Characterization of three novel betapartitiviruses co-infecting the phytopathogenic fungus Rhizoctonia solani

Transfection of entomopathogenic Metarhizium species with a mycovirus confers hypervirulence against two lepidopteran pests

Although most known viruses infecting fungi pathogenic to higher eukaryotes are asymptomatic or reduce the virulence of their host fungi, those that confer hypervirulence to entomopathogenic fungus still need to be explored. Here, we identified and studied a novel mycovirus in Metarhizium flavoviride, isolated from small brown planthopper (Laodelphax striatellus). Based on molecular analysis, we tentatively designated the mycovirus as Metarhizium flavoviride partitivirus 1 (MfPV1), a species in genus Gammapartitivirus, family Partitiviridae. MfPV1 has two double-stranded RNAs as its genome, 1,775 and 1,575 bp in size respectively, encapsidated in isometric particles. When we transfected commercial strains of Metarhizium anisopliae and Metarhizium pingshaense with MfPV1, conidiation was significantly enhanced (t test; P-value < 0. 01), and the significantly higher mortality rates of the larvae of diamondback moth (Plutella xylostella) and fall armyworm (Spodoptera frugiperda), two important lepidopteran pests were found in virus-transfected strains (ANOVA; P-value < 0.05). Transcriptomic analysis showed that transcript levels of pathogenesis-related genes in MfPV1-infected M. anisopliae were obviously altered, suggesting increased production of metarhizium adhesin-like protein, hydrolyzed protein, and destruxin synthetase. Further studies are required to elucidate the mechanism whereby MfPV1 enhances the expression of pathogenesis-related genes and virulence of Metarhizium to lepidopteran pests. This study presents experimental evidence that the transfection of other entomopathogenic fungal species with a mycovirus can confer significant hypervirulence and provides a good example that mycoviruses could be used as a synergistic agent to enhance the biocontrol activity of entomopathogenic fungi.

Horizontal and Vertical Transmission of a Mycovirus Closely Related to the Partitivirus RhsV717 That Confers Hypovirulence in Rhizoctonia solani

Rhizoctonia solani virus717 (RhsV717) was isolated from the Rhizoctonia solani (R. solani) AG-2 strain Rhs717. This study isolated a virus designated as Rhizoctonia solani partitivirus BS-5 (RsPV-BS5) from the R. solani AG-3 strain BS-5, the causal agent of tobacco target spot disease. The virus was identified as a strain of RhsV717. Transmission electron microscopy (TEM) images showed that RsPV-BS5 had virus particles with a diameter of approximately 40 nm. Importantly, it can be horizontally transmitted through hyphal anastomosis and vertically transmitted via sexual basidiospores. Furthermore, this study demonstrated that RsPV-BS5 infection significantly impedes mycelial growth and induces hypovirulence in tobacco leaves. Thus, RsPV-BS5 presents a promising avenue for biocontrolling tobacco target spot disease. Transcriptome analysis unveiled differential expression of four genes related to cell wall-degrading enzymes between two isogenic strains, 06-2-15V and 06-2-15. These findings shed light on the molecular mechanism through which RsPV-BS5 reduces host pathogenicity.

Mycoviruses: Antagonistic Potential, Fungal Pathogenesis, and Their Interaction with Rhizoctonia solani

Mycoviruses, or fungal viruses, are prevalent in all significant fungal kingdoms and genera. These low-virulence viruses can be used as biocontrol agents to manage fungal diseases. These viruses are divided into 19 officially recognized families and 1 unclassified genus. Mycoviruses alter sexual reproduction, pigmentation, and development. Spores and fungal hypha spread mycoviruses. Isometric particles mostly encapsulate dsRNA mycoviruses. The widespread plant-pathogenic fungus Rhizoctonia solani, which has caused a rice sheath blight, has hosted many viruses with different morphologies. It causes significant crop diseases that adversely affect agriculture and the economy. Rice sheath blight threatens the 40% of the global population that relies on rice for food and nutrition. This article reviews mycovirology research on Rhizoctonia solani to demonstrate scientific advances. Mycoviruses control rice sheath blight. Hypovirulence-associated mycoviruses are needed to control R. solani since no cultivars are resistant. Mycoviruses are usually cryptic, but they can benefit the host fungus. Phytopathologists may use hypovirulent viruses as biological control agents. New tools are being developed based on host genome studies to overcome the intellectual challenge of comprehending the interactions between viruses and fungi and the practical challenge of influencing these interactions to develop biocontrol agents against significant plant pathogens.

