Abstract
Soil microbial community changes imposed by the cumulative effects of root-secreted phenolic acids (PAs) promote soil-borne pathogen establishment and invasion under monoculture systems, but the disease-suppressive soil often exhibits less soil-borne pathogens compared with the conducive soil. So far, it remains poorly understood whether soil disease suppressiveness is associated with the alleviated negative effects of PAs, involving microbial degradation. Here, the long-term monoculture particularly shaped the rhizosphere microbial community, for example by the enrichment of beneficial Pseudomonas species in the suppressive soil and thus enhanced disease-suppressive capacity, however this was not observed for the conducive soil. In vitro PA-degradation assays revealed that the antagonistic Pseudomonas species, together with the Xanthomonas and Rhizobium species, significantly increased the efficiency of PA degradation compared to single species, at least partially explaining how the suppressive soil accumulated lower PA levels than the conducive soil. Pot experiments further showed that this consortium harboring the antagonistic Pseudomonas species can not only lower PA accumulation in the 15-year conducive soils, but also confer stronger Fusarium wilt disease suppression compared with a single inoculum with the antagonistic bacteria. Our findings demonstrated that understanding microbial community functions, beyond the single direct antagonism, facilitated the construction of active consortia for preventing soil-borne pathogens under intensive monoculture.
Highlights
Monoculture is the most common agricultural practice that repeatedly cultivated the same plants in soils without rotational cropping, due to limited arable lands and huge demand for foods and other economic plants
Three-week-old Chrysanthemum seedlings were transplanted into the soils, and Fusarium wilt incidence of Chrysanthemum was significantly lower in the suppressive soil after three months of culture (Figure 1a), showing only 17% disease incidence compared to about 68% disease incidence in the conducive soil (Figure 1b), indicating that the soils from the two fields differed distinctly in the suppressiveness against F. oxysporum
Comparative analyses of rhizosphere microbial community characters between the conducive and suppressive soils of Chrysanthemum were conducted, to unravel potential microbiota associated with disease suppressiveness
Summary
Monoculture is the most common agricultural practice that repeatedly cultivated the same plants in soils without rotational cropping, due to limited arable lands and huge demand for foods and other economic plants. Soil microbial community changes are responsible for pathogen establishment and invasion under monoculture systems [3,4]. Soil microbial community can protect plants from certain phytopathogens, which result in disease-suppressive soils [6,7]. Soil disease suppressiveness primarily relies on the mechanisms of nutrient competition and specific antagonism caused by soil micro flora [8]. This disease-control capability can be abolished by soil sterilization, and is transferred into the disease-conducive soil by mixing the disease-suppressive soil, indicating that the microbial community confers the property of the soil to prevent the build-up of pathogens and its invasion [9,10].
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