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.

中文翻译：

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弱寄主植物的根组织和根际土壤的代谢变化可能导致间作南方根结线虫的不同寄主状态和趋化性调节

根结线虫 (RKN) 对全球农业生产造成广泛损害。间作已被认为是对抗 RKN 的可行农业工具，但间作植物调节 RKN 寄生的机制仍不清楚。在这里，我们重点关注黄瓜-苋菜间作系统。我们使用了一系列方法，包括吸引力测定、体外RNA干扰（RNAi）、非靶向代谢组学和毛根转化，以揭示弱宿主植物调节南方根结线虫对宿主植物的趋化性和控制感染的机制。苋菜根通过破坏其趋化性表现出对南方根结线虫的直接排斥性。体外 RNAi 测定表明，Mi-flp-1和Mi-flp-18基因（编码 FMRFamide 样肽）调节南方根结线虫对黄瓜的趋化性并控制感染。此外，南方根结线虫感染刺激黄瓜和苋菜在根组织和根际土壤中积累不同的代谢物。特别是，苋菜根际土壤中特异富集的柚皮素和水杨苷抑制Mi-flp-1和Mi-flp-18的表达。此外，参与泛酸和根皮素生物合成的基因的过度表达（这两种物质都在苋菜根组织中特异性富集）延迟了黄瓜毛状根中南方根结线虫的发育。总之，我们的结果表明，不同的宿主状态和趋化性的破坏都有助于间作中南方根结线虫的抑制。