Hypovirulence and Double-Stranded RNA in Botrytis cinerea

A Mycovirus Representing a Novel Lineage and a Mitovirus of Botrytis cinerea Co-Infect a Basidiomycetous Fungus, Schizophyllum commune

Strain IBc-114 was isolated from a gray mold lesion and was identified as the fungus Schizophyllum commune. In this strain, two mycoviruses, Schizophyllum commune RNA virus 1 (ScRV1, C_AA053475.1) and Botrytis cinerea mitovirus 9 strain IBc-114 (BcMV9/IBc-114, C_AA053476.1), were isolated and characterized. ScRV1 has flexuous filamentous particles about 20 ± 2.1 nm in diameter and 1000 ± 94.2 nm in length. The genome of ScRV1 is 7370 nt in length and contains two open reading frames (ORFs) which encode a polyprotein and a coat protein, respectively. The polyprotein has 1967 aa, including a helicase domain and an RdRp domain which has the highest identity of 28.21% with that of Entomophthora benyvirus E (EbVE). The coat protein has 241 aa which is mostly phylogenetically close to the coat proteins of Alphatetraviridae. Based on the phylogenetic analysis of ScRV1 and viruses selected, ScRV1 might represent a new family (temporarily named Mycobenyviridae) of the order Hepelivirales. The genome of BcMV9/IBc-114 that infects S. commune is 2729 nt in length and has only one ORF encoding an RdRp protein with 719 aa. BcMV9/IBc-114 has the highest identity of 98.61% with Botrytis cinerea mitovirus 9 (BcMV9) (MT089704). ScRV1, but not BcMV9/IBc-114, has certain effects on the host growth of S. commune. Furthermore, BcMV9/IBc-114 has been demonstrated to replicate in the ascomycetous fungi Botrytis cinerea and Sclerotinia sclerotiorum, and it negatively affects the growth and pathogenicity of B. cinerea, but it does not affect S. sclerotiorum. This is the first report of mycoviruses in S. commune and cross-phyla transmission of mitovirus in nature.

A novel ormycovirus isolated from the plant-pathogenic fungus Fusarium graminearum

In this study, we identified a novel mycovirus, Fusarium graminearum ormycovirus 1 (FgOV1), from the pathogenic fungus Fusarium graminearum. The virus has two RNA segments, RNA1 and RNA2, with lengths of 2,591 and 1,801 nucleotides, respectively, excluding the polyA tail. Each segment contains a single open reading frame (ORF). The ORF in RNA1 encodes an RNA-dependent RNA polymerase, while the ORF in RNA2 encodes a hypothetical protein. Phylogenetic analysis showed that FgOV1 belongs to the gammaormycovirus clade, whose members are related to betaormycoviruses. To our knowledge, this is the first report of an ormycovirus in Fusarium graminearum.

Mycologists and Virologists Align: Proposing Botrytis cinerea for Global Mycovirus Studies

Mycoviruses are highly genetically diverse and can significantly change their fungal host's phenotype, yet they are generally under-described in genotypic and biological studies. We propose Botrytis cinerea as a model mycovirus system in which to develop a deeper understanding of mycovirus epidemiology including diversity, impact, and the associated cellular biology of the host and virus interaction. Over 100 mycoviruses have been described in this fungal host. B. cinerea is an ideal model fungus for mycovirology as it has highly tractable characteristics-it is easy to culture, has a worldwide distribution, infects a wide range of host plants, can be transformed and gene-edited, and has an existing depth of biological resources including annotated genomes, transcriptomes, and isolates with gene knockouts. Focusing on a model system for mycoviruses will enable the research community to address deep research questions that cannot be answered in a non-systematic manner. Since B. cinerea is a major plant pathogen, new insights may have immediate utility as well as creating new knowledge that complements and extends the knowledge of mycovirus interactions in other fungi, alone or with their respective plant hosts. In this review, we set out some of the critical steps required to develop B. cinerea as a model mycovirus system and how this may be used in the future.

Characterization of two novel fusariviruses co-infecting a single isolate of phytopathogenic fungus Botrytis cinerea

A wide diversity of mycoviruses has been reported from Botrytis species, some with the potential to suppress the pathogenic abilities of this fungus. Considering their importance, this study was devised to find potential hypovirulence-associated mycoviruses found in Botrytis cinerea strains isolated from Pakistani strawberry fields. Here we report the complete genome characterization of two fusariviruses co-infecting a single isolate of phytopathogenic fungus B. cinerea (Kst14a). The viral genomes were sequenced by deep sequencing using total RNA fractions of the Kst14a isolate. The identified viruses were tentatively named Botrytis cinerea fusarivirus 9 (BcFV9) and Botrytis cinerea fusarivirus 3a (BcFV3a). Both viruses had a single-segmented (ssRNA) genome having a size of 6424 and 8370 nucleotides encoding two discontinuous open reading frames (ORFs). ORF-1 of both mycoviruses encodes for a polyprotein having a conserved domain of RNA-dependent RNA polymerase (RdRP) and a helicase domain (Hel) which function in RNA replication, while ORF2 encodes a hypothetical protein with an unknown function, respectively. Phylogenetic analysis indicated that BcFV9 made a clade with the genus Alphafusarivirus and BcFV3a fall in the genus Betafusarivirus in the family Fusariviridae. To our knowledge, this is the first report of two fusariviruses identified in isolates of B. cinerea from Pakistan. Both mycoviruses successfully transfected to a compatible strain of B. cinerea (Mst11). A comparison of virus-free (VF) and virus-infected (VI) isogenic lines showed the presence of these viruses was causing hypovirulence in infected strains. Virus-infected strains also had a small lesion size while testing the pathogenicity via apple assay.

Possible Biological Control of Ash Dieback Using the Mycoparasite Hymenoscyphus Fraxineus Mitovirus 2

Invasive fungal diseases represent a major threat to forest ecosystems worldwide. As the application of fungicides is often unfeasible and not a sustainable solution, only a few other control options are available, including biological control. In this context, the use of parasitic mycoviruses as biocontrol agents of fungal pathogens has recently gained particular attention. Since the 1990s, the Asian fungus Hymenoscyphus fraxineus has been causing lethal ash dieback across Europe. In the present study, we investigated the biocontrol potential of the mitovirus Hymenoscyphus fraxineus mitovirus 2 (HfMV2) previously identified in Japanese populations of the pathogen. HfMV2 could be successfully introduced via co-culturing into 16 of 105 HfMV2-free isolates. Infection with HfMV2 had contrasting effects on fungal growth in vitro, from cryptic to detrimental or beneficial. Virus-infected H. fraxineus isolates whose growth was reduced by HfMV2 showed overall a lower virulence on ash (Fraxinus excelsior) saplings as compared with their isogenic HfMV2-free lines. The results suggest that mycoviruses exist in the native populations of H. fraxineus in Asia that have the potential for biological control of ash dieback in Europe. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

The good, the bad and the cryptic: The multifaceted roles of mycoviruses and their potential applications for a sustainable agriculture

Mycoviruses are natural inhabitants of fungi and have been identified in almost all fungal taxonomic groups. Mycoviruses that infect phytopathogenic fungi are now becoming a hot research area due to their potential for the biocontrol of important plant pathogens. But, before considering a mycovirus for biocontrol, we should be fully aware of the effects it induces in a fungal host and its interactions with other viruses, fungal strains and even the host plants. Mycoviral infections are generally associated with different effects, ranging from hypovirulence to hypervirulence, but they can often be cryptic (latent infections). The cryptic lifestyle has been associated to many mycoviruses, but thanks to growing knowledge we are now aware that it is often associated to axenic conditions while the real effects can be observed only in nature. Other mycoviruses either promote (hypervirulence) or (hypovirulence) fungal pathogenicity by a strong impact on the fungal physiology or by blocking the production of toxins or effectors. Finally, indirect effects of mycoviral infections can also be provided to the plant that hosts the fungal isolate, highlighting not only their potential as direct biocontrol agents but also as priming agents for plant resilience to biotic and abiotic stresses. This review provides a broad overview of mycoviral interactions both with their hosts and with other mycoviruses, highlighting the most interesting examples. In contrast to what has been observed to date, we believe that the collective availability of these data will not only improve our understanding of mycoviruses, but also increase our confidence in considering them as alternative measures against fungal diseases to improve the sustainable production of food and feed commodities.

