Tomato Bacterial Wilt Disease Research Articles

Immunomodulating melatonin-decorated silica nanoparticles suppress bacterial wilt (Ralstonia solanacearum) in tomato (Solanum lycopersicum L.) through fine-tuning of oxidative signaling and rhizosphere bacterial community

BackgroundTomato (Solanum lycopersicum L.) production is severely threatened by bacterial wilt, caused by the phytopathogenic bacterium Ralstonia solanacearum. Recently, nano-enabled strategies have shown tremendous potential in crop disease management.ObjectivesThis study investigates the efficacy of biogenic nanoformulations (BNFs), comprising biogenic silica nanoparticles (SiNPs) and melatonin (MT), in controlling bacterial wilt in tomato.MethodsSiNPs were synthesized using Zizania latifolia leaves extract. Further, MT containing BNFs were synthesized through the one-pot approach. Nanomaterials were characterized using standard characterization techniques. Greenhouse disease assays were conducted to assess the impact of SiNPs and BNFs on tomato plant immunity and resistance to bacterial wilt.ResultsThe SiNPs and BNFs exhibited a spherical morphology, with particle sizes ranging from 13.02 nm to 22.33 nm for the SiNPs and 17.63 nm to 21.79 nm for the BNFs, indicating a relatively uniform size distribution and consistent shape across both materials. Greenhouse experiments revealed that soil application of BNFs outperformed SiNPs, significantly enhancing plant immunity and reducing bacterial wilt incidence by 78.29% in tomato plants by maintaining oxidative stress homeostasis via increasing the activities of antioxidant enzymes such as superoxide dismutase (31.81%), peroxidase (32.9%), catalase (32.65%), and ascorbate peroxidase (47.37%) compared to untreated infected plants. Additionally, BNFs induced disease resistance by enhancing the production of salicylic acid and activating defense-related genes (e.g., SlPAL1, SlICS1, SlNPR1, SlEDS, SlPD4, and SlSARD1) involved in phytohormones signaling in infected tomato plants. High-throughput 16 S rRNA sequencing revealed that BNFs promoted growth of beneficial rhizosphere bacteria (Gemmatimonadaceae, Ramlibacter, Microscillaceae, Anaerolineaceae, Chloroplast and Phormidium) in both healthy and diseased plants, while suppressing R. solanacearum abundance in infected plants.ConclusionOverall, these findings suggest that BNFs offer a more promising and sustainable approach for managing bacterial wilt disease in tomato plants.Graphical

Tomato bacterial wilt disease outbreaks are accompanied by an increase in soil antibiotic resistance

The presence of soil-borne disease obstacles and antibiotic resistance genes (ARGs) in soil leads to serious economic losses and health risks to humans. One area in need of attention is the evolution of ARGs as pathogenic soil gradually develops, which introduces uncertainty to the dynamic ability of conventional farming models to predict ARGs. Here, we investigated variations in tomato bacterial wilt disease accompanied by the resistome by metagenomic analysis in soils over 13 seasons of monoculture. The results showed that the abundance and diversity of ARGs and mobile genetic elements (MGEs) exhibited a significant and positive correlation with R. solanacearum. Furthermore, the binning approach indicated that fluoroquinolone (qepA), tetracycline (tetA), multidrug resistance genes (MDR, mdtA, acrB, mexB, mexE), and β-lactamases (ampC, blaGOB) carried by the pathogen itself were responsible for the increase in overall soil ARGs. The relationships between pathogens and related ARGs that might underlie the breakdown of soil ARGs were further studied in R. solanacearum invasion pot experiments. This study revealed the dynamics of soil ARGs as soil-borne diseases develop, indicating that these ecological trends can be anticipated. Overall, this study enhances our understanding of the factors driving ARGs in disease-causing soils.

