Crotalaria spectabilis and Raphanus sativus as Previous Crops Show Promise for the Control of Bacterial Wilt of Tomato Without Reducing Bacterial Populations

Ralstonia solanacearum is responsible for bacterial wilt affecting many crops worldwide. The emergent population of R. solanacearum (phylotype IIB/4NPB) wilts previously resistant varieties and has rapidly spread throughout Martinique. No conventional method is known to control it. In this study, previous crops used as sanitizing crops were investigated as an environmentally safe alternative method of control. The ability of the emergent population of R. solanacearum to persist in planta and in the rhizosphere of Brassicaceae, Asteraceae and Fabaceae grown as previous crops was evaluated in controlled conditions, and the incidence of bacterial wilt was assessed in the following tomato crop. Results showed that all species carried R. solanacearum latently. Among Brassicaceae and Asteraceae, the highest density of R. solanacearum was found in planta and in the rhizosphere of Tagetes erecta. The density of the R. solanacearum population in the rhizosphere of Raphanus sativus cv. Karacter was significantly higher than that in Raphanus sativus cv. Melody. In Fabaceae, the density of R. solanacearum population in planta was statistically similar in all species. The density of the R. solanacearum population in the rhizosphere of Crotalaria juncea was significantly higher than that in Crotalaria spectabilis. This study showed for the first time that Crotalaria spectabilis and Raphanus sativus cv. Melody grown as previous crops improve the performance of the following tomato with similar effects on R. solanacearum populations in the soil as bare soil. The incidence of the disease in tomato decreased by 86% and 60%, after R. sativus cv. Melody and C. spectabilis, respectively, and the proportion of infected plants also decreased. These results suggest that C. spectabilis and R. sativus cv. Melody can be used as previous crops to help bacterial wilt control in ecological management strategies without drastic suppression of R. solanacearum population in stem tissues and in the rhizosphere.     

Developing a bacteriophage cocktail for biocontrol of potato bacterial wilt

Bacterial wilt is a devastating disease of potato and can cause an 80% production loss. To control wilt using bacteriophage therapy, we isolated and characterized twelve lytic bacteriophages from different water sources in Kenya and China. Based on the lytic curves of the phages with the pathogen Ralstonia solanacearum, one optimal bacteriophage cocktail, P1, containing six phage isolations was formulated and used for studying wilt prevention and treatment efficiency in potato plants growing in pots. The preliminary tests showed that the phage cocktail was very effective in preventing potato bacterial wilt by injection of the phages into the plants or decontamination of sterilized soil spiked with R. solanacearum. Eighty percent of potato plants could be protected from the bacterial wilt (caused by R. solanacearum reference strain GIM1.74 and field isolates), and the P1 cocktail could kill 98% of live bacteria spiked in the sterilized soil at one week after spraying. However, the treatment efficiencies of P1 depended on the timing of application of the phages, the susceptibility of the plants to the bacterial wilt, as well as the virulence of the bacteria infected, suggesting that it is important to apply the phage therapy as soon as possible once there are early signs of the bacterial wilt. These results provide the basis for the development of bacteriophagebased biocontrol of potato bacterial wilt as an alternative to the use of antibiotics.

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Genetic structure and phylogenetic relationships of Ralstonia solanacearum strains from diverse origins in Guangdong Province,China

Bacterial wilt, caused by Ralstonia solanacearum species complex is a key yield‐limiting factor on crops in Guangdong province, China. The genetic diversity of 110 R. solanacearum strains collected from 16 host plants in different areas of Guangdong province was analysed using biovar and phylotype classification schemes. Of 110 strains, fifty‐five strains belong to biovar 3, fifty‐two strains belong to biovar 4, two strains belong to biovar 2 and one strain belonged to biovar 1. Phylotype‐specific multiplex PCR showed that 108 strains belonged to phylotype I (biovars 1, 3, 4) and two strains belonged to phylotype II (biovar 2). The result of phylogenetic relationships analysis based on egl gene sequences demonstrated that 108 strains of phylotype I were grouped into nine previously described sequevars and a new sequevar 57, and two strains of phylotype II were grouped into sequevar 1. Sequevars 15, 34 and 44 widely distributed in Guangdong were predominant sequevars. Sequevar 45 was first reported on potato and pumpkin in China. These results revealed the genetic structure and phylogenetic relationships of R. solanacearum population in Guangdong and will be helpful in bacterial wilt‐resistance breeding.     

