Study Of A Hypovirulent Strain B36 Of Rhizoctonia Solani

Mycoviruses are those viruses which infect fungi.Mycoviruses have been found to be present in all the major groups of fungi.Mycoviruses have genome with ds RNA,positive ss RNA,negative ss RNA and rarely DNA.Some mycoviruses that could cause hypovirulence on phytopathogenic fungi have potential to develop virocontrol agents for combating fungal diseases.Rhizoctonia solani causing rice sheath blight diseased is responsible for large loss in rice production annual.Screening mycoviruses related to hypovirulence from R.solani population is a potential strategy to control rice sheath blight disease.Based on the previously study of high-though RNA sequencing data of R.solani strains,several virus contigs were related to hypovirus and confirmed to be partial genome of a novel hypovirus.This hypovirus temporarily named as Rhizoctonia solani hypovirus1(Rs HV1).Strain B36 of R.solani was confirmed to harbor Rs HV1 based on RT-PCR results.Strain B36 showed hypovirulent phenotypes including lower virulence on the detached leaves of rice.ds RNA extraction revealed that strain B36 contained five ds RNA elements,and after identification of these elements suggested that strain B36 of R.solani was infected by 4 different mycoviruses including a novel hypovirus-like virus Rs HV1,and three other mycoviruses that related to Rhizoctonia solani RNA virus HN008(accession number: YP＿009158859.1),Rhizoctonia solani ds RNA virus 1(accession number:AFZ85210.1),and Rhizoctonia solani ds RNA virus 2(accession number:YP＿009011230.1),respectively.The RNA sequencing of strain B36 contained 8 contigs from Rs HV1 and gaps between these contigs were confirmed using RT-PCR to finally get7 kb sequence of Rs HV1.The obtained partial sequence of Rs HV1 showed 54% identity with ployprotein of Sclerotinia sclerotiorum hypovirus 2 and 21% similarity with corresponding polyprotein region of Cryphonectria hypovirus 1.Rs HV1 belongs to the genus hypovirus in the family of Hypoviridae.When Rs HV1-free strain 190 and virusinfected strains B36 were grown together on a single PDA and found that Rs HV1 could horizontally transmit from strain B36 to strain 190 via hyphal contact,but other mycoviruses in strain B36 was failed.The newly Rs HV1 infected strain showed hypovirulent,which preliminarily confirmed that Rs HV1 was responsible for hypovirulence on R.solani and had a strong infection compared to other mycoviruses infected strain B36.Strain B36 of R.solani and Rs HV1-free strain N36 of Sclerotinia sclerotiorum were co-cultured in a single PDA plate and result suggested that Rs HV1 could successfully transmit from R.solani to S.sclerotiorum,which revealed that Rs HV1 could break limitation of the vegetative incompatibility of host fungi from different groups of fungi.Summarizing all the research,the hypovirulent strain B36 harbors multiple mycoviruses including a novel hypovirus Rs HV1 that was firstly reported hypovirus in R.solani.Rs HV1 was related to hypovirulent phenotypes of R.solani and could horizontally transmit between strain of R.solani and S.sclerotiorum by hyphal contact,which showed Rs HV1 has great potential of infectivity of fungal pathogens and used for biological control fungal disease.