Ralstonia Solanacearum Biovar Research Articles

Performance of eggplant cultivars grafted on wild and cultivated rootstocks in bacterial wilt infected field

ABSTRACT Bacterial wilt (BW) causes extensive loss in yield of eggplant (Solanum melongena L.) under tropical and humid subtropical conditions. Grafting commercial cultivars onto selected rootstocks is an effective approach to control wilt disease without requiring extensive breeding to develop resistant varieties. Wild and cultivated eggplant genotypes were screened for tolerance to BW disease (Ralstonia solanacearum Biovar IIIA) in artificially created infested beds. Two each of S. torvum Sw. genotypes (BCB ST 1 and IARI ST 1) and cultivated varieties ‘Utkal Anushree’ and ‘Utkal Madhuri’ were identified as most compatible (graft survival was high) rootstocks. Two widely cultivated, susceptible cultivars, ‘Bidhan Suphala’ and ‘Bidhan Supreme’ were grafted as scions on rootstocks and reproductive growth, fruit quality and disease incidence of grafted plants in the bacterial wilt infected experimental and grower fields determined. Although grafted plants had lower mortality and higher yield, fruit quality was not improved. Solanum torvum Sw.-grafted plants exhibited some negative effects on yield and economics compared to cultivated rootstocks, indicating reduced post-transplant compatibility. The ‘Bidhan Suphala’ grafted on cultivated rootstock ‘Utkal Anushree’ had the highest yield and economic return than those grafted on wild rootstocks. ‘Utkal Anushree’ could be effectively used as a rootstock for controlling eggplant wilt through grafting. Grafting eggplant cultivars on rootstock of a cultivated variety over wild species increased yield, extended the harvest and was effective in reducing crop loss caused by BW disease.

Combining ability of tomato inbred lines to bacterial wilt resistance

Tomato is one of the most important crops worldwide. Bacterial wilt (BW), caused by Ralstonia spp., is a major disease for tomato production around the world, especially in tropical and subtropical regions. Currently in Brazil, only commercial hybrids are available as resistant rootstocks for use in infested areas, and we lack information regarding resistance to aggressive strains. Thus, the aims of this work were to estimate combining abilities of five tomato inbred lines and hybrids and to identify resistant genotypes for using as rootstocks resistant to Ralstonia solanacearum biovar 2, phylotype II, one of the most aggressive strains in Brazil. Combining abilities for BW resistance were assessed through full diallel crossings among five tomato inbred lines without reciprocals. The experiment was carried out in a greenhouse, in a complete randomized blocks design, using 15 genotypes (hybrids and parents). Additive genetic effects showed to be the most important for controlling bacterial wilt. The inbred line Hawaii 7996 exhibited the highest general combining ability among the five parents assessed. The hybrid Hawaii 7996 × Rodade was the best crossing in terms of resistance and specific combining ability, which was greater than those of all other hybrids. Although Hawaii 7996 remains as a major source for BW resistance, further researches are needed to better understand the resistance dynamics, seeking to develop hybrids with transgressive segregations and more stable resistance against aggressive strains and thrive under environmental conditions highly favorable to bacterial wilt infection.

Evaluation of antibacterial activity of extract and essential oil of Tagetes patula L. in vitro against Ralstonia solanacearum biovar 2

This work aims to assess the in-vitro antimicrobial activity of the essential oil and hydroalcoholic extract of Tagetes patula against Ralstonia solanacearum the causal of potato wilt disease. Providing necessary information on the antimicrobial activity of the extract and essential oil on this phytopathogen, also contributing to knowledge in the phytopathology area. The antimicrobial activity was carried out through dilution both liquid medium and agar (perforation in well) at different concentrations. The content of flavonoids, polysaccharides, tannins and phenols present in the extract was quantified, and the oil was characterized through gas chromatography–mass spectrometry. The majority compound identified in the oil were piperitone (42.95%) and the extract mostly had polysaccharides (1.54 ± 0.18 mg EG/g DE). Both registered a minimum inhibitory concentration bacteriostatic of 50 μg/mL and the half maximal effective concentrations were 306 μg/mL (oil) and 352 μg/mL (extract). The oil had better yield through the dilution method in liquid medium at concentration of 500 μg/mL, and the hydroalcoholic extract had better bactericide yield of 200 μg/mL. It was concluded that the essential oil and hydroalcoholic extract with further applied studies could be a viable and environmentally friendly alternative to control R. solanacearum.