Anastomosis Groups and Mycovirome of Rhizoctonia Isolates Causing Sugar Beet Root and Crown Rot and Their Sensitivity to Flutolanil, Thifluzamide, and Pencycuron

Anastomosis groups (AGs) or subgroups of 244 Rhizoctonia isolates recovered from sugar beet roots with symptoms of root and crown rot were characterized to be AG-A, AG-K, AG-2-2IIIB, AG-2-2IV, AG-3 PT, AG-4HGI, AG-4HGII, and AG-4HGIII, with AG-4HGI (108 isolates, 44.26%) and AG-2-2IIIB (107 isolates, 43.85%) being predominate. Four unclassified mycoviruses and one hundred and one putative mycoviruses belonging to six families, namely Mitoviridae (60.00%), Narnaviridae (18.10%), Partitiviridae (7.62%), Benyviridae (4.76%), Hypoviridae (3.81%), and Botourmiaviridae (1.90%), were found to be present in these 244 Rhizoctonia isolates, most of which (88.57%) contained positive single-stranded RNA genome. The 244 Rhizoctonia isolates were all sensitive to flutolanil and thifluzamide, with average median effective concentration (EC₅₀) value of 0.3199 ± 0.0149 μg·mL^-1 and 0.1081 ± 0.0044 μg·mL^-1, respectively. Among the 244 isolates, except for 20 Rhizoctonia isolates (seven isolates of AG-A and AG-K, one isolate of AG-4HGI, and 12 isolates of AG-4HGII), 117 isolates of AG-2-2IIIB, AG-2-2IV, AG-3 PT, and AG-4HGIII, 107 isolates of AG-4HGI, and six isolates of AG-4HGII were sensitive to pencycuron, with average EC₅₀ value of 0.0339 ± 0.0012 μg·mL^-1. Correlation index (ρ) of cross-resistance level between flutolanil and thifluzamide, flutolanil and pencycuron, and thifluzamide and pencycuron was 0.398, 0.315, and 0.125, respectively. This is the first detailed study on AG identification, mycovirome analysis, and sensitivity to flutolanil, thifluzamide, and pencycuron of Rhizoctonia isolates associated with sugar beet root and crown rot.

Diversity of Mycoviruses Present in Strains of Binucleate Rhizoctonia and Multinucleate Rhizoctonia, Causal Agents for Potato Stem Canker or Black Scurf

In this study, the diversity of putative mycoviruses present in 66 strains of binucleate Rhizoctonia (BNR, including anastomosis group (AG)-A, AG-Fa, AG-K, and AG-W) and 192 strains of multinucleate Rhizoctonia (MNR, including AG-1-IA, AG-2-1, AG-3 PT, AG-4HGI, AG-4HGII, AG-4HGIII, and AG-5), which are the causal agents of potato stem canker or black scurf, was studied using metatranscriptome sequencing. The number of contigs related to mycoviruses identified from BNR and MNR was 173 and 485, respectively. On average, each strain of BNR accommodated 2.62 putative mycoviruses, while each strain of MNR accommodated 2.53 putative mycoviruses. Putative mycoviruses detected in both BNR and MNR contained positive single-stranded RNA (+ssRNA), double-stranded RNA (dsRNA), and negative single-stranded RNA (-ssRNA) genomes, with +ssRNA genome being the prevalent nucleic acid type (82.08% in BNR and 75.46% in MNR). Except for 3 unclassified, 170 putative mycoviruses found in BNR belonged to 13 families; excluding 33 unclassified, 452 putative mycoviruses found in MNR belonged to 19 families. Through genome organization, multiple alignments, and phylogenetic analyses, 4 new parititviruses, 39 novel mitoviruses, and 4 new hypoviruses with nearly whole genome were detected in the 258 strains of BNR and MNR.