A Novel Mitovirus PsMV2 Facilitates the Virulence of Wheat Stripe Rust Fungus

Wheat stripe rust, caused by the obligate biotrophic fungus Puccinia striiformis f. sp. tritici (Pst), seriously affects wheat production. Here, we report the complete genome sequence and biological characterization of a new mitovirus from P. striiformis strain GS-1, which was designated as "Puccinia striiformis mitovirus 2" (PsMV2). Genome sequence analysis showed that PsMV2 is 2658 nt in length with an AU-rich of 52.3% and comprises a single ORF of 2348 nt encoding an RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis indicated that PsMV2 is a new member of the genus Unuamitovirus within the family Mitoviridae. In addition, PsMV2 multiplied highly during Pst infection and it suppresses programmed cell death (PCD) triggered by Bax. Silencing of PsMV2 in Pst by barley stripe mosaic virus (BSMV)-mediated Host Induced Gene Silencing (HIGS) reduced fungal growth and decreased pathogenicity of Pst. These results indicate PsMV2 promotes host pathogenicity in Pst. Interestingly, PsMV2 was detected among a wide range of field isolates of Pst and may have coevolved with Pst in earlier times. Taken together, our results characterized a novel mitovirus PsMV2 in wheat stripe rust fungus, which promotes the virulence of its fungal host and wide distribution in Pst which may offer new strategies for disease control.

Fungal Viruses Unveiled: A Comprehensive Review of Mycoviruses

Mycoviruses (viruses of fungi) are ubiquitous throughout the fungal kingdom and are currently classified into 23 viral families and the genus botybirnavirus by the International Committee on the Taxonomy of Viruses (ICTV). The primary focus of mycoviral research has been on mycoviruses that infect plant pathogenic fungi, due to the ability of some to reduce the virulence of their host and thus act as potential biocontrol against these fungi. However, mycoviruses lack extracellular transmission mechanisms and rely on intercellular transmission through the hyphal anastomosis, which impedes successful transmission between different fungal strains. This review provides a comprehensive overview of mycoviruses, including their origins, host range, taxonomic classification into families, effects on their fungal counterparts, and the techniques employed in their discovery. The application of mycoviruses as biocontrol agents of plant pathogenic fungi is also discussed.

Viral cross-class transmission results in disease of a phytopathogenic fungus

Interspecies transmission of viruses is a well-known phenomenon in animals and plants whether via contacts or vectors. In fungi, interspecies transmission between distantly related fungi is often suspected but rarely experimentally documented and may have practical implications. A newly described double-strand RNA (dsRNA) virus found asymptomatic in the phytopathogenic fungus Leptosphaeria biglobosa of cruciferous crops was successfully transmitted to an evolutionarily distant, broad-host range pathogen Botrytis cinerea. Leptosphaeria biglobosa botybirnavirus 1 (LbBV1) was characterized in L. biglobosa strain GZJS-19. Its infection in L. biglobosa was asymptomatic, as no significant differences in radial mycelial growth and pathogenicity were observed between LbBV1-infected and LbBV1-free strains. However, cross-species transmission of LbBV1 from L. biglobosa to infection in B. cinerea resulted in the hypovirulence of the recipient B. cinerea strain t-459-V. The cross-species transmission was succeeded only by inoculation of mixed spores of L. biglobosa and B. cinerea on PDA or on stems of oilseed rape with the efficiency of 4.6% and 18.8%, respectively. To investigate viral cross-species transmission between L. biglobosa and B. cinerea in nature, RNA sequencing was carried out on L. biglobosa and B. cinerea isolates obtained from Brassica samples co-infected by these two pathogens and showed that at least two mycoviruses were detected in both fungal groups. These results indicate that cross-species transmission of mycoviruses may occur frequently in nature and result in the phenotypical changes of newly invaded phytopathogenic fungi. This study also provides new insights for using asymptomatic mycoviruses as biocontrol agent.

Construction and Characterization of a Botrytis Virus F Infectious Clone

Botrytis virus F (BVF) is a positive-sense, single-stranded RNA (+ssRNA) virus within the Gammaflexiviridae family of the plant-pathogenic fungus Botrytis cinerea. In this study, the complete sequence of a BVF strain isolated from B. cinerea collected from grapevine fields in Spain was analyzed. This virus, in this work BVF-V448, has a genome of 6827 nt in length, excluding the poly(A) tail, with two open reading frames encoding an RNA dependent RNA polymerase (RdRP) and a coat protein (CP). The 5′- and 3′-terminal regions of the genome were determined by rapid amplification of cDNA ends (RACE). Furthermore, a yet undetected subgenomic RNA species in BVF-V448 was identified, indicating that the CP is expressed via 3′ coterminal subgenomic RNAs (sgRNAs). We also report the successful construction of the first BVF full-length cDNA clone and synthesized in vitro RNA transcripts using the T7 polymerase, which could efficiently transfect two different strains of B. cinerea, B05.10 and Pi258.9. The levels of growth in culture and virulence on plants of BVF-V448 transfected strains were comparable to BVF-free strains. The infectious clones generated in this work provide a useful tool for the future development of an efficient BVF foreign gene expression vector and a virus-induced gene silencing (VIGS) vector as a biological agent for the control of B. cinerea.

Molecular and Biological Characterization of the First Mymonavirus Identified in Fusarium oxysporum

We characterized a negative sense single-stranded RNA mycovirus, Fusarium oxysporum mymonavirus 1 (FoMyV1), isolated from the phytopathogenic fungus Fusarium oxysporum. The genome of FoMyV1 is 10,114 nt, including five open reading frames (ORFs1–5) that are non-overlapping and linearly arranged. The largest, ORF5, encodes a large polypeptide L containing a conserved regions corresponding to Mononegavirales RNA-dependent RNA polymerase and mRNA-capping enzyme region V; the putative functions of the remaining four ORFs are unknown. The L protein encoded by ORF5 shared a high amino acid identity of 65% with that of Hubei rhabdo-like virus 4, a mymonavirus that associated with arthropods. However, the L protein of FoMyV1 also showed amino acid similarity (27–36%) with proteins of mynonaviruses that infect the phytopathogenic fungi Sclerotinia sclerotiorum and Botrytis cineaea. Phylogenetic analysis based on L protein showed that FoMyV1 is clustered with the members of the genus Hubramonavirus in the family Mymonaviridae. Moreover, we found that FoMyV1 could successfully transfer by hyphal anastomosis to a virus-free strain. FoMyV1 reduced the vegetative growth and conidium production of its fungal host but did not alter its virulence. To the best of our knowledge, this is not only the first mymonavirus described in the species F. oxysporum, but also the first Hubramonavirus species found to infect a fungus. However, the incidence of FoMyV1 infections in the tested F. oxysporum strains was only 1%.

Four Novel Mycoviruses from the Hypovirulent Botrytis cinerea SZ-2-3y Isolate from Paris polyphylla: Molecular Characterisation and Mitoviral Sequence Transboundary Entry into Plants

A hypovirulent SZ-2-3y strain isolated from diseased Paris polyphylla was identified as Botrytis cinerea. Interestingly, SZ-2-3y was coinfected with a mitovirus, two botouliviruses, and a 3074 nt fusarivirus, designated Botrytis cinerea fusarivirus 8 (BcFV8); it shares an 87.2% sequence identity with the previously identified Botrytis cinerea fusarivirus 6 (BcFV6). The full-length 2945 nt genome sequence of the mitovirus, termed Botrytis cinerea mitovirus 10 (BcMV10), shares a 54% sequence identity with Fusarium boothii mitovirus 1 (FbMV1), and clusters with fungus mitoviruses, plant mitoviruses and plant mitochondria; hence BcMV10 is a new Mitoviridae member. The full-length 2759 nt and 2812 nt genome sequences of the other two botouliviruses, named Botrytis cinerea botoulivirus 18 and 19 (BcBoV18 and 19), share a 40% amino acid sequence identity with RNA-dependent RNA polymerase protein (RdRp), and these are new members of the Botoulivirus genus of Botourmiaviridae. Horizontal transmission analysis showed that BcBoV18, BcBoV19 and BcFV8 are not related to hypovirulence, suggesting that BcMV10 may induce hypovirulence. Intriguingly, a partial BcMV10 sequence was detected in cucumber plants inoculated with SZ-2-3y mycelium or pXT1/BcMV10 agrobacterium. In conclusion, we identified a hypovirulent SZ-2-3y fungal strain from P. polyphylla, coinfected with four novel mycoviruses that could serve as potential biocontrol agents. Our findings provide evidence of cross-kingdom mycoviral sequence transmission.

