Complete genome sequence of a novel victorivirus isolated from the sesame charcoal rot fungus Macrophomina phaseolina

Molecular characterization of a novel victorivirus isolated from the phytopathogenic fungus Phaeobotryon rhois

Phaeobotryon rhois is an important pathogenic fungus that causes dieback and canker disease of woody hosts. A novel mycovirus, tentatively named "Phaeobotryon rhois victorivirus 1" (PrVV1), was identified in P. rhois strain SX8-4. The PrVV1 has a double-stranded RNA (dsRNA) genome that is 5,224 base pairs long and contains two open reading frames (ORF1 and ORF2), which overlap at a AUGA sequence. ORF1 encodes a polypeptide of 786 amino acids (aa) that contains the conserved coat protein (CP) domain of victoriviruses, while ORF2, encodes a large polypeptide of 826 aa that contains the conserved RNA-dependent RNA polymerase (RdRp) domain of victoriviruses. Our analysis of genomic structure, homology, and phylogeny indicated that PrVV1 is a novel member of the genus Victorivirus in the family Totiviridae. This is the first report of the complete genome sequence of a victorivirus that infects P. rhois.

Complete genome sequence of a novel mitovirus from the phytopathogenic fungus Fusarium oxysporum

Fusarium oxysporum is a cosmopolitan plant pathogen that causes fusarium wilt and fusarium root rot in many economically important crops. There is still limited information about mycoviruses that infect F. oxysporum. Here, a novel mitovirus tentatively named "Fusarium oxysporum mitovirus 1" (FoMV1) was identified in F. oxysporum strain B2-10. The genome of FoMV1 is 2,453 nt in length with a predicted AU content of 71.6% and contains one large open reading frame (ORF) using the fungal mitochondrial genetic code. The ORF putatively encodes an RNA-dependent RNA polymerase (RdRp) of 723 aa with a molecular mass of 84.98 kDa. The RdRp domain of FoMV1 shares 29.01% to 68.43% sequence identity with the members of the family Mitoviridae. Phylogenetic analysis further suggested that FoMV1 is a new member of a distinct species in the genus Mitovirus.

Macrophomina phaseolina : General Characteristics of Pathogenicity and Methods of Control

Macrophomina phaseolina is a generalist soil-borne fungus present all over the world. It cause diseases such as stem and root rot, charcoal rot and seedling blight. Under high temperatures and low soil moisture, this fungus can cause substantial yield losses in crops such as soybean, sorghum and groundnut. The wide host range and high persistence of M. phaseolina in soil as microsclerotia make disease control challenging. Therefore, understanding the basis of the pathogenicity mechanisms as well as its interactions with host plants is crucial for controlling the pathogen. In this work, we aim to describe the general characteristics and pathogenicity mechanisms of M. phaseolina, as well as the hosts defense response. We also review the current methods and most promising forecoming ones to reach a responsible control of the pathogen, with minimal impacts to the environment and natural resources.

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.