Assessing the Efficacy of Broad-Spectrum Antibiotics in Controlling Bacterial Contamination in the In Vitro Micropropagation of Ginger (Zingiber officinale Rosc).

Ginger (Zingiber officinale Rosc) (Zingiberaceae) is a livelihood and commercial crop in Ethiopia. But, the availability of clean and healthy planting materials has become a problem due to wilt disease, caused by Ralstonia solanacearum Biovar 3 Race 4. This problem obliged growers to seek for tens of millions of vigorous and disease-free planting materials very quickly via in vitro micropropagation of shoot tip explants. For this purpose, protocols of sterilizing shoot tip explants and controlling bacterial contamination of one Ethiopian ginger cultivar called Deribo were tested. Hence, this article reports the finding of a study that aimed at testing the (a) effectiveness of three sterilization agents, namely, 0.25% w/v RBK (composed of ridomile, bayleton, and kocide at 1 : 1 : 1 ratio), 0.50% v/v NaOCl, and 70% v/v ethanol at three different treatment times in combination with 0.25% HgCl2; (b) efficacy of four broad-spectrum antibiotics and their combinations in controlling bacterial contaminants of ginger shoot tip explants and in vitro micropropagation media; and (c) effects of the antibiotics on the shooting performances of the explants of the cultivar. A 0.50% v/v NaOCl at exposure time of 20 min followed by 0.25% HgCl2 has resulted in 80% contamination-free and 70% live explants after three weeks of incubation. Likewise, cefotaxime at 50, 100, and 200 mg/L and cefotaxime plus streptomycin at 25, 50, and 100 mg/L yielded 87 to 93% contamination-free microshoots after three weeks of culturing. The number of explants killed by the antibiotics increased with increasing the concentration of the antibiotics. Cefotaxime at 50 mg/L and cefotaxime plus streptomycin at 25 mg/L yielded significantly highest mean microshoots per explant (7.10 ± 0.36 and 7.51 ± 0.27, respectively) and mean shoot length (4.2 ± 0.26 and 3.56 ± 0.17 cm, respectively). Some of the microshoots showed some yellowing. But, they turned green and grew normal after subcultured into fresh, antibiotics-free culture media. These findings are important foundations towards developing more optimized protocols of sterilizing explants and controlling bacterial contaminants for large-scale in vitro micropropagation of the Deribo ginger cultivar.

Characterization of Iranian Ralstonia solanacearum biovar 2 strains by partial sequencing of egl, mutS and pga genes

Analysis of molecular variability in the megaplasmid and chromosomal genes were investigated on Iranian Ralstonia solanacearum biovar 2 strains that were collected from different potato-growing areas in Iran. Based on geographical regions, a set of representative biovar 2 strains were selected and subjected to sequence analysis and virulence assays. Sub-phylotype and sequevar strain analysis using the partial sequence of the egl gene identified all strains as sub-phylotype IIB and sequevar 1 (IIB-1). Sequence analysis of mutS gene showed that the biovar 2 strains belonged to clade 5. Interestingly, there was a clear discrimination between phylotypes and sub-phylotypes based on pga sequencing analysis. It seems that pga gene is a reliable and powerful marker for phylotypes and sub-phylotypes identification. All tested strains were highly aggressive on potato. There was no variability in virulence phenotype among the strains. Based on phylogenetic analysis, a genetic homogeneity was found among IIB-1 strains. Our results indicated that regardless of the geographical distribution, the Iranian IIB-1 strains are a clonal population. Knowledge of populations structure of this pathogen can be useful for the starting and optimization of breeding programs.

Phenotypic Fingerprints of Ralstonia solanacearum Biovar 3 Strains from Tobacco and Tomato in China Assessed by Phenotype MicroArray Analysis

Phenotypic Fingerprints of Ralstonia solanacearum Biovar 3 Strains from Tobacco and Tomato in China Assessed by Phenotype MicroArray Analysis

First Report of Bacterial Wilt Caused by Ralstonia solanacearum Biovar 2 Race 1 on Tomato in Egypt.