Characterization of a Novel Mitovirus Infecting Melanconiella theae Isolated From Tea Plants

A dsRNA segment was identified in the fungus Melanconiella theae isolated from tea plants. The complete dsRNA sequence, determined by random cloning together with RACE protocol, is 2,461 bp in length with an AU-rich content (62.37%) and comprises a single ORF of 2,265-nucleotides encoding an RNA-dependent RNA-polymerase (RdRp, 754 amino acids in size). The terminus sequences can fold into predicted stable stem-loop structures. A BLASTX and phylogenetic analysis revealed the dsRNA genome shows similarities with the RdRp sequences of mitoviruses, with the highest identity of 48% with those of grapevine-associated mitovirus 20 and Colletotrichum fructicola mitovirus 1. Our results reveal a novel member, tentatively named Melanconiella theae mitovirus 1 (MtMV1), belongs to the family Mitoviridae. MtMV1 is capsidless as examined by transmission electron microscope, efficiently transmitted through conidia as 100 conidium-generated colonies were analyzed, and easily eliminated by hyphal tipping method combined with green-leaf tea powder. MtMV1 has a genomic sequence obviously divergent from those of most members in the family Mitoviridae and some unique characteristics unreported in known members. This is the first report of a mycovirus infecting Melanconiella fungi to date.

Molecular Characterization of the First Alternavirus Identified in Fusarium oxysporum

A novel mycovirus named Fusarium oxysporum alternavirus 1(FoAV1) was identified as infecting Fusarium oxysporum strain BH19, which was isolated from a fusarium wilt diseased stem of Lilium brownii. The genome of FoAV1 contains four double-stranded RNA (dsRNA) segments (dsRNA1, dsRNA 2, dsRNA 3 and dsRNA 4, with lengths of 3.3, 2.6, 2.3 and 1.8 kbp, respectively). Additionally, dsRNA1 encodes RNA-dependent RNA polymerase (RdRp), and dsRNA2- dsRNA3- and dsRNA4-encoded hypothetical proteins (ORF2, ORF3 and ORF4), respectively. A homology BLAST search, along with multiple alignments based on RdRp, ORF2 and ORF3 sequences, identified FoAV1 as a novel member of the proposed family "Alternaviridae". Evolutionary relation analyses indicated that FoAV1 may be related to alternaviruses, thus dividing the family "Alternaviridae" members into four clades. In addition, we determined that dsRNA4 was dispensable for replication and may be a satellite-like RNA of FoAV1-and could perhaps play a role in the evolution of alternaviruses. Our results provided evidence for potential genera establishment within the proposed family "Alternaviridae". Additionally, FoAV1 exhibited biological control of Fusarium wilt. Our results also laid the foundations for the further study of mycoviruses within the family "Alternaviridae", and provide a potential agent for the biocontrol of diseases caused by F. oxysporum.

Novel Mycoviruses Discovered in the Mycovirome of a Necrotrophic Fungus

Botrytis cinerea is one of the most important plant-pathogenic fungus. Products based on microorganisms can be used in biocontrol strategies alternative to chemical control, and mycoviruses have been explored as putative biological agents in such approaches. Here, we have explored the mycovirome of B. cinerea isolates from grapevine of Italy and Spain to increase the knowledge about mycoviral diversity and evolution, and to search for new widely distributed mycoviruses that could be active ingredients in biological products to control this hazardous fungus. A total of 248 B. cinerea field isolates were used for our metatranscriptomic study. Ninety-two mycoviruses were identified: 62 new mycoviral species constituting putative novel viral genera and families. Of these mycoviruses, 57 had a positive-sense single-stranded RNA (ssRNA) genome, 19 contained a double-stranded RNA (dsRNA) genome, 15 had a negative-sense ssRNA genome, and 1 contained a single-stranded DNA (ssDNA) genome. In general, ssRNA mycoviruses were widely distributed in all sampled regions, the ssDNA mycovirus was more frequently found in Spain, and dsRNA mycoviruses were scattered in some pools of both countries. Some of the identified mycoviruses belong to clades that have never been found associated with Botrytis species: Botrytis-infecting narnaviruses; alpha-like, umbra-like, and tymo-like ssRNA+ mycoviruses; trisegmented ssRNA- mycovirus; bisegmented and tetrasegmented dsRNA mycoviruses; and finally, an ssDNA mycovirus. Among the results obtained in this massive mycovirus screening, the discovery of novel bisegmented viruses, phylogenetically related to narnaviruses, is remarkable.IMPORTANCE The results obtained here have expanded our knowledge of mycoviral diversity, horizontal transfers, and putative cross-kingdom events. To date, this study presents the most extensive and wide diversity collection of mycoviruses infecting the necrotrophic fungus B. cinerea The collection included all types of mycoviruses, with dsRNA, ssRNA+, ssRNA-, and ssDNA genomes, most of which were discovered here, and some of which were previously reported as infecting B. cinerea or other plant-pathogenic fungi. Some of these mycoviruses are reported for the first time here associated with B. cinerea, as a trisegmented ssRNA- mycovirus and as an ssDNA mycovirus, but even more remarkablly, we also describe here four novel bisegmented viruses (binarnaviruses) not previously described in nature. The present findings significantly contribute to general knowledge in virology and more particularly in the field of mycovirology.

Divergent RNA viruses in Macrophomina phaseolina exhibit potential as virocontrol agents

Macrophomina phaseolina is an important necrotrophic phytopathogenic fungus and cause extensive damage in many oilseed crops. Twelve M.phaseolina isolates with diverse biological phenotypes were selected for a high-throughput sequencing-based metatranscriptomic and bioinformatics analysis to identify viruses infecting M.phaseolina. The analysis identified 40 partial or nearly complete viral genome segments, 31 of which were novel viruses. Among these viral sequences, 43% of the viral genomes were double-stranded RNA (dsRNA), 47% were positive single-stranded RNA (ssRNA+), and the remaining 10% were negative sense-stranded RNA (ssRNA−). The 40 viruses showed affinity to 13 distinct viral lineages, including Bunyavirales (four viruses), Totiviridae (three viruses), Chrysoviridae (five viruses), Partitiviridae (four viruses), Hypoviridae (one virus), Endornaviridae (two viruses), Tombusviridae (three viruses), Narnaviridae (one virus), Potyviridae (one virus), Bromoviridae (one virus), Virgaviridae (six viruses), ‘Fusagraviridae’ (five viruses), and Ourmiavirus (four viruses). Two viruses are closely related to two families, Potyviridae and Bromoviridae, which previously contained no mycovirus species. Moreover, nine novel viruses associated with M.phaseolina were identified in the family Totiviridae, Endornaviridae, and Partitiviridae. Coinfection with multiple viruses is prevalent in M.phaseolina, with each isolate harboring different numbers of viruses, ranging from three to eighteen. Furthermore, the effects of the viruses on the fungal host were analyzed according to the biological characteristics of each isolate. The results suggested that M.phaseolina hypovirus 2, M.phaseolina fusagravirus virus 1-5 (MpFV1-5), M.phaseolina endornavirus 1-2 (MpEV1-2), M.phaseolina ourmia-like virus 1-3 (MpOLV1-3), M.phaseolina mitovirus 4 (MpMV4), and M.phaseolina mycobunyavirus 1-4 (MpMBV1-4) were only detected in hypovirulent isolates. Those viruses associated with hypovirulence might be used as biological control agents as an environmentally friendly alternative to chemical fungicides. These findings considerably expand our understanding of mycoviruses in M.phaseolina and unvailed the presence of a huge difference among viruses in isolates from different hosts in distant geographical regions. Together, the present study provides new knowledge about viral evolution and fungus-virus coevolution.

