Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Next generation biological control – an introduction
    Hesran, Sophie Le; Ras, Erica ; Wajnberg, Eric ; Beukeboom, Leo W. - \ 2019
    Entomologia Experimentalis et Applicata 167 (2019)7. - ISSN 0013-8703 - p. 579 - 583.
    antagonistic micro-organisms - artificial selection - biocontrol - efficacy improvement - experimental evolution - genetic variation - induced plant resistance - molecular tools - natural enemies - parasitoids - pathogens - predators
    The Nesidiocoris tenuis genome manuscript supporting data
    Pannebakker, Bart ; Ferguson, Kimberley - \ 2019
    Wageningen University & Research
    genome - biocontrol - biological control - insect - mirid - Nesidiocoris tenuis - genomics - genome assembly
    In presenting the first mirid genome, Nesidiocoris tenuis, several supporting information is made available. Following the main supplemetary material document (link), the contents are in this database: S1.2. Flow cytometry data for N. tenuis S1.3. Decontamination and potential LGT indentification S1.4. Gene list (UniProtKB list) and DAVID Reports S1.5. Full protein set S1.7. Poolseq results in full
    The Trichogramma brassicae genome, supporting data
    Pannebakker, Bart ; Ferguson, Kimberley - \ 2019
    Wageningen University & Research
    genome - biocontrol - biological control - insect - parasitoid - Trichogramma - Trichogramma brassicae - genome assembly
    In presenting the Trichogramma brassicae genome, supporting information is made available. Following the main supplemetary material document, the contents in this database entry are as follows: S1.2. Contaminated Wolbachia scaffolds from assembly v3.0 (Backbone_1176.fa and Backbone_1392.fa) S1.3. DAVID input gene list S1.5. Full Trichogramma brassicae protein set from annotation.
    The Bracon brevicornis genome, supporting data
    Pannebakker, Bart ; Ferguson, Kimberley - \ 2019
    Wageningen University & Research
    genome - biocontrol - biological control - insect - parasitoid - Trichogramma - Trichogramma brassicae - genome assembly
    In presenting the Bracon brevicornis genome, supporting information is made available. The material available in this database entry are as follows: 1. Contamination scaffolds from decontamination process (note, identified as being neither the carrier DNA of tomato, nor belonging to the group Arthropoda in a BlobTools analysis. For more details, refer to source manuscript. 2. Two sets of pseudohaplotype FASTA files, generated from decontaminated B. brevicornis reads and output from Supernova assembler.
    Genetic variation of biological control relevant traits in natural enemies: a systematic review, supporting data
    Pannebakker, Bart ; Ferguson, Kimberley - \ 2019
    Wageningen University & Research
    genome - biocontrol - biological control - parasitoid - predator - heritability - genetic variation
    This is supplementary material for a systematic review tentatively titled, "Genetic variation of biological control relevant traits in natural enemies: a systematic review" (2019). Three tables are available, and are referenced in the following manner in text: Table S1: Positive control group for search results, based on papers that fit the ideal search returns for the search term. Table S2: Combined search return hits, in unedited format received from CAB Abstracts. Table S3: Articles narrowed down to BCA, with duplicates and unavailable papers removed, prior to assessment for estimation method and traits.
