing regions in the country. The TRST scheme identified 14 TRST haplotypes within the phylotype II sequevar 1 strains with moderate diversity index (HGDI = 0.55). Mapping of TRST haplotypes revealed that a single TRST ‘8-5-12-7-5’ haplotype plays an important epidemiological role in BW of potato in Rwanda. None of the cultivars had complete resistance to the tested phylotypes; the level of susceptibility varied among cultivars. Cultivar Cruza, which is less susceptible to phylotype II and III strains, is recommended when planting potatoes in the fields with history of BW. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Tomato (Lycopersicon esculentum, Mill) is a rich source of vitamins, minerals and lycopene, which has many health benefits. However, its production is hampered by bacterial wilt caused by Ralstonia solanacearum resulting in significant yield losses. Use of chemicals in the control of plant pathogens has detrimental effects on humans and the environment in terms of leaving residues in soil which later find their way into underground waters. Therefore, it is desirable to find an alternative to chemical control of this bacterial pathogen. This study investigates the potential of native Bacillus thuringiensis (Bt) for biological control of Ralstonia solanacearum (Rs) under laboratory conditions. B. thuringiensis was isolated from cultivated soil, non- cultivated soil, stagnant water, sawdust, horse dung, grain dust, dead leaves and poultry manure. R. solanacearum was isolated from stem exudates of bacterial wilt infected plants and its pathogenicity assay was carried out using 2-week-old seedlings of Beske tomato variety. The Bt and R. solanacearum isolates were then characterized phenotypically. Bt isolates were further identified using endospore and parasporal staining techniques. All the Bt isolates were tested for in-vitro antagonistic activity on R. solanacearum using agar well diffusion method. Isolates Bt2, Bt16, Bt17, Bt32 and Bt34 were confirmed as Bacillus thuringiensis while isolate Rs was confirmed as R. solanacearum. Beske showed wilting symptoms from the fourth day of inoculation and eventual death of seedlings. The zone of inhibition exhibited ranged from 0.0 mm to 20.0 mm. Keywords: Bacillus thuringiensis, In-vitro, Bacterial wilt, Ralstonia solanacearum, Tomato

This study aimed to use thyme volatile oil (TVO) to control potato bacterial wilt disease caused by Ralstonia solanacearum and to explore the biochemical responses in relation to defense enzymes that induce resistance against pathogens in plants. In vitro experiments showed that all tested concentrations of TVO (1 µl, 2, 4, 6, 8, and 10 µl ml−1) significantly (P ≤ 0.05) inhibited the growth of the pathogen, with the most significant effect recorded at a concentration of 10 µl ml−1. Under greenhouse conditions, the tested concentration of TVO (10 µl ml−1) significantly (P ≤ 0.05) reduced the incidence of potato bacterial wilt and the population of R. solanacearum pathogens in potato plants. The current study also revealed that TVO (10 µl ml−1) increased the activity of antioxidant enzymes, e.g.,. peroxidase (POX) and phenylalanine ammonia-lyase (PAL), and reduced the activity of catalase (CAT) in treated potato plants. In conclusion, our results showed that TVO (10 µl ml−1) afforded a strong reduction of R. solanacearum radial growth in vitro and a high reduction in the development of potato wilt in vivo. Moreover, we demonstrated that POX and PAL activities can be used as biochemical markers for biocontrol efficacy in the control of potato bacterial wilt.

We find out the antimicrobial potential of partially purified 2,4-diacetylphloroglucinol (DAPG) against Ralstonia solanacearum and fungal plant pathogens isolated from tomato rhizobacterium Pseudomonas fluorescens VSMKU3054. The present study is mainly focused on the control of wilt disease of tomato by our isolate VSMKU3054 and DAPG. The cell free culture filtrate of P. fluorescens VSMKU3054 was significantly arrested the growth of R. solanacearum and fungal pathogens such as Rhizoctonia solani, Sclerotium rolfsii, Macrophomina phaseolina and Fusarium oxysporum compared to control. The existence of DAPG from the crude metabolites of P. fluorescens VSMKU3054 was confirmed on TLC with Rf value 0.34, which is coincide with that of authentic phloroglucinol. The partially purified DAPG exhibited much higher activity against R. solanacearum at 30 µg/ml than the fungal plant pathogens compared to control. The antimicrobial partially purified compound was identified as DAPG by UV, FT-IR and GC–MS analysis. The percentage of live cells of R. solanacearum when supplemented with DAPG at 30 µg/ml, significantly controlled the living nature of R. solanacearum up to 68% compared to tetracycline and universal control observed under high content screening analysis. The selected isolate P. fluorescens VSMKU3054 and DAPG significantly controlled wilt disease of tomato up to 59.5% and 42.12% on 3rd and 7th days compared to positive and negative control by detached leaf assay. Further, in silico analysis revealed that high interaction of DAPG encoding protease with lectin which is associated with R. solanacearum. Based on our findings, we confirmed that P. fluorescens VSMKU3054 and DAPG could be used a potential bio inoculants for the management of bacterial wilt disease of tomato.