Molecular characterization of a novel partitivirus isolated from Rhizoctonia solani

Rhizoctonia solani is a widely distributed plant pathogen that can damage many crops. Here, we identified a novel mycovirus tentatively named Rhizoctonia solani partitivirus 433 (RsPV433) from an R. solani (AG-3) strain which caused tobacco target spot disease on flue-cured tobacco. RsPV433 was consisted of two dsRNA segments with lengths of 2450 and 2273 bp, which encoded an RNA-dependent RNA polymerase and a coat protein, respectively. BLASTP results of RsPV433 showed that the closest relative of RsPV433 was Sarcosphaera coronaria partitivirus (QLC36830.1), with an identity of 60.85% on the RdRp amino sequence. Phylogenetic analysis indicated that RsPV433 belonged to the Betapartitivirus genus in the Partitiviridae family. The virus transmission experiment revealed that RsPV433 can be transmitted horizontally. We further tested the biological effect of RsPV433 on R. solani strains and found that the RsPV433-infected R. solani strain grew slower than the RsPV433-free strain on the PDA medium and RsPV433 seemed to have no obvious impact on the lesion inducing ability of R. solani.

Six Novel Mycoviruses Containing Positive Single-Stranded RNA and Double-Stranded RNA Genomes Co-Infect a Single Strain of the Rhizoctoniasolani AG-3 PT

Six novel mycoviruses that collectively represent the mycovirome of Rhizoctonia solani anastomosis group (AG)-3 PT strain ZJ-2H, which causes potato black scurf, were identified through metatranscriptome sequencing and putatively designated as Rhizoctonia solani fusarivirus 4 [RsFV4, positive single-stranded RNA (+ssRNA)], Rhizoctonia solani fusarivirus 5 (RsFV5, +ssRNA), Rhizoctonia solani mitovirus 40 (RsMV40, +ssRNA), Rhizoctonia solani partitivirus 10 [RsPV10, double-stranded RNA (dsRNA)], Rhizoctonia solani partitivirus 11 (RsPV11, dsRNA), and Rhizoctonia solani RNA virus 11 (RsRV11, dsRNA). Whole genome sequences of RsFV4, RsMV40, RsPV10, RsPV11, and RsRV11, as well as a partial genome sequence of RsFV5, were obtained. The 3'- and 5'- untranslated regions of the five mycoviruses with complete genome sequences were folded into stable stem-loop or panhandle secondary structures. RsFV4 and RsFV5 are most closely related to Rhizoctonia solani fusarivirus 1 (RsFV1), however, the first open reading frame (ORF) of RsFV4 and RsFV5 encode a hypothetical protein that differs from the first ORF of RsFV1, which encodes a helicase. We confirmed that RsPV10 and RsPV11 assemble into the spherical virus particles (approximately 30 nm in diameter) that were extracted from strain ZJ-2H. This is the first report that +ssRNA and dsRNA viruses co-infect a single strain of R. solani AG-3 PT.

Two Novel Rhabdoviruses Related to Hypervirulence in a Phytopathogenic Fungus

Rhabdoviruses are ubiquitous and diverse viruses that propagate owing to bidirectional interactions with their vertebrate, arthropod, and plant hosts, and some of them could pose global health or agricultural threats. However, rhabdoviruses have rarely been reported in fungi. Here, two newly identified fungal rhabdoviruses, Rhizoctonia solani rhabdovirus 1 (RsRhV1) and RsRhV2, were discovered and molecularly characterized from the phytopathogenic fungus Rhizoctonia solani. The genomic organizations of RsRhV1 and RsRhV2 are 11,716 and 11,496 nucleotides (nt) in length, respectively, and consist of five open reading frames (ORFs) (ORFs I to V). ORF I, ORF IV, and ORF V encode the viral nucleocapsid (N), glycoprotein (G), and RNA polymerase (L), respectively. The putative protein encoded by ORF III has a lower level of identity with the matrix protein of rhabdoviruses. ORF II encodes a hypothetical protein with unknown function. Phylogenetic trees based on multiple alignments of N, L, and G proteins revealed that RsRhV1 and RsRhV2 are new members of the family Rhabdoviridae, but they form an independent evolutionary branch significantly distinct from other known nonfungal rhabdoviruses, suggesting that they represent a novel viral evolutionary lineage within Rhabdoviridae. Compared to strains lacking rhabdoviruses, strains harboring RsRhV2 and RsRhV1 showed hypervirulence, suggesting that RsRhV1 and RsRhV2 might be associated with the virulence of R. solani. Taken together, this study enriches our understanding of the diversity and host range of rhabdoviruses. IMPORTANCE Mycoviruses have been attracting an increasing amount of attention due to their impact on important medical, agricultural, and industrial fungi. Rhabdoviruses are prevalent across a wide spectrum of hosts, from plants to invertebrates and vertebrates. This study molecularly characterized two novel rhabdoviruses from four Rhizoctonia solani strains, based on their genomic structures, transcription strategy, phylogenetic relationships, and biological impact on their host. Our study makes a significant contribution to the literature because it not only enriches the mycovirus database but also expands the known host range of rhabdoviruses. It also offers insight into the evolutionary linkage between animal viruses and mycoviruses and the transmission of viruses from one host to another. Our study will also help expand the contemporary knowledge of the classification of rhabdoviruses, as well as providing a new model to study rhabdovirus-host interactions, which will benefit the agriculture and medical areas of human welfare.

