A novel bipartite negative-stranded RNA mycovirus of the order Bunyavirales isolated from the phytopathogenic fungus Fusarium sibiricum.

A novel negative-stranded RNA mycovirus was isolated from the phytopathogenic fungus Fusarium sibiricum strain AH32. This virus, tentatively named "Fusarium sibiricum coguvirus 1" (FsCV1), has a bipartite genome consisting of two RNA segments (RNA1 and RNA2). The negative-sense RNA1 is 6711 nt in length, encoding the RNA-dependent RNA polymerase (RdRp, p251) in the viral complementary (vc) strand. The ambisense RNA2 (1204 nt long) encodes two proteins from overlapping genes: the nucleocapsid protein (NP, p38) in the vc strand and a protein of unknown function (UFP, p36) in the viral (v) strand. In contrast to other Bunyavirales members, in FsCV1, the two open reading frames are separated by a long AU-rich intergenic region (IR). Sequence comparisons and phylogenetic analysis based on RdRp and NP sequences demonstrated that FsCV1 is a novel bipartite negative-stranded RNA mycovirus of the genus Coguvirus, family Phenuiviridae, order Bunyavirales.

First report of a novel partitivirus from the phytopathogenic fungus Fusarium cerealis in China.

To our knowledge, no mycoviruses have been reported in Fusarium cerealis. Here, we describe a novel double-stranded RNA (dsRNA) virus, Fusarium cerealis partitivirus 1 (FcPV1), isolated from F. cerealis strain HN30 from Henan Province, China. The FcPV1 genome consists of two dsRNA segments, 1732 bp (dsRNA1) and 1361 bp (dsRNA2) in length, each containing a single open reading frame potentially encoding a 61.0-kDa protein and a 42.0-kDa protein, respectively. dsRNA1 encodes a putative RNA-dependent RNA polymerase (RdRp), while the dsRNA2 product has no significant similarity to any other capsid proteins (CPs) in the GenBank databases other than limited similarity to hypothetical "capsid" proteins of a few partitiviruses. Sequence alignments and phylogenetic analysis showed that FcPV1 is related to members of the newly proposed genus "Zetapartitivirus" in the family Partitiviridae.

Modulation of Nutritional and Biochemical Properties of Wheat Grains Infected by Blast Fungus Magnaporthe oryzae Triticum Pathotype.

Wheat blast disease caused by the Magnaporthe oryzae Triticum (MoT) pathotype exerts a significant impact on grain development, yield, and quality of the wheat. The aim of this study was to investigate morphological, physiological, biochemical, and nutritional properties of wheat cv. BARI Gom 24 under varying levels of blast disease severity in wheat spikes. Grain morphology, volume, weight, and germination of the infected grains were significantly affected by MoT. Biochemical traits specifically grain N, Ca, Mg, and Fe content significantly increased (up to threefold; p > 0.05), but organic carbon, Cu, Zn, B, and S content in wheat grains significantly decreased with increased severity of MoT infection. The grain crude protein content was about twofold higher (up to 18.5% in grain) in severely blast-infected grains compared to the uninfected wheat (9.7%). Analysis of other nutritional properties such as secondary metabolites revealed that total antioxidant activity, flavonoid, and carotenoid concentrations remarkably decreased (up to threefold) with increasing severity of blast infestation in wheat grain. Grain moisture, lipid, and ash content were slightly increased with the increase in blast severity. However, grain K and total phenolic concentration were increased at a certain level of blast infestation and then reduced with increase in MoT infestation.

Molecular Characterization of a Novel Strain of Fusarium graminearum Virus 1 Infecting Fusarium graminearum.

Fungal viruses (mycoviruses) have attracted more attention for their possible hypovirulence (attenuation of fungal virulence) trait, which may be developed as a biocontrol agent of plant pathogenic fungi. However, most discovered mycoviruses are asymptomatic in their hosts. In most cases, mycovirus hypovirulent factors have not been explored clearly. In this study, we characterized a ssRNA mycovirus in Fusarium graminearum strain HB56-9. The complete nucleotide genome was obtained by combining random sequencing and rapid amplification of cDNA ends (RACE). The full genome was 6621-nucleotides long, excluding the poly(A) tail. The mycovirus was quite interesting because it shared 95.91% nucleotide identities with previously reported Fusarium graminearum virus 1 strain DK21 (FgV1-DK21), while the colony morphology of their fungal hosts on PDA plates were very different. The novel virus was named Fusarium graminearum virus 1 Chinese isolate (FgV1-ch). Like FgV1-DK21, FgV1-ch also contains four putative open reading frames (ORFs), including one long and three short ORFs. A phylogenetic analysis indicated that FgV1-ch is clustered into a proposed family Fusariviridae. FgV1-ch, unlike FgV1-DK21, had mild or no effects on host mycelial growth, spore production and virulence. The nucleotide differences between FgV1-ch and FgV1-DK21 will help to elucidate the hypovirulence determinants during mycovirus-host interaction.

