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

Abstract

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.

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

“…It was documented that Rhizoctonia hosted more than 100 mycoviruses, and most of them were isolated from multinucleate Rhizoctonia (MNR, whose nuclei per cell are at least three) (including R. solani anastomosis group (AG)-1, AG-2, AG-3 PT, and AG-4) and belonged to 8 families, namely Partitiviridae , Mitoviridae , Narnaviridae , Endornaviridae , Hypoviridae , Totiviridae , Bunyaviridae and Fusariviridae , and a proposed family Bipartitiviridae [ 3 , 15 , 16 , 17 , 18 , 19 , 20 ]. Only twelve mycoviruses were found in binucleate Rhizoctonia (BNR, whose nuclei per cell are two) including AG-Ba ( R. fumigate ), AG-DΙ ( R. cerealis ), and AG-Bb ( R. oryzae-sativae ), and belonged to four families ( Partitiviridae , Megabirnaviridae , Endornaviridae, and Mitoviridae ) and a proposed family Bipartitiviridae [ 15 , 21 , 22 , 23 , 24 , 25 , 26 ].…”

An Overview of Mycoviral Curing Strategies Used in Evaluating Fungal Host Fitness

“…The infection of Sclerotinia sclerotiorum hypovirus 2 (SsHV2) and Botrytis virus F (BVF) in Monilinia fructicola fungus was eliminated by treatment with both of these antibiotics but was not successful in eliminating Fusarium poae virus 1 (FpV1) infection [ 25 ]. Partitiviruses are known to cause persistent infection and are difficult to eradicate [ 25 , 49 ]. Rifampicin (a derivative of rifamycin) averts the attachment of RNA polymerase to DNA in order to act as an inhibitor of RNA viruses [ 50 , 51 ].…”