Dothistroma septosporum and Dothistroma pini are severe foliar pathogens of conifers. They infect a broad spectrum of hosts (mainly Pinus spp.), causing chlorosis, defoliation of needles, and eventually the death of pine trees in extreme cases. Mycoviruses represent a novel and innovative avenue for controlling pathogens. To search for possible viruses hosted by Dothistroma spp. we screened a subset of isolates (20 strains of D. septosporum and one D. pini) originating from the Czech Republic, Slovenia, Italy, Austria and Ireland for viral dsRNA segments. Only five of them showed the presence of dsRNA segments. A total of 21 fungal isolates were prepared for total RNA extractions. RNA samples were pooled, and two separate RNA libraries were constructed for stranded total RNA sequencing. RNA-Seq data processing, pairwise sequence comparisons (PASC) and phylogenetic analyses revealed the presence of thirteen novel putative viruses with varying genome types: seven negative-sense single-stranded RNA viruses, including six bunya-like viruses and one new member of the order Mononegavirales; three positive-sense single-stranded RNA viruses, two of which are similar to those of the family Narnaviridae, while the genome of the third correspond to those of the family Gammaflexiviridae; and three double-stranded RNA viruses, comprising two novel members of the family Chrysoviridae and a potentially new species of gammapartitivirus. The results were confirmed with RT-PCR screening that the fungal pathogens hosted all the viruses and showed that particular fungal strains harbour multiple virus infections and that they are transmitted vertically. In this study, we described the narnavirus infecting D. pini. To our knowledge, this is the first virus discovered in D. pini.

• Keywords
• Conifer pathogens, Dothistroma needle blight (DNB), High-throughput sequencing, Total RNA sequencing, Virus diversity,
• MeSH
• Ascomycota * virology   genetics   MeSH
• Pinus * microbiology   MeSH
• RNA, Double-Stranded genetics   MeSH
• Phylogeny * MeSH
• Genome, Viral * MeSH
• Fungal Viruses * genetics   classification   isolation & purification   MeSH
• Plant Diseases * virology   microbiology   MeSH
• RNA, Viral * genetics   MeSH
• RNA Viruses genetics   classification   isolation & purification   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Czech Republic MeSH
• Italy MeSH
• Names of Substances
• RNA, Double-Stranded MeSH
• RNA, Viral * MeSH

The family Partitiviridae consists of dsRNA viruses with genome separated into two segments and encoding replicase and capsid protein only. We examined the nucleotide diversity expressed as the ratio dN/dS of nonsynonymous and synonymous substitutions, which has been calculated for 12 representative viruses of all five genera of partitiviruses. We can state that strong purifying selection works on both the RdRp and CP genes and propose that putative positive selection occurs also on the RdRp genes in two viruses. Among the 95 evaluated viruses, wherein both segments had been sequenced, 8 viruses in betapartitiviruses and 9 in alphapartitiviruses were identified as reassortment candidates because they differ extremely in their CP identity even as they are related in terms of RdRp. Furthermore, there are indications that reassortants are present among isolates of different viruses.

• Keywords
• Capsid protein, Negative/positive selection, RNA polymerase, Reassortment, Symbiosis,
• MeSH
• RNA, Double-Stranded genetics   MeSH
• Genetic Variation MeSH
• Evolution, Molecular * MeSH
• Mutation MeSH
• RNA, Viral genetics   MeSH
• RNA-Dependent RNA Polymerase genetics   MeSH
• RNA Viruses genetics   MeSH
• Capsid Proteins genetics   MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• RNA, Double-Stranded MeSH
• RNA, Viral MeSH
• RNA-Dependent RNA Polymerase MeSH
• Capsid Proteins MeSH

The European race of the ascomycetous species Gremmeniella abietina (Lagerberg) Morelet includes causal agents of shoot blight and stem canker of several conifers in Europe and North America, which are known to host a diverse virome. GaRV6 is the latest and sixth mycovirus species reported within G. abietina. Before its description, one victorivirus and one gammapartitivirus species were described in biotype A, two mitoviruses in both biotypes A and B and a betaendornavirus in biotype B. Possible phenotypic changes produced by mycoviruses on G. abietina mycelial growth have been reported in Spanish mitovirus-free and GaRV6-hosting G. abietina isolates, which had higher growth rates at the optimal temperature of 15 °C, but no other major differences have been observed between partitivirus-like dsRNA and dsRNA-free isolates. In this review, we reappraise the diversity of viruses found in G. abietina so far, and their relevance in clarifying the taxonomy of G. abietina. We also provide evidence for the presence of two new viruses belonging to the families Fusariviridae and Endornaviridae in Spanish isolates.

• Keywords
• Brunchorstia pinea, conifers, dsRNA, evolution, mycovirus, phylogeny, ssRNA,
• MeSH
• Ascomycota virology   MeSH
• Biodiversity * MeSH
• Tracheophyta microbiology   MeSH
• Fungal Viruses classification   isolation & purification   MeSH
• Plant Diseases microbiology   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Geographicals
• Europe MeSH
• North America MeSH