Mycoviruses in Fusarium Species: An Update.

Fusarium is an important genus of plant pathogenic fungi, and is widely distributed in soil and associated with plants worldwide. The diversity of mycoviruses in Fusarium is increasing continuously due to the development and extensive use of state-of-the-art RNA deep sequencing techniques. To date, fully-sequenced mycoviruses have been reported in 13 Fusarium species: Fusarium asiaticum, F. boothii, F. circinatum, F. coeruleum, F. globosum, F. graminearum, F. incarnatum, F. langsethiae, F. oxysporum, F. poae, F. pseudograminearum, F. solani, and F. virguliforme. Most Fusarium mycoviruses establish latent infections, but some mycoviruses such as Fusarium graminearum virus 1 (FgV1), Fusarium graminearum virus-ch9 (FgV-ch9), Fusarium graminearum hypovirus 2 (FgHV2), and Fusarium oxysporum f. sp. dianthi mycovirus 1 (FodV1) cause hypovirulence. Rapid advances in various omics technologies used to elucidate genes or biological processes can facilitate an improved understanding of mycovirus-host interactions. The review aims to illuminate the recent advances in studies of mycoviruses in Fusarium, including those related to diversity, molecular mechanisms of virus-host interaction. We also discuss the induction and suppression of RNA silencing including the role of RNAi components as an antiviral defense response.

Cautionary Notes on Use of the MoT3 Diagnostic Assay for Magnaporthe oryzae Wheat and Rice Blast Isolates.

The blast fungus Magnaporthe oryzae is comprised of lineages that exhibit varying degrees of specificity on about 50 grass hosts, including rice, wheat, and barley. Reliable diagnostic tools are essential given that the pathogen has a propensity to jump to new hosts and spread to new geographic regions. Of particular concern is wheat blast, which has suddenly appeared in Bangladesh in 2016 before spreading to neighboring India. In these Asian countries, wheat blast strains are now co-occurring with the destructive rice blast pathogen raising the possibility of genetic exchange between these destructive pathogens. We assessed the recently described MoT3 diagnostic assay and found that it did not distinguish between wheat and rice blast isolates from Bangladesh. The assay is based on primers matching the WB12 sequence corresponding to a fragment of the M. oryzae MGG_02337 gene annotated as a short chain dehydrogenase. These primers could not reliably distinguish between wheat and rice blast isolates from Bangladesh based on DNA amplification experiments performed in separate laboratories in Bangladesh and in the United Kingdom. Specifically, all eight rice blast isolates tested in this study produced the WB12 amplicon. In addition, comparative genomics of the WB12 nucleotide sequence revealed a complex underlying genetic structure with related sequences across M. oryzae strains and in both rice and wheat blast isolates. We, therefore, caution against the indiscriminate use of this assay to identify wheat blast and encourage further development of the assay to ensure its value in diagnosis.

Emergence of wheat blast in Bangladesh was caused by a South American lineage of Magnaporthe oryzae.

BACKGROUND: In February 2016, a new fungal disease was spotted in wheat fields across eight districts in Bangladesh. The epidemic spread to an estimated 15,000 hectares, about 16 % of the cultivated wheat area in Bangladesh, with yield losses reaching up to 100 %. Within weeks of the onset of the epidemic, we performed transcriptome sequencing of symptomatic leaf samples collected directly from Bangladeshi fields. RESULTS: Reinoculation of seedlings with strains isolated from infected wheat grains showed wheat blast symptoms on leaves of wheat but not rice. Our phylogenomic and population genomic analyses revealed that the wheat blast outbreak in Bangladesh was most likely caused by a wheat-infecting South American lineage of the blast fungus Magnaporthe oryzae. CONCLUSION: Our findings suggest that genomic surveillance can be rapidly applied to monitor plant disease outbreaks and provide valuable information regarding the identity and origin of the infectious agent.