Made available in DSpace on 2021-06-25T10:24:09Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-05-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Knowledge of the ecological survival niches of Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff), the causal agent of bean bacterial wilt, is essential for the efficient disease management. Our study evaluated the survival of Cff in the phyllospheres and rhizospheres of barley, black oat, canola, common bean, forage turnip, maize, pearl millet, ryegrass, sorghum, soybean, sunflower, velvet bean, wheat and white oat planted in a greenhouse. The aerial parts of the plants were inoculated by spraying a bacterial suspension (107 CFU.mL−1) from the strain Feij. 2628A, which is resistant to rifampicin and pathogenic to common bean. The soil of the pots was infested with 200 mL of the same suspension. Cff survival was evaluated every seven days for 70 days, and the survival periods were confirmed by selecting strains from all samples and performing PCR with specific primers. Cff survived for at least seven days in the phyllosphere, and 21 days in the rhizosphere of all evaluated crops. Based on our results, barley, black oat, canola, forage turnip, maize, pearl millet, ryegrass, sorghum, soybean, sunflower, velvet bean, wheat and white oat can be potential asymptomatic hosts for Cff, and their cultivation in succession with common bean is not recommended in areas with a history of bacterial wilt occurrence. Department of Plant Protection São Paulo State University (Unesp) School of Agriculture, Avenida Universitária, 3780 Department of Plant Protection São Paulo State University (Unesp) School of Agriculture, Avenida Universitária, 3780 CAPES: 001

Bacterial wilt caused by Ralstonia solanacearum, is one of the serious soil-borne diseases in flue-cured tobacco production areas in China. However, it was found that the occurrence of bacterial wilt not only varied with different cultivars but also varied with various sites even under the condition of planting the same variety. It suggests that the occurrence of bacterial wilt could be controlled by regulating soil microorganism and the growth environment. Therefore, the relationship between microorganism’s diversity in the rhizosphere and actual incidences were evaluated on the number of symptomatic plants and the functional diversity of soil microorganisms in field trials on two sites. The results showed that the incidence of bacterial wilt in the same cultivar was varied between the two experimental sites. However, the same trend was found in the number of rhizospheric microbes among the three varieties except for fungi. Also, a good relationship was found between the number of pathogens, microbial functional diversity in the rhizosphere, and actual incidences. The utilization intensity of carbohydrates, amino acids, carboxylic acids, polymers, amines, and carbon utilization of rhizospheric soil microbial community was negatively related with the occurrence of bacterial wilt while it was on the opposite for the utilization intensity of phenolic acids. The results revealed that the mechanism for resistance in flue-cured tobacco was directly associated with the number of pathogenic microorganisms in rhizosphere and the diversity of rhizospheric microbes. By improving the diversity of rhizospheric microbes, the incidence of tobacco bacterial wilt disease can be reduced.

Populations of the bacterial wilt pathogen, Burkholderia caryophylli, in infected plants were estimated using our newly developed carnation seedling BIO-PCR assay, which combines pre-incubation in a selective medium and polymerase chain reaction. Bacterial density in leaves and in stems from each node was examined after injured roots on plants were inoculated. B. caryophylli was consistently isolated from the lower leaves from 5 to 35 days after inoculation; thus, leaves can be assayed without sacrificing parent stock. The BIO-PCR assay has higher specificity for closely related species than a conventional assay on the selective medium, and consistently detects B. caryophylli.

Tobacco bacterial wilt (TBW) caused by Ralstonia solanacearum is the most serious soil-borne disease of tobacco. However, molecular mechanism information of R. solanacearum resistance is limited to tobacco, hindering better breeding of resistant tobacco. In this study, the expression profiles of the rootstalks of Yunyan87 (susceptible cultivar) and Fandi3 (resistant cultivar) at different stages after R. solanacearum infection were compared to explore molecular mechanisms of tobacco resistance against the bacterium. Findings from gene-expression profiling indicated that the number of upregulated differentially expressed genes (DEGs) at 3 and 7 days post-inoculation (dpi) increased significantly in the resistant cultivar. WRKY6 and WRKY11 family genes in WRKY transcription factors, ERF5 and ERF15 family genes in ERFs transcription factors, and genes encoding PR5 were significantly upregulated in the resistant cultivar response to the infection. For the first time, WRKY11 and ERF15 were found to be possibly involved in disease-resistance. The Kyoto Encyclopedia of Genes and Genomes analysis demonstrated glutathione metabolism and phenylpropane pathways as primary resistance pathways to R. solanacearum infection. In the resistant cultivar, DEGs encoding CYP450, TCM, CCoAOMT, 4CL, PAL, CCR, CSE, and CADH, involved in the synthesis of plant antitoxins such as flavonoids, stilbenoids, and lignins, enriched in the phenylpropane pathway were upregulated at 3 and 7 dpi. Furthermore, a pot experiment was performed to verify the role of flavonoids in controlling TBW. This study will strongly contribute to a better understanding of molecular interactions between tobacco plants and R. solanacearum.