This study aims to isolate and identify the causal pathogen of tomato bacterial wilt in Egypt. In 2008, tomato plants showing typical symptoms of bacterial wilt disease with no foliar yellowing were observed in Minia, Assiut and Sohag governorates, Egypt. When cut stems of symptomatic plants were submerged in water, whitish ooze was evident and longitudinal sections showed a brown discoloration in the vascular tissues. Bacteria were isolated on triphenyl tetrazolium chloride medium and fifteen isolates shown typical morphological and cultural characteristics were confirmed as Ralstonia solanacearum biovar 2 race 1. Pathogenicity tests showed that all isolates proved to be pathogenic to tomato plants, varied from 52 to 97% wilting. This is the first report of R. solanacearum biovar 2 race 1 causing bacterial wilt in tomato crop in Egypt.

Genome Sequencing of Ralstonia solanacearum Biovar 3, Phylotype I, Strains Rs-09-161 and Rs-10-244, Isolated from Eggplant and Chili in India.

Ralstonia solanacearum Indian strains Rs-09-161 and Rs-10-244 were isolated from the coastal region of Goa and from the Andaman Islands. We report the draft genome sequences of these representative isolates infecting solanaceous vegetables in India.

Phylotype classification of Ralstonia solanacearum biovar 1 strains isolated from banana (Musa spp) in Malaysia

During 2011–2012, 15 bacterial isolates were obtained from wilting banana plants from seven locations in Malaysia. Characterisation of the Malaysian isolates was determined by biovar determination, pathogenicity test, phylotype-specific multiplex PCR (Pmx-PCR) and endoglucanase (egl) gene amplification. Based on the genotype, phenotype and pathogenic characteristics, all isolates were identified as Ralstonia solanacearum. Pmx- and egl-PCRs indicated that all isolates belong to phylotype II of Ralstonia species complex hierarchical classification. The neighbour joining phylogenetic tree of egl sequences also verified the results where the isolates were all clustered into phylotype II, together with the reference sequences strains, UW070 and UW162. Therefore, the results of our study may provide a better understanding on the taxonomy of R. solanacearum species occupying banana plantations in Malaysia. This study is indeed the first report of phylotype II classification of R. solanacearum biovar 1 strains isolated from banana plants in Malaysia.

Anaerobic disinfestation of tare soils contaminated with Ralstonia solanacearum biovar 2 and Globodera pallida

Tare soil is soil attached to harvested products like potato tubers. Tare soil becomes a considerable waste stream after storage, washing and processing of harvested products. There is a high risk on contamination of tare soils with (quarantine) phytopathogens, because of import of harvested products from different regions of the world. Disinfestation is necessary to make tare soils applicable for agricultural production. Anaerobic (non-chemical) soil disinfestation (ASD) and inundation are suitable methods to disinfest tare soils. Two different soils (marine loam and glacial sand) were either treated with five (2011) or four (2012) treatments and these were: (i) no treatment (control), (ii) freshly cut grass, (iii) Herbie 7025, (iv) inundation (five cm water on top of the soil surface), and (v) combination of Herbie 7025 and inundation (2011 only). Containers with treated and untreated soils were inoculated with two quarantine phytopathogens, Ralstonia solanacearum biovar 2 and Globodera pallida. After soil inoculation, the containers were airtight closed and only opened for destructive sampling after 84 days. Then, soils were analysed for the presence of R. solanacearum biovar 2, using immunofluorescence colony staining, and for the presence of viable G. pallida eggs, determined by the number of juveniles hatched from eggs and lured to potato root exudate. Strong (> 99.4 %) declines of both pathogens in treated versus the appropriate control soils were observed. Repetition of the experiment revealed the same pattern and therefore it was concluded that ASD and inundation, as separate treatments, have promise for remediation of tare soils from contaminating quarantine pathogens.

Ralstonia solanacearum ΔPGI-1 Strain KZR-5 Is Affected in Growth, Response to Cold Stress and Invasion of Tomato

