Control Of Tomato Bacterial Wilt Research Articles

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.

Secondary metabolites of the granular form of Pseudomonas fluorescens P60 and its applications to control tomato bacterial wilt

Abstract. Soesanto L, Saputra DA, Sastyawan MWR, Mugiastuti E, Suprapto A, Rahayuniati RF. 2023. Secondary metabolites of the granular form of Pseudomonas fluorescens P60 and its applications to control tomato bacterial wilt. Biodiversitas 24: 2475-2482. Bacterial wilt is one of the important diseases of tomatoes caused by Ralstonia solanacearum (Smith 1896) Yabuuchi et al. 1996. Its control can be achieved by applying secondary metabolites of Pseudomonas fluorescens Migula 1895 P60 in granular form. The study aimed to determine the shelf life of the secondary metabolites P. fluorescens P60' in granular form and its application to manage bacterial wilt and the performance of tomatoes. The study was conducted for five months at the Plant Protection Laboratory and Experimental Farm, Faculty of Agriculture, Universitas Jenderal Soedirman. A randomized block design was used with four replicates and six treatments, consisting of R. solanacearum (control), R. solanacearum + 1, 5, 10, or 15 g, and bactericide (a.i. agrimycin sulphate 20%). Variables observed were inhibition zone, incubation period, disease intensity, the area under disease progress curve (AUDPC), crop height, crop fresh and dry weight, root fresh and dry weight, and phenolic compounds qualitatively. Results of the research showed that the granular formula until the 4th week still had an inhibition zone between 21.67-23.34%. However, the granules stored for as much as 15 g for four weeks effectively reduced disease intensity by 75.00%, decreased AUDPC value by 74.72%, and increased plant height, root dry weight, and fresh crop weight as well 44, 62.5, and 65.65 %, respectively. In addition, the granular formula increased the content of tomato phenolic compounds qualitatively.

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.

Biological Control Efficacy and Action Mechanism of Klebsiella pneumoniae JCK-2201 Producing Meso-2,3-Butanediol Against Tomato Bacterial Wilt.

Bacterial wilt caused by Ralstonia solanacearum is a fatal disease that affects the production of tomatoes and many other crops worldwide. As an effective strategy to manage bacterial wilt, biological control agents using plant growth-promoting rhizobacteria (PGPR) are being developed. In this study, we screened 2,3-butanediol (BDO)-producing PGPR to control tomato bacterial wilt and investigated the action mechanism of the disease control agent. Of the 943 strains isolated from soil, Klebsiella pneumoniae strain JCK-2201 produced the highest concentration of 2,3-BDO. The culture broth of K. pneumoniae JCK-2201 did not show any direct activity on R. solanacearum in vitro, but a 100-fold dilution effectively controlled tomato bacterial wilt with a control value of 77% in vivo. Fermentation utilizing K. pneumoniae JCK-2201 was optimized to produce 48 g/L of meso-2,3-BDO, which is 50% of the sucrose conversion efficiency. In addition, the control efficacy and mechanism of meso-2,3-BDO produced by JCK-2201 in tomato bacterial wilt were determined by comparative analysis with Bacillus licheniformis DSM13 producing meso-2,3-BDO and B. licheniformis DSM13 ΔalsS that did not produce 2,3-BDO, as the step of converting pyruvate to α-acetolactate was omitted. Tomato seedlings treated with the K. pneumoniae JCK-2201 (500-fold dilution) and B. licheniformis DSM13 (100-fold dilution) culture broth produced meso-2,3-BDO that significantly reduced R. solanacearum-induced disease severity with control values of 55% and 63%, respectively. The formulated meso-2,3-BDO 9% soluble concentrate (SL; 1,000-fold dilution) showed 87% control against tomato bacterial wilt in the field condition. Klebsiella pneumoniae JCK-2201 and B. licheniformis DSM13 treatment induced the expression of plant defense marker genes, such as LePR1, LePR2, LePR5, LePR3, and PI-II, in the salicylic acid and jasmonic acid signaling pathways at 4 days after inoculation. These results show that 2,3-BDO-producing bacteria and 2,3-BDO are potential biological control agents that act through induction of resistance for controlling tomato bacterial wilt.