Characterization of a Novel Mycovirus from the Phytopathogenic Fungus Botryosphaeria dothidea

Botryosphaeria dothidea is, globally, one of the most economically important phytopathogenic fungi worldwide, causing the canker and dieback of fruit trees. An increasing number of viruses infecting B. dothidea have lately been reported, several of which could confer hypovirulence. In this study, isolated from strain ZM170285-1 of B. dothidea, a novel double-stranded RNA (dsRNA) mycovirus, tentatively named Botryosphaeria dothidea partitivirus 2 (BdPV2), was identified well. The BdPV2 harbored three dsRNA segments (1–3) with lengths of 1751, 1568, and 1198 bp, which encoded an RNA-dependent RNA polymerase (RdRp), a capsid protein (CP), and a hypothetical protein of unknown function, respectively. BLASTp searches revealed that the predicted protein sequences of dsRNA1 and dsRNA2 had the highest identities (74.95% and 61.01%) with the corresponding dsRNAs of Penicillium stoloniferum virus S (PsV-S), whereas dsRNA3 shared the highest identity (32.95%) with the dsRNA3 of Aspergillus ochraceous virus 1 (AoV1). Phylogenetic analysis indicated that BdPV2 belonged to the Gammapartitivirus genus and Partitiviridae family. To our knowledge, this is the first report of a gammapartitivirus in B. dothidea.

Complete nucleotide sequence of a novel alphapartitivirus from Rhizoctonia solani AG-4 HG III isolate SM03

In this report, the full genome sequence of a novel mycovirus, designated as "Rhizoctonia solani partitivirus SM03" (RsPV-SM03), was determined in Rhizoctonia solani AG-4 HG III isolate SM03. RsPV-SM03 genome consists of two dsRNAs (dsRNA-1 and dsRNA-2), each of them contains one single open reading frame (ORF). ORF1 of dsRNA-1 encodes a putative RNA-dependent RNA polymerase (RdRp), while ORF2 of dsRNA-2 encodes a putative viral coat protein (CP). Phylogenetic analysis indicated that the RdRp and CP of RsPV-SM03 are closely related to those of other members of the genus Alphapartitivirus, family Partitiviridae, suggesting that RsPV-SM03 represents a novel species in the genus Alphapartitivirus.

Complete nucleotide sequence of a novel mycovirus infecting Rhizoctonia fumigata AG-Ba isolate C-314 Baishi

The complete nucleotide sequence of a novel mycovirus, designated as "Rhizoctonia fumigata bipartite virus 1" (RfBV1), from Rhizoctonia fumigata AG-Ba isolate C-314 Baishi was determined. The genome of RfBV1 is composed of two double-stranded RNAs (dsRNA). dsRNA-1 (2311 bp) contains one open reading frame (ORF), which codes for the putative RNA-dependent RNA polymerase (RdRp) of the virus. dsRNA-2 (1690 bp) contains one ORF, which encodes a putative protein whose function is unknown. Phylogenetic analysis indicated that the RdRp of RfBV1 clustered with several unassigned bipartite viruses belonging to the CThTV-like viruses group, but not the family Amalgaviridae or Partitiviridae. Our study suggests that RfBV1 is a novel mycovirus related to the CThTV-like viruses.