The survival and persistence of Ralstonia solanacearum biovar 2 in temperate climates is still poorly understood. To assess whether genomic variants of the organism show adaptation to local conditions, we compared the behaviour of environmental strain KZR-5, which underwent a deletion of the 17.6 kb genomic island PGI-1, with that of environmental strain KZR-1 and potato-derived strains 1609 and 715. PGI-1 harbours two genes of potential ecological relevance, i.e. one encoding a hypothetical protein with a RelA/SpoT domain and one a putative cellobiohydrolase. We thus assessed bacterial fate under conditions of amino acid starvation, during growth, upon incubation at low temperature and invasion of tomato plants. In contrast to the other strains, environmental strain KZR-5 did not grow on media that induce amino acid starvation. In addition, its maximum growth rate at 28°C in rich medium was significantly reduced. On the other hand, long-term survival at 4°C was significantly enhanced as compared to that of strains 1609, 715 and KZR-1. Although strain KZR-5 showed growth rates (at 28°C) in two different media, which were similar to those of strains 1609 and 715, its ability to compete with these strains under these conditions was reduced. In singly inoculated tomato plants, no significant differences in invasiveness were observed among strains KZR-5, KZR-1, 1609 and 715. However, reduced competitiveness of strain KZR-5 was found in experiments on tomato plant colonisation and wilting when using 1:1 or 5:1 mixtures of strains. The potential role of PGI-1 in plant invasion, response to stress and growth in competition at high and moderate temperatures is discussed.

A putative genomic island, PGI-1, in Ralstonia solanacearum biovar 2 revealed by subtractive hybridization

Ralstonia solanacearum biovar 2, a key bacterial pathogen of potato, has recently established in temperate climate waters. On the basis of isolates obtained from diseased (potato) plants, its genome has been assumed to be virtually clonal, but information on environmental isolates has been lacking. Based on differences in pulsed-field gel electrophoresis patterns, we compared the genomes of two biovar 2 strains with different life histories. Thus, genomic DNA of the novel environmental strain KZR-5 (The Netherlands) was compared to that of reference potato strain 715 (Bangladesh) by suppressive subtractive hybridization. Various strain-specific sequences were found, all being homologous to those found in the genome of reference potato strain 1609. Approximately 20% of these were related to genes involved in recombinational processes. We found a deletion of a 17.6-Kb region, denoted as a putative genomic island PGI-1, in environmental strain KZR-5. The deleted region was, at both extremes, flanked by a composite of two insertion sequence (IS) elements, identified as ISRso2 and ISRso3. The PGI-1 region contained open reading frames that putatively encoded a (p)ppGpp synthetase, a transporter protein, a transcriptional regulator, a cellobiohydrolase, a site-specific integrase/recombinase, a phage-related protein and seven hypothetical proteins. As yet, no phenotype could be assigned to the loss of PGI-1. The ecological behavior of strain KZR-5 was compared to that of reference strain 715. Strain KZR-5 showed enhanced tolerance to 4°C as compared to the reference strain, but was not affected in its virulence on tomato.

Genetic and phenotypic diversity of Ralstonia solanacearum biovar 2 strains obtained from Dutch waterways

A novel set of Ralstonia solanacearum biovar 2 isolates was obtained, at several sampling occasions, from Dutch waterways, sediment and bittersweet plants and their genetic and phenotypic diversity was investigated. As reference strains, two previously-described strains obtained from diseased potato plants, denoted 1609 (The Netherlands) and 715 (Bangladesh), were included in the analyses. All novel isolates showed BOX and GTG5 PCR based genomic profiles similar to those of the reference strains. Also, PCR-restriction fragment length polymorphism analysis of the phcA and hrp genomic regions, as well as sequence analysis of six selected genomic loci, revealed great homogeneity across the strains. In contrast, pulsed field gel electrophoresis of restricted genomic DNA revealed the distribution of all strains across four groups, denoted pulsotypes A through D (pulsotypes C and D had one representative each). Moreover, pulsotype B, consisting of five strains, could be separated from the other pulsotypes by a divergent genomic fingerprint when hybridized to a probe specific for insertion element ISRso3. Representatives of pulsotypes A, B and C were selected for growth and metabolic studies. They showed similar growth rates when grown aerobically in liquid media. Assessment of their metabolic capacity using BIOLOG GN-2 revealed a reduced utilization of compounds as compared to the reference strains, with some variation between strains.

Detection of Ralstonia solanacearum in Irrigation Ponds and Aquatic Weeds Associated with the Ponds in North Florida

