A soil column split-root experiment was designed to investigate the ability of apple replant disease (ARD)-causing agents to spread in soil. ‘M26’ apple rootstocks grew into a top layer of Control soil, followed by a barrier-free split-soil layer (Control soil/ARD soil). We observed a severely reduced root growth, concomitant with enhanced gene expression of phytoalexin biosynthetic genes and phytoalexin content in roots from ARD soil, indicating a pronounced local plant defense response. Amplicon sequencing (bacteria, archaea, fungi) revealed local shifts in diversity and composition of microorganisms in the rhizoplane of roots from ARD soil. An enrichment of operational taxonomic units affiliated to potential ARD fungal pathogens (Ilyonectria and Nectria sp.) and bacteria frequently associated with ARD (Streptomyces, Variovorax) was noted. In conclusion, our integrated study supports the idea of ARD being local and not spreading into surrounding soil, as only the roots in ARD soil were affected in terms of growth, phytoalexin biosynthetic gene expression, phytoalexin production and altered microbiome structure. This study further reinforces the microbiological nature of ARD, being likely triggered by a disturbed soil microbiome enriched with low mobility of the ARD-causing agents that induce a strong plant defense and rhizoplane microbiome dysbiosis, concurring with root damage.

中文翻译：

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根部暴露于苹果再植病害土壤会引发局部防御反应和根平面微生物群落失调

设计了一个土壤柱裂根实验，以研究导致苹果再植病 (ARD) 的物质在土壤中传播的能力。'M26' 苹果砧木长成顶层对照土壤，然后是无障碍分裂土壤层（对照土壤/ARD 土壤）。我们观察到根系生长严重减少，伴随着植物抗毒素生物合成基因的基因表达和来自 ARD 土壤的根中植物抗毒素含量的增强，表明了明显的局部植物防御反应。扩增子测序（细菌、古生菌、真菌）揭示了 ARD 土壤根部根平面中微生物多样性和组成的局部变化。注意到与潜在 ARD 真菌病原体（Ilyonectria 和 Nectria sp.）和经常与 ARD 相关的细菌（Streptomyces, Variovorax）相关的操作分类单元的丰富。总之，我们的综合研究支持 ARD 是局部的并且不会扩散到周围土壤的想法，因为只有 ARD 土壤中的根在生长、植物抗毒素生物合成基因表达、植物抗毒素产生和改变的微生物组结构方面受到影响。这项研究进一步强化了 ARD 的微生物学性质，可能是由富含 ARD 致因剂的低流动性的受干扰的土壤微生物组触发的，这些剂会导致强烈的植物防御和根际微生物组生态失调，同时伴有根部损伤。