Mixtures of suppressive bacteria enhance biological control of tomato bacterial wilt

Tomato bacterial wilt is one of the most destructive soil-borne plant diseases in the world, causing considerable economic losses. Biological control is an effective and environmentally friendly strategy to reduce disease incidence and yield loss. In this study, six Streptomyces-like strains, NEAU-Z2, NEAU-D18, NEAU-88, NEAU-174, NEAU-C12 and NEAU-66 exhibiting high antagonistic activities against Ralstonia solanacearum were isolated from tomato rhizosphere soil and used for further study. Of which strains NEAU-D18 and NEAU-88 were compatible with each other and the mixed strain (NEAU-D18 + NEAU-88) showing the strongest antibacterial activity against R. solanacearum were prepared. Hydroponic experiment at seedling stage showed that strains NEAU-D18 and NEAU-88 had the best control efficacy at the spore concentration of 108 cfu ml−1, which were 66.6% and 80%, respectively. Therefore, strains NEAU-D18 and NEAU-88 were inoculated into tomato seedling roots with different proportions (i.e., 1:1, 1:2, and 2:1) at the spore concentration of 108 cfu ml−1, and the ratio of 1:1 showed the best control efficacy (100%) on tomato bacterial wilt. Pot experiment also indicated that the mixed strain (NEAU-D18 + NEAU-88) had better biocontrol efficacy than that of single strains. Moreover, the mixed strain and R. solanacearum could utilize 31 of 51 tested compounds of tomato root exudates, indicating the mixed strain was more competitive than the single strains (27, 29) in theory. Furthermore, in vitro nutritional competition experiment showed that the incidence of tomato bacterial wilt with the addition of compounds that could not be utilized by R. solanacearum and mixed strain was equal to that of the control group (CK4-1), but the biocontrol efficacy was great different after adding six compounds that could be utilized by R. solanacearum and mixed strain, which confirmed that the nutritional competition occurred between the mixed strain and R. solanacearum. In addition, solid-state fermentation was used to prepare bioorganic fertilizer of mixed strain. The application of bioorganic fertilizer could effectively suppress the occurrence of tomato bacterial wilt, and the incidence was only 21.67 at 14 days post-challenge inoculation, while 85% of tomato plants developed bacterial wilt with organic fertilizer treatment. In conclusion, this study demonstrated that the mixed strain (NEAU-D18 + NEAU-88) showed better control efficacy than that of single strains and was a potential biocontrol agent for controlling tomato bacterial wilt.

Wheat straw biochar amendment suppresses tomato bacterial wilt caused by Ralstonia solanacearum: Potential effects of rhizosphere organic acids and amino acids

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.

Control of tomato bacterial wilt using resistant rootstocks with soil disinfection treatments

Control of tomato bacterial wilt using resistant rootstocks with soil disinfection treatments

Effects of Combined Application of Potassium Silicate and Salicylic Acid on the Defense Response of Hydroponically Grown Tomato Plants to Ralstonia solanacearum Infection