Four Novel Botourmiaviruses Co-Infecting an Isolate of the Rice Blast Fungus Magnaporthe oryzae

Via virome sequencing, six viruses were detected from Magnaporthe oryzae strains YC81-2, including one virus in the family Tombusviridae, one virus in the family Narnaviridae and four viruses in the family Botourmiaviridae. Since the RNA-dependent RNA polymerase (RdRp) of one botourmiavirus show the highest identity (79%) with Magnaporthe oryzae ourmia-like virus 1 (MOLV1), the virus that was grouped into the genus Magoulivirus was designated as Magnaporthe oryzae botourmiavirus 2 (MOBV2). The three other novel botourmiaviruses were selected for further study. The complete nucleotide sequences of the three botourmiaviruses were determined. Sequence analysis showed that virus 1, virus 2, and virus 3 were 2598, 2385, and 2326 nts in length, respectively. The variable 3' untranslated region (3'-UTR) and 5'-UTR of each virus could be folded into a stable stem-loop secondary structure. Each virus consisted of a unique ORF encoding a putative RdRp. The putative proteins with a conserved GDD motif of RdRp showed the highest sequence similarity to RdRps of viruses in the family Botourmiaviridae. Phylogenetic analysis demonstrated that these viruses were three distinct novel botourmiaviruses, clustered into the Botourmiaviridae family but not belonging to any known genera of this family. Thus, virus 1, virus 2, and virus 3 were designated as Magnaporthe oryzae botourmiavirus 5, 6, and 7 (MOBV5, MOBV6, and MOBV7), respectively. Our results suggest that four distinct botourmiaviruses, MOBV2, MOBV5, MOBV6, and MOBV7, co-infect a single strain of Magnaporthe oryzae, and MOBV5, MOBV6, and MOBV7 are members of three unclassified genera in the family Botourmiaviridae.

Cryphonectria nitschkei chrysovirus 1 with unique molecular features and a very narrow host range

Cryphonectria nitschkei chrysovirus 1 (CnCV1), was described earlier from an ascomycetous fungus, Cryphonectria nitschkei strain OB5/11, collected in Japan; its partial sequence was reported a decade ago. Complete sequencing of the four genomic dsRNA segments revealed molecular features similar to but distinct from previously reported members of the family Chrysoviridae. Unique features include the presence of a mini-cistron preceding the major large open reading frame in each genomic segment. Common features include the presence of CAA repeats in the 5'-untranslated regions and conserved terminal sequences. CnCV1-OB5/11 could be laterally transferred to C. nitschkei and its relatives C. radicalis and C. naterciae via coculturing, virion transfection and protoplast fusion, but not to fungal species other than the three species mentioned above, even within the genus Cryphonectria, suggesting a very narrow host range. Phenotypic comparison of a few sets of CnCV1-infected and -free isogenic strains showed symptomless infection in new hosts.

Investigating the Pea Virome in Germany-Old Friends and New Players in the Field(s)

Peas are an important legume for human and animal consumption and are also being used as green manure or intermediate crops to sustain and improve soil condition. Pea production faces constraints from fungal, bacterial, and viral diseases. We investigated the virome of German pea crops over the course of three successive seasons in different regions of pea production to gain an overview of the existing viruses. Pools from 540 plants, randomly selected from symptomatic and asymptomatic peas, and non-crop plants surrounding the pea fields were used for ribosomal RNA-depleted total RNA extraction followed by high-throughput sequencing (HTS) and RT-PCR confirmation. Thirty-five different viruses were detected in addition to nine associated nucleic acids. From these viruses, 25 are classified as either new viruses, novel strains or viruses that have not been reported previously from Germany. Pea enation mosaic virus 1 and 2 were the most prevalent viruses detected in the pea crops, followed by pea necrotic yellow dwarf virus (PNYDV) and turnip yellows virus which was also found also in the surrounding non-legume weeds. Moreover, a new emaravirus was detected in symptomatic peas in one region for two successive seasons. Most of the identified viruses are known to be aphid transmissible. The results revealed a high virodiversity in the German pea fields that poses new challenges to diagnosticians, researchers, risk assessors and policy makers, as the impact of the new findings are currently unknown.

A Survey of Mycoviral Infection in Fusarium spp. Isolated from Maize and Sorghum in Argentina Identifies the First Mycovirus from Fusarium verticillioides

Mycoviruses appear to be widespread in Fusarium species worldwide. The aim of this work was to identify mycoviral infections in Fusarium spp., isolated from maize and sorghum grown in Argentina, and to estimate their potential effects on the pathogenicity and toxigenesis of the host fungus towards maize. Mycoviruses were identified in 2 out of 105 isolates analyzed; Fusarium verticillioides strain Sec505 and Fusarium andiyazi strain 162. They were characterized as members of the genus Mitovirus by high-throughput sequencing and sequence analysis. The F. verticillioides mitovirus was a novel mycovirus whereas the F. andiyazi mitovirus was found to be a new strain of a previously identified mitovirus. We have named these mitoviruses, Fusarium verticillioides mitovirus 1 (FvMV1) and Fusarium andiyazi mitovirus 1 strain 162 (FaMV1-162). To our knowledge, FvMV1 is the first mycovirus reported as naturally infecting F. verticillioides, the major causal agent of ear rot and fumonisin producer in corn. Both mitoviruses exhibited 100% vertical transmission rate to microconidia. The Fa162 strain infected with FaMV1-162 did not show phenotypic alterations. In contract, F. verticillioides Sec505 infected with FvMV1 showed increased virulence as well as microconidia and fumonisin-B1 production, compared with two uninfected strains. These results suggest that FvMV1 could have a role in modulating F. verticillioides pathogenicity and toxin production worth further exploring.

Molecular characterization of a novel botoulivirus from the phytopathogenic fungus Sclerotinia minor

In this study, the complete genomic sequence of a novel botoulivirus (Sclerotinia minor botoulivirus 1, SmBV1) from the phytopathogenic fungus Sclerotinia minor strain LC45 was determined. The genome of SmBV1 is 2,882 nucleotides in length and contains a single large open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp). Phylogenetic analysis showed that SmBV1 clustered with the botoulivirus clade within the family Botourmiaviridae. This is the first report of a botoulivirus in S. minor.

Metatranscriptomic reconstruction reveals RNA viruses with the potential to shape carbon cycling in soil

Viruses impact nearly all organisms on Earth, with ripples of influence in agriculture, health, and biogeochemical processes. However, very little is known about RNA viruses in an environmental context, and even less is known about their diversity and ecology in soil, 1 of the most complex microbial systems. Here, we assembled 48 individual metatranscriptomes from 4 habitats within a planted soil sampled over a 22-d time series: Rhizosphere alone, detritosphere alone, rhizosphere with added root detritus, and unamended soil (4 time points and 3 biological replicates). We resolved the RNA viral community, uncovering a high diversity of viral sequences. We also investigated possible host organisms by analyzing metatranscriptome marker genes. Based on viral phylogeny, much of the diversity was Narnaviridae that may parasitize fungi or Leviviridae, which may infect Proteobacteria. Both host and viral communities appear to be highly dynamic, and rapidly diverged depending on experimental conditions. The viral and host communities were structured based on the presence of root litter. Clear temporal dynamics by Leviviridae and their hosts indicated that viruses were replicating. With this time-resolved analysis, we show that RNA viruses are diverse, abundant, and active in soil. When viral infection causes host cell death, it may mobilize cell carbon in a process that may represent an overlooked component of soil carbon cycling.

Defective RNA of a Novel Mycovirus with High Transmissibility Detrimental to Biocontrol Properties of Trichoderma spp

Trichoderma species are a group of fungi which is widely distributed in major terrestrial ecosystems; they are also commonly used as biocontrol agents for many plant diseases. A virus, namely Trichoderma harzianum hypovirus 1 (ThHV1), was identified in T. harzianum isolate T-70, and also infected isolate T-70D, together with its defective RNA (ThHV1-S). The ThHV1 genome possessed two Open Reading Frames (ORFs), namely ORF1 and ORF2. The start codon of ORF2 overlapped with the stop codon of ORF1 in a 43 nt long region. The polypeptide encoded by ORF2 of ThHV1 shared sequence similarities with those of betahypoviruses, indicating that ThHV1 is a novel member of Hypoviridea. Isolate T-70D, carrying both ThHV1 and ThHV1-S, showed abnormal biological properties, notably a decreased mycoparasitism ability when compared with isolate T-70. Both ThHV1 and ThHV1-S could be vertically transmitted to conidia and horizontally transmitted to T. harzianum isolate T-68 and T. koningiopsis T-51. The derivative strains carrying both ThHV1 and ThHV1-S showed decreased mycoparasitism ability, whereas strains carrying ThHV1 alone were normal, indicating that ThHV1-S is closely associated with the decreased mycoparasitism ability of T. harzianum isolate T-70D. ThHV1 was widely detected in isolates of T. harzianum, T. koningiopsis and T. atroviride originating from soil of China. Therefore, viruses in fungal biocontrol agents may also be a factor associated with the stability of their application.

