JournalofVirologicalMethods194 (2013) 1–6
ContentslistsavailableatScienceDirect
Journal
of
Virological
Methods
j o ur na l h o me pa g e :w w w . e l s e v i e r . c o m / l o c a t e / j v i r o m e t
Variation
in
the
transmission
of
barley
yellow
dwarf
virus-PAV
by
different
Sitobion
avenae
clones
in
China
Wenjuan
Yu
a,b,
Zhaohuan
Xu
c,
Frédéric
Francis
b,
Yong
Liu
e,
Dengfa
Cheng
a,
Claude
Bragard
d,∗∗,
Julian
Chen
a,∗aStateKeyLaboratoryforBiologyofPlantDiseaseandInsectPests,InstituteofPlantProtection,ChineseAcademyofAgriculturalSciences,Beijing100193,
China
bFunctionalandEvolutionaryEntomology,GemblouxAgro-BioTech,UniversityofLiege,PassagedesDéportés2,B-5030Gembloux,Belgium
cCollegeofAgronomy,JiangxiAgriculturalUniversity,Nanchang330045,China
dEarthandLifeInstitute,AppliedMicrobiologye-Phytopathology,UniversitécatholiquedeLouvain,CroixduSud2bte3,1348Louvain-la-Neuve,Belgium
eCollegeofPlantProtection,ShandongAgriculturalUniversity,Taian271018,China
Articlehistory:
Received10April2013
Receivedinrevisedform15July2013
Accepted18July2013
Available online xxx Keywords:
Transmissionefficiency
Barleyyellowdwarfvirus
Sitobionavenae
RT-PCR TAS-ELISA
a
b
s
t
r
a
c
t
FourteenSitobionavenaeFabricius(Hemiptera:Aphididae)clonallines(clones)originatingfromChina weretestedfortheirabilitytotransmitBYDV-PAV(oneisolatefromBelgiumandanotherfromChina) usingwheatplants.Bysequenceanalysis,thecoatproteingeneofBYDV-PAV-BEwasdistinguishable fromBYDV-PAV-CN.AlloftheclonescouldtransmitBYDV-PAV,andthetransmissionvariedfrom24.42% to66.67%withBYDV-PAV-BEandfrom23.55%to56.18%withBYDV-PAV-CN.Thesedatasuggestthat S.avenaehasnospecialtyinBYDV-PAVisolate.Significantdifferencesinthetransmissionfrequencies betweenthecloneswithBYDV-PAV-BEandBYDV-PAV-CNwereobserved.Thetransmissionefficiencies ofaphidclonesfromthemiddle-lowerreachesofYangtzeRiver(AH,HD,HDE,HZ,JZ,JYandSJ)andYunnan province(YH)weresimilar.Nevertheless,differencesinthevirustransmissionefficienciesoftheclones fromnorthern(STandSTA)andnorthwestern(QX,SBandXS)regionswereassessed.Thetransmission efficiencyofS.avenaefromnorthernandnorthwesternChina,whereBYDVimpactismoreimportant, washigherthanthatfromthemiddle-lowerreachesoftheYangtzeRiverandYunnanprovince.This workemphasizestheimportanceofconsideringaphidvectorclonaldiversityinadditiontovirusstrain variabilitywhenassessingBYDVtransmissionefficiency.
© 2013 Elsevier B.V. All rights reserved.
1. Introduction
Barleyyellowdwarfisoneofthemostdamagingcereal dis-easesworldwide.Itiscausedpredominantlybydifferentviruses currently classified into two genera, Luteovirus and Polerovirus of theplantvirusfamily Luteoviridae (Mayo and D’Arcy,1999). BYDVsdisplayahighdegreeofvectorspecificityamongdifferent aphidspecies.EachBYDVstrainistransmittedefficientlybyonlya limitednumberofaphidspecies.Nevertheless,oneaphidspecies canefficientlytransmitmorethanonevirusstrain(Rochow,1959). Four BYDV (GPV, PAV, GAV, and RMV) isolates exist in China according toRochow’s system(Zhou et al., 1987; Wang et al., 2001;Liuetal.,2007).BYDV-GAVissimilartoBYDV-MAV,which istransmittednonspecificallybytheSitobionavenaeandSchizaphis
∗ Correspondingauthor.Tel.:+861062813685;fax:+861062895365.
∗∗ Correspondingauthor.fax:+3210478697.