Bacterial wilt, caused by soilborne pathogenic bacterium Ralstonia solanacearum, is a serious and widespread disease that affects global tomato production. Both silicon (Si) and salicylic acid (SA) play important roles in enhancing tomato resistance against bacterial wilt, however, their combined effects on the defense responses of infected tomato plants remain unknown. Hence, the combined effects of Si and SA on physiological and biochemical parameters of R. solanacearum-infected tomato plants were investigated. The combination treatment of Si and SA significantly decreased disease incidences, lipoxygenase (LOX) activity and ethylene (ET) production. The combined treatments were more prominent in improving the morphological traits of root systems, such as root length, root surface area, average root diameter and root volume. The activities of polyphenol oxidase (PPO) and peroxidase (POD) and the concentrations of total soluble phenolics (TSPs) and lignin-thioglycolic acid (LTGA) derivatives were significantly increased in the plants with combined treatments. Si in combination with SA could significantly enhance neutral invertase (NI) and acid invertases (AI) activities in the leaves of tomato plants at 3 days post-infection (dpi) compared with application of Si alone. Three defense-related genes, PAL, POD and pathogenesis-related protein 1 (PR1), were significantly induced in Si+SA treatment at 7 dpi when compared with individual application of Si or SA. The expression level of salicylic acid-binding protein 2 (SABP2) was significantly higher for combination treatment when compared with treatment of Si or SA alone. The possible mechanisms involved in the synergistic effects of Si and SA on the control of tomato bacterial wilt were proposed. This study indicates that under hypertonic conditions, the combined application of 2.0 mM potassium silicate (K2SiO3) and 0.5 mM SA had a synergistic effect on the control of tomato bacterial wilt.

Mixtures of Suppressive Bacteria Enhance Biological Control of Tomato Bacterial Wilt

Mixtures of Suppressive Bacteria Enhance Biological Control of Tomato Bacterial Wilt

Bacillus amyloliquefaciens Strain PMB05 Intensifies Plant Immune Responses to Confer Resistance Against Bacterial Wilt of Tomato

Tomato is an economic crop worldwide. Many limiting factors reduce the production of tomato, with bacterial wilt caused by Ralstonia solanacearum being the most destructive disease. Our previous study showed that the disease resistance to bacterial soft rot is enhanced by Bacillus amyloliquefaciens strain PMB05. This enhanced resistance is associated with the intensification of pathogen-associated molecular patterns (PAMP)-triggered immunity (PTI). To determine whether the PTI-intensifying Bacillus spp. strains are able to confer disease resistance to bacterial wilt, their effects on PTI signals triggered by PAMP from R. solanacearum and on the occurrence of bacterial wilt were assayed. Before assay, a gene that encodes harpin from R. solanacearum, PopW, was applied as a PAMP. Results revealed that the B. amyloliquefaciens strain PMB05 was the one strain among 9 Bacillus rhizobacterial strains which could significantly intensify the PopW-induced hypersensitive response (HR) on Arabidopsis leaves. Moreover, we observed that the signals of PopW-induced reactive oxygen species generation and callose deposition were increased, confirming that the PTI was intensified by PMB05. The intensification of the PopW-triggered HR by PMB05 in Arabidopsis was reduced upon treatment with inhibitors in PTI pathways. Furthermore, the application of Bacillus spp. strains on tomato plants showed that only the use of PMB05 resulted in significantly increased resistance to bacterial wilt. Moreover, the PTI signals were also intensified in the tomato leaves. Taken together, we demonstrated that PMB05 is a PTI-intensifying bacterium that confers resistance to tomato bacterial wilt. Screening of plant immunity intensifying rhizobacteria is a possible strategy to control tomato bacterial wilt.[Formula: see text] Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

7, 8- Dihydroxyflavone, An Effective Natural Product Reduce Ralstonia solanacearum Populations and Control Tomato Bacterial Wilt

In this study, 7, 8- dihydroxyflavone (DHF) was isolated first time from medicinal plant Oroxylum indicum and its antibacterial potential against plant pathogen Ralstonia solanacearum was determined. The minimum inhibitory and bactericidal concentrations of DHF were 20 µg/mL and 80 µg/mL respectively. The biofilm formation and inhibition of DHF against R.solanacearum was investigated via scanning electron microscopy indicated that destruction of the cell wall. The inhibition of biofilm formation and molecular assays revealed that DHF binds lumen periplasm side of the outer membrane protein (EpsA) was identified. Moreover, DHF effectively reduced the bacterial wilt disease and control efficiency is as high as 89.10% at nine days after inoculation. Altogether, the antibacterial potential of DHF against R.solanacearum displayed effective agent can attenuates bacterial wilt disease in tomato plant.