Application of Endophytic Bacteria from Tomato Stems to Control Bacterial Wilt Disease in Tomato and Enhance Plant Growth

Application of Endophytic Bacteria from Tomato Stems to Control Bacterial Wilt Disease in Tomato and Enhance Plant Growth

Greenhouse tomato farmers' knowledge, perceptions, and management of tomato bacterial wilt (Ralstonia solanacearum) disease

A major constraint to tomato cultivation is bacterial wilt disease. The use of greenhouses to cultivate tomato is vital to controlling the bacterial wilt disease. Bacterial wilt can be successfully managed when farmers are well-informed with better knowledge of bacterial wilt in tomatoes. This study was conducted to assess farmers’ knowledge and experiences on the cultivation practices, prevalence, detection, spread, and control of bacterial wilt disease in tomato in greenhouses in the Volta, Eastern, Central, and Greater Accra regions of Ghana. Questionnaires were administered for fifty (50) greenhouse farmers, purposefully selected using a database of greenhouse tomato producers in southern Ghana provided by the Ministry of Food and Agriculture (MOFA). Frequency data was analyzed using descriptive statistical analysis. The majority (86%) of respondents had formal education. Most of the greenhouses in operation were in the Greater Accra Region, and none was under cultivation in the Volta region at the time of the study. Most respondents have been involved in greenhouse tomato cultivation for barely three years. The frequency of greenhouse tomatoes production varied from one region to the other. Only 28% of greenhouse farmers knew the test to detect the disease with 64% of greenhouse farmers without any knowledge about how the disease spreads. 62% of respondents used roughing and burying of the infected plants to control the disease. Out of the 54 greenhouses (domes) surveyed, 12 were infected with the bacterial wilt disease. Greenhouse farmers had little knowledge on the spread, detection, and control of the bacterial wilt disease of tomato. The findings of this study would lead to the design of targeted training programs on cultivation practices, detection, spread and management of bacterial wilt of tomato to increase yield and boost income levels of greenhouse tomato farmers in Ghana. Key words: bacterial wilt, tomatoes, spread, detection, control, greenhouse, farmers, constraints

Research progress in biological control of tomato bacterial wilt.

Bacterial wilt caused by the infection of Ralstonia solanacearum, is one of the most harmful diseases to tomatoes, one of the most important greenhouse vegetables in China. R. solanacearum can survive and remain active in the deep soil for a long time, and the chemical control of tomato bacterial wilt is consequently limited. In this study, we introduced the characteristics of tomato bacterial wilt disease and the types of R. solanacearum, and systematically reviewed the research progresses of biological control methods from the aspects of botanical insecticides, agricultural antibiotics, biocontrol bacteria. We emphatically introduced the principle and current status of these methods, discussed the limitations and the improvement strategies, and prospected a new environmental protection and efficient biological control system based on micro-ecological regulation would be the development direction of biological control of tomato bacterial wilt.

Response of bacterial biovars to inheritance pattern of bacterial wilt disease in tomato

ABSTRACT Knowledge of the genetic control of disease tolerance is necessary for effective transfer of desirable genes in resultant progenies leading to development of disease tolerant cultivars and hybrids. Bacterial wilt (BW) disease-resistant varieties of tomato (Solanum lycopersicum L.) express differential reactions to bacterial biovars distributed in specific regions. Genetic control of host tolerance to BW disease was studied using the generations P1, P2, F1, F2, BC1, BC2 of three tolerant × susceptible crosses (“Utkal Kumari × CLN- 2460E;” “Utkal Kumari × CLN-2764A;” “Utkal Deepti × CLN-2460E”) involving two tolerant (“Utkal Kumari,” “Utkal Deepti”), and two susceptible (“CLN-2460E” and “CLN-2764A”) genotypes exposed to the virulent bacterial biovars III and VI. The inheritance pattern indicated tolerance to BW disease was conditioned by a single dominant gene in three crosses when exposed to both biovars. Genetic control of bacterial wilt resistance did not depend on the interaction between genotype and bacterial biovars tested. Predominance of non-additive gene action and duplicate epistasis for conditioning of first appearance and incidence of BW disease in crosses indicated hindrance in progress through conventional selection. Selection for improvement of BW disease-related traits should be delayed to later segregating generations. The modified bulk method of selection appeared to be best for improving BW disease-related traits of tomato. Tomato hybrids tolerant to BW disease could be developed with the involvement of one parent tolerant to this disease.