Potato is an important vegetable crop of Bangladesh which is facing challenges worldwide due to a quarantine pathogen, Ralstonia solanacearum. It is a very successful bacterial pathogen against most of the traditional management practices. Suspension of ten bioactive compounds viz. propolis, honey, turmeric powder+oil, turmeric powder, magnesium chloride, boiled rice fluid, boiled rice fluid+iodine, sun dried cow dung powder, honey+iodine and sodium bicarbonate were evaluated and compared with control (sterile water), commercial bactericide (Krosin AG) and farmers practice (stable bleaching powder). In vitro assessment was done by comparing the inhibition zones produced on TZC (tetrazolium chloride) solid medium in disc diffusion method. All of those compounds produced larger inhibition zones as compared to control which indicated the effectiveness of the test compounds against the bacteria. To screen out the performances of those compounds in vivo, potato seedlings were inoculated in sterilized soil by soil soak method. Later, mature plants were inoculated in unsterilized soil to find the better resulting compound(s) in field soil condition against the disease. Finally, suspension of cow dung (@25%), propolis (@ 6mg/ml) and turmeric powder (@25%) were selected for trial as soil and seed treatment against the pathogen. It was found that, cow dung reduced 28.89% disease severity index which was followed by 26.67% in propolis and 22.22% in turmeric powder as compared to control (84.44%) in artificially inoculated potato plants against R. solanacearum. J. Biodivers. Conserv. Bioresour. Manag. 2020, 6(1): 65-76

Incorporation of compost amendments into the soil is a promising strategy for the control of some soil-borne plant diseases. The aim of this study was to evaluate the effect of compost amendments f...

Made available in DSpace on 2021-06-25T10:49:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-03-01 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) A crop rotation system can reduce phytopathogen inoculum, and consequently reduce the incidence and severity of disease. Bean bacterial wilt is an important disease and several crops can act as inoculum sources for Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff). The aim was to evaluate the influence of crop rotation systems on 10 common bean cultivars against bacterial wilt. Experiments were located in two different areas in Brazil (2012), cultivated under a no-tillage system and with a history of the disease. The evaluated rotation systems were black oat, wheat and fallow followed by common bean. After harvest, 10 dry bean cultivars were sown, together with a fallow area. Disease incidence and severity were assessed at 45, 60 and 80 days after sowing. Also evaluated were four agronomical parameters: pod numbers, grain numbers, total weight of grains per plant and weight of 100 grains. Epiphytic and endophytic colonization by Cff was evaluated in black oat and wheat, and in crop debris. The rotation systems significantly influenced the incidence and severity of bacterial wilt in common bean cultivars in both areas and negatively affected the four agronomic parameters. The cultivars BRS Campeiro, BRS Estilo, IPR Tuiuiú, IPR Tangará and IPR Campos Gerais presented low severity and incidence of the disease and higher productivity. Cff strains were recovered from black oat, wheat and crop debris. Our results reinforce the importance of planting non-Cff host crops in rotation systems with common bean, as well as planting cultivars with a level of resistance to bacterial wilt. Departamento de Proteção Vegetal Faculdade de Ciências Agronômicas (FCA) Universidade Estadual Paulista “Júlio de Mesquita Filho” (UNESP), Avenida Universitária, 3780 Departamento de Proteção Vegetal Faculdade de Ciências Agronômicas (FCA) Universidade Estadual Paulista “Júlio de Mesquita Filho” (UNESP), Avenida Universitária, 3780

Worldwide, potato (Solanum tuberosum L) is rated as one of the most important food crops after wheat, rice and maize. Bacterial wilt, caused by Ralstonia solanacearum (Rs), is one of the most economically important diseases of potato. The purpose of this study was to identify diploid germplasm with resistance to bacterial wilt. The wilting degree was assessed by analyzing the wilt percentage of six Solanum commersonii clones which were artificially inoculated with Rs in a growth chamber. Two Rs strains (CMR15 and UW551) were used to inoculate the clones evaluate resistance. MSEE912–08, a selfed progeny from PI320266 was identified as the most resistant of the clones in this study exhibiting the lowest RAUDPC for wilting and a Wilting Degree rating of 0.4 (less than 25% wilted leaves) 20 days post inoculation when inoculated with the UW551 Rs strain, and 1.3 with the CMR15 strain. The resistance observed was characterized by reduction in wilting over time, rather than lack of disease. The most resistant clone from this study was self-pollinated to create a mapping population to identify single nucleotide polymorphic (SNP) markers associated with Rs resistance.