Compost Amendments Based on Vinegar Residue Promote Tomato Growth and Suppress Bacterial Wilt Caused by Ralstonia Solanacearum.

Tomato bacterial wilt caused by Ralstonia solanacearum (RS) is one of the most devastating soil-borne diseases, and compost is to be considered as a resource-saving and environment-friendly measure to control the disease. Herein, a pot experiment was implemented to explore the effects of vinegar residue matrix amendments on the growth performances of tomato seedlings and to examine the suppression ability against bacterial wilt under vinegar residue substrate (VRS), and peat substrate (Peat) with RS inoculation. The results revealed that VRS effectively suppressed the disease incidence of bacterial wilt, increased the number of bacteria and actinomycetes, decreased fungi populations, promoted soil microbial populations and microbial activities, enhanced the growths of tomato seedlings, and modulated defense mechanism. In addition, VRS efficiently inhibited the oxidative damage in RS inoculated leaves via the regulation of excess reactive oxide species (O2•− and H2O2) production, lessening of malondialdehyde (MDA) content, and causing less membrane injury; resulting in enhancements of antioxidants enzymes activities accompanying with modulating their encoding gene expression. The transcription levels of NPR1, PIN2, PR1b, ACO1, EDS1, PR1B, MAPK3, PIN2, and RRS1 were also modulated with the pathogens inoculated in tomato leaves both in VRS and Peat treatments, which indicated that systemic-acquired resistance possesses cross-talk between salicylic acid, jasmonic acid, and the ethylene-dependent signaling pathway. Besides, the RS inoculation significantly inhibited the growth of tomato seedlings, and all growth indices of plants grown in VRS were considerably higher than those produced in Peat. Taken together, VRS represents a new strategy to control tomato bacterial wilt through boosting the soil microbial populations and microbial activities. Furthermore, VRS promotes the plant immune response to provide a better growth environment for plants surviving in disease conditions.

Potential Use of L-arabinose for the Control of Tomato Bacterial Wilt.

The present study aimed to investigate the potential of simple sugars for use as protection agents in the control of tomato bacterial wilt caused by Ralstonia pseudosolanacearum. Based on the sugar assimilation patterns of the pathogen, four unassimilable sugars (L-arabinose, maltose, D-raffinose, and D-ribose) were selected from 10 representative sugars present in tomato root exudates. These sugars were evaluated for their effects on bacterial wilt using a tomato seedling bioassay. The application of 0.25% L-arabinose significantly reduced disease severity and was, thus, selected as a candidate for further evaluations in a pot experiment under glasshouse conditions. The results obtained showed that the disease suppressive effects of L-arabinose slightly increased at higher concentrations; drench treatments at 0.1, 0.25, and 0.5% reduced disease severity by ca. 48, 70, and 87%, respectively. The drench treatment with 0.5% L-arabinose significantly reduced the pathogen population in the rhizosphere and stem tissues of tomato plants without any antibacterial activity. Real-time reverse-transcription PCR revealed that the expression of salicylic acid-dependent and ethylene-dependent defense genes was significantly enhanced in the stem tissues of L-arabinose-treated tomato plants following the pathogen inoculation. These results suggest that soil drenching with L-arabinose effectively suppresses tomato bacterial wilt by preventing pathogen proliferation in the rhizosphere and stem tissues of tomato plants. This is the first study to report the potential of L-arabinose as a safe, eco-friendly, and cost-effective plant protection agent for the control of tomato bacterial wilt.

Biocontrol of Tomato Bacterial Wilt by Foliar Spray Application of a Novel Strain of Endophytic <i>Bacillus</i> sp.

