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Dandong has become the largest strawberry production and export base in China. Strawberry black spot disease is widespread and causes significant economic losses to strawberry growers in both the growing and harvest seasons. Until now, no study has reported the presence of the Alternaria species, the pathogen of strawberry black spot disease, in Dandong, Liaoning province, China. In 2020–2022, 108 isolates were obtained from strawberry leaves with typical symptoms of strawberry black spot disease from 56 major professional growing operations. Combined with morphological and molecular characteristics, the majority of isolates were identified as A. tenuissima (78 isolates, 72.2%), which had established total supremacy, followed by A. alternata (30 isolates, 27.8%). The pathogenicity results show that A. tenuissima and A. alternata are the two main pathogenic factors of strawberry black spot disease, the disease indexes of which were designated as 49.6–100.0% and 20.4–59.5%. To our knowledge, this paper is the first to identify A. tenuissima and A. alternata as causing black spot disease in strawberries in Dandong, China. [ABSTRACT FROM AUTHOR]

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-5-1hyg (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. [ABSTRACT FROM AUTHOR]

A double-stranded RNA (dsRNA) mycovirus from the phytopathogenic fungus Alternaria alternata, which causes watermelon leaf blight, was characterized. The genome of this virus has eight dsRNA segments, ranging from 1039 bp to 2398 bp. DsRNAs 1-6 each contain a single large open reading frame (ORF), while dsRNAs 7 and 8 each dsRNA contain two ORFs. The RNA-dependent RNA polymerase (RdRp) encoded by dsRNA1 and the viral methyltransferase encoded by dsRNA3 share 97.6% and 98.9% amino acid sequence identity, respectively, with the corresponding proteins of Plasmopara viticola lesion associated polymycovirus 1. The dsRNA5-encoded proline-alanine-serine-rich protein shows 48.1% sequence identity to that of Beauveria bassiana polymycovirus 3. The proteins encoded on dsRNAs 2, 4, and 8 have 99.7%, 98.2%, and 65.1% sequence identity, respectively, to the corresponding proteins of a mycovirus identified in Alternaria sp. FA0703 (AltR1). The proteins encoded by dsRNAs 6 and 7 do not match any known proteins of mycoviruses. Phylogenetic analysis of the RdRp domain showed that the virus clustered with members of the family Polymycoviridae. Based on these characteristics, the mycovirus was identified as a polymycovirus and designated as "Alternaria alternata polymycovirus 1" (AaPmV1). This is the first report of a polymycovirus associated with A. alternata. [ABSTRACT FROM AUTHOR]

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A new double-stranded RNA (dsRNA) virus named Alternaria alternata botybirnavirus 1 (AaBRV1) was isolated from Alternaria alternata strain SD-BZF-19, a phytopathogenic fungus infecting watermelon in China. The genome of AaBRV1 consists of two dsRNA segments (dsRNAs 1 and 2), 6,130 and 5,862 bp in size, respectively. The sequence contains two putative open reading frames (ORFs) which encode two polyproteins of 1,874 and 1,784 amino acids, respectively. Nucleotide sequence comparisons revealed that the two ORFs of AaBRV1 have the highest similarity 60.3% and 56.7%, respectively, with dsRNAs 1 and 2 of Botrytis porri RNA virus 1 (BpRV1). The two polyproteins encoded by dsRNA1 and dsRNA2 shared the highest amino acid identities with the cap-pol fusion protein (60.2%) and hypothetical protein (53.7%) of BpRV1, respectively. AaBRV1 is composed of isometric particles, approximately 35 nm in diameter. Phylogenetic analysis of the RNA dependent RNA polymerase (RdRp) domain of the polyprotein revealed that AaBRV1 clusters together with members of the genus Botybirnavirus. These findings support the discovery of a new botybirnavirus in A. alternata. [ABSTRACT FROM AUTHOR]

Pectin-derived bioactive molecules have been used as elicitors of defense response and other physiological processes in plants, including harvested fruit. In the present study, the postharvest use of a pectic oligosaccharide (POS) was investigated for its ability to inhibit blue mold (Penicillium expansum) and black rot (Alternaria alternata) in artificially-inoculated kiwifruit, as well as naturally-occurring infection. Results demonstrated that POS markedly inhibited blue mold and black rot, as well as natural infection in kiwifruit, relative to untreated, control fruit. POS upregulated the expression of defense-related and antioxidant enzyme genes, and corresponding enzyme activity, including chitinase, β-1,3-glucanase and superoxide dismutase. Our data indicate that POS induces host defense responses in kiwifruit that increase resistance to postharvest decay pathogens. POS-treated fruit also maintained a higher level of fruit firmness and total phenolic compounds than untreated, control fruit, and exhibited a reduced level of weight loss. Collectively, our study indicates that the use of POS may represent a potential strategy for prolonging the postharvest quality of kiwifruit. • Pectic oligosaccharide (POS) inhibited blue mold and black rot on kiwifruit. • POS reduced natural infection incidence of kiwifruit. • POS elicited defensive response in kiwifruit at transcriptional and enzymatic levels. • POS maintained kiwifruit quality well. • POS may represent a promising treatment for preservation of harvested kiwifruit. [ABSTRACT FROM AUTHOR]

• A novel strain of Alternaria alternata chrysovirus 1 (AaCV1) from A. tenuissima SD-BZF-12 was designated as AaCV1-AT1. • It was the first chrysovirus infecting A. tenuissima. • AaCV1-AT1 can reduce colony growth rate and spore production ability of its host fungus. • AaCV1-AT1 can increase the median effective concentration of difenoconazole or tebuconazole on its host. The leaf blight caused by the genus Alternaria is one of the most epidemic diseases on watermelon, and A. tenuissima is the dominant pathogenic species in China. Mycoviruses are found ubiquitously in filamentous fungi, and an increasing number of novel mycoviruses infecting the genus Alternaria have been reported. In this study, a mycovirus from A. tenuissima strain SD-BZF-12 was identified and characterized, whose genome size was very similar with Alternaria alternata chrysovirus 1-N18 (AaCV1-N18). The dsRNA1- and dsRNA2-encoded proteins of the virus had 99 % identities with counterparts of AaCV1-N18; and the dsRNA3- and dsRNA4-encoded proteins of the virus showed the 80 % and 94 % sequence identities with proteins deduced from dsRNA4 and dsRNA3 of AaCV1-N18, respectively. Intriguingly, dsRNA5 of the virus encoded a truncated protein with 68 amino acids (aa) by comparing with 115 aa of AaCV1-N18 dsRNA5. Phylogenetic analysis of RNA-dependent RNA polymerase domain suggested that the virus clustered together with AaCV1-N18. Based on these characteristics, the mycovirus was identified to be a novel strain of AaCV1 and designated as AaCV1-AT1. In addition, no obvious differences were observed on colony morphology between AaCV1-AT1-infected and virus-cured strains of A. tenuissima ; however, AaCV1-AT1 infection reduced colony growth rate and spore production ability on host fungus, and increased the median effective concentration of difenoconazole or tebuconazole on its host. This is the first report of AaCV1-AT1 associated with A. tenuissima. [ABSTRACT FROM AUTHOR]