Sint-Katelijne-Waver, Belgium
Sint-Katelijne-Waver, Belgium

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Bosmans L.,Catholic University of Leuven | De Bruijn I.,Netherlands Institute of Ecology | Gerards S.,Netherlands Institute of Ecology | Moerkens R.,Research Center Hoogstraten vzw Meerle | And 10 more authors.
Frontiers in Microbiology | Year: 2017

Rhizogenic Agrobacterium biovar 1 is the causative agent of hairy root disease (HRD) in the hydroponic cultivation of tomato and cucumber causing significant losses in marketable yield. In order to prevent and control the disease chemical disinfectants such as hydrogen peroxide or hypochlorite are generally applied to sanitize the hydroponic system and/or hydroponic solution. However, effective control of HRD sometimes requires high disinfectant doses that may have phytotoxic effects. Moreover, several of these chemicals may be converted to unwanted by-products with human health hazards. Here we explored the potential of beneficial bacteria as a sustainable means to control HRD. A large collection of diverse bacterial genera was screened for antagonistic activity against rhizogenic Agrobacterium biovar 1 using the agar overlay assay. Out of more than 150 strains tested, only closely related Paenibacillus strains belonging to a particular clade showed antagonistic activity, representing the species P. illinoisensis, P. pabuli, P. taichungensis, P. tundrae, P. tylopili, P. xylanexedens, and P. xylanilyticus. Assessment of the spectrum of activity revealed that some strains were able to inhibit the growth of all 35 rhizogenic agrobacteria strains tested, while others were only active against part of the collection, suggesting a different mode of action. Preliminary characterization of the compounds involved in the antagonistic activity of two closely related Paenibacillus strains, tentatively identified as P. xylanexedens, revealed that they are water-soluble and have low molecular weight. Application of a combination of these strains in greenhouse conditions resulted in a significant reduction of HRD, indicating the great potential of these strains to control HRD. © 2017 Bosmans, De Bruijn, Gerards, Moerkens, Van Looveren, Wittemans, Van Calenberge, Paeleman, Van Kerckhove, De Mot, Rozenski, Rediers, Raaijmakers and Lievens.

Bosmans L.,Campus Management | lvarez-Prez S.,Complutense University of Madrid | Moerkens R.,Research Center Hoogstraten vzw | Wittemans L.,Research Station for Vegetable Production vzw | And 6 more authors.
FEMS Microbiology Ecology | Year: 2015

Rhizogenic Agrobacterium biovar 1 strains have been found to cause extensive root proliferation on hydroponically grown Cucurbitaceae and Solanaceae crops, resulting in substantial economic losses. As these agrobacteria live under similar ecological conditions, infecting a limited number of crops, it may be hypothesized that genetic and phenotypic variation among such strains is relatively low. In this study we assessed the phenotypic diversity as well as the phylogenetic and evolutionary relationships of several rhizogenic Agrobacterium biovar 1 strains from cucurbit and solanaceous crops. A collection of 41 isolates was subjected to a number of phenotypic assays and characterized by MLSA targeting four housekeeping genes (16S rRNA gene, recA, rpoB and trpE) and two loci from the root-inducing Ri-plasmid (part of rolB and virD2). Besides phenotypic variation, remarkable genotypic diversity was observed, especially for some chromosomal loci such as trpE. In contrast, genetic diversity was lower for the plasmid-borne loci, indicating that the studied chromosomal housekeeping genes and Ri-plasmid-borne loci might not exhibit the same evolutionary history. Furthermore, phylogenetic and network analyses and several recombination tests suggested that recombination could be contributing in some extent to the evolutionary dynamics of rhizogenic Agrobacterium populations. Finally, a genomospecies-level identification analysis revealed that at least four genomospecies may occur on cucurbit and tomato crops (G1, G3, G8 and G9). Together, this study gives a first glimpse at the genetic and phenotypic diversity within this economically important plant pathogenic bacterium. © FEMS 2015.

Bosmans L.,Catholic University of Leuven | Van Calenberge B.,Research Station for Vegetable Production vzw | Paeleman A.,Scientia | Moerkens R.,Research Center Hoogstraten vzw | And 5 more authors.
Journal of Applied Microbiology | Year: 2016

Aims: Rhizogenic Agrobacterium strains are the causative agent of hairy root disease (HRD), an increasing problem in the hydroponic cultivation of tomato and cucumber in Europe. A previous study has demonstrated that different lineages of rhizogenic agrobacteria are able to form biofilms. Although hydrogen peroxide (H2O2) is a frequently used biocide in hydroponic systems, until now its effectiveness to remove rhizogenic agrobacteria has not been unequivocally demonstrated. Therefore, the main objective of this study was to assess the efficacy of H2O2 in controlling Agrobacterium-containing biofilms. Methods and Results: Using lab-scale experiments, we found a huge variation between different rhizogenic Agrobacterium strains in EC50 values, ranging from 18·8 to 600 ppm H2O2, representing the lowest and highest concentration tested respectively. Using pilot-scale experiments in which different H2O2 concentrations were tested, treatment with 25 ppm H2O2 was found to be ineffective. In contrast, treatment with 50 ppm significantly affected a catalase-negative Agrobacterium population, while a catalase-positive population was only marginally affected. For the catalase-positive Agrobacterium population, a treatment of 100 ppm H2O2 was required to be effective. Finally, H2O2 treatment of HRD in two commercial greenhouses was monitored, and showed that the H2O2 concentration decreased considerably towards the end of the irrigation circuits. Further, a clear correlation was found between the actual concentration of H2O2 and the incidence of HRD. Conclusion: We showed that H2O2 may be effective to reduce biofilm formation by rhizogenic bacteria. Nevertheless, it was clear from our results that the required H2O2 concentration depends on the particular Agrobacterium strain(s) present in the greenhouse. Significance and Impact of the Study: This is the first study that examined the effectiveness of H2O2 to control HRD in hydroponic systems, and the effect of catalase activity on H2O2 effectiveness. Our study has direct relevance for the highly intensive horticultural sector. © 2016 The Society for Applied Microbiology

Bosmans L.,Campus Management | Paeleman A.,Scientia | Moerkens R.,Research Center Hoogstraten vzw | Wittemans L.,Research Station for Vegetable Production vzw | And 5 more authors.
European Journal of Plant Pathology | Year: 2016

Agrobacterium biovar 1 strains harbouring a Ri-plasmid cause extensive root proliferation (so-called “hairy roots”) on hydroponically grown Cucurbitaceae and Solanaceae crops, resulting in severe economic losses. The aim of this study was to develop a SYBR Green-based quantitative real-time PCR (qPCR) assay based on the rol locus of the Ri-plasmid for detection and quantification of these rhizogenic agrobacteria in hydroponic systems. The assay is designed based on all rolB sequences currently available in GenBank and developed using a collection of both target and non-target strains, and was specific for rhizogenic Agrobacterium biovar 1 strains. Based on a calibration with artificially contaminated water samples mimicking hydroponic conditions, unknown bacterial concentrations could be accurately quantified in water samples from surveys carried out in different greenhouses. Further, a detection limit was obtained of less than one cell per mL water, following filtration of a volume of 500 mL. Altogether, our results illustrate the power of this qPCR assay for routine detection of rhizogenic Agrobacterium biovar 1 strains in aqueous samples. Importantly, the assay can be used for pathogen assessment at the presymptomatic stage of infection, enabling adequate control of the disease in hydroponics before plants become infected. © 2016 Koninklijke Nederlandse Planteziektenkundige Vereniging

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