    Xylem Sap Proteomics Reveals Distinct Differences Between R Gene- and Endophyte-Mediated Resistance Against Fusarium Wilt Disease in Tomato
    Lamo, Francisco J. de; Constantin, Maria E. ; Fresno, David H. ; Boeren, Sjef ; Rep, Martijn ; Takken, Frank L.W. - \ 2018
    Frontiers in Microbiology 9 (2018). - ISSN 1664-302X
    biocontrol - endophyte - exosomes - Fusarium wilt disease - NP24 - PR-5x - proteomics

    Resistance (R) genes and endophytic organisms can both protect plants against pathogens. Although the outcome of both processes is the same, little is known about the commonalities and differences between both immune responses. Here we set out to phenotypically characterize both responses in the tomato-Fusarium pathosystem, and to identify markers to distinguish these responses at the molecular level. As endophyte Fusarium oxysporum (Fo) strain Fo47 was employed, which confers protection against various pathogens, including the vascular wilt fungus F. oxysporum f.sp. lycopersici (Fol). As R-gene conferring Fol resistance, the I-2 gene of tomato (Solanum lycopersicum) was used. Fol colonizes the xylem vessels of susceptible and I-2 resistant tomato plants, but only causes disease in the former. Fol was found to colonize the vasculature of endophyte-colonized plants, and could be isolated from stems of non-diseased plants co-inoculated with Fo47 and Fol. Because the xylem vessels form the main interface between plant and pathogen, the xylem sap proteomes during R gene- and Endophyte-Mediated Resistance (RMR and EMR) were compared using label-free quantitative nLC-MS/MS. Surprisingly, both proteomes were remarkably similar to the mock, revealing only one or two differentially accumulated proteins in the respective resistant interactions. Whereas in I-2 plants the accumulation of the pathogenesis-related protein PR-5x was strongly induced by Fol, the endophyte triggered induction of both NP24, another PR-5 isoform, and of a β-glucanase in the presence of Fol. Notably, over 54% of the identified xylem sap proteins have a predicted intracellular localization, which implies that these might be present in exosomes. In conclusion, whereas both resistance mechanisms permit the pathogen to colonize the vasculature, this does not result in disease and this resistance coincides with specific induction of two distinct PR-5 isoforms and a β-glucanase.

    Data from: Modelling mobile agent-based ecosystem services using kernel weighted predictors
    Goedhart, P.W. ; Lof, M.E. ; Bianchi, F.J.J.A. ; Baveco, J.M. ; Werf, W. van der - \ 2018
    conservation planning - biocontrol - natural pest control - pollination - source-sonk dynamics - kernel - landscape - statistical model - spatial distribution - spatial extent
    1. Agriculture benefits from ecosystem services provided by mobile agents, such as biological pest control by natural enemies and pollination by bees. However, methods that can generate spatially explicit predictions and maps of these ecosystem services based on empirical data are still scarce. 2. Here we propose a generic statistical model to derive kernel functions to characterize the spatial distribution of ecosystem services provided by mobile agents. The model is similar in spirit to a generalized linear model, and uses data of landscape composition and ecosystem services assessed at target sites to estimate parameters of the kernel. The approach is tested in a simulation study and illustrated by an empirical case study on parasitism rates of the diamondback moth Plutella xylostella. 3. The simulation study shows that the scale parameter of the exponential power kernel can be estimated with limited bias, whereas estimation of the shape parameter is difficult. For the case study the model provides biologically relevant estimates for the kernel associated with parasitism of Plutella xylostella. These estimates can be used to generate ecosystem service maps for existing or planned landscapes. The case study reveals that predictions can be sensitive to the parameter values for the width and shape of the kernel, and to the link function used in the statistical model. 4. In the last two decades numerous empirical studies assessed ecosystem services at target sites and related these to the surrounding landscape. Our method can take advantage of these data by estimating underlying kernels that can be used to map the spatial distribution of ecosystem services. However, empirical data that can discriminate between alternative kernel shapes remain critical.
    Data from: Experimental evolution to increase the efficacy of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes: effects on mycelial growth and virulence
    Valero Jimenez, C.A. ; Kan, J.A.L. van; Koenraadt, C.J.M. ; Zwaan, B.J. ; Schoustra, S.E. - \ 2016
    experimental evolution - biocontrol - malaria
    Entomopathogenic fungi such as Beauveria bassiana are currently considered as a potential control agent for malaria mosquitoes. The success of such strategies depends among others on the efficacy of the fungus to kill its hosts. As B. bassiana can use various resources for growth and reproduction, increasing the dependency on mosquitoes as a nutritional source may be instrumental for reaching this goal. Passage of entomopathogenic fungi through an insect host has been shown to increase its virulence. We evaluated the virulence, fungal outgrowth, mycelial growth rate, and sporulation rate of two B. bassiana isolates (Bb1520 and Bb8028) that underwent 10 consecutive selection cycles through malaria mosquitoes (Anopheles coluzzii) using an experimental evolution approach. This cycling resulted in an altered capacity of evolved B. Bassiana lineages to grow on different substrates while maintaining the ability to kill insects. Notably, however, there were no significant changes in virulence or speed of outgrowth when comparing the evolved lineages against their un-evolved ancestors. These results suggest that fungal growth and sporulation evolved through successive and exclusive use of an insect host as a nutritional resource. We discuss the results in the light of biocontrol and provide suggestions to increase fungal virulence.