The aim of the present study was to identify a strain of endophytic Bacillus species that control tomato bacterial wilt by foliar spray application. Fifty heat-tolerant endophytic bacteria were isolated from the surface-sterilized foliar tissues of symptomless tomato plants that had been pre-inoculated with the pathogen Ralstonia pseudosolanacearum. In the primary screening, we assessed the suppressive effects of a shoot-dipping treatment with bacterial strains against bacterial wilt on tomato seedlings grown on peat pellets. Bacillus sp. strains G1S3 and G4L1 significantly suppressed the incidence of tomato bacterial wilt. In subsequent pot experiments, the biocontrol efficacy of foliar spray application was examined under glasshouse conditions. G4L1 displayed consistent and significant disease suppression, and, thus, was selected as a biocontrol candidate. Moreover, the pathogen population in the stem of G4L1-treated plants was markedly smaller than that in control plants. A quantitative real-time PCR analysis revealed that the foliar spraying of tomato plants with G4L1 up-regulated the expression of PR-1a and LoxD in stem and GluB in roots upon the pathogen inoculation, implying that the induction of salicylic acid-, jasmonic acid-, and ethylene-dependent defenses was involved in the protective effects of this strain. In the re-isolation experiment, G4L1 efficiently colonized foliar tissues for at least 4‍ ‍weeks after spray application. Collectively, the present results indicate that G4L1 is a promising biocontrol agent for tomato bacterial wilt. Furthermore, to the best of our knowledge, this is the first study to report the biocontrol of bacterial wilt by the foliar spraying with an endophytic Bacillus species.

Combined use of a microbial restoration substrate and avirulent Ralstonia solanacearum for the control of tomato bacterial wilt

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

Biological control of tomato bacterial wilt by oxydifficidin and difficidin-producing Bacillus methylotrophicus DR-08

Bacillus methylotrophicus DR-08 exhibited strong antibacterial activity against Ralstonia solanacearum, a causal agent of tomato bacterial wilt. This study aimed to identify the antibacterial metabolites and evaluate the efficacy of the strain as a biocontrol agent for tomato bacterial wilt. A butanol extract of the DR-08 broth culture completely inhibited the growth of 14 phytopathogenic bacteria with minimum inhibitory concentration (MIC) values of 1.95–500 μg/mL. R. solanacearum was highly sensitive to the DR-08 extract, with an MIC value of 12.62 μg/mL. Two antibacterial metabolites were isolated and identified as difficidin and oxydifficidin derivatives through bioassay-guided fractionation and instrumental analyses. Both metabolite derivatives inhibited the growth of most of the phytopathogenic bacteria tested and the oxydifficidin derivatives generally presented a stronger antibacterial activity than the difficidin derivatives. A 30% suspension concentrate of DR-08, at a 500-fold dilution, effectively suppressed the development of tomato bacterial wilt in pot and field experiments. It also effectively reduced the development of bacterial leaf spot symptoms on peach and red pepper. The results of this study suggests that B. methylotrophicus DR-08 can be utilized as a biocontrol agent for various bacterial plant diseases including tomato bacterial wilt.

The impact of Paenibacillus polymyxa HY96-2 luxS on biofilm formation and control of tomato bacterial wilt

The focus of this study was to investigate the effects of luxS, a key regulatory gene of the autoinducer-2 (AI-2) quorum sensing (QS) system, on the biofilm formation and biocontrol efficacy against Ralstonia solanacearum by Paenibacillus polymyxa HY96-2. luxS mutants were constructed and assayed for biofilm formation of the wild-type (WT) strain and luxS mutants of P. polymyxa HY96-2 in vitro and in vivo. The results showed that luxS positively regulated the biofilm formation of HY96-2. Greenhouse experiments of tomato bacterial wilt found that from the early stage to late stage postinoculation, the biocontrol efficacy of the luxS deletion strain was the lowest with 50.70 ± 1.39% in the late stage. However, the luxS overexpression strain had the highest biocontrol efficacy with 75.66 ± 1.94% in the late stage. The complementation of luxS could restore the biocontrol efficacy of the luxS deletion strain with 69.84 ± 1.09% in the late stage, which was higher than that of the WT strain with 65.94 ± 2.73%. Therefore, we deduced that luxS could promote the biofilm formation of P. polymyxa HY96-2 and further promoted its biocontrol efficacy against R. solanacearum.

