Biological Control Of Bacterial Wilt Research Articles

Biological control of bacterial wilt in tomato through the metabolites produced by the biocontrol fungus, Trichoderma harzianum

BackgroundRalstonia solanacearum causes bacterial wilt disease in tomato and other crops resulting in huge economic losses worldwide. Several measures have been explored for the control of R. solanacearum, but the desired control level of the disease through sustainable and ecofriendly way is still awaited.Main bodyIn this study, fungal metabolites produced by Trichoderma harzianum were investigated in the form of crude extract for the management of R. solanacearum both in vitro and in planta in tomato plants. In in vitro investigation, fungal metabolites were checked for their antibacterial potential at different concentrations (30, 60, 90, 120, 150, and 180 mg ml−1) and bacterial cell morphology was observed under scanning electron microscopy (SEM). In a greenhouse experiment, different application times (0, 3, and 6 days before transplantation DBT) and doses (0, 3, 6, and 9%) of the fungal metabolites were tested for their effects on soil bacterial population, disease severity and plant growth of tomato plants. The in vitro evaluation showed a strong antibacterial activity of fungal metabolites in concentration dependent manner. The highest concentration 180 mg ml−1 produced maximum inhibition zone (20.2 mm) having non-significant difference with the inhibition zone (20.5 mm) produced by the standard antibiotic streptomycin. The SEM analysis revealed severe morphological destructions of bacterial cells. In case of greenhouse experiment, the highest decrease in soil bacterial population, lowest disease severity, and maximum increase in plant growth parameters were obtained by highest dose (9%) and longest application time (6 DBT).ConclusionThe fungal metabolites produced by T. harzianum could be used as low-cost, environment-friendly, and sustainable management strategy for the control of R. solanacearum in tomato plants.

Biological control of bacterial wilt of solanaceous vegetable crops - a review

Bacterial wilt of solanaceous crops is caused by Ralstonia solanacearum (Smith) Yabuuchi et al. which includes a “species complex” that provides it high heterogeneity. The wilt disease reduces the production of crops significantly. The bacterium R. solanacearum is gram-negative, small rod with rounded ends, non-fluorescent, non-endospore forming, strict aerobe and has polar flagella (when present). All phylotypes i.e. I, IIA, IIB, III & IV, race 1 & 3 and biovars 1, 2 2T, 3 & 4 infect solanaceous crops to cause wilt disease. The pathogen has variability during its survival in the soil for a longer period which restricts the control of wilt disease. Besides, there are no such chemicals available to control wilt disease effectively at field level. An alternative approach is biological control which is ecofriendly and very effective in integrating with other management practices for controlling the disease. Biological control includes microbes, organic matter, botanicals, animal wastes and resistant varieties which are used either alone or combined with other methods to improve disease management. The microbes particularly fungi and bacteria have advantage over chemical control such as self-sustaining, self-spreading, reduced input by renewal capacity, long-term disease suppression and eco-friendly.

Isolation, Identification and Characterization of Rhizobacteria Strains for Biological Control of Bacterial Wilt (Ralstonia solanacearum) of Eggplant in China

Bacterial wilt of eggplant is the most destructive disease caused by Ralstonia solanacearum throughout the world. Eleven bacterial strains with high antagonistic activity were obtained from 245 rhizobacteria. Based on analysis of morphology, 16S rRNA sequences, fatty acid profiles, gyrA and rpoB genes, they were identified as Pseudomonas putida (IMA3), Paenibacillus polymyxa (IMA5), Bacillus cereus (IMA4, IMA7 and IMA11) and the “operational group Bacillus amyloliquefaciens” (IMA1, IMA2, IMA6, IMA8, IMA9 and IMA10). The lipopeptide compounds produced by each strain also were determined. The biocontrol tests demonstrated that co-inoculation by strain IMA5 and the pathogen gave the greatest biocontrol efficiency of 87.0% and 69.2% 30 and 40 days after co-inoculation, respectively. Plant growth promotion tests revealed that IMA5 markedly promoted eggplant growth, enhancing aboveground seedling length and biomass by 60.8% and by 107.6% and underground root length and biomass by 33.0% and 69.2%, respectively. Hence, strain IMA5 could be considered for developing potential biocontrol agents and for promoting plant growth characteristics, to aid the management of the pathogen R. solanacearum in eggplants.