Potential use of vermicompost against tomato bacterial canker and wilt disease

Potential use of vermicompost against tomato bacterial canker and wilt disease

Boosting the Biocontrol Efficacy of Bacillus amyloliquefaciens DSBA-11 through Physical and Chemical Mutagens to Control Bacterial Wilt Disease of Tomato Caused by Ralstonia solanacearum.

Bacterial wilt disease of tomato (Solanum lycopersicum L.), incited by Ralstonia solanacearum (Smith), is a serious agricultural problem in India. In this investigation, chemical mutagenic agents (NTG and HNO2 treatment) and ultraviolet (UV) irradiation have been used to enhance the antagonistic property of Bacillus amyloliquefaciens DSBA-11 against R. solanacearum UTT-25 towards an effective management of tomato wilt disease. The investigation established the fact that maximum inhibition to R. solanacearum UTT-25 was exerted by the derivative strain MHNO2-20 treated with nitrous acid (HNO2) and then by the derivative strain MNTG-21 treated with NTG. The exertion was significantly higher than that of the parent B. amyloliquefaciens DSBA-11. These two potential derivatives viz. MNTG-21, MHNO2-20 along with MUV-19, and a wild derivative strain of B. amyloliquefaciens i.e.,DSBA-11 were selected for GC/MS analysis. Through this analysis 18 major compounds were detected. Among the compounds thus detected, the compound 3-isobutyl hexahydropyrrolo (1,2), pyrazine-1,4-dione (4.67%) was at maximum proportion in the variant MHNO2-20 at higher retention time (RT) of 43.19 s. Bio-efficacy assessment observed a record of minimum intensity (9.28%) in wilt disease and the highest bio-control (88.75%) in derivative strain MHNO2-20-treated plants after 30 days of inoculation. The derivative strain MHNO2-20, developed by treating B. amyloliquefaciens with nitrous acid (HNO2), was therefore found to have a higher bio-efficacy to control bacterial wilt disease of tomato under glasshouse conditions than a wild-type strain.

ETI signaling nodes are involved in resistance of Hawaii 7996 to Ralstonia solanacearum-induced bacterial wilt disease in tomato

ABSTRACT Bacterial wilt caused by the soil-borne pathogen Ralstonia solanacearum is a destructive disease of tomato. Tomato cultivar Hawaii 7996 is well-known for its stable resistance against R. solanacearum. However, the resistance mechanism of Hawaii 7996 has not yet been revealed. Here, we showed that Hawaii 7996 activated root cell death response and exhibited stronger defense gene induction than the susceptible cultivar Moneymaker after R. solanacearum GMI1000 infection. By employing virus-induced gene silencing (VIGS) and CRISPR/Cas9 technologies, we found that SlNRG1-silenced and SlADR1-silenced/knockout mutant tomato partially or completely lost resistance to bacterial wilt, indicating that helper NLRs SlADR1 and SlNRG1, the key nodes of effector-triggered immunity (ETI) pathways, are required for Hawaii 7996 resistance. In addition, while SlNDR1 was dispensable for the resistance of Hawaii 7996 to R. solanacearum, SlEDS1, SlSAG101a/b, and SlPAD4 were essential for the immune signaling pathways in Hawaii 7996. Overall, our results suggested that robust resistance of Hawaii 7996 to R. solanacearum relied on the involvement of multiple conserved key nodes of the ETI signaling pathways. This study sheds light on the molecular mechanisms underlying tomato resistance to R. solanacearum and will accelerate the breeding of tomatoes resilient to diseases.

