The Diversity Analysis Of Mycoviruses In Fusarium Asiaticum And Molecular Characteristics Of Bunyavirus FaBV1

Fusarium head blight(FHB)is a worldwide spread serious fungal disease of wheat,which is caused by Fusarium spp,and is resporsible for the huge loss ofproduction and quality of wheat.This disease usually occures in the winter wheat planting area of middle and lower reaches of Yangtze river basin,northeastern spring wheat-planting area,and the south part of northern wheat area.At present,the control stratigies of FHB are mainly relay on chemical controls.However,this methord can easily lead to a series of problems,including pesticide residues,the environment pollution,and the induction of resistance and so on.Mycoviruses have potential to biocontrol plant fungal diseases.The RNA mycovirus(CHV1)has been successful applied in controlling European chestnut blight,and a DNA mycovirus(SsHADV-1)can reduce the incidence of rapeseed stem rot disease under natural conditions.In this research,the virus diversity of F.asiaticum was analysized via HighThroughput Sequencing,and we found some new mycoviruses in F.graminearum.Oure research provided potential mycovirus resources for FHB biocontrol.The main results of our research were shown as following.F.asiaticum harbors rich diversity viruses.In the present study,the diseased wheat tissues were collected from Xiaogan,Suizhou of Hubei Province and Nanjing of Jiangsu Province and used for pathogen isolation.Finally,350 purified F.asiaticum strains were obtained,and all of the isolates of Fusarium asiaticum were identificated.Mycoviused were screened by deep sequencing,and 68 contigs that were related to reported viruses were detected in total.Homology analysis indicated that the nucleic acid type of these viruses can be divided into three types including +ssRNA,-ssRNA and dsRNA.Among them,63% contigs are related to +ssRNA viruses,which are mainly belonging to Hypoviridae,Narnaviridae,Alphaflexivridae,Fusariviridae and some unclassified virus families;10% contigs are related to-ssRNA viruses,which were mainly belonging to Mymonaviridae and unclassificated virus families within Bunyavirales;27% contigs are related to dsRNA viruses,which are mainly belonging to Partitivivirdae,Botybirnaviridae and unclassified virus families.The molecular characterizations of a bunyavirus FaBV1 of F.graminearum were analysized.The full length cDNA of large(L-)segment and small(S-)segments of FaBV1 were obtained by transcriptome sequencing analysis and RACE techque,but the middle(M-)segment of FaBV1 was still unknown.The full length of L-segment is composed of 6468 nts,which contains a single ORF encoded L-protein.L-protein has a conserved domain that was identified to Bunyavirus replicase.The cDNA of S-segment is composed of 1420 nts which contained a single ORF encoded a viral nucleocapsid protein.The terminal sequences of L and S segment from FaBV1 genome have 11 highly conserved nucleotides(3'-UGUGUUUCUGG---CCAGAAACACA-5').Moreover,the highlyconserved 5' and 3' sequences are reverse complementarity.Multiple alignment analysis and phylogenetic analysis were conducted based on FaBV1 L-protein and nucleocapsid protein sequences,which showed FaBV1 belongs to Bunyavirus,but still forms an independent phylogenetical branch.Considering the difference of natural host of viruses,we proposed to create a new family Fusarbunyavidae and a new genus Fusarbunyavirus to accommodate FaBV1(Fusarium asiaticum bunyavirus 1).One hundred conidiospores were respectively isolated from strain XG-7 and only two conidiospore-isolates habor FaBV1,which suggests that the transmission efficiency via monospores is low.The biological characteristics of the single-spore strains xg-7-001vf(virus-free)and xg-7-022(FaBV1-infected)was compared,and the virus infected strain xg-7-022 showed a slow growth rate and has lower virulence on its host.Thus,our results suggested that FaBV1 could responsible for hypovirulence on F.asiaticum.