Relationship Between Ralstonia solanacearum Diversity and Severity of Bacterial Wilt Disease in Tomato Fields in China

A field survey was conducted to determine the relationship between Ralstonia solanacearum diversity and severity of bacterial wilt disease in tomato plants grown in plastic greenhouses. Both vegetative and reproductive stages of the plants were surveyed, and the symptoms were empirically categorized into five scales: 0 (asymptomatic): 1st, 2nd, 3rd and 4th. The bacterial wilt pathogen was isolated from infected plants at each disease scale; pathogenic characteristics and population densities of the bacterial strains were assessed. Two hundred and eighty‐two isolates were identified as R. solanacearum, which were divided into three pathogenic types, virulent, avirulent and interim, using the attenuation index (AI) method and a plant inoculation bioassay. Ralstonia solanacearum was detected in all asymptomatic and symptomatic tomato plants, with population numbers, ranging from 10.5 to 86.7 × 105 cfu/g. However, asymptomatic plants harboured only avirulent or interim R. solanacearum, whereas tomato plants displaying 1st or 2nd disease degree contained interim and virulent strains. Additionally, 3rd and 4th degree plants harboured only virulent strains. The disease was more severe in vegetative‐stage plants (disease severity index (DSI) 0.20) with higher total numbers of interim and virulent R. solanacearum strains than those in reproductive‐stage plants (DSI 0.12). Three pathotypes of R. solanacearum coexisted in a competitive growth system in the tomato field, and their distribution closely correlated with the severity of tomato bacterial wilt.     

Evaluation of rhizosphere bacteria and derived bio-organic fertilizers as potential biocontrol agents against bacterial wilt (Ralstonia solanacearum) of potato

Aims

Potato bacterial wilt (Ralstonia solanacearum) is a soil-borne disease that affects the potato plant (Solanum tuberosum) worldwide and causes serious economic losses in southern China. The objective of this study is to study the effect of bacterial antagonists and bio-organic fertilizers on potato bacterial wilt and rhizosphere soil microbial population.

Methods

In the present study, pot and field experiments were conducted to evaluate the LH23 (Bacillus amyloliquefaciens) and LH36 (Bacillus subtilis) strains and their derived bio-organic fertilizers (BIO23 and BIO36) as potential biocontrol agents against potato bacterial wilt.

Results

BIO23 and BIO36 decreased the incidence of bacterial wilt disease and increased potato yields. In pot experiments, the disease incidence of BIO23 and BIO36 was 8.9 % and 11.1 % respectively, much lower than the control (57.7 %). The biocontrol efficiency of BIO23 was 84.6 %, which was the most successful treatment and BIO36 was the second with a biocontrol efficiency of 80.8 %. The increased percentages of potato yields when compared with the control were 63.5 % (BIO23), 64.7 % (BIO36) 34.8 % (LH23), 33.6 % (LH36) and 20.7 % (OF). The counts of antagonists, bacteria and actinobacteria in the rhizosphere soil were significantly increased in BIO23 and BIO36 treatments, whereas the counts of R. solanacearum and fungi in the soil in the both treatments decreased. In field experiments, 70 days after treatment, the biocontrol efficacies of BIO23 and BIO36 treatments were 92.0 % and 84.0 %, and the yield increases of BIO23 and BIO36 treatments were 42.3 % and 28.8 %, respectively, when compared with the organic fertilizer treatment. In addition, the changes in the microbial populations were the same as those observed in the greenhouse experiment.