Deciphering the antimicrobial activity of multifaceted rhizospheric biocontrol agents of solanaceous crops viz., Trichoderma harzianum MC2, and Trichoderma harzianum NBG.

The Solanaceae family is generally known to be the third most economically important plant taxon, but also harbors a host of plant pathogens. Diseases like wilt and fruit rot of solanaceous crops cause huge yield losses in the field as well as in storage. In the present study, eight isolates of Trichoderma spp. were obtained from rhizospheric micro-flora of three solanaceous crops: tomato, brinjal, and chili plants, and were subsequently screened for pre-eminent biocontrol activity against three fungal (Fusarium oxysporum f. sp. lycopersicum, Colletotrichum gloeosporioides, and Rhizoctonia solani) and one bacterial (Ralstonia solanacearum) pathogen. Morphological, ITS, and tef1α marker-based molecular identification revealed eight isolates were different strains of Trichoderma. Seven isolates were distinguished as T. harzianum while one was identified as T. asperellum. In vitro antagonistic and biochemical assays indicated significant biocontrol activity governed by all eight isolates. Two fungal isolates, T. harzianum MC2 and T. harzianum NBG were further evaluated to decipher their best biological control activity. Preliminary insights into the secondary metabolic profile of both isolates were retrieved by liquid chromatography-mass spectrometry (LC-MS). Further, a field experiment was conducted with the isolates T. harzianum MC2 and T. harzianum NBG which successfully resulted in suppression of bacterial wilt disease in tomato. Which possibly confer biocontrol properties to the identified isolates. The efficacy of these two strains in suppressing bacterial wilt and promoting plant growth in the tomato crop was also tested in the field. The disease incidence was significantly reduced by 47.50% and yield incremented by 54.49% in plants treated in combination with both the bioagents. The results of scanning electron microscopy were also in consensus with the in planta results. The results altogether prove that T. harzianum MC2 and T. harzianum NBG are promising microbes for their prospective use in agricultural biopesticide formulations.

Plant Disease Resistance-Related Pathways Recruit Beneficial Bacteria by Remodeling Root Exudates upon Bacillus cereus AR156 Treatment.

The environmentally friendly biological control strategy that relies on beneficial bacterial inoculants to improve plant disease resistance is a promising strategy. Previously, it has been demonstrated that biocontrol bacteria treatments can change the plant rhizosphere microbiota but whether plant signaling pathways, especially those related to disease resistance, mediate the changes in rhizosphere microbiota has not been explored. Here, we investigated the complex interplay among biocontrol strains, plant disease resistance-related pathways, root exudates, rhizosphere microorganisms, and pathogens to further clarify the biocontrol mechanism of biocontrol bacteria by using plant signaling pathway mutants. Bacillus cereus AR156, which was previously isolated from forest soil by our laboratory, can significantly control tomato bacterial wilt disease in greenhouse and field experiments. Moreover, compared with the control treatment, the B. cereus AR156 treatment had a significant effect on the soil microbiome and recruited 35 genera of bacteria to enrich the rhizosphere of tomato. Among them, the relative rhizosphere abundance of nine genera, including Ammoniphilus, Bacillus, Bosea, Candidimonas, Flexivirga, Brevundimonas, Bordetella, Dyella, and Candidatus_Berkiella, was regulated by plant disease resistance-related signaling pathways and B. cereus AR156. Linear correlation analysis showed that the relative abundances of six genera in the rhizosphere were significantly negatively correlated with pathogen colonization in roots. These rhizosphere bacteria were affected by plant root exudates that are regulated by signaling pathways. IMPORTANCE Our data suggest that B. cereus AR156 can promote the enrichment of beneficial microorganisms in the plant rhizosphere by regulating salicylic acid (SA) and jasmonic acid (JA)/ethylene (ET) signaling pathways in plants, thereby playing a role in controlling bacterial wilt disease. Meanwhile, Spearman correlation analysis showed that the relative abundances of these beneficial bacteria were correlated with the secretion of root exudates. Our study reveals a new mechanism for SA and JA/ET signals to participate in the adjustment of plant resistance whereby the signaling pathways adjust the rhizosphere microecology by changing the root exudates and thus change plant resistance. On the other hand, biocontrol strains can utilize this mechanism to recruit beneficial bacteria by activating disease resistance-related signaling pathways to confine the infection and spread of pathogens. Finally, our data also provide a new idea for the in-depth study of biocontrol mechanisms.

