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Agronomy 2017, 7(2), 44;

Rhizoctonia solani and Bacterial Inoculants Stimulate Root Exudation of Antifungal Compounds in Lettuce in a Soil-Type Specific Manner

Department of Nutritional Crop Physiology, Institute of Crop Science (340h), University of Hohenheim, 70599 Stuttgart, Germany
Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung, 06466 Gatersleben, Germany
Department Plant Health, Leibniz Institute of Vegetable and Ornamental Crops Großbeeren/Erfurt e.V., 14979 Großbeeren, Germany
Julius Kühn-Institut-Federal Research Centre for Cultivated Plants, Institute for Epidemiology and Pathogen Diagnostics, 38104 Braunschweig, Germany
Author to whom correspondence should be addressed.
Academic Editor: Robert J. Kremer
Received: 4 May 2017 / Revised: 8 June 2017 / Accepted: 12 June 2017 / Published: 18 June 2017
(This article belongs to the Special Issue Soil Microbial Functional Groups and Plant Growth)
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Previous studies conducted on a unique field site comprising three contrasting soils (diluvial sand DS, alluvial loam AL, loess loam LL) under identical cropping history, demonstrated soil type-dependent differences in biocontrol efficiency against Rhizoctonia solani-induced bottom rot disease in lettuce by two bacterial inoculants (Pseudomonas jessenii RU47 and Serratia plymuthica 3Re-4-18). Disease severity declined in the order DS > AL > LL. These differences were confirmed under controlled conditions, using the same soils in minirhizotron experiments. Gas chromatography-mass spectrometry (GC-MS) profiling of rhizosphere soil solutions revealed benzoic and lauric acids as antifungal compounds; previously identified in root exudates of lettuce. Pathogen inoculation and pre-inoculation with bacterial inoculants significantly increased the release of antifungal root exudates in a soil type-specific manner; with the highest absolute levels detected on the least-affected LL soil. Soil type-dependent differences were also recorded for the biocontrol effects of the two bacterial inoculants; showing the highest efficiency after double-inoculation on the AL soil. However, this was associated with a reduction of shoot growth and root hair development and a limited micronutrient status of the host plants. Obviously, disease severity and the expression of biocontrol effects are influenced by soil properties with potential impact on reproducibility of practical applications. View Full-Text
Keywords: lettuce; soil microbiome; root exudates; plant health lettuce; soil microbiome; root exudates; plant health

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Windisch, S.; Bott, S.; Ohler, M.-A.; Mock, H.-P.; Lippmann, R.; Grosch, R.; Smalla, K.; Ludewig, U.; Neumann, G. Rhizoctonia solani and Bacterial Inoculants Stimulate Root Exudation of Antifungal Compounds in Lettuce in a Soil-Type Specific Manner. Agronomy 2017, 7, 44.

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