Occurrence Of Main Viruses Infecting Wheat In China And Molecular Diversity Of BYDV-PAV Between China And The Czech Republic

Wheat is the second most important cereal crop in the world.In its growth,more than 50 viruses will affect its the production.However,detailed knowledge of virus occurrence and dynamic in wheat in China in recent years is very limited.In this study,a survey for insect-transmitted viruses was carried out over 3-years,covering major wheat-growing regions of China.Furthermore,a comparison was done between coat protein(CP)and readthrough proteins(RTP)of Barley yellow dwarf virus(BYDV)-PAV from China and the Czech Republic.Additionally,a novel iflavirus from Psammotettix alienus(Hemiptera: Cicadellidae)was identified and characterized.In order to determine the prevalence of different viruses in wheat,747 plant samples of wheat,barley and oat showing typical symptoms of virus infection were collected from different regions of China from 2017 to 2019.Seven wheat viruses viz.,barley yellow dwarf virus-PAV,BYDV-GAV,BYDVGPV,wheat dwarf virus(WDV),barley yellow striate mosaic virus(BYSMV),rice black-streaked dwarf virus(RBSDV)and northern cereal mosaic virus(NCMV)were detected simultaneously using multiplex reverse transcriptase-polymerase chain reaction(M-RT-PCR).Maximum 48.5,39.37 and 38.96% of the samples were positive to BYDV-PAV from 2017 to 2019,respectively.Prevalence of BYDV-GAV(14.5,11.3 and 7%),BYDV-GPV(1.5,0.9 and 0.92%),WDV(5.5,9.95 and 12.31%),BYSMV(7.0,6.33 and 2.45%)and RBSDV(7.5,5.43 and 2.76%)was determined during 2017-2019,respectively,whereas NCMV was detected only in 2019 with 0.92%.These results indicated that BYDV-PAV is prevailing and the most dominant in different growing regions of China.Therefore,a sustainable management strategy focusing BYDV-PAV should be planned to avoid any severe epidemic in future.The CP and RTP gene sequences of sixty BYDV-PAV isolates were compared among the isolates collected from different regions in China.Reconstruction of the phylogenetic tree formed two clades in both genes.CP sequences: SDJN17-1,SDJN18-1,SDJN18-3,SDJN-19-1,SDJN19-3 and SXLF19-1 showed the highest variation comparing to the other isolates.In RTP analysis,SDJN17-1 formed one clade with other country's isolates,clade number(2),separately;and other Chinese isolates were divided into two small subclades.All samples collected from Kunming,Yunnan(YNKM)and Yangling,Shaanxi(SXYL)were clustered in the same subclade number(2)together with some samples from Linfen,Shanxi(SXLF),Hanzhong,Shaanxi(SXHZ),Tianshui,Gansu(GSTS),and Yuanyang,Henan(HNYY).The isolates from Linfen,Shanxi(SXLF),Dongyang,Shanxi(SXDY),Hancheng,Shaanxi(SXHC),Chengdu,Sichuan(SCCD),Zhengzhou,Henan(HNZZ),Jinan,Shandong(SDJN),Shijiazhuang,Hebei(HBSJZ),Yuanyang,Henan(HNYY),Mianyang,Sichuan(SCMY)and Wuhan,Hubei(HBWH)were together in subclade number(1).The RTP gene of SDJN17-1 was showing the highest diversity among all isolates of different regions.Nucleotide identity level for CP and RTP was ranging between(80.8-99.9%)and(73.3-99.9%)among the isolates respectively.Genetic diversity is an essential part of the biology of viruses that has directly affected the epidemiology of the disease.To study the molecular diversity and population structure of BYDVs in China and Czech Republic,the CP and RTP genes of 24 Chinese isolates and 18 Czech isolates of BYDV-PAV collected from different regions of China and the Czech Republic were sequenced.Together with 7 CP,16 RTP sequences of BYDV-PAV from NCBI database,the molecular diversity of BYDV-PAV was compared by nucleotide identity position,phylogenetic analysis and nucleotide diversity.The nucleotide identities of Chinese isolates were CP(76.1-99.3%),RTP(ORF5)(55.2-89.1%)and RTP(ORF3+ORF5)(62-97.9%)to that of other isolates.Phylogenetic analysis showed that 20 Chinese isolates were formed in the same clade in all gene analysis;however,SDJN17-1,SDJN18-1,SDJN19-1 and SXLF-19-1 sequences were clustered different clade in CP and RTP analysis;whereas SDJN17-1 was more related to the Czech isolates in RTP analysis.However,according to nucleotide diversity test,estimated BYDV-PAV population was more expanded and slightly higher diversity in the Czech Republic than China.In addition,the full genome of a novel iflavirus was identified in leafhopper P.alienus collected from Langfang in Northern China.According to the genome organization and phylogenetic analysis,the virus is a novel iflavirus in the order Picornavirales.The full genomic sequence was 10,710 nt in length,including poly-A tail and was tentatively named Langfang leafhopper iflavirus(LfLHV).Its genome consists of only one open reading frame(ORF),9,453 nt in length,encoding a polyprotein(3150 aa).Both phylogenetic analysis of polyprotein and RdRp showed that Lf LHV was closely related to the members of the family Iflaviridae.LfLHV genome sequence showed 45.52% amino acid sequence identity to a hypothetical protein of Hubei-picorna like virus 29.