| Rice sheath blight is one of the three major diseases in rice production,which is seriously harmful to the yield and quality of rice.So far,no rice cultivars with high resistance to sheath blight have been available,so the control of the disease mainly depends on chemical methods.Because of the harm of chemical control to the environment,it is particularly important to open up new green and environmentally friendly control methods for rice sheath blight.Mycovirus(fungal virus)is a kind of virus that infects fungi and lives in them,some of which have a remarkable effect on weakening the pathogenicity of their fungal hosts and these mycoviruses possess wide application value for biological control.The fact provides a new thinking for the control of rice sheath blight.However,the research of mycoviruses in Rhizoctonia solani AG-1 IA starts relatively lately and the progress is slow.Based on the reported mycoviruses in R.solani AG-1 IA,in this research,the strains of R.solani AG-1 IA stored in our laboratory were used as the research materials to detect the dsRNAs in R.solani AG-1 IA by molecular detection technique,in order to discover more novel mycoviruses.Moreover,the mycovirus in strain D168 was extracted and its genome sequence was obtained,and its genomic structure and phylogenetic status were investigated.The main results of this paper are as follows:(1)On the basis of the mycoviruses(RsRV1,RsPV2 and RsRV-HN008)reported in R.solani AG-1 IA,eight strains with novel mycoviruses were obtained from sixteen strains of R.solani AG-1 IA,which contained mycoviruses and screened in the previous study of our laboratory.The mycovirus in strain D168 was selected for further investigation.(2)Based on the mycoviruses(RsRV1,RsPV2,RsRV3,RsRV-HN008 and RsRV4)discovered in R.solani AG-1 IA,a total of four strains with novel mycoviruses were obtained by further screening of the strains of R.solani AG-1 IA stored in our laboratory,including the strains with mycoviruses screened in the previous study of our laboratory.(3)A novel mycovirus was isolated from the strain D168 of R.solani AG-1 IA,which consists of two dsRNA fragments,named dsRNA-1 and RNA-2.The result of sequence homology analysis showed the novel mycovirus has the highest similarity of 61% with RsPV2 reported in R.solani AG-1 IA.Therefore,the novel mycovirus was preliminarily identified as a novel mycovirus of Alphapartitivirus and designated as Rhizoctonia solani dsRNA virus 4(RsRV4),whose sequence has been submitted to the NCBI database.(4)The result of RsRV4 genomic structure analysis showed that the length of dsRNA-1 and dsRNA-2 were 1990 bp and 1731 bp,respectively,and Both dsRNA-1 and dsRNA-2 contain a ORF,which codes RNA-dependent RNA polymerase(RdRp)and coating protein(CP),respectively.The terminal alignment of the RsRV4 showed that there are high conservatism between the 5 ’end of dsRNA-1 and the 5’ end of dsRNA-2 and between the 3 ’end of dsRNA-1 and the 3’ end of dsRNA-2.(5)The result of phylogenetic analysis based on the RdRps of RsRV4 and twenty-three other mycoviruses showed that RsRV4,Rhizoctonia solani dsRNA virus 2,Spinach cryptic virus 1,Beet cryptic virus 1 and White clover cryptic virus 1 clustered in the same pedigree with Alphapartitivirus pedigree.Moreover,RsRV4 and RsPV2,the virus of Alphapartitivirus that was previously found in our laboratory,clustered in the same branch,indicating that the relationship between RsRV4 and RsPV2 is the closet,which further proved that RsRV4 is a novel mycovirus of Alphapartitivirus.(6)The amount of sclerotia for both strain A and strain B is relatively abundan and the growth rates of strain D168 and strain GD118 are similar,but the pathogenicity of strain D168 is weaker,speculating that RsRV4 may cause a certain effect on the pathogenicity of strain D168. |