CHEMOTHERAPEUTIC MANAGEMENT OF RALSTONIA SOLANACEARUM CAUSING BACTERIAL WILT OF TOMATO

Bacterial wilt is an important disease of tomato caused by Ralstonia solanacearum, which causes 90% yield losses. The present research was done to evaluate the effect of different chemicals against bacterial wilt of tomato. By using inhibition zone technique, five chemicals (Oxyrich, Forum top, Electus Super, Cabriotop and Kocide) at three different concentrations (250, 300 and 350 ppm) along with control were evaluated against R. solanacearum under lab conditions with Complete Randomized Design (CRD). Among all the treatments, maximum inhibition zone was expressed by Oxyrich (20.687mm). Under field conditions using Randomized Complete Block Design (RCBD), Oxyrich and kocide were evaluated alone and in combination at three different concentrations (2, 2.5 and 3%) along with control. Among these treatments, maximum reduction in disease incidence was expressed by combination of Oxyrich + Kocide (18.38%). Difference among treatments was observed using least significant difference (LSD) at probability level of 0.05%. It is concluded that identification of different chemicals will be helpful in future studies for the management of bacterial wilt disease of tomato.

Isolation and characterization of Ralstonia solanacearum causing wilt disease in tomato

Bacterial wilt, caused by Ralstonia solanacearum, is the most serious and common disease that affects tomatoes globally. Tomato bacterial wilt is among the worst and most prevalent diseases in Ethiopia. It causes substantial tomato production losses in various parts of the country. The purpose of this study was to isolate and characterize Ralstonia solanacearum causing wilt disease in tomato. Ralstonia solanacearum isolates were isolated from wilted tomato stem samples using Casamino Acid Peptone Glucose Agar (CPG) plates and incubated at 28 ± 2 °C for 48 h. Bacterial colonies showing big, irregular smooth, and cream-white, were considered presumptive Ralstonia solanacearum isolates. Morphological, biochemical, and pathological characterization were used for identification of the bacterium. Biovar identification was determined based on the utilization of carbohydrates. A total of 76 Ralstonia solanacearum isolates were screened and identified as Ralstonia solanacearum. Out of all the isolates, 28.9% of the isolates were isolated from Mecha, followed by Fogera (27.6%), Dera (23.7%), and Bahir Dar Zuria (19.7%) districts. The pathogenicity test results also revealed that all Ralstonia solanacearum isolates tested caused wilt symptoms in tomato plants and had varying levels of virulence on tomato plants, ranging from highly virulent (G1B1, G2M2, G3H1, and G4F3 isolates) to moderately virulent (G1B1, G2M1, G2M3, G3H2, G4F1, and G4F2 isolates). Besides, 48 Ralstonia solanacearum isolates were identified as Biovar II, and 28 Ralstonia solanacearum isolates were identified as biovar III. The overall findings of this study could provide valuable information for integrated tomato bacterial wilt disease management. The molecular characterization should be carried out on Ralstonia solanacearum in different host ranges.

Managingtomato bacterial wilt by suppressing Ralstonia solanacearum population in soil and enhancing host resistance through fungus-derived furoic acid compound.