Molecular characterization of three novel mycoviruses in the plant pathogenic fungus Exobasidium

The plant pathogen Exobasidium gracile, which belongs to the basidiomycetous genus Exobasidium, can lead to swollen and thicker leaves of C. oleifera. To our knowledge, there have been no reports of mycoviruses infecting Exobasidium gracile. This study characterized three mycoviruses coinfecting the plant pathogen Exobasidium gracile strain Z-1. Based on phylogenetic and genomic analyses, E. gracile strain Z-1 was infected two putative Totiviruses designated Exobasidium gracile Totivirus 1 (EgTV1) and Exobasidium gracile Totivirus 2 (EgTV2) and a putative Zybavirus of the family Amalgaviridae defined Exobasidium gracile Zybavirus 1 (EgZV1). Similar to the genomic organization of other Totiviruses, the EgTV1 and EgTV2 genomes are composed of one dsRNA segment that exhibits two large ORFs encoding a CP (capsid protein) and an RdRp (RNA-dependent RNA polymerase), respectively. Moreover, EgTV1 and EgTV2 genomes with a candidate -1 slippery heptamer sequence were discovered between CP and RdRp, respectively. Similar to other Zybaviruses of the family Amalgaviridae, the EgZV1 genome is composed of one dsRNA segment that contains two large ORFs encoding an unknown protein and an RdRp. In addition, the EgZV1 genome has a candidate +1 slippery heptamer sequence between an unknown protein and RdRp.

Omnipresence of Partitiviruses in Rice Aggregate Sheath Spot Symptom-Associated Fungal Isolates from Paddies in Thailand

Partitiviruses are one of the most prevalent double-stranded RNA viruses that have been identified mostly in filamentous fungi and plants. Partitiviruses generally infect host fungi asymptomatically but infrequently exert significant effect(s) on morphology and virulence, thus being considered a potential source of biological control agents against pathogenic fungi. In this study, we performed a screening for mycoviruses of a collection of Thai isolates of rice fungal pathogen Rhizoctonia oryzae-sativae, a causal agent of rice aggregated sheath spot disease. As a result, 36% of tested isolates carried potentially viral double-stranded RNAs with sizes ranging from 2 to 3 kbp. By conventional cDNA library construction and RNA-seq, we determined six new alphapartitiviruses that infected three isolates: tentatively named Rhizoctonia oryzae-sativae partitivirus 1 to 6 (RosPV1-6). Furthermore, RT-PCR detection of each virus revealed their omnipresent nature in different R. oryzae-sativae isolates. Although virus-curing of basidiomycetous fungi is generally difficult, our repeated attempts successfully obtained virus-free (for RosPV1, RosPV2, and uncharacterized partitiviruses), isogenic strain of R. oryzae-sativae TSS190442. The virus-cured strain showed slightly faster colony growth on the synthetic media and severe symptom development on the rice sheath compared to its virus-infected counterpart. Overall, this study shed light on the distribution of partitiviruses in R. oryzae-sativae in a paddy environment and exemplified a virus-curing protocol that may be applicable for other basidiomycetous fungi.

Genome Organizations and Functional Analyses of a Novel Gammapartitivirus from Rhizoctonia solani AG-1 IA Strain D122

Here, we describe a novel double-stranded (ds) RNA mycovirus designated Rhizoctonia solani dsRNA virus 5 (RsRV5) from strain D122 of Rhizoctonia solani AG-1 IA, the causal agent of rice sheath blight. The RsRV5 genome consists of two segments of dsRNA (dsRNA-1, 1894 bp and dsRNA-2, 1755 bp), each possessing a single open reading frame (ORF). Sequence alignments and phylogenetic analyses showed that RsRV5 is a new member of the genus Gammapartitivirus in the family Partitiviridae. Transmission electron microscope (TEM) images revealed that RsRV5 has isometric viral particles with a diameter of approximately 20 nm. The mycovirus RsRV5 was successfully removed from strain D122 by using the protoplast regeneration technique, thus resulting in derivative isogenic RsRV5-cured strain D122-P being obtained. RsRV5-cured strain D122-P possessed the traits of accelerated mycelial growth rate, increased sclerotia production and enhanced pathogenicity to rice leaves compared with wild type RsRV5-infection strain D122. Transcriptome analysis showed that three genes were differentially expressed between two isogenic strains, D122 and D122-P. These findings provided new insights into the molecular mechanism of the interaction between RsRV5 and its host, D122 of R. solani AG-1 IA.

