Preliminary Studies on the Effects of Oyster Mushroom Spherical Virus China Strain on the Mycelial Growth and Fruiting Body Yield of the Edible Mushroom Pleurotus ostreatus

Abstract

Oyster mushroom spherical virus (OMSV) is a positive-sense single-stranded RNA mycovirus which is associated with a devastating oyster mushroom die-back disease. However, little is known about its diversity, and the effects of OMSV infection on its fungal host are not well understood. In this study, we determined the nearly complete nucleotide sequence of OMSV isolated from cultivated oyster mushrooms in China. Sequence analysis suggested that the virus represents a new strain of OMSV (referred to here as OMSV-Ch). A GenBank BLAST search of the genomic sequences demonstrated that the OMSV-Ch had the highest identity (74.9%) with the OMSV from Korea (OMSV-Kr). At the amino acid–sequence level, these two strains shared 84.1% identity in putative replication protein (RP) and 94.1% identity in coat protein (CP). Phylogenetic analysis based on RP showed that OMSV-Ch clustered with OMSV-Kr, closely related to Tymoviridae. Phylogenetic analysis based on both the RP and CP showed that OMSV had a distant clade relationship with tymoviruses, marafiviruses, and maculaviruses. We obtained the OMSV-Ch-free Pleurotus ostreatus strain via single hyphal tip cultures combined with high-temperature treatment. Preliminary studies indicate that OMSV-Ch can significantly inhibit mycelial growth, cause malformations of the fruiting bodies, and reduce the yield of P. ostreatus. Co-cultivation resulted in horizontal transmission of the OMSV-Ch to a virus-cured strain. The findings of our study contribute to the prevention and control of mycoviral diseases in the future.

Multiplex Detection of Pleurotus ostreatus Mycoviruses

“…To evaluate specificity for the P. ostreatus mycoviruses detection, the established multiplex RT-PCR assay was used to determine the incidence of mycoviruses. The healthy P. ostreatus sample (virus-cured strain 8129 [ 31 ]) acted as a negative control with no observed virus amplification, as expected. The incidence of both single or mixed infections in different P. ostreatus strains produced clear and specific target bands on an agarose gel ( Figure 4 ).…”

“…After PCR amplification, the products were examined by electrophoresis in 1.5% agarose gel. The healthy P. ostreatus sample (virus-cured strain 8129 [ 31 ]) acted as a negative control.…”

“…Pleurotus ostreatus (oyster mushroom) is a widely cultivated edible fungus worldwide, with high nutritional and medicinal values [ 28 ]. Several mycoviruses have been previously discovered and identified in P. ostreatus , including dsRNA viruses, such as an oyster mushroom isometric virus (OMIV), Pleurotus ostreatus spherical virus (POSV), Pleurotus ostreatus virus 1 (PoV1), and (the only ssRNA virus) oyster mushroom spherical virus (OMSV) [ 12 , 15 , 29 , 30 , 31 ]. Infection with various mycoviruses differs in the effects on the morphology and physiology of P. ostreatus .…”

“…A recent transmission study on A. bisporus revealed that the mushroom virus X (MVX) can be horizontally transferred via mycelia from an infected strain to five other uninfected strains [ 35 ]. Our previous studies have shown that the OMSV can be horizontally transmitted from the OMSV-infected strain to a virus-cured strain [ 31 ]. Due to these transmission patterns, it can be a challenge to prevent mycovirus diseases, especially in edible mushrooms.…”

“…As reported, a few attempts to eliminate mycovirus infections have been described for several edible mushroom species. For example, the methods of growth on a limited nutrient medium containing cAMP and rifamycin, single hyphal tip cultures combined with high-temperature treatment, protoplast regeneration, or mycelial fragmentation were used for curing the OMSV, OMIV, POSV, and PoV-ASI2792 from the virus infected P. ostreatus strains [ 12 , 28 , 31 , 36 ]. Moreover, ribavirin treatment and mycelial fragmentation were also used for curing Lentinula edodes mycovirus HKB (LeV-HKB) and L. edodes partitivirus 1 (LePV1) from Lentinula edodes [ 37 ].…”