Extreme Diversity of Mycoviruses Present in Isolates of Rhizoctonia solani AG2-2 LP From Zoysia japonica From Brazil

Zoysia japonica, in Brazil, is commonly infected by Rhizoctonia solani (R. solani) in humid and cool weather conditions. Eight isolates of R. solani, previously identified as belonging to the AG2-2 LP anastomosis group, isolated from samples from large path symptoms, were collected from three counties in São Paulo state (Brazil) and investigated for the presence of mycoviruses. After detection of double-strand RNA (dsRNA) in all samples, RNA_Seq analysis of ribosomal RNA-depleted total RNA from in vitro cultivated mycelia was performed. Forty-seven partial or complete viral unique RNA dependent-RNA polymerase (RdRp) sequences were obtained with a high prevalence of positive sense ssRNA viruses. Sequences were sufficiently different from the first match in BLAST searches suggesting that they all qualify as possible new viral species, except for one sequence showing an almost complete match with Rhizoctonia solani dsRNA virus 2, an alphapartitivirus. Surprisingly four large contigs of putative viral RNA could not be assigned to any existing clade of viruses present in the databases, but no DNA was detected corresponding to these fragments confirming their viral replicative nature. This is the first report on the occurrence of mycoviruses in R. solani AG2-2 LP in South America.

Comparative Transcriptomic Analysis of MAPK-Mediated Regulation of Sectorization in Cryphonectria parasitica

Fungal sectorization is a complex trait that is still not fully understood. The unique phenotypic changes in sporadic sectorization in mutants of CpBck1, a mitogen-activated protein kinase kinase kinase (MAPKKK) gene, and CpSlt2, a mitogen-activated protein kinase (MAPK) gene, in the cell wall integrity pathway of the chestnut blight fungus Cryphonectria parasitica have been previously studied. Although several environmental and physiological factors cause this sectoring phenotype, genetic variants can also impact this complex morphogenesis. Therefore, RNA sequencing analysis was employed to identify candidate genes associated with sectorization traits and understand the genetic mechanism of this phenotype. Transcriptomic analysis of CpBck1 and CpSlt2 mutants and their sectored progeny strains revealed a number of differentially expressed genes (DEGs) related to various cellular processes. Approximately 70% of DEGs were common between the wild-type and each of CpBck1 and CpSlt2 mutants, indicating that CpBck1 and CpSlt2 are components of the same MAPK pathway, but each component governs specific sets of genes. Functional description of the DEGs between the parental mutants and their sectored progenies revealed several key pathways, including the biosynthesis of secondary metabolites, translation, amino acid metabolism, and carbohydrate metabolism; among these, pathways for secondary metabolism and translation appeared to be the most common pathway. The results of this comparative study provide a better understanding of the genetic regulation of sector formation and suggest that complex several regulatory pathways result in interplays between secondary metabolites and morphogenesis.

Mitovirus and Mitochondrial Coding Sequences from Basal Fungus Entomophthora muscae

Fungi constituting the Entomophthora muscae species complex (members of subphylum Entomophthoromycotina, phylum Zoopagamycota) commonly kill their insect hosts and manipulate host behaviors in the process. In this study, we made use of public transcriptome data to identify and characterize eight new species of mitoviruses associated with several different E. muscae isolates. Mitoviruses are simple RNA viruses that replicate in host mitochondria and are frequently found in more phylogenetically apical fungi (members of subphylum Glomeromyoctina, phylum Mucoromycota, phylum Basidiomycota and phylum Ascomycota) as well as in plants. E. muscae is the first fungus from phylum Zoopagomycota, and thereby the most phylogenetically basal fungus, found to harbor mitoviruses to date. Multiple UGA (Trp) codons are found not only in each of the new mitovirus sequences from E. muscae but also in mitochondrial core-gene coding sequences newly assembled from E. muscae transcriptome data, suggesting that UGA (Trp) is not a rarely used codon in the mitochondria of this fungus. The presence of mitoviruses in these basal fungi has possible implications for the evolution of these viruses.

Molecular Characterization of a Debilitation-Associated Partitivirus Infecting the Pathogenic Fungus Aspergillus flavus

The opportunistic human pathogenic fungus Aspergillus flavus is known to be infected with mycoviruses. In this study, we report a novel mycovirus A. flavus partitivirus 1 (AfPV1) that was originally isolated from the abnormal colonial morphology isolate LD-3-8 of A. flavus. AfPV1 has spherical virus-like particles about 40 nm in diameter, and three double-stranded RNA (dsRNA) segments (dsRNA1, 2, and 3 with lengths of 1.7, 1.4, and 1.1 kbp, respectively) were packaged in the virions. dsRNA1, dsRNA2, and dsRNA3 each contained a single open reading frame and potentially encoded 62, 42, and 32 kDa proteins, respectively. The dsRNA1 encoded protein shows similarity to the RNA-dependent RNA polymerase (RdRp) of partitiviruses, and the dsRNA2 product has no significant similarity to any other capsid protein (CP) in the GenBank databases, beside some homology with the hypothetical "capsid" protein of a few partitiviruses. The dsRNA3 encodes a protein with no similarity to any protein in the GenBank database. SDS-PAGE and polypeptide mass fingerprint-mass spectrum (PMF-MS) analyses indicated that the CP of the AfPV1 was encoded by dsRNA2. Phylogenetic analysis showed that the AfPV1 and relative viruses were found in an unclassified group inside the Partitiviridae family. AfPV1 seems to result in debilitation symptoms, but had no significant effects to murine pathogenicity. These findings provide new insights into the partitiviruses taxonomy and the interactions between viruses and A. flavus.

Investigation of Host Range of and Host Defense against a Mitochondrially Replicating Mitovirus

Mitoviruses (genus Mitovirus, family Narnaviridae) are mitochondrially replicating viruses that have the simplest positive-sense RNA genomes of 2.2 to 4.4 kb with a single open reading frame (ORF) encoding an RNA-dependent RNA polymerase. Cryphonectria parasitica mitovirus 1 (CpMV1) from U.S. strain NB631 of the chestnut blight fungus, Cryphonectria parasitica, was the first virus identified as a mitochondrially replicating virus. Despite subsequent discovery of many other mitoviruses from diverse fungi, no great advances in understanding mitovirus biology have emerged, partly because of the lack of inoculation methods. Here we developed a protoplast fusion-based protocol for horizontal transmission of CpMV1 that entailed fusion of recipient and donor protoplasts, hyphal anastomosis, and single-conidium isolation. This method allowed expansion of the host range to many other C. parasitica strains. Species within and outside the family Cryphonectriaceae, Cryphonectria radicalis and Valsa ceratosperma, also supported the replication of CpMV1 at a level comparable to that in the natural host. No stable maintenance of CpMV1 was observed in Helminthosporium victoriae PCR-based haplotyping of virus-infected fungal strains confirmed the recipient mitochondrial genetic background. Phenotypic comparison between CpMV1-free and -infected isogenic strains revealed no overt effects of the virus. Taking advantage of the infectivity to the standard strain C. parasitica EP155, accumulation levels were compared among antiviral RNA silencing-proficient and -deficient strains in the EP155 background. Comparable accumulation levels were observed among these strains, suggesting the avoidance of antiviral RNA silencing by CpMV1, which is consistent with its mitochondrial replication. Collectively, the results of study provide a foundation to further explore the biology of mitoviruses.IMPORTANCE Capsidless mitoviruses, which are ubiquitously detected in filamentous fungi, have the simplest RNA genomes of 2.2 to 4.4 kb, encoding only RNA-dependent RNA polymerase. Despite their simple genomes, detailed biological characterization of mitoviruses has been hampered by their mitochondrial location within the cell, posing challenges to their experimental introduction and study. Here we developed a protoplast fusion-based protocol for horizontal transfer of the prototype mitovirus, Cryphonectria parasitica mitovirus 1 (CpMV1), which was isolated from strain NB631 of the chestnut blight fungus (Cryphonectria parasitica), a model filamentous fungus for studying virus-host interactions. The host range of CpMV1 has been expanded to many different strains of C. parasitica and different fungal species within and outside the Cryphonectriaceae. Comparison of CpMV1 accumulation among various RNA silencing-deficient and -competent strains showed clearly that the virus was unaffected by RNA silencing. This study provides a solid foundation for further exploration of mitovirus-host interactions.

