Dual-Stress Mitigation of Sclerotinia under Microplastic Toxicity by Nano-Selenium: Redox Balance, Pathogen Suppression, and Transcriptome Reprogramming

Microplastics (MPs) and<i>Sclerotinia sclerotiorum</i> (HP) impair plant growth; however, their combined effects and selenium nanoparticles (SeNPs) mitigation remain unclear. This study assessed SeNPs' protective role in rapeseed (<i>Brassica napus</i> L.) under combined biotic-abiotic stress using physiological, biochemical, and transcriptomic analyses. SeNPs enhanced seed germination and vigor, whereas MPs reduced the rate of growth. Co-application of SeNPs with MPs alleviated stress by improving photosynthesis, chlorophyll, nitrogen assimilation, and leaf moisture. SeNPs showed strong antifungal activity against <i>S. sclerotiorum</i> (EC₅₀ = 9.15 mg/L), resulting in hyphal distortion and reducing the secretion of cellulase, polygalacturonase, and oxalic acid. Under combined stress, SeNPs decreased ROS and lipid peroxidation, modulated H₂O₂, and enhanced antioxidant enzymes, glutathione, and PAL. Transcriptomic analysis revealed that SeNPs restored photosynthetic and defense-related gene expression, modulated MAPK signaling, and enhanced redox balance. Overall, SeNPs mitigate MP-induced phytotoxicity and fungal pathogenicity, highlighting their regulatory potential and the need to consider health risks from environmental MP exposure.