Arbuscular mycorrhizal symbiosis suppresses tomato bacterial wilt by coordinating plant systemic resistance with microbiome antagonism.

Tomato bacterial wilt, caused by Ralstonia solanacearum, is a globally devastating soil-borne disease that poses a serious threat to the sustainable development of tomato production. Arbuscular mycorrhizal fungi (AMF) are well-recognized beneficial soil microorganisms that significantly promote plant growth, enhance nutrient uptake, and improve resistance to various biotic and abiotic stresses. However, a comprehensive understanding of the potential of AMF to suppress tomato bacterial wilt is still lacking. In this study, we demonstrate that AMF inoculation remarkably reduces the disease index of bacterial wilt in tomato plants, upregulates the expression of pathogenesis-related (PR) genes, and enhances antioxidant enzyme activities, collectively strengthening systemic disease resistance. High-throughput 16 S rRNA gene sequencing revealed that AMF colonization drives substantial reassembly of the rhizosphere microbiome. Notably, AMF colonization promoted the recruitment of beneficial bacterial genera, including Bacillus and Brevibacillus, while significantly suppressing the abundance of Ralstonia. Furthermore, we isolated two Brevibacillus strains, designated AQC211 and AQC296, from the mycorrhizosphere of healthy tomato plants, both exhibited antagonistic activity against R. solanacearum in vitro. Pot experiments confirmed that inoculation with the AQC211 strain significantly reduced the incidence and severity of bacterial wilt. These findings indicate that AMF can not only directly prime plant systemic resistance but also indirectly enhance protection against bacterial wilt by shaping a disease-suppressive rhizosphere microbiome.