The discovery of exotic Ralstonia solanacearum biovar 1 strains on geranium in north Florida led to a concern that this strain may have become established. Therefore, we monitored irrigation ponds and potential alternative aquatic weeds from 2002 to 2005 for the presence of this strain. We report that this strain, possibly originating from the Caribbean, has become established in several ponds in Gadsden County, FL. Cladistic taxonomy was used to subclassify the bacterium at the species level into four groups or phylotypes based on multiplex polymerase chain reaction of the internal transcribed spacer (ITS) region. The bacterium was further divided into sequevars by sequencing the endoglucanase gene (egl). The strains were determined to belong to phylotype II/sequevar 4 NPB (nonpathogenic on banana) that was recently reported in Martinique. Partial sequencing of the egl followed by phylogenetic analysis placed the new Caribbean strains in a different clade than the typical Florida endemic strains. Pulsed-field gel electrophoresis (PFGE) revealed different haplotypes upon comparison of the collected pond strains and the Floridian strains. Based on PFGE polymorphism, egl sequencing, and phylogenetic analysis, the Caribbean strains were shown to be identical to the strain isolated from infected geranium plants. Experiments were undertaken to monitor R. solanacearum in irrigation ponds and associated weeds. R. solanacearum was detected in surface-disinfested common aquatic weeds growing in the irrigation ponds, including Hydrocotyle ranunculoides (dollar weed) and Polygonum pennsylvanicum (Pennsylvania smart weed). Both weeds were latently infected and showed no signs of wilt when collected. Two different Hydrocotyle spp. were artificially inoculated with R. solanacearum under greenhouse conditions and both developed symptoms 14 days post inoculation (dpi) and the bacterium was recovered from the tissues 42 dpi. There was a positive correlation between ambient temperature and R. solanacearum populations in irrigation water, as previously shown by other researchers.

Ralstonia solanacearum biovar 1 associated with a new outbreak of potato brown rot in Portugal

In May 2007, potato plants exhibiting symptoms possibly of brown rot were collected in some potato fields in the Baixo Mondego region (Center), Portugal, as a part of a nationwide programme to monitor Ralstonia solanacearum. All laboratory procedures laid down in Commission Directive 2006/63/EC, including dilution plating on semi-selective medium SMSA, indirect imunofluorescence (IIF), polymerase chain reaction (PCR) using specific primers and bioassays on tomato plants, were strictly followed and the causal agent of the disease was identified as Ralstonia solanacearum. The identity of the pure cultures of the isolated organism was confirmed by PCR, IIF and pathogenicity tests on several other plant species (eggplant, tobacco, pelargonium and eucalyptus). In biovar determination, the failure of the isolates to utilise/oxidise certain carbon sources indicated that the isolates were all biovar 1. This biovar has a broader host range than biovar 2 strains, and affects several crops of economic importance including ornamental plants and forest trees. Comparative analysis of 16S rRNA and endoglucanase (egl) gene sequences of these isolates with sequences that have been deposited at the GenBank revealed a similarity higher than 99% for several Ralstonia solanacearum isolates from biovar 1, including isolate DAR 64836 (Accession number DQ011551). This is the first report of Ralstonia solanacearum biovar 1 in Portugal. All control measures specified in the Commission Directive are being implemented.

Effects of plant genotype and growth stage on the structure of bacterial communities associated with potato (Solanum tuberosum L.)

The effects of genotype, plant growth and experimental factors (soil and year) on potato-associated bacterial communities were studied. Cultivars Achirana Inta, Désirée, Merkur and transgenic Désirée line DL12 (containing T4 lysozyme gene) were assessed in two field experiments. Cross-comparisons between both experiments were made using Désirée plants. Culture-dependent and -independent approaches were used to demonstrate effects on total bacterial, actinobacterial and Pseudomonas communities in bulk and rhizosphere soils and endospheres. PCR-denaturing gradient gel electrophoresis fingerprints prepared with group-specific primers were analyzed using multivariate analyses and revealed that bacterial communities in Achirana Inta plants differed most from those of Désirée and Merkur. No significant effects were found between Désirée and DL12 lines. Plant growth stage strongly affected different plant-associated communities in both experiments. To investigate the effect of plant-associated communities on plant health, 800 isolates from rhizospheres and endospheres at the flowering stage were tested for suppression of Ralstonia solanacearum biovar 2 and/or Rhizoctonia solani AG3. A group of isolates closely resembling Lysobacter sp. dominated in young plants. Its prevalence was affected by plant growth stage and experiment rather than by plant genotype. It was concluded that plant growth stage overwhelmed any effect of plant genotype on the bacterial communities associated with potato.