Bacterial wilt (BW), caused by Ralstonia solanacearum species complex (RSSC), is a major disease affecting tomato and other solanaceous crops produced in Louisiana and worldwide. The most effective and economic management strategy for BW is the use of crop genetic resistance. However, regional genetic variation among RSSC strains has made stable and durable resistance elusive. A collection of tomato, eggplant and pepper (TEP) accessions that responds to globally diverse strains in the RSSC was screened for resistance to six RSSC strains, belonging to phylotypes I and II, from Louisiana, United States (US). Wilt severity was quantified from six days up to 25 days post-inoculation (DPI). Wilting increased most rapidly to 10 DPI and was generally more severe with Phylotype II strains. However, wilt response profiles depended on the accession-strain combination. Differences in aggressiveness, as measured by the area under the disease progress stairs, were observed among the phylotype I and II strains on TEP. Wilting responses were the most severe with the tomato accessions. Hawaii 7996, TML46, CLN1463 and R3034 were highly resistant to all phylotype I strains, but Hawaii 7996 displayed the best resistance to phylotype II strains. Remarkably, eggplant accession Ceylan SM 164 was resistant to all six strains. Eggplant accessions SM6, Surya, and AG91–25, as well as pepper accessions CA8 and MC4, were moderately to highly resistant to all six strains. Although resistance spectrum and levels of these tomato, eggplant and pepper accessions need to be confirmed by further experiments, our results already indicate that these accessions are potential BW-resistant rootstock candidates for grafting to susceptible market-driven tomato, eggplant and pepper produced in this US state.

The study was conducted with 75 tomato entries at the farm of Olericulture Division, Horticulture Research Centre (HRC), Bangladesh Agricultural Research Institute (BARI), Gazipur, Bangladesh during the winter season of 2020-21 to evaluate insect and disease reaction. Among the various insect and diseases of tomatoes, the late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation are most common in Bangladesh. The TYLCV infection was observed 0% to 27% infection, while 47 entries showed zero percent infection. The range of bacterial wilt infection was 0% to 10% and zero percent infection was observed in 62 entries. In case of leaf miner infestation and fruit borer infestation, the range was 0% to 43% and 0% to 10%, respectively. Considering tolerance to late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation, fruit size, fruit shape, plant growth nature, cluster nature of fruit, type of fruit ten entries AVTO 1010, AVTO 1706, AVTO 1713, AVTO 1829, AVTO 1909, AVTO 1911, AVTO 1915, AVTO 1921, AVTO 1954 and SLA 011 were found zero percent late blight, TYLCV, bacterial wilt infection and leaf miner, fruit borer infestation. So, these ten entries can be selected for disease and insect tolerant tomato varieties development as well as developing disease and insect tolerant hybrid tomato varieties.

Bacterial wilt is the most damaging disease of tomato in Benin. To select resistant varieties of tomato against bacterial wilt, 21 tomato varieties were evaluated twice under screen house and field conditions in a randomized complete block design with four replicates and 21 treatments which are the tested varieties. Three weeks old tomato seedlings were inoculated by crown flooding with 40 ml of a bacterial suspension of R. solanacearum strain CR-1103-2, phylotype I sequvar 14. At 28 days after inoculation, the control resistant varieties Hawaii 7997 and PADMA maintained their resistance and the known susceptible variety Tohounvi showed to be susceptible to the bacterial wilt. Among the hybrid tomato varieties, only Cobra 26 was moderately resistant. No resistant line was found among the tested local varieties. The hybrid varieties Buffalo, Petomech, Tropimech, Sumo, Prado, Ninja, Jaguar, Anaya, Topaze, Cobra 34, Heinz, Kiara, Euclid and local Kekefo, Akikonkouin, Agbotrui and Adjaa were all susceptible. In conclusion, Cobra 26 emerges as a new variety of tomato moderately resistant to bacterial wilt. This is a new finding since it adds. All the tested varieties, regardless of their resistance, were colonized by R. solanacearum. This is a challenge for tomato farmers who must practice sanitation in their fields when producing tomato susceptible or resistant varieties. The variety Cobra 26 must be scaled up to farmers.