    Genome mining and metabolic profiling of the rhizosphere bacterium Pseudomonas sp. SH-C52 for antimicrobial compounds
    Voort, M. van der; Meijer, H.J.G. ; Schmidt, Y. ; Watrous, J. ; Dekkers, E. ; Mendes, R. ; Dorrestein, P.C. ; Gross, H. ; Raaijmakers, J.M. - \ 2015
    Frontiers in Microbiology 6 (2015). - ISSN 1664-302X - 14 p.
    ii secretion system - phytophthora-infestans - biological-activity - functional-analysis - mass-spectrometry - natural functions - phospholipase-d - corrugata - biocontrol - lipopeptides
    The plant microbiome represents an enormous untapped resource for discovering novel genes and bioactive compounds. Previously, we isolated Pseudomonas sp. SH-C52 from the rhizosphere of sugar beet plants grown in a soil suppressive to the fungal pathogen Rhizoctonia solani and showed that its antifungal activity is, in part, attributed to the production of the chlorinated 9-amino-acid lipopeptide thanamycin (Mendes et al., 2011). To get more insight into its biosynthetic repertoire, the genome of Pseudomonas sp. SH-C52 was sequenced and subjected to in silico, mutational and functional analyses. The sequencing revealed a genome size of 6.3 Mb and 5579 predicted ORFs. Phylogenetic analysis placed strain SH-C52 within the Pseudomonas corrugata clade. In silico analysis for secondary metabolites revealed a total of six non-ribosomal peptide synthetase (NRPS) gene clusters, including the two previously described NRPS clusters for thanamycin and the 2-amino acid antibacterial lipopeptide brabantamide. Here we show that thanamycin also has activity against an array of other fungi and that brabantamide A exhibits anti-oomycete activity and affects phospholipases of the late blight pathogen Phytophthora infestans. Most notably, mass spectrometry led to the discovery of a third lipopeptide, designated thanapeptin, with a 22-amino-acid peptide moiety. Seven structural variants of thanapeptin were found with varying degrees of activity against P. infestans. Of the remaining four NRPS clusters, one was predicted to encode for yet another and unknown lipopeptide with a predicted peptide moiety of 8-amino acids. Collectively, these results show an enormous metabolic potential for Pseudomonas sp. SH-C52, with at least three structurally diverse lipopeptides, each with a different antimicrobial activity spectrum.
    Legacy effects of anaerobic soil disinfestation on soil bacterial community composition and production of pathogen-suppressing volatiles
    Os, G.J. van; Agtmaal, M. van; Hol, G. ; Hundscheid, M.P.J. ; Runia, W.T. ; Hordijk, C. ; Boer, W. de - \ 2015
    Frontiers in Microbiology 6 (2015). - ISSN 1664-302X
    pythium root-rot - soilborne plant-diseases - microbial-populations - organic amendments - biological-control - bulbous iris - fungistasis - growth - biocontrol - diversity
    There is increasing evidence that microbial volatiles (VOCs) play an important role in natural suppression of soil-borne diseases, but little is known on the factors that influence production of suppressing VOCs. In the current study we examined whether a stress-induced change in soil microbial community composition would affect the production by soils of VOCs suppressing the plant-pathogenic oomycete Pythium. Using pyrosequencing of 16S ribosomal gene fragments we compared the composition of bacterial communities in sandy soils that had been exposed to anaerobic disinfestation (AD), a treatment used to kill harmful soil organisms, with the composition in untreated soils. Three months after the AD treatment had been finished, there was still a clear legacy effect of the former anaerobic stress on bacterial community composition with a strong increase in relative abundance of the phylum Bacteroidetes and a significant decrease of the phyla Acidobacteria, Planctomycetes, Nitrospirae, Chloroflexi, and Chlorobi. This change in bacterial community composition coincided with loss of production of Pythium suppressing soil volatiles (VOCs) and of suppression of Pythium impacts on Hyacinth root development. One year later, the composition of the bacterial community in the AD soils was reflecting that of the untreated soils. In addition, both production of Pythium-suppressing VOCs and suppression of Pythium in Hyacinth bioassays had returned to the levels of the untreated soil. GC/MS analysis identified several VOCs, among which compounds known to be antifungal, that were produced in the untreated soils but not in the AD soils. These compounds were again produced 15 months after the AD treatment. Our data indicate that soils exposed to a drastic stress can temporarily lose pathogen suppressive characteristics and that both loss and return of these suppressive characteristics and that both loss and return of these suppressive characteristics coincides with shifts in the soil bacterial community composition. Our data are supporting the suggested importance of microbial VOCs in the natural buffer of soils against diseases caused by soil-borne pathogens.