Conclusions

Potato bacterial wilt could be well controlled by the application bio-organic fertilizer containing a specific antagonist, mainly through the alternation of soil microbial community     

Detection,Identification and Phylogenetic Analysis of Indian Ralstonia solanacearum Isolates by Comparison of Partial hrpB Gene Sequences

A species‐specific Polymerase Chain Reaction (sPCR) method was developed to identify and detect isolates of Ralstonia solanacearum, the cause of bacterial wilt disease in chilli. PCR primers for R. solanacearum were identified by alignment of hrpB gene sequences and selection of sequences specific for R. solanacearum at their 3′ ends. The primers were shown to be specific for R. solanacearum, as no PCR product was obtained when genomic DNA from other bacterial species including closely related Ralstonia species, were used as test species. Lone pair of primers (RshrpBF and RshrpBR) was designed using hrpB gene sequence, unique to R. solanacearum which amplified a predicted PCR product of 810 bp from 20 different isolates. Phylogenetic analysis was also attempted to understand the evolutionary divergence of Indian R. solanacearum isolates. Based on phylogenetic analysis, Indian isolates showed homology with the standard reference isolates from other countries but, interestingly, one new isolate showed complete evolutionary divergence by forming an out‐group.     

The influence of mixed cropping on the control of potato bacterial wilt (Pseudomonas solanacearum)

Experiments with bacterial wilt (Pseudomonas solanacearum) race 3 showed that the practice of intercropping potato with maize or haricot beans markedly reduced the incidence and rate of disease development in the potato crop. This reduction in disease was considered to be an effect of the increased distances between individual potato plants, their spatial arrangement and the presence between potato plants of root systems of other plant species, all of which resulted in a reduction in plant-to-plant transmission, via the roots. The lower potato plant population associated with intercropping resulted in a slower rate of inoculum build-up in the soil and the presence of an intercrop further markedly reduced the inoculum build-up. Where farmers retain tubers for seed, but where roguing of diseased plants is not practised, the isolation of plants through intercropping was considered to facilitate an efficient selection of healthy tubers.     

Pseudomonads: major antagonistic endophytic bacteria to suppress bacterial wilt pathogen, <Emphasis Type="Italic">Ralstonia solanacearum</Emphasis> in the eggplant (<Emphasis Type="Italic">Solanum melongena</Emphasis> L.)

Endophytic bacteria of eggplant, cucumber and groundnut were isolated from different locations of Goa, India. Based on in vitro screening, 28 bacterial isolates which effectively inhibited Ralstonia solanacearum, a bacterial wilt pathogen of the eggplant were characterized and identified. More than 50% of these isolates were Pseudomonas fluorescens in which a vast degree of variability was found to exist when biochemical characteristics were compared. In greenhouse experiments, the plants treated with Pseudomonas isolates (EB9, EB67), Enterobacter isolates (EB44, EB89) and Bacillus isolates (EC4, EC13) reduced the wilt incidence by more than 70%. All the selected isolates reduced damping off by more than 50% and improved the growth of seedlings in the nursery stage. Most of the selected antagonists produced an antibiotic, DAPG, which inhibited R. solanacearum under in vitro conditions and might have been responsible for reduced wilt incidence under in vivo conditions. Also production of siderophores and IAA in the culture medium by the antagonists was recorded, which could be involved in biocontrol and growth promotion in crop plants. From our study we conclude that Pseudomonas is the major antagonistic endophytic bacteria from eggplants which have the potential to be used as a biocontrol agent as well as plant growth-promoting rhizobacteria. Large scale field evaluation and detailed knowledge on antagonistic mechanism could provide an effective biocontrol solution for bacterial wilt of solanaceous crops.     

Evaluation of rhizosphere bacterial antagonists for their potential to bioprotect potato (Solanum tuberosum) against bacterial wilt (Ralstonia solanacearum)