Molecular Characterization of a Novel Endornavirus Conferring Hypovirulence in Rice Sheath Blight Fungus Rhizoctonia solani AG-1 IA Strain GD-2

The complete sequence and genome organization of a novel Endornavirus from the hypovirulent strain GD-2 of Rhizoctonia solani AG-1 IA, the causal agent of rice sheath blight, were identified using a deep sequencing approach and it was tentatively named as Rhizoctonia solani endornavirus 1 (RsEV1). It was composed of only one segment that was 19,936 bp in length and was found to be the longest endornavirus genome that has been reported so far. The RsEV1 genome contained two open reading frames (ORFs): ORF1 and ORF2. ORF1 contained a glycosyltransferase 1 domain and a conserved RNA-dependent RNA polymerase domain, whereas ORF2 encoded a conserved hypothetical protein. Phylogenetic analysis revealed that RsEV1 was phylogenetically a new endogenous RNA virus. A horizontal transmission experiment indicated that RsEV1 could be transmitted from the host fungal strain GD-2 to a virulent strain GD-118P and resulted in hypovirulence in the derivative isogenic strain GD-118P-V1. Metabolomic analysis showed that 32 metabolites were differentially expressed between GD-118P and its isogenic hypovirulent strain GD-118P-V1. The differential metabolites were mainly classified as organic acids, amino acids, carbohydrates, and the intermediate products of energy metabolism. Pathway annotation revealed that these 32 metabolites were mainly involved in pentose and glucuronate interconversions and glyoxylate, dicarboxylate, starch, and sucrose metabolism, and so on. Taken together, our results showed that RsEV1 is a novel Endornavirus, and the infection of virulent strain GD-118P by RsEV1 caused metabolic disorders and resulted in hypovirulence. The results of this study lay a foundation for the biocontrol of rice sheath blight caused by R. solani AG1-IA.

A Victorivirus and Two Novel Mitoviruses Co-Infected the Plant Pathogen Nigrospora oryzae

Three dsRNAs, in sizes of approximately 2.5⁻5 kbp, were detected in the plant pathogenic fungus Nigrospora oryzae strain CS-7.5-4. Genomic analysis showed that the 5.0 kb dsRNA was a victorivirus named as Nigrospora oryzae victorivirus 2 (NoRV2). The genome of NoRV2 was 5166 bp in length containing two overlapping open reading frames (ORFs), ORF1 and ORF2. ORF1 was deduced to encode a coat protein (CP) showing homology to the CPs of viruses belonging to the Totiviridae family. The stop codon of ORF1 and the start codon of ORF2 were overlapped by the tetranucleotide sequence AUGA. ORF2 was predicted to encode an RNA-dependent RNA polymerase (RdRp), which was highly similar to the RdRps of victoriviruses. Virus-like particle examination demonstrated that the genome of NoRV2 was solely encapsidated by viral particles with a diameter of approximately 35 nm. The other two dsRNAs that were less than 3.0 kb were predicted to be the genomes of two mitoviruses, named as Nigrospora oryzae mitovirus 1 (NoMV1) and Nigrospora oryzae mitovirus 2 (NoMV2). Both NoMV1 and NoMV2 were A-U rich and with lengths of 2865 and 2507 bp, respectively. Mitochondrial codon usage inferred that each of the two mitoviruses contains a major large ORF encoding a mitoviral RdRp. Horizontal transfer experiments showed that the NoMV1 and NoMV2 could be cotransmitted horizontally via hyphal contact to other virus-free N. oryzae strains and causes phenotypic change to the recipient, such as an increase in growth rate. This is the first report of mitoviruses in N. oryzae.

A Novel Partitivirus in the Hypovirulent Isolate QT5-19 of the Plant Pathogenic Fungus Botrytis cinerea

A pink isolate (QT5-19) of Botrytis cinerea was compared with three gray isolates of B. cinerea for growth and morphogenesis on potato dextrose agar (PDA), and for pathogenicity on tobacco. A double-stranded (ds) RNA mycovirus infecting QT5-19 was identified based on its genome feature and morphology of the virus particles. The results showed that QT5-19 grew rapidly and established flourishing colonies as the gray isolates did. However, it is different from the gray isolates, as it failed to produce conidia and sclerotia asthe gray isolates did. QT5-19 hardly infected tobacco, whereas the gray isolates aggressively infected tobacco. Two dsRNAs were detected in QT5-19, dsRNA 1 and dsRNA 2, were deduced to encode two polypepetides with homology to viral RNA-dependent RNA polymerase (RdRp) and coat protein (CP), respectively. Phylogenetic analysis of the amino acid sequences of RdRp and CP indicated that the two dsRNAs represent the genome of a novel partitivirus in the genus Alphapartitivirus, designated here as Botrytis cinerea partitivirus 2 (BcPV2). BcPV2 in QT5-19 was successfully transmitted to the three gray isolates through hyphal contact. The resulting BcPV2-infected derivatives showed rapid growth on PDA with defects in conidiogenesis and sclerogenesis, and hypovirulence on tobacco. This study suggests that BcPV2 is closely associated with hypovirulence of B. cinerea.

Sclerotinia minor Endornavirus 1, a Novel Pathogenicity Debilitation-Associated Mycovirus with a Wide Spectrum of Horizontal Transmissibility

Sclerotinia minor is a phytopathogenic fungus causing sclerotinia blight on many economically important crops. Here, we have characterized the biological and molecular properties of a novel endornavirus, Sclerotinia minor endornavirus 1 (SmEV1), isolated from the hypovirulent strain LC22 of S. minor. The genome of SmEV1 is 12,626 bp long with a single, large open reading frame (ORF), coding for a putative protein of 4020 amino acids. The putative protein contains cysteine-rich region (CRR), viral methyltransferase (MTR), putative DEXDc, viral helicase (Hel), and RNA-dependent RNA polymerase (RdRp) domains. The putative protein and the conserved domains are phylogenetically related to endornaviruses. SmEV1 does not contain a site-specific nick characteristic of most previously described endornaviruses. Hypovirulence and associated traits of strain LC22 and SmEV1 were readily cotransmitted horizontally via hyphal contact to isolates of different vegetative compatibility groups of S. minor. Additionally, SmEV1 in strain LC22 was found capable of being transmitted vertically through sclerotia. Furthermore, mycelium fragments of hypovirulent strain LC22 have a protective activity against attack by S. minor. Taken together, we concluded that SmEV1 is a novel hypovirulence-associated mycovirus with a wide spectrum of transmissibility, and has potential for biological control (virocontrol) of diseases caused by S. minor.

Novel Mitoviruses and a Unique Tymo-Like Virus in Hypovirulent and Virulent Strains of the Fusarium Head Blight Fungus, Fusarium boothii

Hypovirulence of phytopathogenic fungi are often conferred by mycovirus(es) infections and for this reason many mycoviruses have been characterized, contributing to a better understanding of virus diversity. In this study, three strains of Fusarium head blight fungus (Fusarium boothii) were isolated from Ethiopian wheats as dsRNA-carrying strains: hypovirulent Ep-BL13 (>10, 3 and 2.5 kbp dsRNAs), and virulent Ep-BL14 and Ep-N28 (3 kbp dsRNA each) strains. The 3 kbp-dsRNAs shared 98% nucleotide identity and have single ORFs encoding a replicase when applied to mitochondrial codon usage. Phylogenetic analysis revealed these were strains of a new species termed Fusarium boothii mitovirus 1 in the genus Mitovirus. The largest and smallest dsRNAs in Ep-BL13 appeared to possess single ORFs and the smaller was originated from the larger by removal of its most middle part. The large dsRNA encoded a replicase sharing the highest amino acid identity (35%) with that of Botrytis virus F, the sole member of the family Gammaflexiviridae. Given that the phylogenetic placement, large genome size, simple genomic and unusual 3′-terminal RNA structures were far different from members in the order Tymovirales, the virus termed Fusarium boothii large flexivirus 1 may form a novel genus and family under the order.

