Abstract
Soil-borne diseases are often less severe in organic farms, possibly because of the recruitment of beneficial microorganisms by crops. Here, the suppressiveness of organic, integrated, and conventionally managed soils to pepper blight (Phytophthora capsici) was studied in growth chamber experiments. Disease incidence was 41.3 and 34.1% lower in the soil from an organic farming system than in either the soil from the integrated or from the conventional farming systems, respectively. Beta-diversity of rhizospheric microbial communities differed among treatments, with enrichment of Bacillus, Sporosarcina, Acidobacteria Gp5, Gp6, Gp22, and Ignavibacterium by the organic soil. Cultivation-dependent analysis indicated that 50.3% of in vitro antagonists of P. capsici isolated from the rhizosphere of healthy peppers were affiliated to Bacillus. An integration of in vitro antagonists and bacterial diversity analyses indicated that Bacillus antagonists were higher in the rhizosphere of pepper treated by the organic soil. A microbial consortium of 18 in vitro Bacillus antagonists significantly increased the suppressiveness of soil from the integrated farming system against pepper blight. Overall, the soil microbiome under the long-term organic farming system was more suppressive to pepper blight, possibly owing to Bacillus antagonism in the rhizosphere. This study provided insights into microbiome management for disease suppression under greenhouse conditions.
Highlights
Increasing evidence suggests that soil microbiomes, or those associated with crops, play key roles on plant health (Gómez Expósito et al, 2017)
principle coordinate analysis (PCoA) based on BrayCurtis dissimilarities revealed that the rhizospheric bacterial community was different among treatments (Figure 2B), with more fluctuation detected by the soil in the conventional farming system (Figure 2B)
Chao1 richness in the rhizospheric bacterial community was slightly higher in treatment by the organic soils than that by soil from the conventional farming system (Figure 2C)
Summary
Increasing evidence suggests that soil microbiomes, or those associated with crops, play key roles on plant health (Gómez Expósito et al, 2017). Alterations in physicochemical properties likely shape biogeochemical interfaces in the soil where microorganisms live; such changes may affect the activities and fate of both phytopathogens (Strunnikova et al, 2015) and other microorganisms (Pronk et al, 2017). Overall, it is still unclear whether, or to what extent, changes in soil microbiome after long-term organic farming may contribute to soil-borne disease suppressiveness
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