Beheersing van Pseudomonas syringae pathovar porri, de veroorzaker van bacterievlekkenziekte in prei, onder Nederlandse teeltomstandigheden

Verslag van veldonderzoek door verschillende partijen voor beheersing van Pseudomonas syringae pathovar porri

Pseudomonas chlororaphis and organic amendments controlling Pythium infection in tomato

To create more resilient growing systems for greenhouse crops, the efficacy of different organic amendments alone and in combination with the biocontrol strain Pseudomonas chlororaphis 4.4.1 was tested to suppress Pythium disease in tomato plants. Four independent greenhouse experiments were performed with young tomato plants in potting soil. Inoculating the pathogen Pythium aphanidermatum to the potting soil prior to sowing resulted in significant losses of tomato plants; i.e. 94–98% healthy plants in pathogen-free control compared to 43–68% healthy plants when the pathogen was added. P. chlororaphis 4.4.1 inoculations increased the number of healthy plants in the potting soil up to 80% on average; soil and seed treatment were both effective. Numbers of P. chlororaphis in the rhizosphere had increased 4 to 100 fold 3 weeks after its inoculation (qPCR detection). All compost types reduced Pythium disease in potting soil resulting in 80–95% healthy plants. Animal bone char was not effective against P. aphanidermatum, whereas with plant-based biochar there was an effect, although not significantly different from the control treatment. Phosphorous and potassium uptake by the plants were elevated by the different organic amendments. These results demonstrate the potential of the organic amendments to enhance sustainability of growing media such as potting soil by increasing its disease suppressiveness, the re-use of nutrients and replacement of peat by using organic amendments. In addition, inoculating the growing medium or tomato seeds with the biocontrol strain P. chlororaphis 4.4.1 enhanced Pythium control in the susceptible growing media

Genotypic and phenotypic variation among Lysobacter capsici strains isolated from Rhizoctonia suppressive soils

Four Gram-negative bacterial strains, recovered from clay soils cultivated with different crops in the Netherland, were subjected to a polyphasic taxonomic study in order to clarify their taxonomic status. Comparative analysis of the 16S rRNA gene sequences revealed that they belong to the genus Lysobacter and to be highly related to the type strains of L. antibioticus DSM 2044T, L. gummosus DSM 6980T, and L. capsici DSM 19286T, displaying 99.1–99.3%, 99.2–99.6% and 99.4–100% sequence similarities, respectively, to these species. The results of DNA–DNA hybridization studies unambigiously indicated that the four strains belonged to the species L. capsici. Nevertheless,DNAfingerprinting and phenotypic haracterization indicated that there was a considerable diversification and niche differentiation among the strains belonging to L. capsici. The newly identified L. capsici strains strongly inhibit Rhizoctonia solani AG2 and originate from Rhizoctonia-suppressive soils where also populations of L. antibioticus and L. gummosus were present. This is the first report of the presence of combined populations of closely related Lysobacter spp. within agricultural soil

Selection of phosphorus solubilizing bacteria with biocontrol potential for growth in phosphorus rich animal bone charcoal

Bacteria with the ability to solubilize phosphorus (P) and to improve plant health were selected and tested for growth and survival in P-rich animal bone charcoal (ABC). ABC is suggested to be suitable as a carrier for biocontrol agents, offering them a protected niche as well as delivering phosphate to plants, meanwhile re-using P from waste of the food chain. Ninety-seven bacterial isolates from different soils were tested for their potential to dissolve P from ABC. Of these isolates, 60% showed positive scores; they belonged to the genera Arthrobacter, Bacillus, Burkholderia, Collimonas, Paenibacillus, Pseudomonas, Serratia, and Streptomyces. Twelve isolates from different taxonomic groups were selected for further research on growth ability and survival in ABC, and on their potential to control plant pathogens. The highest concentrations of P were dissolved by Pseudomonas chlororaphis and Bacillus pumilus, followed by Paenibacillus polymyxa, Burkholderia pyrrocinia and three Streptomyces isolates. P. chlororaphis and P. polymyxa showed strongest growth inhibition of plant pathogenic Pythium and Fusarium sp., followed by the Streptomyces spp. isolates. Research highlights Describes a stepwise selection procedure with the aim to find beneficial bacteria that can grow in animal bone charcoal (ABC). This research was part of an EU project, with the aim to recycle and upgrade waste from the food chain. The results show that several interesting beneficial bacteria could proliferate and survive in this ABC carrier. Keywords: Biological control; Phosphorus mobilization; Antagonistic bacteria; Animal bone charcoal; Pythium aphanidermatum; Fusarium oxysporum f.sp. radicis lycopersic

