Metabolic variations in root tissues and rhizosphere soils of weak host plants potently lead to distinct host status and chemotaxis regulation of Meloidogyne incognita in intercropping.

Root-knot nematodes (RKNs) inflict extensive damage to global agricultural production. Intercropping has been identified as a viable agricultural tool for combating RKNs, but the mechanisms by which intercropped plants modulate RKN parasitism are still not well understood. Here, we focus on the cucumber-amaranth intercropping system. We used a range of approaches, including the attraction assay, in vitro RNA interference (RNAi), untargeted metabolomics, and hairy root transformation, to unveil the mechanisms by which weak host plants regulate Meloidogyne incognita chemotaxis towards host plants and control infection. Amaranth roots showed a direct repellence to M. incognita through disrupting its chemotaxis. The in vitro RNAi assay demonstrated that the Mi-flp-1 and Mi-flp-18 genes (encoding FMRFamide-like peptides) regulated M. incognita chemotaxis towards cucumber and controlled infection. Moreover, M. incognita infection stimulated cucumber and amaranth to accumulate distinct metabolites in both root tissues and rhizosphere soils. In particular, naringenin and salicin, enriched specifically in amaranth rhizosphere soils, inhibited the expression of Mi-flp-1 and Mi-flp-18. In addition, overexpression of genes involved in the biosynthesis of pantothenic acid and phloretin, both of which were enriched specifically in amaranth root tissues, delayed M. incognita development in cucumber hairy roots. Together, our results reveal that both the distinct host status and disruption of chemotaxis contribute to M. incognita inhibition in intercropping.