Abstract
Plant-parasitic nematodes are a major constraint on agricultural production. They significantly impede crop yield. To complete their parasitism, they need to locate, disguise, and interact with plant signals exuded in the rhizosphere of the host plant. A specific subset of the soil microbiome can attach to the surface of nematodes in a specific manner. We hypothesized that host plants recruit species of microbes as helpers against attacking nematode species, and that these helpers differ among plant species. We investigated to what extend the attached microbial species are determined by plant species, their root exudates, and how these microbes affect nematodes. We conditioned the soil microbiome in the rhizosphere of different plant species, then employed culture-independent and culture-dependent methods to study microbial attachment to the cuticle of the phytonematode Pratylenchus penetrans. Community fingerprints of nematode-attached fungi and bacteria showed that the plant species govern the microbiome associated with the nematode cuticle. Bacteria isolated from the cuticle belonged to Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Firmicutes. The isolates Microbacterium sp. i.14, Lysobacter capsici i.17, and Alcaligenes sp. i.37 showed the highest attachment rates to the cuticle. The isolates Bacillus cereus i.24 and L. capsici i.17 significantly antagonized P. penetrans after attachment. Significantly more bacteria attached to P. penetrans in microbiome suspensions from bulk soil or oat rhizosphere compared to Ethiopian mustard rhizosphere. However, the latter caused a better suppression of the nematode. Conditioning the cuticle of P. penetrans with root exudates significantly decreased the number of Microbacterium sp. i.14 attaching to the cuticle, suggesting induced changes of the cuticle structure. These findings will lead to a more knowledge-driven exploitation of microbial antagonists of plant-parasitic nematodes for plant protection.
Highlights
The root-lesion nematodes (RLN) from the genus Pratylenchus are migratory endoparasites feeding on a vast number of economical crops
As it was shown that the root exudates of different plants affect the attachment of Pasteuria spores to root-knot nematodes [21,22], and can directly affect changes in nematode gene expression [23,24], we studied whether the root exudates affect changes in the attachment of soil microbes or single bacterial isolates to P. penetrans
PCR-Denaturing gradient gelelectrophoresis (DGGE) fingerprinting of fungal internal transcribed spacers (ITS) and bacterial 16S rRNA gene fragments was used to compare the microbial communities that attached to P. penetrans in the rhizosphere of different plant species or in bulk soil
Summary
The root-lesion nematodes (RLN) from the genus Pratylenchus are migratory endoparasites feeding on a vast number of economical crops. RLN are among the most damaging plant-parasitic nematodes worldwide [1]. RLN reside inside roots or in the soil. Inside the root, they move intracellularly causing direct damage by lesions and feeding. They move intracellularly causing direct damage by lesions and feeding This leads to wilting, yellowing, necrosis, and increased susceptibility to secondary diseases [2]. While searching for a suitable host or surviving adverse conditions, these nematodes migrate through soil where they are exposed to a great variety of microorganisms. Depending on the nature of plant–nematode-microbe interactions in soil, plants may be protected by specific mutualistic microbes [3,4,5].
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