E-mailaddresses:claude.bragard@uclouvain.be(C.Bragard),jlchen@ippcaas.cn
(J.Chen).
graminum aphids (Wang et al., 2001), whereas the BYDV-GPV strainismorecloselyrelatedtoBYDV-RPV,whichistransmitted bybothS.graminumandRhopalosiphumpadi(Wangetal.,1998). R.padiandS.avenaeefficienttransmitPAV,whereasRMVisbest transmittedbyR.maidis(WangandZhou,2003;Zhouetal.,1984, 1987;WangandZhou,2003).Lastly,theBYDV-GPVstrainhasonly beenobservedinChina(Zhouetal.,1987).
BYDVs are transmittedby aphids in a persistent or circula-tivemanner.Acquisitionandinfectionfeedingperiodsof48hours or more are required tomaximize thetransmission rate.Once acquired,thevirusisretainedfor numerousdays,oftenfor the entirelifeofthevector.Thecirculativeviralroutethroughtheaphid bodyhasbeenpartiallycharacterized.Aphidsacquiretheviruses from infected phloem cells while feeding using their piercing-suckingstylets.Thevirionstravelupthestyletfoodcanalandinto theaphid’sgutlumen.Subsequently,thevirionstraversethe lin-ingofthehindgut,arereleasedintothebodycavity(hemocoel), andbegintocirculateinthehemolymph.Thevirionssuspendedin thehemolymphthatcontactthepairedaccessorysalivaryglands (ASG)areactivelyendocytosedintotheASGcells,transportedinto
0166-0934/$–seefrontmatter © 2013 Elsevier B.V. All rights reserved.
Fig.1. Locations(Chineseprovince&city)ofSitobionavenaeclonescollection.AH,AnhuiHefei;HD,HubeiDanjiangkou;HDE,HenanDengzhou;HL,HenanLuoyang;HZ,
HubeiZaoyang;JY,JiangsuYancheng;JZ,JiangsuZhenjiang;QX,QinghaiXining;SB,ShaanxiBaoji;SJ,SichuanJiangyou;ST,ShandongTaian;STA,ShanxiTaiyuan;XS,Xinjiang
Shihezi;YH,YunnanHonghe.
thesalivaryduct,fromwhichtheycaninfectpotentialhostplants (Gildow,1985,1993;GildowandGray,1993;Yangetal.,2008). Virus-aphidspecificitylikelyresultsfromtherecognitionbetween virionsofaspecificisolateandtheviralreceptorsintheaccessory salivaryglandsofaparticularaphidspecies(GildowandRochow, 1980;GildowandGray,1993;Peifferetal.,1997;Bencharkietal., 2000).
Althoughtheviraltransmissionefficiencyiswellknowntodiffer betweenaphidspecies(evenifthemolecularmechanismsarestill unknown),themechanismsthatdifferentiatetheabilityofdistinct aphidclonestotransmitvariousBYDVvariantsremainunknown. Atpresent,studiesonintra-specificvariationofBYDVtransmission thatwereperformedmainlywithS.graminumandR.padialways usedonevirusstrain,whichdidnotalwayscorrespondtoorigin ofthetested aphidclones(Gildowand Rochow,1983;Guo and Moreau,1996;Guoet al.,1997a,1997b;Bencharki etal.,2000; Smyrnioudisetal.,2001;Papuraetal.,2002;Dedryveretal.,2005; Duetal.,2007).
GiventhatS.avenaeisoneofthemostcommonanddestructive wheatpestsandisaprimaryvectorforBYDV-PAV,weassessedthe viraltransmissionefficiencyofadiversityofaphidclonesandvirus strainsusingawheatmodelinthisstudy.AlargecollectionofS. avenaeaphidclonesthroughoutChinawereattainedandtestedfor BYDV-PAVtransmissionintwodifferentgeographicisolates,one fromChinaandonefromEurope(Belgium).
2. Materialsandmethods
2.1. CollectionandrearingofS.avenae
FourteenS.avenaeclones werecollectedfromwinterwheat (TriticumaestivumL.)fieldsinthewheat-growingareasofChina, includingtheHuang-Huai winter (autumnsowing)wheat area,
Yangtze River winter (autumn sowing) wheat area, Xinjiang winter-springwheatarea,Qinghai-Tibetspring-winterwheatarea andtheSouthwestwinter(autumnsowing)wheatarea(Fig.1)in 2009.Allclonesweremaintainedseparatelyonseedlingsfroma susceptibleaphidwheatcultivar(cv.Toisond’or).Alloftheaphids wererearedunderconditionsthatminimizedthecontamination riskbetweenclones,i.e.,theaphidisolatesweretransferredtopots ofwheatseedlingsatthesecondstage,andeachpotwasseparated withatransparentplasticcylindercagecoveredwithgauze(12cm heightand24cmindiameter).Theaphidsandplantswere main-tainedinagreenhousecompartmentat22◦C±1,60–70%relative humidityanda16hourlightphotoperiod.