    Health of farmer-saved maize seed in north-east Nigeria
    Biemond, P.C. ; Oguntade, O. ; Stomph, T.J. ; Lava Kumar, P. ; Termorshuizen, A.J. ; Struik, P.C. - \ 2013
    European Journal of Plant Pathology 137 (2013)3. - ISSN 0929-1873 - p. 563 - 572.
    macrophomina-phaseolina - fusarium-verticillioides - charcoal rot - population - biocontrol - drought - cowpea - system
    Many Nigerian farmers depend for their seed on seed-producing farmers, the so-called informal Seed System (SS), but seed quality of the SS is unknown. Farmers planting low quality seed risk poor field emergence and low plant vigour as a result of low physiological quality or infection with seed-borne pathogens. The objective of this research was to test seed quality of maize seed from the informal SS in north-east Nigeria. A total of 46,500 seeds (93 samples of 500 seeds each) were tested for germination, off-types and seed health. Seed pathology was quantified by plating disinfected seeds onto agar, and identifying the fungi present after 3 days incubation. Twelve seed-borne pathogens were identified including Bipolaris maydis (found in 45 % of the farmer-produced samples), Botryodiplodia theobromae (97 %) and Curvularia lunata (38 %). All samples were infected with Fusarium verticillioides, with a median infection incidence of 59 % (2009) and 51 % (2010). None of the 93 samples tested passed the demands for certified seed of the National Agricultural Seeds Council (NASC) in Nigeria, in particular the maximum limit of five off-types per kg seed sample. Based on these results, seed-producing farmers must improve the health of seed. The NASC should revise the standards for off-type seeds to minimize the time spent by farmers sorting planting material.
    Biological control of aphids in the presence of thrips and their enemies
    Messelink, G.J. ; Bloemhard, C.M.J. ; Sabelis, M.W. ; Janssen, A. - \ 2013
    BioControl 58 (2013)1. - ISSN 1386-6141 - p. 45 - 55.
    intraguild predation - generalist predators - alternative prey - apparent competition - suppression - biocontrol - biodiversity - communities - parasitoids - predictions
    Generalist predators are often used in biological control programs, although they can be detrimental for pest control through interference with other natural enemies. Here, we assess the effects of generalist natural enemies on the control of two major pest species in sweet pepper: the green peach aphid Myzus persicae (Sulzer) and the western flower thrips Frankliniella occidentalis (Pergande). In greenhouses, two commonly used specialist natural enemies of aphids, the parasitoid Aphidius colemani Viereck and the predatory midge Aphidoletes aphidimyza (Rondani), were released together with either Neoseiulus cucumeris Oudemans, a predator of thrips and a hyperpredator of A. aphidimyza, or Orius majusculus (Reuter), a predator of thrips and aphids and intraguild predator of both specialist natural enemies. The combined use of O. majusculus, predatory midges and parasitoids clearly enhanced the suppression of aphids and consequently decreased the number of honeydew-contaminated fruits. Although intraguild predation by O. majusculus on predatory midges and parasitoids will have affected control of aphids negatively, this was apparently offset by the consumption of aphids by O. majusculus. In contrast, the hyperpredator N. cucumeris does not prey upon aphids, but seemed to release aphids from control by consuming eggs of the midge. Both N. cucumeris and O. majusculus did not affect rates of aphid parasitism by A. colemani. Thrips were also controlled effectively by O. majusculus. A laboratory experiment showed that adult predatory bugs feed on thrips as well as aphids and have no clear preference. Thus, the presence of thrips probably promoted the establishment of the predatory bugs and thereby the control of aphids. Our study shows that intraguild predation, which is potentially negative for biological control, may be more than compensated by positive effects of generalist predators, such as the control of multiple pests, and the establishment of natural enemies prior to pest invasions. Future work on biological control should focus on the impact of species interactions in communities of herbivorous arthropods and their enemies.