Epidemiological analysis of clones and cultivars of potato in soil naturally infested with Ralstonia solanacearum biovar 2

The objectives of this study were to evaluate the progress of Ralstonia solanacearum bacterial potato wilt biovar 2 (race 3) in 14 potato (Solanum tuberosum L.) cultivars or clones, the resistance of potato clone MB 03 (selected in Brasília, Brazil) to race 1 of R. solanacearum, and the occurrence of the pathogen in tubers harvested from asymptomatic potato plants. During the spring (September to the end of November in the southern hemisphere) of 1999 and 2000, 14 cultivars or clones were grown in a field naturally infested with R. solanacearum biovar 2, in Caxias do Sul, RS. The number of wilted potato plants was recorded each week and a disease progress curve plotted, the resistance of the potato genotypes to bacterial wilt being evaluated by determining the area under the curve. Various models were evaluated to fit the curves, with the logistic model being the best fit. At the end of each growing season tubers produced by asymptomatic plants were harvested and stored until budding and then tested for the presence of R. solanacearum. Cultivar Cruza 148 and clone MB 03 were the most resistant but both showed tubers with latent infections. The epidemiological implications of the incidence of R. solanacearum biovar 2 (race 3) in potato crops, as well as the resistance of certain genotypes that may harbor latent infections, are important aspects to be considered in the integrated management of bacterial wilt.

DETECTION OF LATENT INFECTIONS OF RALSTONIA SOLANACEARUM BIOVAR 2, RACE 3 IN TOMATO CROPS

A protocol was set up to detect latent infections of Ralstonia solanacearum biovar 2, race 3 in field tomatoes. For two growing seasons, healthy tomato plants were inoculated with a virulent strain, and monitored for between 7 and 55 days. Final extracts used for direct isolation on Kelman’s medium and for indirect immunofluorescence staining were prepared from 1 cm segments collected from the base of the lowest side shoots. Reisolations were identified by colony morphology, PCR, IFAS, and pathogenicity tests on tomato plantlets. Reisolation was successful from 18 days onwards, with a frequency that constantly increased in the following weeks. Samples prepared by mixing one latently infected segment with increasing numbers of healthy segments revealed a sensitivity threshold of 1: 999. This non-destructive protocol was shown to be appropriate for monitoring in the open field.

Characteristics of Ralstonia solanacearum Biovar N2 Strains in Asia

Abstract Ralstonia solanacearum biovar N2 strains isolated in Asia were compared by biochemical tests with biovar N2 strains from South America and biovar 2 (race 3) strains from Africa, America, Asia and Europe. Distinct differences were found between Asian and South American strains of biovar N2, and between Asian biovar N2 and biovar 2 strains with respect to their ability to utilize several carbon sources. Using cluster analysis based on repetitive sequence‐based polymerase chain reaction (rep‐PCR) genomic fingerprints, the Asian biovar N2 strains were divided into two groups, group 1 containing Japanese strains and group 2 containing Indonesian and Philippine strains. The fingerprints showed the genetic diversity of biovar N2 strains in Asia.

Pig slurry reduces the survival of Ralstonia solanacearum biovar 2 in soil.

The effect of added pig slurry and solarization on the survival of Ralstonia solanacearum biovar 2 strain 1609 in soil was analysed in soil microcosms and field plots. In addition, the invasion of potato plants by R. solanacearum and the development of disease symptoms were determined, as measures of induced disease suppressiveness. In untreated soil, R. solanacearum showed slow population declines in both microcosms and the field from, initially, 10(6-)10(7) to 10(3)-10(4) CFU.(g dry soil)(-1) in about 9 weeks. The suppressiveness assays of these untreated soils after this period revealed that most of the plants that were used developed wilting symptoms and (or) contained the pathogen in their lower stem parts, as shown by immunofluorescence colony staining and PCR. The addition of pig slurry resulted in a significantly lower population size of R. solanacearum as well as reduced numbers of infected and (or) diseased plants in the soil suppressiveness tests. On the other hand, solarization of soil also decreased R. solanacearum survival but did not enhance soil suppressiveness as measured by development of disease symptoms and (or) plant invasion after 9 weeks. Combined soil solarization and pig slurry addition showed an additive effect of both treatments. Healthy-looking plants, primarily from soils treated with pig slurry and solarization, incidentally revealed the latent presence of R. solanacearum in the lower stem parts. The mechanism behind the enhanced population declines and disease suppressiveness induced by pig slurry is unclear but shifts in community profiles were clearly discernible by PCR - denaturing gradient gel electrophoresis 9 weeks after pig slurry addition in the field experiment, indicating induced changes in the bacterial community structure.