A novel alphapartitivirus from binucleate Rhizoctonia fumigata AG-Ba isolate C-314 Baishi

The full-length nucleotide sequence and genome organization of a novel mycovirus designated as "Rhizoctonia fumigata partitivirus 1" (RfPV1) from Rhizoctonia fumigata AG-Ba strain C-314 Baishi was determined. The genome of RfPV1 consists of two double-stranded RNAs (dsRNAs): dsRNA1 (2003 bp) and dsRNA2 (1802 bp). Each of the two dsRNAs contains one open reading frame, coding for a putative RNA-dependent RNA polymerase and a coat protein, respectively. The 5' untranslated regions (UTRs) of both dsRNAs were conserved, and the 3'-UTRs of the two dsRNAs had interrupted poly(A) tails, similar to other partitiviruses. Phylogenetic analysis indicated that RfPV1 is a new species in the genus Alphapartitivirus, family Partitiviridae.

Synthesis of a series of validoxylamine A esters and their biological activities

BACKGROUND

The worldwide reduction in food production due to pests and diseases is still an important challenge facing today. Validoxylamine A (VAA) is a natural polyhydroxyl compound derived from validamycin, acting as an efficient trehalase inhibitor with insecticidal and antifungal activities. To extend the application and discover green pesticide, a series of ester derivatives were prepared based on VAA as a lead compound. Their biological activities were investigated against three typically agricultural disease, Rhizoctonia solani, Sclerotinia sclerotiorum and Aphis craccivora.

RESULTS

This study involved 30 novel validoxylamine A fatty acid esters (VAFAEs) synthesized by Novozym 435 and they were characterized with high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) and proton nuclear magnetic resonance (¹ H-NMR). Of these 30 derivatives, most compounds showed improved antifungal activity, and 12 novel compounds showed improved insecticidal activity. When reacted with pentadecanoic acid, compound 14 showed the highest inhibitory activity against R. solani [median effective concentration (EC₅₀ ) 0.01 μmol L^-1 ], while the EC₅₀ value of VAA was 34.99 μmol L^-1 . Furthermore, 21 novel VAFAEs showed higher inhibitory activity against S. sclerotiorum. Validoxylamine A oleic acid ester, compound 21, exhibited the highest insecticidal activity against A. craccivora [median lethal concentration (LC₅₀ ) 39.63 μmol L^-1 ], while the LC₅₀ value of Pymetrozine was 50.45 μmol L^-1 , a commercialized pesticide against A. craccivora.

CONCLUSION

Combining our results, esterification of VAA by introducing different acyl donors was beneficial for the development of new eco-friendly drugs in the field of pesticides.

A novel putative betapartitivirus isolated from the plant-pathogenic fungus Rhizoctonia solani

In this study, we describe the genome sequence of a novel double-stranded RNA (dsRNA) mycovirus, designated as "Rhizoctonia solani partitivirus 15" (RsPV15), from the phytopathogenic fungus Rhizoctonia solani. RsPV15 consists of two genomic double-stranded RNA segments, dsRNA-1 and dsRNA-2, which are 2433 bp and 2350 bp long, respectively. Each of the dsRNA segments contains a single open reading frame, encoding the putative RNA-dependent RNA polymerase and coat protein, respectively. Homology searches and phylogenetic analysis suggested that RsPV15 is a new member of the genus Betapartitivirus within the family Partitiviridae.

Viruses Infecting the Plant Pathogenic Fungus Rhizoctonia solani

The cosmopolitan fungus Rhizoctonia solani has a wide host range and is the causal agent of numerous crop diseases, leading to significant economic losses. To date, no cultivars showing complete resistance to R. solani have been identified and it is imperative to develop a strategy to control the spread of the disease. Fungal viruses, or mycoviruses, are widespread in all major groups of fungi and next-generation sequencing (NGS) is currently the most efficient approach for their identification. An increasing number of novel mycoviruses are being reported, including double-stranded (ds) RNA, circular single-stranded (ss) DNA, negative sense (−)ssRNA, and positive sense (+)ssRNA viruses. The majority of mycovirus infections are cryptic with no obvious symptoms on the hosts; however, some mycoviruses may alter fungal host pathogenicity resulting in hypervirulence or hypovirulence and are therefore potential biological control agents that could be used to combat fungal diseases. R. solani harbors a range of dsRNA and ssRNA viruses, either belonging to established families, such as Endornaviridae, Tymoviridae, Partitiviridae, and Narnaviridae, or unclassified, and some of them have been associated with hypervirulence or hypovirulence. Here we discuss in depth the molecular features of known viruses infecting R. solani and their potential as biological control agents.