Alternaria alternata botybirnavirus 1 (AaBRV1) Infection Affects the Biological Characteristics of Its Host Fungus Alternaria alternata

A botybirnavirus, Alternaria alternata botybirnavirus 1 (AaBRV1), had been identified from <i>Alternaria alternata</i> strain SD-BZF-19 isolated from diseased watermelon leaves in our previous study. In the current study, AaBRV1 was eliminated from its host fungus strain SD-BZF-19 using single hyphal tip culture method combined with high-temperature treatment to obtain the AaBRV1-free strain, which was named SD-BZF-19-G14. Compared with strain SD-BZF-19-G14, following AaBRV1 infection, colony color of strain SD-BZF-19 changed, and colony growth rate, dry weight of mycelial biomass, and sensitivity to difenoconazole, fludioxonil, and tebuconazole of strain SD-BZF-19 all decreased. However, the virulence of strain SD-BZF-19 was not significantly different from strain SD-BZF-19-G14, with disease index of watermelon leaves inoculated with SD-BZF-19 and SD-BZF-19-G14 being 90.83 and 81.67, respectively. A total of 1244 differentially expressed genes (DEGs) were identified in a comparative transcriptome analysis between the two strains, SD-BZF-19 and SD-BZF-19-G14. Relative to strain SD-BZF-19, the number of upregulated and downregulated DEGs in strain SD-BZF-19-G14 was 660 and 584, respectively. Notably, Pfam database annotated that the number of DEGs related to Major Facilitator Superfamily (MFS) and Cytochrome P450 (CYP450) was 36 and 28, respectively. To our knowledge, this is the first documentation of biological characteristics induced by AaBRV1 infection in <i>A. alternata</i>.