Kemampuan Campuran Bacillus sp., Pseudomonas fluorescens, dan Trichoderma sp. untuk Mengendalikan Penyakit Layu Bakteri pada Tanaman Tomat

Ability of Bacillus sp., Pseudomonas fluorescens, and Trichoderma sp. to Control Tomato Bacterial Wilt DiseaseRalstonia solanacearum is known as the causal agent of bacterial wilt on tomato. The bacteria may infect all stadia of plant growth and decrease tomato production. Biological control using antagonistic microbes is considered as a potential control alternative for the disease. This research was aimed to assay the ability of combination treatment of Bacillus sp., Pseudomonas fluorescens, and Trichoderma sp. in controlling R. solanacearum and its effect on growth and yield of tomato in the field. The treatments consisted of control (without antagonistic microbes), mixed combination of Bacillus sp. B8 + Bacillus sp. B11 + Trichoderma sp.; Bacillus sp. B8 + Pseudomonas flourescens P8 + Trichoderma sp.; and Streptomisin sulfat 20%. Antagonistic microbes was applied at planting time, as much as 100 mL per plant. The result showed that mixed combination of Bacillus sp. B8 + Bacillus sp. B11 + Trichoderma sp. was the best treatment in controlling the disease as indicated by delaying incubation period up to 6.2 days, decreasing disease incidence up to 12.3%, increasing plant growth up to 42.80%, and increasing yield up to 14.99%.

Efficacy of Leaf Oil from Pimenta racemosa var. racemosa in Controlling Bacterial Wilt of Tomato

Bacterial wilt, caused by Ralstonia solanacearum, is a major plant disease throughout the Caribbean. The ability of the essential oil from Pimenta racemosa var. racemosa to control bacterial wilt of tomato (R. solanacearum, phylotype IIB/4NPB) was investigated. Lemongrass (chemotype 1)-, aniseed (chemotype 2)-, and clove (chemotype 3)-scented chemotypes of P. racemosa var. racemosa essential oil were tested. Six concentrations of emulsified essential oil (from 0.01 to 0.14% [v/v]) were evaluated by in vitro culture amendment assays and by in vivo experiments in greenhouse. Chemotype 3 displayed remarkable in vitro antibacterial activity against R. solanacearum, because the minimum inhibitory concentration was only 0.03%, compared with 0.14% for chemotypes 1 and 2. In greenhouse experiments, no incidence of bacterial wilt was observed in tomato plants grown in soil treated with chemotype 3 of P. racemosa var. racemosa at a concentration of 0.14%. In the untreated control soil, 62% of plants displayed symptoms of bacterial wilt. Treatment with chemotype 3 significantly increased the growth of tomato plants compared with untreated controls. These results suggest that chemotype 3 of P. racemosa var. racemosa essential oil is a good candidate for further development as a soil biofumigant for the control of tomato bacterial wilt.

Effectiveness of Egyptian propolis on control of tomato bacterial wilt caused by Ralstonia solanacearum

This study was conducted to evaluate Egyptian propolis to control tomato bacterial wilt caused by Ralstonia solanacearum under in vitro and in vivo conditions. In vitro, three concentrations of water extract of propolis [1 mg/mL (PC1); 10 mg/mL (PC2); and 100 mg/mL (PC3)] showed antagonistic activity against R. solanacearum. All concentrations significantly reduced the growth of the pathogen compared to control treatment, PC3 caused the highest growth reduction while PC1 caused the lowest reduction compared to water treatment. When the above three concentrations were applied to tomato seeds under laboratory conditions, they improved seed germination relative to control seeds treated with sterile distilled water. In both greenhouse and field experiments, PC3 gave a higher reduction in disease severity than PC1 and PC2; also this concentration caused the highest biomass percentage under greenhouse conditions. As recorded in field experiments, PC3 treatment resulted in a control efficacy of 76.9 and 71.7%, respectively, in two trial seasons. The highest increase percentage of yield per plant was recorded for PC3.