The soil-borne bacterium Ralstonia solanacearum continues to represent a major threat to flue-cured tobacco (Nicotiana tabacum) production in the southeastern United States and other major producing regions throughout the world. Beneficial microorganisms naturally found in the soil represent an alternative solution for R. solanacearum’s suppression that may reduce soil health impacts of current management strategies. Biological controls and microbiota manipulation together represent a unique opportunity to reduce disease caused by R. solanacearum. Current high-throughput DNA sequencing technologies and advances in bioinformatic analyses enable culture-independent approaches to study root-associated microorganisms and their interactions. The structure and dynamics of tobacco root-associated microbiota, as well as functional capacities of certain taxa, may improve how we apply disease management strategies in the field. Through this review we summarize our current understanding on (i) the role of bacterial microbiota on R. solanacearum survival, (ii) the impacts of current management strategies on the soil bacterial communities, (iii) the rhizospheric and core microbiome composition and inheritance, (iv) the manipulation of the microbiota for enhanced disease suppression, and (v) the shortcomings of the application of plant-associated bacteria for disease suppression.

Goss’s bacterial wilt and leaf blight of corn (Zea mays), caused by Clavibacter nebraskensis, is a reemerging disease in the Midwestern United States. From 2011 to 2013, field studies and a greenhouse study were conducted to assess the University of Illinois maize inbred collection for putative sources of resistance to Goss’s bacterial wilt and leaf blight. This inbred collection consisted of over 2,000 diverse inbred corn lines that have been collected from all over the world. An initial field screen of over 1,000 inbred lines from the collection was conducted in Urbana, IL in 2011. These lines were inoculated with a C. nebraskensis cell suspension and rated for Goss’s bacterial wilt and leaf blight severity using a 1-to-9 scale, with a score of 1 being most resistant. Means for Goss’s bacterial wilt and leaf blight ratings ranged from 1 to 8.5. The initial screen identified over 150 lines that had high levels of resistance (severity score of ≤2.5). In total, 177 lines were used in the second stage of field screening. In the second stage, average Goss’s bacterial wilt and leaf blight severity ranged from 1.1 to 7.4. Nine lines with high levels of resistance in 2011 and 2012 were advanced to the third stage of field screening. The mean Goss’s bacterial wilt and leaf blight severity rating of the resistant lines in the last stage was 1.9, while the susceptible check had a mean score of 6.4. These nine lines were also used in the greenhouse to assess whether resistance varied based on inoculating roots, stems, or leaves. Disease severity was significantly (P ≤ 0.05) less when roots were inoculated compared with both leaf and stem inoculations, which were not significantly different from each other. Lines having high levels of field resistance were also found to be resistant in greenhouse screening regardless of inoculation method. Clustering of pedigree distance of the 34 resistant lines (severity score of ≤2.5) with known pedigree information found that 21 clustered with the Lancaster heterotic family, 4 were related to the Iowa Stiff Stalk Synthetic family, and 9 did not cluster with an identifiable heterotic family. These results show that the Lancaster family is an excellent source of Goss’s wilt resistance, and that fewer sources of resistance were found in other families. The most resistant lines identified from this research are potential sources of resistance to Goss’s bacterial wilt and leaf blight, and their lineage can be used in corn breeding programs to develop resistant hybrids.

Biological control agents and soil amendments have been applied to control tobacco bacterial wilt, but the mechanism is not well-known. In the present study, a field experiment was performed to investigate the soil physicochemical properties, disease index (DI) and disease incidence of tobacco bacterial wilt, and rhizosphere microbial community. The results show that the control efficacy of single application of antagonistic bacteria and calcium cyanamide was 46.43% and 51.92%, respectively. While the combined control efficacy of antagonistic bacteria and calcium cyanamide was 65.79%. Besides, the combined application of antagonistic bacteria and calcium cyanamide could increase soil pH, total N alkaline N, and exchangeable Ca, which were negatively associated with the microbial diversity, soil-borne pathogenic microorganisms, and incidence of tobacco bacterial wilt. Additionally, the combination of antagonistic bacteria and calcium cyanamide can improve the proportion of some antagonistic microbial species, and these antagonistic microbial species were inversely associated with the DI of tobacco bacterial wilt. In conclusion: The integrated measure may influence soil microbial communities through enhancing soil physicochemical properties and rebuild healthy soil microbial community structure to mitigate tobacco bacterial wilt. The current study presented valuable insights into the mechanisms enhancing soil health in the integrated measure.