Bacterial wilt (Ralstonia solanacearum) is one of the production constraints of potato (Solanum tuberosum). The intent of the study was to evaluate potential of bacterial antagonists to suppress bacterial wilt disease development and evaluate the role of the strains as plant growth-promoting rhizobacteria (PGPR) in potato. One hundred-twenty rhizosphere bacterial isolates were screened against virulent strain of Ralstonia solanacearum PPRC-Rs. After in vitro screening, six antagonistic strains (PFMRI, BS-DFS, PF9, PF20, BC, and BS-wly) with inhibition diameter >11 mm were selected and studied further in the greenhouse, in vivo. During in vivo study, the strains were evaluated for their effect in suppressing disease development in terms of area under disease progress curve (AUDPC) and increasing biomass (plant height and dry weight) of potato. Accordingly, PFMRI, BS-DFS, and PF9, significantly reduced AUDPC by 78.6, 66, and 64.3%, and wilt incidence by 82.7, 66.2, and 65.7%, respectively, compared to the control. During the sole application, the strains significantly (P < 0.0001) increased plant height by 35.6, 45.9, and 45%, and dry matter by 111, 130.4, and 129%, respectively compared to non-bacterized control. In the presence of the pathogen strain PFMRI, BS-DFS, and PF9 increased plant height by 66, 50, and 48.2%, and dry matter by 153.8, 96.8, and 92.5%, respectively compared to the pathogen treated control. Hence, the study shows that PFMRI, BS-DFS, and PF9 strains have potential use in potato bioprotection, as PGPR or in an integrated bacterial wilt management; whose effectiveness under a variety of field conditions should be investigated.     

Understanding Reaction of Potato (Solanum tuberosum) to Ralstonia solanacearum and Relationship of Wilt Incidence to Latent Infection

Bacterial wilt caused by Ralstonia solanacearum is one of the most important diseases affecting more than 200 plant species, including solanaceous crops. The pathogen is known to cause complicated symptoms ranging from visible to latent ones. Understanding crop's reaction to the pathogen and the underlying relatedness of latent infection to wilt incidence is of paramount importance. Thus, a number of potato cultivars including improved and otherwise were evaluated under greenhouse and field conditions. Accordingly, twenty‐eight of the cultivars tested under greenhouse conditions were resistant to the pathogen with scores ranging from 0.77 to 1.17 of 5. Nonetheless, under field conditions, only 2 of 28 cultivars found to be ‘resistant’ under greenhouse conditions, showed adequate resistance to the pathogen, indicating the significant impact of environment on the activity of the pathogen and reaction of the crop. Percentage wilt incidence and latent infection showed significant (P < 0.05) positive correlation, with r = 0.9438. Thus, evaluation of crop's performance based on the combination of the parameters like field wilt incidence and proportion of latent infection gave us better picture of the overall crop feat, than using wilt incidence as a sole parameter of evaluation as has been the case in most studies. Moreover, the established correlation of latent infection with field wilt incidence will also help us understand the disease epidemiology and design effective management measures, accordingly.     

First Report of Curtobacterium flaccumfaciens pv. flaccumfaciens Causing Cowpea Bacterial Wilt in Iran

During surveys in cowpea fields of Marand County, East Azerbaijan province, Iran, in the summer of 2013, a suspected bacterial disease was observed on cowpea leaves as tan spots and interveinal necrotic lesions surrounded by chlorotic margins. The disease was of high incidence where some fields had been fully destroyed and severity of the disease in some fields had reached up to 70%. Gram‐positive, yellow‐pigmented, coryneform bacteria were isolated from infected leaves. Pathogenicity of isolates was confirmed on 20‐day‐old cowpea (cv. Khoy) plants, and they were identified as Curtobacterium flaccumfaciens pv. flaccumfaciens based on biochemical test results confirmed using specific PCR primers. This is the first report of C. flaccumfaciens pv. flaccumfaciens, the causal agent of cowpea bacterial wilt in Iran.     

Molecular and phenotypic characterization of potential plant growth-promoting <Emphasis Type="Italic">Pseudomonas</Emphasis> from rice and maize rhizospheres

In this study, Pseudomonas species were isolated from the rhizospheres of two plant hosts: rice (Oryza sativa cultivar Pathum Thani 1) and maize (Zea mays cultivar DK888). The genotypic diversity of isolates was determined on basis of amplified rDNA restriction analysis (ARDRA). This analysis showed that both plant varieties selected for two distinct populations of Pseudomonas. The actual biocontrol and plant promotion abilities of these strains was confirmed by bioassays on fungal (Verticillum sp., Rhizoctonia solani and Fusarium sp.) and bacterial (Ralstonia solanacearum and Bacillus subtilis) plant pathogens, as well as indole-3-acetic acid (IAA) production and carbon source utilization. There was a significant difference between isolates from rice and maize rhizosphere in terms of biological control against R.  solanacearum and B.  subtilis. Interestingly, none of the pseudomonads isolated from maize rhizosphere showed antagonistic activity against R.  solanacearum. This study indicated that the percentage of pseudomonad isolates obtained from rice rhizosphere which showed the ability to produce fluorescent pigments was almost threefold higher than pseudomonad isolates obtained from maize rhizosphere. Furthermore, the biocontrol assay results indicated that pseudomonad isolated from rice showed a higher ability to control bacterial and fungal root pathogens than pseudomonad isolates obtained from maize. This work clearly identified a number of isolates with potential for use as plant growth-promoting and biocontrol agents on rice and maize.     

