Dimethyl Phthalate, a Major Non-Host-Specific Phytotoxin Produced by Pyrenophora chaetomioides , Drives the Pathogenic Progression in Oat Leaves

Pyrenophora chaetomioides poses a significant threat to oat crops by affecting their above-ground parts and impacting economic yield. This study assessed the toxicity of crude toxins from three regional strains of P. chaetomioides on 10 oat cultivars. The most virulent strain, NM-1, was identified for comprehensive toxin analysis and pathogenic mechanisms. Initially, 15 secondary metabolites were isolated from NM-1 through rice medium fermentation and ethyl acetate extraction, categorized into six classes: long-chain fatty acids, amides, sugars, steroids, phenyl derivatives, and nitrogenous compounds. In vitro leaf tests showed that dimethyl phthalate (DMP) and eutypinic acid (EA) have substantial phytotoxicity to oats, with relative lesion areas of 54.11% and 40.12%, respectively, and also exhibit non-host toxicity to alfalfa and Nicotiana benthamiana. Physiological assessments indicated that DMP increases leaf relative electrical conductivity from 11.08% to 69.00%, disrupting membrane integrity. Ultrastructural observations revealed mitochondrial swelling, disorganized chloroplast lamellae, and abnormal stomata. Transcriptome analysis revealed DMP's significant downregulation of 12 photosensory chlorophyll protein complex genes and altered antioxidant enzyme profiles, triggering ROS bursts and membrane lipid peroxidation, ultimately inducing programmed cell death. These insights into DMP's pathogenic pathway offer a theoretical basis for developing disease-resistant oat varieties and green pest control strategies.