Soil Microbial Volatile Organic Compounds (mVOCs) of Pseudomonas fluorescens HT1 as a Novel Biocontrol Agent against the Soilborne Pathogen Sclerotium rolfsii in Coptis chinensis

Pseudomonas fluorescens HT1, isolated from the rhizosphere soil of Coptis chinensis, exhibits potent antagonistic activity against the causal agent of southern blight, Sclerotium rolfsii. This study investigated that the VOCs produced by P. fluorescens HT1 markedly inhibited mycelial growth by 88.31% and sclerotial germination by 79.17% of S. rolfsii LC1. Gas chromatography–mass spectrometry (GC–MS) analysis identified key VOC constituents, namely, chloromethyl methyl sulfide, propionic anhydride, 2-methyl-5-(methylthio)-furan, 2-decanone, 2-undecanone, isobutyl benzoate, and 3-cyclohexyl-1-propanol, demonstrating potent antifungal activity. RNA-seq analysis further revealed that the VOCs markedly altered the transcriptome of S. rolfsii LC1, specifically downregulating genes associated with growth factor and transmembrane transport. In addition, P. fluorescens HT1 successfully colonized C. chinensis tissues and enhanced host resistance against S. rolfsii. This study elucidated the biocontrol mode of action of P. fluorescens HT1 and provides a basis for developing VOC-based management strategies to manage soilborne southern blight in C. chinensis.