    Efficacy of four phosphate-mobilizing bacteria applied with an animal bone charcoal formulation in controlling Pythium aphanidermatum and Fusarium oxysporum f.sp. radicis lycopersici in tomato
    Postma, J. ; Clematis, F. ; Nijhuis, E.H. ; Someus, E. - \ 2013
    Biological Control 67 (2013)2. - ISSN 1049-9644 - p. 284 - 291.
    pseudomonas-chlororaphis pa23 - rock phosphate - growth promotion - nutrient-uptake - damping-off - soil - phosphorus - biocontrol - diversity - suppressiveness
    Four taxonomically different bacteria, with the ability to mobilize phosphate (P) and to colonize animal bone charcoal (ABC), were tested for their capacity to control plant pathogens. Tests were performed in the greenhouse with young tomato plants in (potting) soil and in rockwool. Plants were infested with Pythium aphanidermatum and Fusarium oxysporum f.sp. radicis-lycopersici (FORL) causing respectively damping off and crown and root rot. ABC is a porous, phosphorous containing waste product from the food industry, and was used as carrier to introduce the bacteria into the growing media. Scanning electron microscopy (SEM) pictures showed the intensive colonization of the bacteria in the interior of ABC. Of the four tested strains, Pseudomonas chlororaphis 4.4.1 was most effective in controlling the diseases. It controlled P. aphanidermatum and FORL in tomato in each of the tests. The strain appeared to be a very good root colonizer, since 1–8% of the cultural bacterial population on the tomato roots or in rhizosphere soil consisted of the introduced strain. Population densities of P. chlororaphis 4.4.1 were 0.5–5 × 107 CFU g-1 root or rhizosphere soil. Peanibacillus polymyxa 12.4.1 and Streptomyces pseudovenezuelae 13.4.2 significantly controlled P. aphanidermatum in two tests in potting soil, whereas Bacillus pumilus 4.4.2 was not effective. FORL could be controlled by B. pumilus 4.4.2 and S. pseudovenezuelae 13.4.2 in only part of the tests, whereas P. polymyxa 12.4.1 was not effective. ABC is a novel carrier for delivery of biocontrol bacteria into soil or substrate and combines biocontrol with recycling a phosphorous-rich waste product
    Evaluation of non-chemical seed treatment methods for control of Alternaria brassicicola on cabbage seeds
    Amein, T. ; Wright, S. Al; Wikstrom, M. ; Koch, E. ; Schmitt, A. ; Stephan, D. ; Jahn, M. ; Tinivella, F. ; Gullino, M.L. ; Forsberg, G. ; Werner, S. ; Wolf, J.M. van der; Groot, S.P.C. - \ 2011
    Journal of Plant Diseases and Protection 118 (2011)6. - ISSN 1861-3829 - p. 214 - 221.
    vegetable seed - carrot seed - cauliflower - antagonists - fungicides - biocontrol - hot
    Due to the lack of foliar fungicide use, the organic production of Brassica seeds free of Alternaria spp. is difficult. Therefore, effective seed treatments certified for use in organic farming are needed to eradicate or at least effec­tively reduce the seed-borne inoculum. We here report results of greenhouse and field experiments in which non-chemical seed treatments were tested for control of A. brassicicola on cabbage seeds naturally infested with the pathogen. In greenhouse experiments, significant improvements were obtained by seed treatment with some commercialised and experimental microbial biocontrol agents, an emulsion of thyme oil in water (0.1%) and by the tested physical seed treatments methods ( i.e. hot water, aerated steam and electron seed treatment). Resistance inducers tended to increase the percentage of healthy plants, but the effects were statistically not significant. Generally the combination of physical treatments with the effective agents did not result in improved performance. Positive effects on crop establishment and yield by the same treatments were also observed in field tests. Overall the results indicate that several options for non-chemical control of A. brassicicola on Brassica seeds exist that are comparable in efficacy to the chemical standard Aatiram (active ingredient thiram) used in this study. german version
    On the risk of extinction of a wild plant species through spillover of a biological control agent: Analysis of an ecosystem compartment model.