Effect of temperature,cultivars, injury of root and inoculums load of Ralstonia solanacearum to cause bacterial wilt of tomato

Bacterial wilt, caused by Ralstonia solanacearum , is responsible for severe losses in tomato crops in the world. In the present study, the effect of temperature, cultivars of tomato, injury of root system and inoculums load of R. solanacearum to cause bacterial wilt disease under control conditions was undertaken. Three strains UTT-25, HPT-3 and JHT-5 of R. solanacearum were grown at 5–40?°C in vitro to study, the effect of temperature on the growth of bacteria and maximum growth was found at 30?°C after 72?h in all the strains. Twenty-one days old seedlings of two cultivars of tomato i.e. N-5 (moderately resistant) and Pusa Ruby (highly susceptible) were transplanted into the pots and inoculated with R. solanacearum strain UTT-25 (5 × 10⁸?cfu/ml), mechanically injured and uninjured roots of the plant. The plants were allowed to grow at 20, 25, 30 and 35?°C at National Phytotron Facility, IARI, New Delhi to study the effect of temperature on intensity of bacterial wilt disease. Maximum wilt disease intensity was found 98.73 and 95.9 % in injured roots of Pusa Ruby and N-5 cultivars of tomato at 35?°C on 11th days of inoculation, respectively. However, no wilt disease was observed in both the cultivars at 20?°C up to 60?days. For detection of R. solanacearum from asymptomatic tomato plants, hrpB-based sequence primers (Hrp_rs2F and Hrp_rs2R) amplified at 323?bp was used in bio-PCR to detect R. solanacearum from crown, mid part of stem and upper parts of the plant. Another experiment was conducted to find out the inoculum potential of R. solanacearum strain UTT-25 to cause bacterial wilt in susceptible cultivar Pusa Ruby. The bacteria were inoculated at concentration of bacterial suspension 10 to 10¹⁰?cfu/ml in injured and uninjured roots of the plants separately and injured root accelerated wilt incidence and able to cause wilt disease 63.3% by 100?cfu/ml of R. solanacearum, while no disease appeared at 10?cfu/ml on the 11th day of inoculation in injured and uninjured roots of the plant.     

Ralstonia solanacearum colonization of tomato roots infected by Meloidogyne incognita

Bacterial wilt, caused by Ralstonia solanacearum, is one of the most serious diseases of tomato (Solanum lycopersicum). Concomitant infection of R. solanacearum and root‐knot nematode Meloidogyne incognita increases the severity of bacterial wilt in tomato, but the role of this nematode in disease complexes involving bacterial pathogens is not completely elucidated. Although root wounding by root‐knot nematode infection seems to play an important role, it might not entirely explain the increased susceptibility of plants to R. solanacearum. In the present study, green fluorescent protein (GFP)‐labelled R. solanacearum distribution was observed in the root systems of the tomato cultivar Momotaro preinoculated with root‐knot nematode or mock‐inoculated with tap water. Fluorescence microscopy revealed that GFP‐labelled R. solanacearum mainly colonized root‐knot nematode galls, and little or no green fluorescence was observed in nematode‐uninfected roots. These results suggest that the gall induced by the nematode is a suitable location for the growth of R. solanacearum. Thus, it is crucial to control both R. solanacearum and root‐knot nematode in tomato production fields to reduce bacterial wilt disease incidence and effects.     