Synthetic chemical pesticides are primarily used to manage plant pests and diseases, but their widespread and unregulated use has resulted in major health and environmental hazards. Using biocontrol microbes and their bioactive compounds is a safe and sustainable approach in plant protection. In this study, a furoic acid (FA) compound having strong antibacterial activity against soil-borne phytopathogenic bacterium Ralstonia solanacearum [causal agent of bacterial wilt (BW) disease] was isolated from Aspergillus niger and identified as 5-(hydroxymethyl)-2-furoic acid compound through spectroscopic analyses (liquid chromatography-mass spectrometry (MS), electron ionization MS, and NMR). The SEM study of bacterial cells indicated the severe morphological destructions by the FA compound. The FA was further evaluated to check its potential in enhancing host resistance and managing tomato BW disease in a greenhouse experiment and field tests. The results showed that FA significantly enhanced the expression of resistance-related genes (PAL, LOX, PR1, and PR2) in tomato and caused a significant reduction (11.2 log10 colony-forming units/g) of the R. solanacearum population in soil, resulting in the reduction of bacterial wilt disease severity on tomato plants and increase in plant length (58 ± 2.7cm), plant biomass (28 ± 1.7g), and root length (13 ± 1.2cm). The findings of this study suggested that the fungus-derived FA compound can be a potential natural compound of biological source for the soil-borne BW disease in tomato.

Selection, Formulation, and Field Evaluation of Bacillus amyloliquefaciens PMB01 for Its Application to Manage Tomato Bacterial Wilt Disease

Bacterial wilt caused by the soil-borne pathogen Ralstonia solanacearum is one of the most devastating diseases in solanaceous plants. No agrochemicals are available to manage bacterial wilt effectively. A Bacillus amyloliquefaciens strain designated PMB01 was recovered from the cabbage rhizosphere and was found to be capable of inhibiting the growth of R. solanacearum. The PMB01 strain was highly resistant to extreme pH, heat, high salt salinity, and various fungicides. In contrast, PMB01 was sensitive to copper-based compounds, streptomycin, and tetracycline. The efficacy of the PMB01 strain in suppressing R. solanacearum and bacterial wilt in tomatoes was significantly improved when the culture medium was supplemented with 1% (w/v) soybean meal. PMB01 was in a 500-liter tank for the pilot production, and the resultant broth could effectively reduce the severity of tomato bacterial wilt in greenhouse trials. The PMB01 fermentation broth was mixed with 10% corn starch and 30% maltodextrin to make a wettable powder (WP). PMB01 could survive in the wettable powder for more than two years without losing its antagonistic activity. In ten field trials, tomato plants treated with 50, 100, or 200-fold dilutions of PMB01 WP reduced bacterial wilt severity by more than 67% compared to the mock (water control) treatment. This work revealed that the effectiveness of the rhizobacterium PMB01 to antagonize R. solanacearum was greatly improved when the culture medium was supplemented with 1% (w/v) soybean meal, indicating that PMB01 is an ideal bio-agent candidate. A durable format suitable for storage was also developed. Similar concepts may be applied to other bio-agent candidates to improve their effectiveness in disease management.

Plant Growth Promoting Rhizobacteria for Biocontrol of Tomato Bacterial Wilt Caused by Ralstonia solanacearum