    Chalak, M. ; Hemerik, L. ; Werf, W. van der; Ruijs, A. ; Ierland, E.C. van - \ 2010
    Ecological Modelling 221 (2010)16. - ISSN 0304-3800 - p. 1934 - 1943.
    agricultural landscapes - biocontrol - insect - weed - management - dispersal - habitats - invasion - prey
    Invasive plant species can be controlled by introducing natural enemies (insect herbivores) from their native range. However, such introduction entails the risk that the introduced herbivores attack indigenous plant species in the area of introduction. Here, we study the effect of spillover of a herbivore from a managed ecosystem compartment (agriculture) to a natural compartment (non-managed) and vice versa. In the natural compartment, an indigenous plant species is attacked by the introduced herbivores, whereas another indigenous plant species, which competes with the first, is not attacked. The combination of competition and herbivory may result in extinction of the attacked wild plant species. Using a modelling approach, we determine model parameters that characterize the risk of extinction for a wild plant species. Risk factors include: (1) a high attack rate of the herbivores on the wild non-target species, (2) niche overlap expressed as strong competition between the attacked non-target species and its competitor(s), and (3) factors favouring large spillover from the managed ecosystem compartment to the natural compartment; these include (3a) a high dispersal ability, and (3b) a moderate attack rate of the introduced herbivore on the target species, enabling large resident populations of the insect herbivore in the managed compartment. The analysis thus indicates that a high attack rate on the target species, which is a selection criterion for biocontrol agents with respect to their effectiveness, also mitigates risks resulting from spillover and non-target effects. While total eradication of an invasive plant species is not possible in the one-compartment-one-plant-one-herbivore system, natural enemy spillover from a natural to a managed compartment can make the invasive weed go extinct.
    "Protected biological control"- Biological pest management in the greenhouse industry
    Pilkington, L.J. ; Messelink, G.J. ; Lenteren, J.C. van; Mottee, K. Le - \ 2010
    Biological Control 52 (2010)3. - ISSN 1049-9644 - p. 216 - 220.
    parasitoid encarsia-formosa - western flower thrips - phytoseiid predators - control agents - intraguild predation - biocontrol - populations - pesticides - cucumber - benefits
    This paper briefly describes the foundations and characteristics of biological control in protected cropping and what drivers are behind adoption of this management system within this industry. Examining a brief history of biological control in greenhouses and what makes it a successful management strategy within the industry, the authors describe the rapid growth of biological control in parts of Europe and what this may mean for the industry in other parts of the world. The reaction of the greenhouse industry to several consumer led campaigns aimed at reducing the incidence of pesticides in the marketplace may be replicated in many other parts of the world. The size and robustness of the biological control industry in greenhouses, which is a reflection of the inherent characteristics of this industry that lends itself to biological control, is strong and growing with indications that this trend will be followed in many areas of the world
    Biological control of Pythium aphanidermatum in cucumber with a combined application of Lysobacter enzymogenes strain 3.1T8 and chitosan
    Postma, J. ; Stevens, L.H. ; Wiegers, G.L. ; Davelaar, E. ; Nijhuis, E.H. - \ 2009
    Biological Control 48 (2009)3. - ISSN 1049-9644 - p. 301 - 309.