Molecular Characterization and Geographic Distribution of a Mymonavirus in the Population of Botrytis cinerea

Here, we characterized a negative single-stranded (-ss)RNA mycovirus, Botrytis cinerea mymonavirus 1 (BcMyV1), isolated from the phytopathogenic fungus Botrytis cinerea. The genome of BcMyV1 is 7863 nt in length, possessing three open reading frames (ORF1⁻3). The ORF1 encodes a large polypeptide containing a conserved mononegaviral RNA-dependent RNA polymerase (RdRp) domain showing homology to the protein L of mymonaviruses, whereas the possible functions of the remaining two ORFs are still unknown. The internal cDNA sequence (10-7829) of BcMyV1 was 97.9% identical to the full-length cDNA sequence of Sclerotinia sclerotiorum negative stranded RNA virus 7 (SsNSRV7), a virus-like contig obtained from Sclerotinia sclerotiorum metatranscriptomes, indicating BcMyV1 should be a strain of SsNSRV7. Phylogenetic analysis based on RdRp domains showed that BcMyV1 was clustered with the viruses in the family Mymonaviridae, suggesting it is a member of Mymonaviridae. BcMyV1 may be widely distributed in regions where B. cinerea occurs in China and even over the world, although it infected only 0.8% of tested B. cinerea strains.

Biological Control of Botrytis cinerea: Interactions with Native Vineyard Yeasts from Washington State

Native yeasts are of increasing interest to researchers, grape growers, and vintners because of their potential for biocontrol activity and their contributions to the aroma, flavor, and mouthfeel qualities of wines. To assess biocontrol activity, we tested 11 yeasts from Washington vineyards, representing isolates of Candida saitoana, Curvibasidium pallidicorallinum, Metschnikowia chrysoperlae, M. pulcherrima, Meyerozyma guilliermondii, Saccharomyces cerevisiae, and Wickerhamomyces anomalus, for ability to colonize Thompson Seedless grape berries, inhibit the growth of Botrytis cinerea in vitro, and suppress disease symptoms on isolated berries. The yeast-like fungus Aureobasidium pullulans was also included based on its known biocontrol activity against B. cinerea in studies on apple and grape. All yeast strains multiplied rapidly in grape berries and reached densities of over log 6 cells per wound as early as 2 days after inoculation with 200 cells. One of the Botrytis isolates used in this study was much less virulent than the others and was provisionally identified as B. prunorum based on multilocus sequence analysis. Suppression of the growth of B. cinerea isolates 111bb, 207a, 207cb, and 407cb occurred on berries treated with A. pullulans P01A006, Metschnikowia chrysoperlae P34A004 and P40A002, M. pulcherrima P01A016 and P01C004, Meyerozyma guilliermondii P34D003, and S. cerevisiae HNN11516. Inhibition of Botrytis isolates by the yeast strains was more common on berries than in vitro, suggesting the possibility that niche competition was a more likely biocontrol mechanism than antibiosis in planta. Metabolic profiling of yeast strains and B. cinerea isolates using Biolog YT plates revealed seven distinct metabolic groups. Furthermore, the yeast strains showed partial to complete tolerance to the commonly used fungicides fluopyram, triflumizole, metrafenone, pyraclostrobin, and boscalid. Implications of these findings for field deployment of native Washington yeasts as biocontrol agents against B. cinerea are discussed.

Two Novel Hypovirulence-Associated Mycoviruses in the Phytopathogenic Fungus Botrytis cinerea: Molecular Characterization and Suppression of Infection Cushion Formation

Botrytis cinerea is a necrotrophic fungus causing disease on many important agricultural crops. Two novel mycoviruses, namely Botrytis cinerea hypovirus 1 (BcHV1) and Botrytis cinerea fusarivirus 1 (BcFV1), were fully sequenced. The genome of BcHV1 is 10,214 nt long excluding a poly-A tail and possesses one large open reading frame (ORF) encoding a polyprotein possessing several conserved domains including RNA-dependent RNA polymerase (RdRp), showing homology to hypovirus-encoded polyproteins. Phylogenetic analysis indicated that BcHV1 may belong to the proposed genus Betahypovirus in the viral family Hypoviridae. The genome of BcFV1 is 8411 nt in length excluding the poly A tail and theoretically processes two major ORFs, namely ORF1 and ORF2. The larger ORF1 encoded polypeptide contains protein domains of an RdRp and a viral helicase, whereas the function of smaller ORF2 remains unknown. The BcFV1 was phylogenetically clustered with other fusariviruses forming an independent branch, indicating BcFV1 was a member in Fusariviridae. Both BcHV1 and BcFV1 were capable of being transmitted horizontally through hyphal anastomosis. Infection by BcHV1 alone caused attenuated virulence without affecting mycelial growth, significantly inhibited infection cushion (IC) formation, and altered expression of several IC-formation-associated genes. However, wound inoculation could fully rescue the virulence phenotype of the BcHV1 infected isolate. These results indicate the BcHV1-associated hypovirulence is caused by the viral influence on IC-formation-associated pathways.

Evidence for contemporary plant mitoviruses

Mitoviruses have small RNA(+) genomes, replicate in mitochondria, and have been shown to infect only fungi to date. For this report, sequences that appear to represent nearly complete plant mitovirus genomes were recovered from publicly available transcriptome data. Twenty of the refined sequences, 2684-2898 nt long and derived from 10 different species of land plants, appear to encompass the complete coding regions of contemporary plant mitoviruses, which furthermore constitute a monophyletic cluster within genus Mitovirus. Complete coding sequences of several of these viruses were recovered from multiple transcriptome (but not genome) studies of the same plant species and also from multiple plant tissues. Crop plants among implicated hosts include beet and hemp. Other new results suggest that such genuine plant mitoviruses were immediate ancestors to endogenized mitovirus elements now widespread in land plant genomes. Whether these mitoviruses are wholly cryptic with regard to plant health remains to be investigated.

Distribution of Viruses Inhabiting Heterobasidion annosum in a Pine-Dominated Forest Plot in Southern Finland

We investigated the diversity and spatial distribution of viruses infecting strains of the root rot fungus Heterobasidion annosum collected from pine stumps at a heavily infected forest site. Four different partitiviruses were detected in 14 H. annosum isolates at the study site, constituting approximately 29% of all Heterobasidion isolates investigated (N = 48). Two of the viruses detected were new partitiviruses designated here as Heterobasidion partitivirus 16 (HetPV16) and HetPV20, and two were previously known partitiviruses: HetPV7 and HetPV13. The two new partitiviruses found, HetPV16-an1 and HetPV20-an1, shared ~70% RdRp nucleotide sequence identity with the alphapartitivirus Rosellinia necatrix partitivirus 2, and less than 40% identity with known viruses of Heterobasidion spp. HetPV7-an1 was closely similar to HetPV7-pa1 isolated earlier from Heterobasidion parviporum, supporting the view of conspecific virus pools in different Heterobasidion species. Three fungal isolates were found to be co-infected with two different partitivirus strains (HetPV7-an1 and HetPV13-an2 or HetPV16-an1 and HetPV20-an1). Different isolates representing each host clone had variable virus compositions, and virus strains occurring in more than one host clone showed minor sequence variations between clones.

Detection and analysis of mycovirus-related RNA viruses from grape powdery mildew fungus Erysiphe necator

The fungus, Erysiphe necator Schw., is an important plant pathogen causing powdery mildew disease in grapevines worldwide. In this study, high-throughput sequencing of double-stranded RNA extracted from the fungal tissue combined with bioinformatics was used to examine mycovirus-related sequences associated with E. necator. The results showed the presence of eight mycovirus-related sequences. Five of these sequences representing three new mycoviruses showed alignment with sequences of viruses classified in the genus Alphapartitivirus in the family Partitiviridae. Another three sequences representing three new mycoviruses showed similarity to classifiable members of the genus Mitovirus in the family Narnaviridae. These mycovirus isolates were named Erysiphe necator partitivirus 1, 2, and 3 (EnPV 1-3) and Erysiphe necator mitovirus 1, 2, and 3 (EnMV 1-3) reflecting their E. necator origin and their phylogenetic affiliation with other mycoviruses.

