Rhizosphere microbes facilitate the break of chlamydospore dormancy and root colonization of rice false smut fungi

Dormant chlamydospore germination of fungal pathogens directly affects disease occurrence and severity. The rice false smut (RFS) fungus Ustilaginoidea virens produces abundant chlamydospores, but their germination process and roles in plant infection remain unclear. Here, we found that soil-borne chlamydospores are a major source of U. virens inoculum and impact RFS development. Rhizosphere microbiome analysis of high-susceptibility (HS) and low-susceptibility (LS) rice varieties revealed that HS varieties recruited bacteria from the Sphingomonadaceae family, thereby facilitating the breakdown of chlamydospore dormancy through secreted exopolysaccharides. Hyphae formed by germinating chlamydospores grew on the root surfaces, invaded the root cortex, and grew intercellularly, potentially spreading further to aboveground plant parts. Furthermore, field experiments confirmed that treating the root with 30% prothioconazole and 20% zinc thiazole effectively reduced RFS incidence. Overall, these findings enhance our understanding of chlamydospore germination in natural environments and inform strategies for disease control.