Abstract
The pathogen Alternaria alternata infects a variety of plants and crops, notably poplars, and results in large financial losses. Using twelve chemical fungicides for fungicide sensitivity tests (FSTs) on A. alternata, the result showed that prochloraz (PCZ), mancozeb (MZ), and fludioxonil (FLU) have potent inhibitory effects against the pathogen through different mechanisms. To investigate how the pathogen responded to fungicide-induced stress, transcriptome and physiological investigations were carried out after treatments with three fungicides at their corresponding 50% effective concentration (EC(50)) doses. The MZ treatment produced a distinct genetic response; FLU treatment produced the greatest number of differentially expressed genes (DEGs), followed by PCZ. DEGs from FLU treatment were mostly engaged in ribosome biosynthesis, those from MZ treatment in lipid and carbohydrate metabolism, and those from PCZ treatment in carbohydrate metabolism, according to Gene Ontology (GO) analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed that FLU and PCZ treatments were associated with ribosome biogenesis, whereas MZ treatment was linked to the pyruvate metabolic pathway. Collinear trend analysis indicates that MZ exhibits a unique pattern, with FLU treatment causing the most significant overexpression of genes, followed by PCZ. The six categories of 88 elevated DEGs associated with fungal resistance include tyrosinase, ATP-binding cassette (ABC) transporters, major facilitator superfamily (MFS) transporters, antioxidant and cellular resilience genes, as well as genes involved in cell wall and membrane biosynthesis. Notably, the pathways involved in the synthesis of melanin and ergosterol exhibited the strongest response to FLU. The results of a correlation analysis between physiological indices and resistance-related genes indicated that melanin content, malondialdehyde (MDA) content, and tyrosinase activity were positively correlated with the majority of resistance-related DEGs, whereas soluble protein content, superoxide dismutase (SOD) activity, and catalase (CAT) activity were negatively correlated, which is consistent with the observed trends in the measured physiological indicators. Taken together, this study provides a theoretical basis for developing more effective fungicides and chemical control strategies against A. alternata.