<scp> <i>Pseudomonas chlororaphis</i> IRHB3 </scp> suppresses Soybean <scp>mosaic virus</scp> by coordinating photosynthetic protection, <scp>ROS</scp> homeostasis and hormone‐mediated immunity

Abstract BACKGROUND Soybean mosaic virus (SMV) causes substantial yield losses of soybean worldwide. Although Pseudomonas chlororaphis IRHB3 is known to promote soybean growth and suppress fungal diseases, however, its efficacy against SMV has remained unclear. This study evaluated IRHB3 impacts on SMV infection and explored the underlying physiological and molecular mechanism. RESULTS Foliar application of IRHB3 significantly reduced SMV disease index, with control efficacy of 52.69%, and decreased viral accumulation in inoculated and systemic leaves. IRHB3 also alleviated SMV‐induced growth inhibition and partially rescued yield‐related traits. Mechanistically, IRHB3 preserved chloroplast ultrastructure and mitigated photosynthetic damage, increasing net photosynthetic rate, stomatal conductance, chlorophyll contents by 29.95%, 36.11%, and 24.31%, respectively, relative to SMV‐infected plants, while also improving chlorophyll fluorescence parameters (effective quantum yield of photosystem II ( Φ PSII ), electron transport rate (ETR), non‐photochemical quenching (NPQ), and the maximum quantum yield of photosystem II (Fv/Fm)). In parallel, IRHB3 elevated antioxidant enzyme activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and reduced reactive oxygen species (ROS) and malondialdehyde (MDA) accumulation, and thereby alleviated oxidative damage. IRHB3 also up‐regulated photosynthesis‐related genes and activated defense‐associated genes in the jasmonic acid (JA) and salicylic acid (SA) signaling pathways. CONCLUSION These results indicate that IRHB3 protects soybean against SMV through coordinated effects on viral accumulation, chloroplast integrity, photosynthetic performance, redox homeostasis, and hormone‐mediated immunity, highlighting its potential as a biocontrol agent for viral diseases management in soybean. © 2026 Society of Chemical Industry.