Bixafen Induces Programmed Cell Death in Rhizoctonia solani by Damaging Mitochondrial Integrity

Rice sheath blight caused by Rhizoctonia solani is one of the most destructive diseases of rice. Bixafen has been proposed as a promising control agent with moderate resistance risk; however, its cellular mode of action remains unclear. Therefore, this study investigated the antifungal mechanism of bixafen from the perspective of programmed cell death (PCD). Bioassays showed that bixafen strongly inhibited R. solani, with a median effective concentration (EC50) of 1.16 μg/mL. Morphologically, bixafen induced hyphae collapse, vacuolization, chromatin aggregation, and mitochondrial disruption. Transcriptome analysis further revealed that bixafen significantly altered the expression of genes involved in the tricarboxylic acid cycle and PCD pathways. In addition, bixafen, at the concentration of EC50, triggered ROS accumulation accompanied by increased malondialdehyde (MDA) levels. These oxidative effects led to mitochondrial damage, characterized by loss of membrane potential, reduced Tomm20 expression, and decreased Aco-2 activity. Subsequently, bixafen activated apoptosis, as evidenced by induction of the mitochondria-associated inducer of death (AMID), down-regulation of Bcl-2, and DNA fragmentation. Moreover, bixafen also induced autophagy by reducing p62 and increasing Beclin-1 expression, which suggests the clearance of damaged mitochondria. Collectively, these results demonstrated that bixafen induced mitochondrial-dependent apoptosis and autophagy in R. solani, which provided novel insights into its cellular antifungal mechanism and supported its potential as a PCD-targeted fungicide.