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A botybirnavirus, Alternaria alternata botybirnavirus 1 (AaBRV1), had been identified from Alternaria alternata 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 A. alternata. Full article

Alternaria alternata botybirnavirus 1 (AaBRV1) was isolated from a strain of Alternaria alternata, causing watermelon leaf blight in our previous research. The effect of AaBRV1 on the phenotype of its host fungus, however, was not determined. In the present study, a novel strain of AaBRV1 was identified in A. tenuissima strain TJ-NH-51S-4, the causal agent of cotton Alternaria leaf spot, and designated as AaBRV1-AT1. A mycovirus AaBRV1-AT1-free strain TJ-NH-51S-4-VF was obtained by protoplast regeneration, which eliminated AaBRV1-AT1 from the mycovirus AaBRV1-AT1-infected strain TJ-NH-51S-4. Colony growth rate, spore production, and virulence of strain TJ-NH-51S-4 were greater than they were in TJ-NH-51S-4-VF, while the sensitivity of strain TJ-NH-51S-4 to difenoconazole, as measured by the EC₅₀, was lower. AaBRV1-AT1 was capable of vertical transmission via asexual spores and horizontal transmission from strain TJ-NH-51S-4 to strain XJ-BZ-5-1_hyg (another strain of A. tenuissima) through hyphal contact in pairing cultures. A total of 613 differentially expressed genes (DEGs) were identified in a comparative transcriptome analysis between TJ-NH-51S-4 and TJ-NH-51S-4-VF. Relative to strain TJ-NH-51S-4-VF, the number of up-regulated and down-regulated DEGs in strain TJ-NH-51S-4 was 286 and 327, respectively. Notably, the expression level of one DEG-encoding cytochrome P450 sterol 14α-demethylase and four DEGs encoding siderophore iron transporters were significantly up-regulated. To our knowledge, this is the first documentation of hypervirulence and reduced sensitivity to difenoconazole induced by AaBRV1-AT1 infection in A. tenuissima. Full article