We have reported 15 agarose gel band patterns of double-stranded RNA (dsRNA) from Trichoderma spp. We describe herein that band pattern IX in Trichoderma harzianum NFCF319, which appeared to be a single band but consisted of two dsRNAs of similar size, was identified as a novel mycovirus, designated Trichoderma harzianum partitivirus 1 (ThPV1). The larger segment (dsRNA1) of the ThPV1 genome comprised 2,289 bp and contained a single open reading frame (ORF) encoding an RNA-dependent RNA polymerase (RdRp). The smaller segment (dsRNA2) consisted of 2,245 bp with a single ORF encoding a capsid protein (CP). Evaluation of the deduced amino acid sequence and phylogenetic analysis indicated that ThPV1 is a new member of the genus Betapartitivirus in the family Partitiviridae. Curing of virus infection by single-sporing generated 31 virus-free single-spore clones. No significant differences in growth rate, conidia production, or pigmentation were observed between ThPV1-infected and -cured isogenic strains. In addition, comparison of the newly ThPV1-transmitted isolates with their ThPV1-cured parental strain showed no significant difference in colony morphology or pigmentation. However, inhibition of growth in co-cultured Pleurotus ostreatus and Rhizoctonia solani by T. harzianum was increased in ThPV1-containing strains compared with ThPV1-cured isogenic strains. Moreover, β-1,3-glucanase activity was significantly increased in the ThPV1-containing strains. However, no difference in chitinase activity was observed, suggesting that ThPV1 regulates the activity of a specific fungal enzyme.

An increasing number of novel mycoviruses have been described in fungi. Here, we report the molecular characteristics of a novel bisegmented double-stranded RNA (dsRNA) virus from the fungus Trichoderma atroviride NFCF394. We designated this mycovirus as Trichoderma atroviride partitivirus 1 (TaPV1). Electron micrographs of negatively stained, purified viral particles showed an isometric structure approximately of 30 nm in diameter. The larger segment (dsRNA1) of the TaPV1 genome comprised 2023 bp and contained a single open reading frame (ORF) encoding 614 amino acid (AA) residues of RNA-dependent RNA polymerase (RdRp). The smaller segment (dsRNA2) consisted of 2012 bp with a single ORF encoding 577 AA residues of capsid protein (CP). The phylogenetic analysis, based on deduced amino acid sequences of RdRp and CP, indicated that TaPV1 is a new member of the genus Alphapartitivirus in the family Partitiviridae. Virus-cured isogenic strains did not show significant changes in colony morphology. In addition, no changes in the enzymatic activities of β-1,3-glucanase and chitinase were observed in virus-cured strains. To the best of our knowledge, this is the first report of an Alphapartitivirus in T. atroviride.

During a survey of myxozoan parasites of common carp Cyprinus carpio in Honghu Lake, Hubei Province, China, a parasite was collected that was identified as Myxobolus dispar based on an earlier description from China. However, the small subunit ribosomal DNA of this species shared only 90 % similarity with M. dispar, instead matching M. musseliusae with 100 % identity. To resolve this apparent taxonomic conflict, the validity of M. dispar reported from China was investigated. The species encountered here and in the earlier report from China both bear spores that are notably smaller than those of M. dispar in Europe. In the present study, a mucous envelope was adhered to the posterior of many fresh spores and was observed to expand and surround the spore. This structure has never been reported from fresh spores of M. dispar. Histology showed extravascular plasmodia in the gill filaments in close contact with the cartilaginous ray of the filament, which contrasts with the plasmodia of M. dispar which develop in the arteries of the gill filaments. Phylogenetically, the current species is distinct from M. dispar, instead forming a sister group with M. musseliusae. The data presented here allow us to conclude that the species isolated is M. musseliusae and that prior reports of M. dispar in China are unsubstantiated.

We previously identified a protein spot that showed down‐regulation in the presence of Cryphonectria hypovirus 1 (CHV1) and tannic acid supplementation as a Hsp90 co‐chaperone p23 gene ( CpCop23 ). The CpCop23 ‐null mutant strain showed retarded growth with less aerial mycelia and intense pigmentation. Conidia of the CpCop23 ‐null mutant were significantly decreased and their viability was dramatically diminished. The CpCop23 ‐null mutant showed hypersensitivity to Hsp90 inhibitors. However, no differences in responsiveness were observed after exposure to other stressors such as temperature, reactive oxygen species, and high osmosis, the exception being cell wall‐disturbing agents. A severe reduction in virulence was observed in the CpCop23 ‐null mutant. Interestingly, viral transfer to the CpCop23 ‐null mutant from CHV1‐infected strain via anastomosis was more inefficient than a comparable transfer with the wild type as a result of decreased hyphal branching of the CpCop23 ‐null mutant around the peripheral region, which resulted in less fusion of the hyphae. The CHV1‐infected CpCop23 ‐null mutant exhibited recovered mycelial growth with less pigmentation and sporulation. The CHV1‐transfected CpCop23 ‐null mutant demonstrated almost no virulence, that is, even less than that of the CHV1‐infected wild type (UEP1), a further indication that reduced virulence of the mutant is not attributable exclusively to the retarded growth but rather is a function of the CpCop23 gene. Thus, this study indicates that CpCop23 plays a role in ensuring appropriate mycelial growth and development, spore viability, responses to antifungal drugs, and fungal virulence. Moreover, the CpCop23 gene acts as a host factor that affects CHV1‐infected fungal growth and maintains viral symptom development.