Synergistic control of rapeseed sclerotinia stem rot by Penicillium oxalicum CAD211 and biosynthesized silver nanoparticles through host defense activation and rhizosphere microbiome remodeling

Sclerotinia stem rot (SSR), caused by Sclerotinia sclerotiorum , severely threatens rapeseed production, while prolonged fungicide use raises safety concerns, highlighting the need for sustainable alternatives. Herein, an indigenous Penicillium oxalicum strain CAD211 was isolated and used to biosynthesize spherical AgNPs (12.73–25.48 nm) with potent dose-dependent antifungal activity against S. sclerotiorum . In vitro assays showed that 20 μg mL −1 AgNPs significantly inhibited mycelial growth and sclerotial germination of S. sclerotiorum . Under controlled pot conditions, the combined application of CAD211 and AgNPs achieved complete disease suppression through synergistic antagonism and restored rapeseed fresh and dry weights to 2.14- and 1.79-fold of the sole S. sclerotiorum -inoculated plants, respectively, while maintaining soil Ag content within the environmental safety threshold. Furthermore, the combined treatment reactivated the host oxidative burst, restored antioxidant enzyme activity, and ultimately contributed to an interactive network among rapeseed, S. sclerotiorum , soil nutrients and the rhizosphere microbiome. Specifically, it elevated soil organic matter (SOM) and available phosphorus (AP) contents to optimize rhizosphere nutrient supply, reshaped microbial community structure, enhanced microbial diversity, and enriched potentially beneficial taxa ( Acidovorax, Cellvibrio and Sphingomonas ). Furthermore, gene expression analysis uncovered the core dual molecular mechanism whereby the combined treatment suppressed the key S. sclerotiorum virulence genes ( SsdchA , SsPKS12 , SsPKS13 , SsTHR1 and SsSCD1 ) and activated host defense genes ( BnaA07.MKK9 and BnCYP71A13 ), while restoring the expression of growth-related genes ( BnaC04.BIL1 and BnaA10.HY5 ), thereby balancing plant immunity and growth. Overall, this study provides a potential sustainable strategy for controlling soil-borne fungal diseases under controlled pot conditions, although further field validation is needed.