    growth-promoting rhizobacteria - damping-off disease - root-rot - bacteria - plants - rhizosphere - suppression - biocontrol - rockwool - pepper
    Pythium aphanidermatum (Edson) Fitzp., causing root and crown rot in cucumber, was successfully managed by Lysobacter enzymogenes strain 3.1T8. Greenhouse experiments were performed with cucumber plants grown in rockwool blocks up to 5 weeks with a recirculated nutrient solution. Application of L. enzymogenes 3.1T8 in combination with chitosan (the deacetylated derivative of chitin) reduced the number of diseased plants by 50–100% in four independent experiments relative to the Pythium control. Application of chitosan or the bacterial inoculant alone was not effective. Washed bacterial cells plus chitosan inhibited Pythium-induced disease, but the supernatant without bacterial cells combined with chitosan was not effective. The most effective and convenient type of commercially available chitosan was selected. Chitosan disappeared from the hydroponic system within 24 h after application, which we attribute to enzyme expression of L. enzymogenes 3.1T8 induced by the exposure to chitosan. Plate counts of the nutrient solution on a general bacterial medium showed the dominance of the inoculated strain, and an increased bacterial population growing on chitin and chitosan as single carbon source. The population density of L. enzymogenes 3.1T8 on the cucumber roots was investigated with a strain specific real-time TaqMan PCR. Highest chitosan concentrations applied (0.1 and 0.03 g/plant) resulted in the highest numbers of L. enzymogenes 3.1T8 present on roots; i.e. 108–109 cells/g root. Substantially higher numbers of bacterial cells were observed by scanning electron microscopy after application of chitosan; no morphological or other qualitative differences were found. The results indicate that addition of chitosan enhanced the biocontrol efficacy of L. enzymogenes 3.1T8; either chitosan serves as C- and N-source for the antagonist, induces antagonistic gene expression, or both. Keywords: Biological control; Lysobacter enzymogenes; Chitosan; Synergistic effect; Quantitative PCR; Root colonization
    Protozoan-induced regulation of cyclic lipopeptide biosynthesis Is an effective predation defense mechanism for Pseudomonas fluorescens
    Mazzola, M. ; Bruijn, I. de; Cohen, M.F. ; Raaijmakers, J.M. - \ 2009
    Applied and Environmental Microbiology 75 (2009)21. - ISSN 0099-2240 - p. 6804 - 6811.
    amebas acanthamoeba-castellanii - planktonic bacteria - biological-control - biofilm formation - plant-disease - putisolvin-ii - sugar-beet - soil - biocontrol - growth
    Environmental bacteria are exposed to a myriad of biotic interactions that influence their function and survival. The grazing activity of protozoan predators significantly impacts the dynamics, diversification, and evolution of bacterial communities in soil ecosystems. To evade protozoan predation, bacteria employ various defense strategies. Soil-dwelling Pseudomonas fluorescens strains SS101 and SBW25 produce the cyclic lipopeptide surfactants (CLPs) massetolide and viscosin, respectively, in a quorum-sensing-independent manner. In this study, CLP production was shown to protect these bacteria from protozoan predation as, compared to CLP-deficient mutants, strains SS101 and SBW25 exhibited resistance to grazing by Naegleria americana in vitro and superior persistence in soil in the presence of this bacterial predator. In the wheat rhizosphere, CLP-producing strains had a direct deleterious impact on the survival of N. americana. In vitro assays further showed that N. americana was three times more sensitive to viscosin than to massetolide and that exposure of strain SS101 or SBW25 to this protozoan resulted in upregulation of CLP biosynthesis genes. Enhanced expression of the massABC and viscABC genes did not require physical contact between the two organisms as gene expression levels were up to threefold higher in bacterial cells harvested 1 cm from feeding protozoans than in cells collected 4 cm from feeding protozoans. These findings document a new natural function of CLPs and highlight that bacterium-protozoan interactions can result in activation of an antipredator response in prey populations
    Evaluation of non-chemical seed treatment methods for the control of Phoma valerianellae on lamb`s lettuce seeds
    Schmitt, A. ; Koch, E. ; Stephan, D. ; Kromphardt, C. ; Jahn, M. ; Krauthausen, H.J. ; Forsberg, G. ; Werner, S. ; Amein, T. ; Wright, S.A.I. ; Tinivella, F. ; Wolf, J.M. van der; Groot, S.P.C. - \ 2009
    Journal of Plant Diseases and Protection 116 (2009)5. - ISSN 1861-3829 - p. 200 - 207.