Biological control of bacterial wilt of tomato caused by Ralstonia solanacearum using Pseudomonas species isolated from the rhizosphere of tomato plants

Tomato bacterial wilt, caused by Ralstonia solanacearum, is one of the devastating soil-borne diseases of tomato plants in Nigeria. We investigated the potentiality of indigenous Pseudomonas species in controlling bacterial wilt of tomato. Seven Pseudomonas species were isolated and identified from the rhizosphere of tomato plants. The isolates were screened for enzyme production, and in vitro antimicrobial activity against pathogenic R. solanacearum using dual plate culture method. The biocontrol and growth-promoting efficacy of the Pseudomonas species were studied in the screenhouse using a completely randomised design. P. aeruginosa, P. syringae and P. fluorescens produced lipase, protease and α-amylase enzymes. All the Pseudomonas isolates except P. aureofaciens inhibited the growth of R. solanacearum. Since the tested species reduced the incidence of bacterial wilt and promoted the growth of the tested tomato genotypes, the indigenous Pseudomonas strain could be used to develop active biocontrol agents of tomato bacterial wilt in Nigeria.

A practical random mutagenesis system for Ralstonia solanacearum strains causing bacterial wilt of Pogostemon cablin using Tn5 transposon.

A practical random mutagenesis system of Ralstonia solanacearum by electroporation with Tn5 transposon was established, which may be utilized to provide genetic approach to study virulence genes of R. solanacearum strains and create nonpathogenic mutants for biological control of bacterial wilt in Pogostemon cablin. R. solanacearum strain PRS-84 used in this study was isolated from P. cablin plants infected with bacterial wilt. The bacterial suspension of R. solanacearum strain PRS-84 was mixed with Tn5 transposome complex and the mixture was transformed by electroporation. The electroporated cells were then spread on the 2, 3, 5-triphenyltetrazolium chloride agar plates containing kanamycin to select the kanamycin-resistant colonies. Several factors which determined the bacterial transformation efficiency were optimized. The transformation process was shown to be optimal at the electric field strength of 12.5kVcm-1. Bacterial cells harvested at mid-exponential phase gave the highest transformation efficiency. 10µgmL-1 kanamycin was found to be the optimal concentration for transformant selection. Tn5 insertion mutants of R. solanacearum strain PRS-84 were identified by PCR amplification and Southern blot analysis. Mutants subcultured for 100 passages were also detected by PCR amplification and Southern blot analysis. Furthermore, pathogenicity screening test of mutants was performed by inoculating in vitro regenerated patchouli plants. Results revealed that mutants with a single Tn5 insertion in their genomes were obtained from R. solanacearum strain PRS-84, and the Tn5 insertion could be stably inherited in the mutants. Then, mutants with reduced pathogenicity were selected.

Bacterial wilt and canker of tomato: fundamentals of a complex biological system

Tomato (Solanum lycopersicum) is well-known as a model for study of plant–pathogen interactions, since it is a crop of global relevance and susceptible to multiple bacterial, fungal, viral and nematode pathogens. Among bacterial phytopathogens, the actinomycete Clavibacter michiganensis subsp. michiganensis (Cmm) is the causal agent of bacterial wilt and canker of tomato, considered a quarantine disease at international level. The tomato–Cmm interaction has been studied to decipher the pathogenicity mechanisms in Cmm, susceptibility mechanisms in tomato, molecular basis of resistance to Cmm in wild species relative to domesticated tomato, and the level of genetic variability in Cmm. The objective of this review is to discuss recent advances in tomato–Cmm compatible interaction, which can be integrated for application in early diagnosis and biological control of bacterial wilt and canker of tomato. Further study of plant–microorganism interactions is a promising field for improvements in tomato pathogen resistance.

