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

Sokty Neang,Lakha Salaipeth,Pisut Keawmanee,Ikuo Sato,Ratiya Pongpisutta,Sansern Rangsuwan,Daigo Takemoto,Chainarong Rattanakreetakul,Soriya Rin,Hideki Kondo,Sotaro Chiba,Nobuhiro Suzuki,Masao Arakawa,Santiti Bincader,Subha Das

doi:10.3390/v13112269

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.

Highlights

These results suggested that most of the six partitiviruses were widespread in R. oryzaeTSS190401 could not bethe detectable similarFor contigs of RosPV3 could be sativae population with ability tobycoinfect a single example, TSD190113 was coinfected by RosPV2, RosPV3, RosPV6, and Rhizoctonia oryzae-sativae partitivirus 1 (RosPV1)-like viruses
A total of 21% of all tested fungal isolates carry multiple double-stranded RNA (dsRNA) elements with a potential of viral origin (Figure 1, Tables 2 and 3), dsRNA-negative isolates might carry mycoviruses that were below the detection limit
Sequence alone is not sufficient to accurately confirm the fungal taxonomic placement, it showed that R. oryzae-sativae TSD190106, TSD190113, TSD190119, and TSD190133 were considered genetically close (100% identical internal transcribed spacer (ITS) sequences) despite harboring marginally different dsRNA profiles (Figure 1E, Table S2)

Summary

Introduction

Rice (Oryza sativa L.) is a staple food crop in most Asian countries, and its production is threatened by many pathogenic microbes, such as Rhizoctonia solani (rice sheath blight), Pyricularia oryzae (leaf blast), and Xanthomonas oryzae pv. Oryzae (bacterial blight) [1]. R. oryzae and R. oryzae-sativae (teleomorph: Waitea circinata, Ceratobasidium oryzaesativae, respectively) are soil-borne basidiomycetous fungal pathogens known to cause aggregate sheath spots on rice plants worldwide [2,3]. Aggregated sheath spots diseases are reported to cause yield loss up to

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