Linalool-triggered plant-soil feedback drives defense adaptation in dense maize plantings

High planting density boosts crop yields but also heightens pest and pathogen risks. How plants adapt their defenses under these conditions remains unclear. In this study, we reveal that maize enhances its defense in high-density conditions through a plant-soil feedback mechanism triggered by the leaf volatile linalool. Linalool activates jasmonate signaling in neighboring plants and promotes root exudation of benzoxazinoids, especially 2-(2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one)-β-d-glucopyranose (HDMBOA-Glc). These exudates in turn reshape the rhizosphere microbiome composition to favor growth of specific bacterial taxa that trigger broad-spectrum resistance, albeit at the cost of maize growth. This microbiome-driven feedback loop is governed by salicylic acid signaling. Our findings uncover intricate chemical signaling in high-density cropping, which is instrumental for improving soil health and designing sustainable strategies that balance the trade-off between plant growth and defense.