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  • 1
    Language: English
    In: Frontiers in Microbiology, 01 February 2018, Vol.9
    Description: Biocontrol inoculants often show inconsistency in their efficacy at field scale and the reason for this remains often unclear. A high rhizosphere competence of inoculant strains is assumed to be a key factor for successful biocontrol effects as the biocontrol strain has to compete with the indigenous microbial community in the rhizosphere. It is known that many factors, among them plant species and soil type shape the rhizosphere microbial community composition. However, microbial community composition in the rhizosphere can also be influenced by the presence of a pathogen. We hypothesized that plant species, soil type, and a pathogen affect the rhizosphere competence of a biocontrol strain and its biocontrol effect against a soil-borne pathogen. To test the hypothesis, we used an experimental plot system with three soil types (diluvial sand, alluvial loam, loess loam) kept under similar agricultural management at the same field site for 12 years. We investigate the rhizosphere competence of Pseudomonas sp. RU47 in two plant species (potato and lettuce) and its biocontrol effect against Rhizoctonia diseases. The colonization density of a rifampicin resistant mutant of RU47 in the rhizosphere of both crops was evaluated by plate counts. Bacterial community compositions were analyzed by denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from total community DNA. The inoculant RU47 was able to colonize the rhizosphere of both model crops in a sufficient density and to reduce disease severity of black scurf on potato and bottom rot on lettuce in all three soils. DGGE indicated that RU47 affected the bacterial community composition stronger in the rhizosphere of lettuce than in the potato rhizosphere. In contrast, the effect of the pathogen Rhizoctonia solani on the bacterial community was much stronger in the rhizosphere of potato than in the lettuce rhizosphere. A significant effect of RU47 on the Pseudomonas-specific gacA fingerprints of the rhizosphere was only observed in lettuce in alluvial soil. The soil type and plant species independent biocontrol effects of RU47 and its minor influence on the indigenous bacterial community composition might be important criteria for the registration and use of RU47 as biocontrol strain.
    Keywords: Rhizoctonia Solani ; Plant Health ; Biocontrol ; Plant Disease ; Bacterial Community ; Dgge ; Biology
    E-ISSN: 1664-302X
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  • 2
    Language: English
    In: Soil Biology and Biochemistry, February 2019, Vol.129, pp.17-28
    Description: The profound intensification of agricultural practices by increased application of agro-chemicals, short crop rotations and ploughing resulted in loss of soil fertility, erosion and accumulation of soil-borne plant pathogens. Soil microbial communities are key players in ecosystem processes and are intimately linked to crop productivity and health. Thus a better understanding of how farming practices affect soil microbiota is needed in order to promote sustainable agriculture. The long-term field trial in Bernburg (Germany) established in 1992 provides a unique opportunity to assess the effects of i) the crop (maize rapeseed) preceding the actual winter wheat culture, ii) tillage practice (mouldboard plough cultivator tillage) and iii) standard nitrogen (N)-fertilization intensity with application of growth regulators and fungicides (intensive) compared to reduced N-fertilization without growth regulators and fungicides (extensive). We hypothesized that these different farming practices affect the soil prokaryotic community structures with consequences for their functional potential. Total community-DNA was extracted directly from soils sampled at wheat harvest. Illumina sequencing of 16S rRNA genes amplified from total community-DNA revealed a significant effect of tillage practice and the preceding crop on prokaryotic community structures, whereas the influence of N-fertilization intensity was marginal. A number of differentially abundant prokaryotic genera and their predicted functions between mouldboard plough cultivator tillage as well as between different preceding crops were identified. Compared to extensive N-fertilization, intensive N-fertilization resulted in higher abundances of bacterial but not of archaeal genes, that are involved in ammonia oxidation. Our data suggest that long-term farming strategies differently shape the soil prokaryotic community structure and functions, which should be considered when evaluating agricultural management strategies regarding their sustainability, soil health and crop performance.
    Keywords: Bacterial Community Composition ; Tillage ; Fertilization ; Crop Rotation ; 16s Rrna Gene Amplicon Sequencing ; Soil Microbiome ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 3
    In: Environmental Microbiology, July 2019, Vol.21(7), pp.2426-2439
    Description: Long‐term agricultural fertilization strategies gradually change soil properties including the associated microbial communities. Cultivated crops recruit beneficial microbes from the surrounding soil environment root exudates. In this study, we aimed to investigate the effects of long‐term fertilization strategies across field sites on the rhizosphere prokaryotic ( and ) community composition and plant performance. We conducted growth chamber experiments with lettuce ( L.) cultivated in soils from two long‐term field experiments, each of which compared organic versus mineral fertilization strategies. 16S rRNA gene amplicon sequencing revealed the assemblage of a rhizosphere core microbiota shared in all lettuce plants across soils, going beyond differences in community composition depending on field site and fertilization strategies. The enhanced expression of several plant genes with roles in oxidative and biotic stress signalling pathways in lettuce grown in soils with organic indicates an induced physiological status in plants. Lettuce plants grown in soils with different fertilization histories were visibly free of stress symptoms and achieved comparable biomass. This suggests a positive aboveground plant response to belowground plant–microbe interactions in the rhizosphere. Besides effects of fertilization strategy and field site, our results demonstrate the crucial role of the plant in driving rhizosphere microbiota assemblage.
    Keywords: Soil Microbiology – Physiological Aspects ; Soil Microbiology – Analysis ; Plant Genetics – Physiological Aspects ; Plant Genetics – Analysis ; Plants (Organisms) – Physiological Aspects ; Plants (Organisms) – Analysis ; Soil Ecology – Physiological Aspects ; Soil Ecology – Analysis ; Microbiota (Symbiotic Organisms) – Physiological Aspects ; Microbiota (Symbiotic Organisms) – Analysis ; RNA – Physiological Aspects ; RNA – Analysis;
    ISSN: 1462-2912
    E-ISSN: 1462-2920
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