Development of a mode of application of bioorganic fertilizer for improving the biocontrol efficacy to <Emphasis Type="Italic">Fusarium</Emphasis> wilt

More effective ways of applying biocontrol products should be developed based both on the characteristics of the biocontrol agents and the normal practices of the agricultural producer. A new system was developed to improve the biocontrol efficacy of Fusarium wilt for watermelon production, and this system was tested in pot and field experiments. Biocontrol was achieved by applying a novel bioorganic fertilizer product (BIO) to Fusarium-infested soil. The best biocontrol was obtained by application of a bioorganic fertilizer, BIO, into soil during the nursery phase of watermelon seedling followed by a second application to Fusarium-infested soil when watermelon seedlings were transplanted. In comparison with the controls, the incidence of the disease was reduced by 60–100% in the pot experiment and by 59–73% in the field experiment when the BIO was applied during the nursery stage. After application of BIO during the nursery stage, the number of colony-forming units of Fusarium oxysporum in rhizospheric soil was significantly (P < 0.05) inhibited compared to the controls. An in vitro experiment showed that the antagonist Paenibacillus polymyxa in the BIO could effectively colonize the rhizosphere of watermelon and proliferate along the extending plant roots. This inhibited growth of Fusarium oxysporum in the rhizosphere of watermelon and protected the watermelon roots from attack by the pathogens. The method used for biocontrol Fusarium wilt disease in watermelon should be a useful strategy to improve field efficacy of other biocontrol agents.     

Rhizocompetence and antagonistic activity towards genetically diverse Ralstonia solanacearum strains – an improved strategy for selecting biocontrol agents

Bacterial wilt caused by Ralstonia solanacearum is a serious threat for agricultural production in China. Eight soil bacterial isolates with activity against R. solanacearum TM15 (biovar 3) were tested in this study for their in vitro activity towards ten genetically diverse R. solanacearum isolates from China. The results indicated that each antagonist showed remarkable differences in its ability to in vitro antagonize the ten different R. solanacearum strains. Strain XY21 (based on 16S rRNA gene sequencing affiliated to Serratia) was selected for further studies based on its in vitro antagonistic activity and its excellent rhizocompetence on tomato plants. Under greenhouse conditions XY21 mediated biocontrol of tomato wilt caused by seven different R. solanacearum strains ranged from 19 to 70 %. The establishment of XY21 and its effects on the bacterial community in the tomato rhizosphere were monitored by denaturing gradient gel electrophoresis of 16S rRNA gene fragments PCR-amplified from total community DNA. A positive correlation of the in vitro antagonistic activities of XY21 and the actual biocontrol efficacies towards seven genetically different R. solanacearum strains was found and further confirmed by the efficacy of XY21 in controlling bacterial wilt under field conditions.     

Gene expression profile of Ralstonia Solanacearum for the rhizosphere ecological niche of Solanum tuberosum

Plant root secretion can be regarded as signal molecules, which exerts impact on microorganisms in the rhizosphere ecological niche. We obtained gene expression profile of Ralstonia solanacearumPO41 under the root secretions environment of Solanum tuberosum at the time points of 8 hrs, 16 hrs and 24 hrs, respectively, after infection with RNA microarray technology. Bioinformatics tools of differential genes expression analysis, GO functional analysis, cluster analysis and pathway analysis were conducted to find out the pathogenic genes and other related genes. We found that the virulence factors of R. solanacearum mainly focused on the output pathways of toxic protein (Sec pathway, Tat pathway and type III secretion system (T3SS)), the aggregation and transfer of exopolysaccharides and the chemotactic movement and adhesion of flagellum in the potato root secretion ecological niche, while the virulence factors in the atypical output pathway mainly distributed in Sec (secB, secDF, yidc) and Tat (tatA, tatC) pathways to promote the output of folded and unfolded toxic proteins. The fliIATPase was obviously upregulated 8 hrs postinoculation, suggesting that type III secretion system was only active at the early stage of PO41 infection. The upregulated expression of phosphoglucomutase and epimerase showed that the virulence factor of exopolysaccharides (EPS) was synthesized at the early stage of R. solanacearum infection. Chemotactic receptor and motor protein were obviously upregulated within 24 hrs postinoculation. Our study revealed that R. solanacearumPO41 had already colonized to the roots within 24 hrs with the stimulating of root secretion. Some pathogenic genes were upregulated during this period.     

Eco-friendly application of nano-chitosan for controlling potato and tomato bacterial wilt

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.