Studies on biological control of bacterial wilt caused by Ralstonia solanacearum using endophytic bacteria

Studies on biological control of bacterial wilt caused by Ralstonia solanacearum using endophytic bacteria

Biological control of bacterial wilt of common bean by plant growth-promoting rhizobacteria

Bacterial wilt (BW) caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is an emerging, seed-transmitted disease of common bean (Phaseolus vulgaris) in Brazil, and plant growth-promoting rhizobacteria (PGPR) have the potential to be used in disease management. The present work aimed at determining the potential of selected PGPR on the biological control of BW through seed treatment, growth promotion and induced resistance. Bean seeds cv. ‘Pérola’ were artificially inoculated with Cff, immersed in a PGPR suspension, and sown in 4L pots containing a soil: sand mixture (2:1). Plants were assessed for seedling emergence (SE), speed emergence index (SEI), relative growth index (RGI), root dry weight (RDW), shoot dry weight (SDW), as well as biochemical plant responses in the presence or absence of Cff. The disease control ranged from 42% to 76%, respectively, for Bacillus subtilis UFLA285 and ALB629 compared to the untreated control. PGPR treatments also increased RGI, SDW, and RDW. Upon Cff inoculation, UFLA285 increased phenolics’ content and ALB629 in the lignin accumulation compared to the untreated control. Without the pathogen inoculation, both PGPR promoted an increase in phenylalanine ammonia lyase activity and total phenolics content and UFLA285 in the lignin accumulation. Our findings demonstrated the potential of selected PGPR for disease control, enhancement of the RGI and biomass accumulation. Surprisingly, instead of a priming effect of PGPR, Cff apparently blocks the defense response development although the overall phenotype is disease control, suggesting there is a complementary and/or compensatory mode of action involved.

Improvement for Bacterial Wilt Resistance in Potato By Conventional and Biotechnological Approaches

Bacterial wilt (BW) of potato caused by the bacterium Ralstonia solanacearum (Rs) is considered a serious problem particularly in tropical, subtropical and warm temperate regions. Chemical-, cultural- and biological control of BW has limited success. Thus, the control of BW through resistance breeding and biotechnology is considered to be very important and necessary. Rs is considered a ‘species complex’ and has significant variation at physiological, serological and genetic levels. The bacterium has an unusually wide host range with over 400 hosts belonging to more than 50 botanical families. A large number of Solanum species have been screened for resistance to this bacterium, but so far no Solanum species has been found to have complete immunity. A high degree of resistance to Rs was found only in S. phureja, a diploid relative of cultivated tetraploid potatoes. The resistance has been transferred from S. phureja to cultivated potatoes through introgression breeding as well as somatic hybridization. Although moderate to highly resistant potato varieties have been released, high frequency of latent infection in tubers is still a major problem. Further, the resistant cultivars are not adapted to different agro-climatic zones and are not effective against all the strains of the pathogen. Biotechnological approaches involving the use of antimicrobial peptides, plant defence genes and plant resistance genes are being tried. This paper reviews the global situation with regard to screening of genetic resources and their utilization in resistance breeding for BW in potato and also the status and the opportunities that biotechnology offers to combat this disease.

Biological Control of Bacterial Wilt of Tomato by Plant Growth Promoting Rhizobacteria

Biological Control of Bacterial Wilt of Tomato by Plant Growth Promoting Rhizobacteria

Soil-borne antagonists for biological control of bacterial wilt disease caused by Ralstonia solanacearum in tomato and pepper.

Bacterial wilt is an important disease of tomatoes and peppers, causing plant death and significant yield losses. Control methods include use of resistant varieties, crop rotation, etc. Biological control is desirable because control with other methods gives variable results. This paper describes the effectiveness of microbial antagonists isolated from soils. Of 73 isolated antagonists, eight were screened and evaluated in vitro and in vivo against Ralstonia solanacearum. They all significantly reduced disease symptoms. The effects of carbon and nitrogen source, incubation temperature and broth culture pH were evaluated for production of inhibitory substances. Results indicated that the optima were sucrose 2.5% (w/v), peptone 2% (w/v), temperature 28°C, and initial medium pH of 7. Three antagonists isolated from soil (Bacillus megaterium, Enterobacter cloacae, Pichia guillermondii) and Candida ethanolica showed high potential for disease suppression and also increased fruit weight, biomass and plant height. These results provide encouragement for continued research on biological control of bacterial wilt by antagonistic isolates from soil.