Bacterial wilt induced by Ralstonia solanacearum is one of the most damaging and widespread diseases of tomatoes in the world. Biological control with rhizobacteria is one of the efficient components of integrated pest management methods used to control the disease and enhance production. To this end, plant growth-promoting rhizobacteria (Bacillus isolate BDUA1, and Pseudomonas isolates BBDUA2 and BDUA3) isolated from the tomato rhizosphere were evaluated for their plant growth-promoting traits using standard methods, and selected isolates were also tested for their biocontrol efficacy on tomato bacterial wilt disease under greenhouse conditions. All isolates produced cellulase and lipase, and only BDUA1 and BDUA3 produced protease and amylase. Besides, BDUA1 and BDUA2 showed phosphate solubilization and production of indole-3-acetic acid, HCN, and siderophore, while BDUA3 solubilized phosphate and produced HCN and siderophore. Our results showed that BDUA1 and BDUA2 reduced bacterial wilt incidence on the Maya variety by 51.9% and 48.5%, respectively, and on the Melkesalsa variety by 51.8% and 48.5%, respectively. Treatment of the Melkesalsa variety with BDUA1 displayed the highest height (36.91 cm), followed by treatment with BDUA2 (31.74 cm) on the same variety. BDUA1 induced the highest effect on increasing the dry weight of shoots and roots by 4.16 g and 0.59 g in the Maya variety and in the Melkesalsa variety by 3.63 g and 0.48 g, respectively. Similarly, BDUA2 had the greatest effect on increasing the dry weight of shoots and roots by 3.8 g and 0.54 g of the Maya variety and on the Melkesalsa variety by 3.12 g and 0.41 g, respectively. The overall result showed that BDUA1 and BDUA2 could be used as promising plant growth promotion and biocontrol agents for the management of tomato bacterial wilt disease provided they were validated under field conditions.

Comprehensive Analysis of Subcellular Localization, Immune Function and Role in Bacterial wilt Disease Resistance of Solanum lycopersicum Linn. ROP Family Small GTPases.

ROPs (Rho-like GTPases from plants) belong to the Rho-GTPase subfamily and serve as molecular switches for regulating diverse cellular events, including morphogenesis and stress responses. However, the immune functions of ROPs in Solanum lycopersicum Linn. (tomato) is still largely unclear. The tomato genome contains nine genes encoding ROP-type small GTPase family proteins (namely SlRop1–9) that fall into five distinct groups as revealed by phylogenetic tree. We studied the subcellular localization and immune response induction of nine SlRops by using a transient overexpression system in Nicotiana benthamiana Domin. Except for SlRop1 and SlRop3, which are solely localized at the plasma membrane, most of the remaining ROPs have additional nuclear and/or cytoplasmic distributions. We also revealed that the number of basic residues in the polybasic region of ROPs tends to be correlated with their membrane accumulation. Though nine SlRops are highly conserved at the RHO (Ras Homology) domains, only seven constitutively active forms of SlRops were able to trigger hypersensitive responses. Furthermore, we analyzed the tissue-specific expression patterns of nine ROPs and found that the expression levels of SlRop3, 4 and 6 were generally high in different tissues. The expression levels of SlRop1, 2 and 7 significantly decreased in tomato seedlings after infection with Ralstonia solanacearum (E.F. Smith) Yabuuchi et al. (GMI1000); the others did not respond. Infection assays among nine ROPs showed that SlRop3 and SlRop4 might be positive regulators of tomato bacterial wilt disease resistance, whereas the rest of the ROPs may not contribute to defense. Our study provides systematic evidence of tomato Rho-related small GTPases for localization, immune response, and disease resistance.

Characterization and Assessment of 2, 4-Diacetylphloroglucinol (DAPG)-Producing Pseudomonas fluorescens VSMKU3054 for the Management of Tomato Bacterial Wilt Caused by Ralstonia solanacearum.

Microbial bio-products are becoming an appealing and viable alternative to chemical pesticides for effective management of crop diseases. These bio-products are known to have potential to minimize agrochemical applications without losing crop yield and also restore soil fertility and productivity. In this study, the inhibitory efficacy of 2,4-diacetylphloroglucinol (DAPG) produced by Pseudomonas fluorescens VSMKU3054 against Ralstonia solanacearum was assessed. Biochemical and functional characterization study revealed that P. fluorescens produced hydrogen cyanide (HCN), siderophore, indole acetic acid (IAA) and hydrolytic enzymes such as amylase, protease, cellulase and chitinase, and had the ability to solubilize phosphate. The presence of the key antimicrobial encoding gene in the biosynthesis of 2,4-diacetylphloroglucinol (DAPG) was identified by PCR. The maximum growth and antimicrobial activity of P. fluorescens was observed in king’s B medium at pH 7, 37 °C and 36 h of growth. Glucose and tryptone were found to be the most suitable carbon and nitrogen sources, respectively. DAPG was separated by silica column chromatography and identified by various methods such as UV-Vis, FT-IR, GC-MS and NMR spectroscopy. When R. solanacearum cells were exposed to DAPG at 90 µg/mL, the cell viability was decreased, reactive oxygen species (ROS) were increased and chromosomal DNA was damaged. Application of P. fluorescens and DAPG significantly reduced the bacterial wilt incidence. In addition, P. fluorescens was also found effective in promoting the growth of tomato seedlings. It is concluded that the indigenous isolate P. fluorescens VSMKU3054 could be used as a suitable biocontrol agent against bacterial wilt disease of tomato.