    borne pathogens - carrot seed - germination - biocontrol - bacteria - diseases - field - soil - hot
    The aim of the present study was to identify seed treatment methods for eradicating Phoma valerianellae from lamb`s lettuce seeds in organic vegetable production. Using seeds naturally infested with the pathogen, the effect of three physical methods (hot water, aerated steam, electron treatment) and different agents of natural origin (micro-organisms, plant derived products, resistance inducers) was tested on moist filter paper, in seed trays under controlled conditions and in the field. In an initial screening, none of the tested putative resistance inducers prevented infection by P. valerianellae , while two out of seven formulated micro-organism preparations and six out of 16 experimental microbial strains were effective. When selected agents and the three physical seed treatment methods were compared in blotter and seed tray tests, the physical methods were generally the most effective treatments, while the micro-organism treatments were clearly less efficacious. However, in field experiments with the same seed lots and the same treatments, a statistically significant increase in plant stand was not obtained with any of the treatments. Combinations of the three physical treatment methods with selected non-chemical agents did not perform better than the physical treatments alone. The most effective alternative seed treatments identified in the present study, aerated steam, hot water, electron treatment and thyme oil (0.1%), can be recommended for eradication of P. valerianellae from lamb`s lettuce seeds in organic farming. Because their efficacy was generally as high as that of the chemical fungicide Aatiram (active ingredient thiram), they are also potentially suited for use in conventional vegetable production
    Functional, genetic and chemical characterization of biosurfactants produced by plant growth-promoting Pseudomonas putida 267
    Kruijt, M. ; Tran, H. ; Raaijmakers, J.M. - \ 2009
    Journal of Applied Microbiology 107 (2009)2. - ISSN 1364-5072 - p. 546 - 556.
    cyclic lipopeptide production - phytophthora-infestans - biological-control - bacillus-subtilis - biofilm formation - fluorescens dr54 - pythium-ultimum - putisolvin-ii - biocontrol - viscosinamide
    Aims: Plant growth-promoting Pseudomonas putida strain 267, originally isolated from the rhizosphere of black pepper, produces biosurfactants that cause lysis of zoospores of the oomycete pathogen Phytophthora capsici. The biosurfactants were characterized, the biosynthesis gene(s) partially identified, and their role in control of Phytophthora damping-off of cucumber evaluated. Methods and Results: The biosurfactants were shown to lyse zoospores of Phy. capsici and inhibit growth of the fungal pathogens Botrytis cinerea and Rhizoctonia solani. In vitro assays further showed that the biosurfactants of strain 267 are essential in swarming motility and biofilm formation. In spite of the zoosporicidal activity, the biosurfactants did not play a significant role in control of Phytophthora damping-off of cucumber, since both wild type strain 267 and its biosurfactant-deficient mutant were equally effective, and addition of the biosurfactants did not provide control. Genetic characterization revealed that surfactant biosynthesis in strain 267 is governed by homologues of PsoA and PsoB, two nonribosomal peptide synthetases involved in production of the cyclic lipopeptides (CLPs) putisolvin I and II. The structural relatedness of the biosurfactants of strain 267 to putisolvins I and II was supported by LC-MS and MS-MS analyses. Conclusions: The biosurfactants produced by Ps. putida 267 were identified as putisolvin-like CLPs; they are essential in swarming motility and biofilm formation, and have zoosporicidal and antifungal activities. Strain 267 provides excellent biocontrol activity against Phytophthora damping-off of cucumber, but the lipopeptide surfactants are not involved in disease suppression. Significance and Impact of the Study: Pseudomonas putida 267 suppresses Phy. capsici damping-off of cucumber and provides a potential supplementary strategy to control this economically important oomycete pathogen. The putisolvin-like biosurfactants exhibit zoosporicidal and antifungal activities, yet they do not contribute to biocontrol of Phy. capsici and colonization of cucumber roots by Ps. putida 267. These results suggest that Ps. putida 267 employs other, yet uncharacterized, mechanisms to suppress Phy. capsici.
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