Specific detection of Lysobacter enzymogenes (Christensen and Cook 1978) strain 3.1T8 with TaqMan® PCR

Aims: To develop a strain-specific TaqMan® PCR method for detecting and quantifying the biocontrol strain Lysobacter enzymogenes 3.1T8. Methods and Results: A primer–probe combination was designed on the basis of a strain-specific sequence selected using REP-PCR (repetitive extragenic palindromic-polymerase chain reaction). The specificity of this combination was demonstrated by 14 other Lysobacter strains that did not react with the selected primer–probe combination. To quantify strain 3.1T8 in cucumber root samples, a calibration curve was prepared by spiking roots with a 10-fold dilution series of the strain. Detection of the biocontrol strain 3.1T8 with this method showed that the strain survived well for 22 days on root tips as well as on older cucumber roots. Survival was higher when the strain was inoculated to younger plants. In a cucumber production system with large volumes of substrate, strain 3.1T8 was detected in high numbers on cucumber roots 3 weeks after inoculation. Conclusions: The primer–probe combination developed was strain specific, because it did not react with other strains of the same species and genus. The TaqMan® PCR method successfully quantified the inoculated biocontrol strain on cucumber roots grown in different cropping systems. Significance and Impact of the Study: The developed TaqMan® PCR method is a strain-specific real-time detection method that can be used to assess the population dynamics of L. enzymogenes strain 3.1T8 for further optimization of its biocontrol efficac

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

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 produc

The role of crop waste and soil in Pseudomonas syringae pathovar porri infection of leek (Allium porrum)

Pseudomonas syringae pv. porri, the causal agent of bacterial blight of leek, is a current threat for leek (Allium porrum) production in the Netherlands. The roles of post-harvest crop waste and plant invasion from soil in leek plant infection was investigated with the purpose to gain better understanding on the ecology and epidemiology of this pathogen. In a survey done over 167 leek fields, P. syringae pv. porri was present in 101 fields. About a tenfold higher P. syringae pv. porri average infection rate was recorded in leek plants from fields where post-harvest crop waste was returned than in those from fields where no waste was returned. P. syringae pv. porri could survive for at least 1 month in shredded plant material made from infected plants (mimicking crop waste in practice). Field experiments done over three successive years revealed that leek plants that were treated with crop waste at the nursery and production growth stages consistently showed higher infection rates than plants that remained untreated. Plants that were treated with crop waste only at one of both stages revealed intermediate infection rates. In a plant-soil microcosm study, it appeared that P. syringae pv. porri strain P55R colony numbers in the leek rhizosphere were approximately 4 orders in magnitude higher than in corresponding bulk soils. P. syringae pv. porri was shown to colonize leek roots and cells of the pathogen were also present in the leaves. It was concluded that post-harvest crop waste play an important role in the epidemiology of P. syringae pv. porri in leek production. The following route for primary infection of leek plants is proposed, from crop plant residues via soil to leek roots and plants. (C) 2010 Elsevier B.V. All rights reserved

Bodemweerbaarheid verhogen: de rol van organische stof toevoegingen en het microbioom in de bodem.

De landbouwsector kan efficiënter en duurzamer worden als schone organische reststoffen - van compost tot verenmeel - aan de bodem worden toegevoegd. Er zijn dan namelijk minder voedingsstoffen via kunstmest nodig. Maar het gebruik van organische materialen heeft meer voordelen: ze zijn een bron van voedsel voor het bodemleven en nuttige micro-organismen in de bodem kunnen de bodem weerbaarder maken tegen bepaalde ziekteverwekkers in gewassen. Dit vermindert de afhankelijkheid en het gebruik van chemische bestrijdingsmiddelen

Bodemweerbaarheid verhogen: de rol van organische stof toevoegingen en het microbioom in de bodem.

De landbouwsector kan efficiënter en duurzamer worden als schone organische reststoffen - van compost tot verenmeel - aan de bodem worden toegevoegd. Er zijn dan namelijk minder voedingsstoffen via kunstmest nodig. Maar het gebruik van organische materialen heeft meer voordelen: ze zijn een bron van voedsel voor het bodemleven en nuttige micro-organismen in de bodem kunnen de bodem weerbaarder maken tegen bepaalde ziekteverwekkers in gewassen. Dit vermindert de afhankelijkheid en het gebruik van chemische bestrijdingsmiddelen