Biocontrol of tomato wilt by plant growth-promoting rhizobacteria

In greenhouse experiments, three strains of plant growth-promoting rhizobacteria (PGPR), Serratia sp. J2, fluorescent pseudomonad J3, and Bacillus sp. BB11, were evaluated for biological control of bacterial wilt of tomato caused by Ralstonia solanacearum. A total of four field trials were conducted, each in a different location in Jiangsu and the Hebei provinces. Strains J2, J3, and BB11 provided disease control and increased yield. In trial one in Qixia (1999), disease was reduced 66.1, 73.6, and 68.4% by J2, J3, and BB11, respectively, compared to the control. Yield increases with bacteria in this trial ranged from 49.5 to 70.8%. In trial two in Huaian (2000), disease was reduced 78.1, 94.1, and 86.9% by J2, J3, and BB11, respectively. Yield increases ranged from 180 to 237%. In trial three in Handan (1999), biocontrol efficiencies of 71.3, 63.6, and 78.2% were achieved by J2, J3, and BB11, respectively. Yield increases ranged from 53.5 to 76.2%. In trial 4 in Handan (2000), disease was reduced 74.4, 75.1, and 81.9% by J2, J3, and BB11, respectively, compared to the control. Yield increases with these bacteria ranged from 46.3 to 78.5%. Additional tests were conducted with 1-year-old and 2-year-old formulations of each PGPR strain. Populations of PGPR in the 1-year-old formulations were nearly identical to freshly prepared PGPR formulations. Biological control efficacy was retained by the stored formulations of all three PGPR strains, with 1-year-old formulations providing 68.4–99.5% control and 2-year-old formulations providing 63.4–78.5% control. Yield increases with stored formulations ranged from 35.4 to 67.0%. We conclude that our method of formulating PGPR products provides stable formulations that retain biological control and plant growth-promoting activities.

Biological Control of Bacterial Wilt of Tomato by an Avirulent Strain of Pseudomonas solanacearum Isolated from Strelitzia reginae.

Bacteriocinogenic strelitzia strain (Str-10) of Pseudomonas solanacearum was tested for its ability to suppress development of bacterial wilt of tomato in a greenhouse. The spontaneous avirulent mutant of strain Str-10 i.e. strain Str-10 op type, significantly protected tomato plants from bacterial wilt. The strain suppressed the development of bacterial wilt incited either by bacteriocin-sensitive or bacteriocin-resistant strains. The protection was more pronounced when the temperature was low (18-25°C). However, at high temperature (30-37°C) the protection effect was lost. Population of strain Str-10 op type was maintained in the rhizosphere and rhizoplane. At 28 days after inoculation, population of strain Str-10 op type in the rhizoplane was 2×106cfu/g fresh weight of root and 2×105cfu/g dry weight of soil in the rhizosphere. The bacterium also invaded root and stem tissue a few centimeters above ground. The promising protection due to the strain Str-10 op type was obtained when the population ratio of the challenge strains to Str-10 op type was smaller than 1. Although the strain Str-10 op type exists in the greater amount in the root system, the bacteriocin was unlikely involved in suppression of bacterial wilt of tomato. The ability of strain Str-10 op type in suppressing the development of bacterial wilt was presumed to be derived from induced resistance of host plant.

Biological control of bacterial wilt caused by Pseudomonas solanacearum in India with antagonistic bacteria

From among 125 strains of fluorescent and 52 strains of nonfluorescent bacteria initially screened in the laboratory for their antibiosis towards the bacterial wilt pathogen, Pseudomonas solanacearum, strain Pfcp of Pseudomonas fluorescens and strains B33 and B36 of Bacillus spp., were chosen and evaluated further in greenhouse and field tests. Pfcp treated banana (Musa balbisiana), eggplant and tomato plants were protected from wilt upto 50, 61 and 95% in greenhouse and upto 50, 49 and 36% respectively in field. Protection afforded by the Bacillus strains was lower. In bacteria-treated plants which were subsequently inoculated with P. solanacearum plant height and biomass values increased and were close to those of nontreated and noninoculated control plants.