Hypovirulence of Sclerotium rolfsii Caused by Associated RNA Mycovirus

Mycoviruses associated with hypovirulence are potential biological control agents and could be useful to study the pathogenesis of fungal host pathogens. Sclerotium rolfsii, a pathogenic fungus, causes southern blight in a wide variety of crops. In this study, we isolated a series of dsRNAs from a debilitated S. rolfsii strain, BLH-1, which had pronounced phenotypic aberrations including reduced pathogenicity, mycelial growth and deficient sclerotia production. Virus-curing and horizontal transmission experiments that eliminated or transmitted, respectively, all dsRNA elements showed that the dsRNAs were involved in the hypovirulent traits of BLH-1. Ultrastructure examination also showed hyphae fracture and cytoplasm or organelle degeneration in BLH-1 hyphal cells compared to the virus-free strain. Three assembled cDNA contigs generated from the cDNA library cloned from the purified dsRNA indicated that strain BLH-1 was infected by at least three novel mycoviruses. One has similarity to the hypovirulence-associated Sclerotinia sclerotiorum hypovirus 2 (SsHV2) in the family Hypoviridae, and the other two are related to two different unclassified dsRNA mycovirus families. To our knowledge, this is the first report of S. rolfsii hypovirulence that was correlated with its associated dsRNA.

Characterization of the Mycelial Compatibility Groups and Mating Type Alleles in Populations of Sclerotinia minor in Central China

Ninety-five single-sclerotium isolates were obtained from lettuce and weeds in three counties in central China. They were identified belonging to Sclerotinia minor based on colony morphology and the S. minor-specific DNA marker. Mycelial compatibility groups (MCGs) and the mating type (MAT) alleles in these isolates were determined using the methods of paired cultures and specific PCR, respectively, and the MCG data were used to calculate Shannon's H index (H) and Simpson index (S), thereby evaluating diversity of S. minor. Eight MCGs (MCG1 to MCG8) and two MAT alleles (Inv+, Inv-) were identified in these isolates. Low diversity was detected for the total 95 isolates (H = 1.748, S = 0.786). Isolates of different MCGs or with different MAT alleles did not significantly differ (P > 0.05) in mycelial growth rate on potato dextrose agar (PDA, 20°C) or lesion diameter on lettuce leaves (20°C), but slightly differed in the number of sclerotia produced on PDA (20°C). Furthermore, this study reported five new host plants of S. minor in China, including Capsella bursa-pastoris, Oenanthe javanica, Fragaria gracilis, Ranunculus ternatus, and Salvia plebeia, and identified three hypovirulent isolates. These results broaden our understanding about the population biology of S. minor.

Molecular characterization of a novel endornavirus from the phytopathogenic fungus Botrytis cinerea

The complete sequence of a novel endornavirus (Botrytis cinerea endornavirus 1, BcEV1) from the phytopathogenic fungus Botrytis cinerea strain HBtom-372 was determined. The BcEV1 coding strand is 11,557 nucleotides long, possessing an open reading frame (ORF) that codes for a polyprotein of 3,787 amino acid residues and lacks a site-specific nick. The polyprotein contains viral methyltransferase (MTR) domain, a cysteine-rich region (CRR), two putative viral helicase (DEXDc-like and Hel-1) domains, and an RNA-dependent RNA polymerase_2 (RdRp_2) domain. In phylogenetic analysis, BcEV1 clustered with several fungal endornaviruses, forming an independent clade, and it was detected in 4.2 % of B. cinerea strains collected from central China.

Characterization of Five Novel Mitoviruses in the White Pine Blister Rust Fungus Cronartium ribicola

The white pine blister rust (WPBR) fungus Cronartium ribicola (J.C. Fisch.) is an exotic invasive forest pathogen causing severe stem canker disease of native white pine trees (subgenus Strobus) in North America. The present study reports discovery of five novel mitoviruses in C. ribicola by deep RNA sequencing. The complete genome of each mitovirus was determined by rapid amplification of cDNA ends (RACE) and reverse transcriptase-polymerase chain reaction (RT-PCR). A single open reading frame (ORF) encoding a putative RNA-dependent RNA polymerase (RdRp) was detected in each of the viral genomes using mitochondrial genetic codes. Phylogenetic analysis indicated that the C. ribicola mitoviruses (CrMV1 to CrMV5) are new putative species of the genus Mitovirus. qRT-PCR and RNA-Seq analyses revealed that viral RNAs were significantly increased in fungal mycelia in cankered pine stems compared to expression during two different stages of spore development, suggesting that viral genome replication and transcription benefit from active growth of the host fungus. CrMVs were widespread with relatively high levels of minor allele frequency (MAF) in western North America. As the first report of mitoviruses in the Class Pucciniomycetes, this work allows further investigation of the dynamics of a viral community in the WPBR pathosystem, including potential impacts that may affect pathogenicity and virulence of the host fungus.

Botrytis pyriformis sp. nov., a novel and likely saprophytic species of Botrytis

A novel species of Botrytis from Sedum sarmentosum was described based on morphology and analyses of DNA sequences of nuc rDNA ITS regions and three nuclear genes (G3PDH, HSP60, RPB2). Meanwhile pathogenicity in 32 plant species, response to temperature for growth and conidial germination for the species were determined. The Botrytis species was named Botrytis pyriformis sp. nov. It was characterized by formation of grayish mycelia, brownish conidia and melanized sclerotia on PDA. The conidia are pear-shaped, melanized and covered with abundant villiform appendages on the conidial surface. Comparison of the ITS sequences confirmed its placement in the genus Botrytis Phylogenetic analysis based on DNA sequences of G3PDH, HSP60 and RPB2 genes indicated that B. pyriformis and other 30 Botrytis species form a monophyletic clade, which was further divided into three subclades. Subclade I comprised B. pyriformis alone, whereas subclades II and III comprised six and 24 Botrytis species, respectively. Botrytis pyriformis could not infect 32 plant species including S. sarmentosum, possibly due to deficiency in formation of infection cushions. This study presents a formal description and illustrations for B. pyriformis and provides experimental evidence, indicating that B. pyriformis might be a saprophytic species.

Full genome sequence of a putative novel mitovirus isolated from Rhizoctonia cerealis

A putative novel mitovirus was found in isolate R1084 of the fungus Rhizoctonia cerealis, the causal agent of sharp eyespot of wheat in China. The full genome sequence of the virus was determined and analyzed. The complete cDNA sequence is 3149 nucleotides long with 59.7% A+T content. Using either the fungal mitochondrial or universal genetic code, the viral genome was found to contain a single large open reading frame that is predicted to encode a protein of 812 amino acids with an RNA-dependent RNA polymerase (RdRp) domain that is conserved in the mitovirus RdRp superfamily. The amino acid sequence of the RdRp domain is only 50% identical to the corresponding domain in Sclerotinia sclerotiorum mitovirus 11, and therefore, this virus is proposed to be a novel mitovirus, designated as Rhizoctonia cerealis mitovirus 1-R1084 (RcMV1-R1084). The distinct codon usage of RcMV1-R1084 hints that this virus is potentially able to replicate not only in mitochondria but also in the cytoplasm. This is the first report of a full-length genomic sequence of a putative mitovirus in R. cerealis.

Isolation and characterization of two mitoviruses and a putative alphapartitivirus from Fusarium spp

The filamentous fungus Fusarium spp. includes several important plant pathogens. We attempted to reveal presence of double-stranded (ds) RNAs in the genus. Thirty-seven Fusarium spp. at the MAFF collection were analyzed. In the strains of Fusarium coeruleum, Fusarium globosum and Fusarium solani f. sp. pisi, single dsRNA bands were detected. The strains of F. coeruleum and F. solani f. sp. pisi cause potato dry rot and mulberry twig blight, respectively. Sequence analyses revealed that dsRNAs in F. coeruleum and F. globosum consisted of 2423 and 2414 bp, respectively. Using the fungal mitochondrial translation table, the positive strands of these cDNAs were found to contain single open reading frames with the potential to encode a protein of putative 757 and 717 amino acids (molecular mass 88.5 and 84.0 kDa, respectively), similar to RNA-dependent RNA polymerases of members of the genus Mitovirus. These dsRNAs in F. coeruleum and F. globosum were assigned to the genus Mitovirus (family Narnaviridae), and these two mitoviruses were designated as Fusarium coeruleum mitovirus 1 and Fusarium globosum mitovirus 1. On the other hand, a positive strand of cDNA (1950 bp) from dsRNA in F. solani f. sp. pisi contained an ORF potentially encoding a putative RdRp of 608 amino acids (72.0 kDa). The putative RdRp was shown to be related to those of members of the genus of Alphapartitivirus (family Partitiviridae). We coined the name Fusarium solani partitivirus 2 for dsRNA in F. solani f. sp. pisi.