Enhanced suppression of soil-borne phytopathogenic bacteria Ralstonia solanacearum in soil and promotion of tomato plant growth by synergetic effect of green synthesized nanoparticles and plant extract.

Because of severe economic losses and food security concerns caused by plant pathogenic bacteria, Ralstonia solanacearum, there is a need to develop novel control methods. This study was aimed to green synthesize the zinc oxide nanoparticles (ZnO NPs) through Withania coagulans leaf extracts and checked their antibacterial potential alone or in combination with W. coagulans leaf extract for the management of R. solanacearum causing bacterial wilt disease in tomato. ZnO NPs were synthesized through an eco-friendly approach using leaves extract of W. coagulans and characterized through various spectroscopic approaches, that is Fourier transform infrared spectroscopic, UV-visible spectroscopy and energy dispersive spectroscopy. The antibacterial effect of W. coagulans leaf extract and ZnO NPs alone and in combination was tested in vitro and in vivo against bacterial wilt pathogen in tomato plants. The results showed that combine application of leaf extract and ZnO NPs inhibited in vitro growth of R. solanacearum more than applying alone. Three application times (0, 6 and 12days before transplantation) of leaf extract, ZnONPs and their combine application were tested in vivo. The combine treatment and longest application time (12days before transplantation) were more effective in suppressing soil population of R. solanacearum, reducing disease severity and enhancing plant growth than applying alone and smaller application time. It is concluded that W. coagulans leaf extract and ZnO NPs have strong antibacterial potential against R. solanacearum in vitro and in vivo. The results of this study suggest the potential application of leaf extract and ZnO nanoparticles for controlling R. solanacearum as safe, eco-friendly and less expensive integrated disease management strategy in tomato crop.

Deterministic Process Dominated Belowground Community Assembly When Suffering Tomato Bacterial Wilt Disease

Soil microbial communities are closely associated with ecosystem functions. However, unravelling the complex nature of the microbial world and successfully utilizing all positive interactions for multipurpose environmental benefits is still a major challenge. Here, we describe the soil bacterial communities in different niches of healthy and diseased tomatoes under natural conditions. A higher abundance of the pathogen Ralstonia solanacearum and lower bacterial diversity were observed in the disease samples. The healthy tomato rhizosphere harbored more plant-beneficial microbes, including Bacillus and Streptomyces. Also, the co-occurrence network in the healthy rhizosphere samples was more complicated, so as to better adapt to the soil-borne pathogen invasion. Both the beta nearest-taxon-index (βNTI) and normalized stochasticity ratio (NST) analyses demonstrated that healthy rhizosphere communities were less phylogenetically clustered and mainly dominated by dispersal limitation, while homogeneous selection was the major assembly process driving the rhizosphere community of diseased samples. The results obtained with community assembly methods and co-occurrence network analysis revealed that healthy rhizosphere bacterial communities possessed potentially broader environmental stress (soil-borne pathogen stress) adaptability compared with diseased rhizosphere bacterial communities. In conclusion, this study contributed to widening our understanding of the potential mechanisms of soil bacterial community composition and assembly responding to soil-borne pathogen invasion.