Biocontrol of bacterial wilt of potato with an avirulent strain ofpseudomonas solanacearum: interactions with root-knot nematodes

Field tests for biological control of bacterial wilt of potatoes, caused byPseudomonas solanacearum, were conducted in Florida in 1984 and 1985. Potato seedpieces of tolerant (Ontario) and susceptible (Pungo and/or Atlantic) cultivars were immersed in a suspension of the avirulent, non-bacteriocinogenic strain ofP. solanacearum, B82, prior to planting in naturally-infested soil. Relatively low populations ofP solanacearum (2 to 4 log cfu/g soil) and root-knot nematodes (0 to 33 larvae ofMeloidogyne incognita/100 cm3 soil) were present in the soil before planting. In 1984, there was approximately a 50% reduction in incidence of bacterial wilt and brown rot in B82-treated plants of cultivar Atlantic, as compared with controls. With cultivar Ontario, on the other hand, disease incidence was very low and differences between treatments were not significant. In 1985, the incidence of bacterial wilt was low in all plots. Treatment with strain B82 reduced incidence of tuber brown rot in all cultivars, but differences between treatments were not significant at P = 0.05. There was a significant correlation, however, between incidence of wilt and root-knot nematode populations in the soil. Therefore, the possibility that control of bacterial wilt in 1984 was indirect,i e, via an effect of B82 treatment on root infection byM incognita, was examined. Greenhouse tests were conducted to determine the potential effect of seedpiece treatment with strain B82 on nematode infection of cultivars Atlantic and Ontario. In two out of three trials, the B82 treatment significantly reduced incidence of root knot. These results suggest that interactions of the biocontrol agent with root-knot nematodes may determine the effectiveness of a treatment designed for bacterial wilt control in the field.

Use of avirulent mutants of Pseudomonas solanacearum for the biological control of bacterial wilt of tomato plants

Tn5-induced avirulent mutants derived from the virulent GMI1229 strain of Pseudomonas solanacearum were investigated as possible antagonists for the control of bacterial wilt of tomato. Significant protection was obtained by making simultaneous or sequential root inoculations, when the relative inoculum ratio of virulent to avirulent cells was equal to or lower than, 0·1. Under conditions favourable for disease development, the virulent strain failed to multiply within the plant when inoculated together with different Tn5-induced avirulent mutants, which multiplied to some degree. Although some mutants were invasive, most of them showed reduced colonization and multiplication within the host compared with the virulent strain. The use of Tn5-induced avirulent mutants as biological agents for the control of bacterial wilt is discussed.

Evaluation of an avirulent strain ofPseudomonas solanacearum for biological control of bacterial wilt of potato

An avirulent strain ofPseudomonas solanacearum, B82, was tested for its ability to protect the potato cultivar, Ontario, from bacterial wilt caused by virulent strains of this bacterium. Strain B82 was not antagonistic to 124 virulent strains ofP. solanacearum and was not bacteriocinogenic. When potato seedpieces were soaked for 5 hr in suspensions of B82 (108 to 109 cfu/ml), reduction in disease severity (up to 50%) was noted in some experiments. The treated plants, grown in the greenhouse or growth room for 4–5 wk, were challenged by stem inoculation, soil drenching, or root-to-root infection with virulent strains (276 or Br5) of the bacterium. Protection was not obtained consistently, however, and much of the variability could be attributed to differences in ambient temperature and light conditions in the greenhouse between experiments. In general, high ambient temperatures and/or reduced sunlight resulted in no protection. Protection appeared to depend on the ability of strain B82 to multiply in the vascular system in the crown region and to colonize the rhizosphere of treated plants. Soil temperatures above 24 C affected the ability of strain B82 to survive in the rhizosphere. The close dependence of protection on environmental conditions suggests that this method of control may not be practical under field conditions.

Biological Control of Bacterial Wilt of Potatoes: Attempts to Induce Resistance by Treating Tubers with Bacteria

Biological Control of Bacterial Wilt of Potatoes: Attempts to Induce Resistance by Treating Tubers with Bacteria