2.2. Virusstrains
The BYDV strains were obtained from Belgium, Louvain-la-Neuve (BYDV-PAV-BE) in 2009 and China, Yangling - Shannxi province (BYDV-PAV-CN)in 2011.They weremaintained sepa-ratelyonwheatseedlingscv.Toisond’orinfestedwithS.avenaeina greenhousecompartmentat20±1◦Canda16hlightphotoperiod.
2.3. RT-PCR
RT-PCR was used to identify the BYDV strain using the primer pair P5 (5-CCAGTGGTTGTGGTC-3) and P3 (5 -GGAGTCTACCTATTT-3)(Duetal.,2007).TotalRNAwasextracted fromtheplantmaterialusingtheRNeasyplantmini-kit(Qiagen, Germany)followingthemanufacturer’sinstructions.cDNA synthe-siswithRT-PCRandPCRwereperformedasdescribedbyRobertson etal.(1991)andDuetal.(2007),respectively.Theamplified prod-uctswerepurifiedandsequenced,andthesequenceswerealigned usingClustalW.ThealignedRNAsequenceswereimportedinto
W.Yuetal./JournalofVirologicalMethods194 (2013) 1–6 3
Fig.2. RT-PCRproductsofthecoatproteingenefromtheBYDV-PAV-BEisolate
usingtheprimerpairP5andP3.CN:BYDV-PAV-Chinaisolate(503bp);BE:
BYDV-PAV-Belgiumisolate(534bp).
MEGA4.0 (Tamura et al., 2007) for sequence comparison and variationanalysis.
2.4. Viraltransmissionefficiencyassays
Theplants wereassessed forthepresence of theviruswith DAS-ELISA(DSMZ,Braunschweig).Plantswithsimilaroptical den-sities (OD) were used as virus inoculums in the transmission experiments.Two-day-oldS.avenaenymphswerefedanartificial diet (infected tissue ground in a 15% sucrose-containing solu-tion)throughparaffinmembranefora48houracquisitionaccess period.Aphidswereremovedfromthemembrane,andthreewere transferredontoeachtestplant.Thirtyplantswereusedforeach condition.Aftera72hinfectionaccessperiod, theaphidswere killed.Thewheatplantswerestoredinagreenhousefor15days before observation. Transmission by each S. avenae clone was repeatedinthreeseparateexperiments.
ThepresenceoftheBYDV-PAVvirusintheleavesofinfected plantswasassessedusingDAS-ELISAfollowingthemanufacturer’s instructions(DrS. Winter,DSMZ,Braunschweig,Germany).The sampleswereconsideredpositivewhentheODvaluesweregreater thanthreetimesthemeanoftheresultsfromuninfectedcontrol leaves.
2.5. Dataanalyses
Ananalysisofvariance(ANOVAs)wasperformedusingtheGLM procedureintheSASsystem(SASInstituteInc.2001).Aone-way analysisofvariancewithtreatedaphidcloneswasconductedfor allvariables,andthemeanswereseparatedbyTukey’sstudentized rangetest(HSD)atP=0.05.
3. Results
3.1. MoleculardiagnosisofBYDVstrain
Twounique534bpand 503bpRT-PCR productwere ampli-fied for the BYDV strain from Belgium and China (Fig. 2) and were separately sequenced. In comparisons with other known Luteoviridaememberssequences,theBYDVstrainsequencefrom BelgiumwassimilartotheBYDV-PAV-Swedenisolate(Accession number:AJ563413)sequence,andtheBYDVstrainsequencefrom ChinawassimilartotheBYDV-PAV-CNisolate(Accessionnumber: EU332318.1)sequence.ThisstudyemployedtheBYDV-PAVstrain. Geneticdistanceanalysisbasedonthecoatproteingenesequences indicatedthattheBYDV-PAV-BEisolatewasdistinguishablefrom
Fig.3. GeneticdistanceanalysisforBYDV-PAVinthisstudyandotherPAVisolates
basedoncoatproteingenesequences.Accessionnumbersofpreviouslysequenced
BYDVcoatproteingenesequencesareinparentheses.BYDV-RMV(Z14123)was
usedasoutgroup.TheirgeneticdistanceswereanalyzedwithMEGA4.0usingthe
neighbor-joiningmethodwithabootstrapvalueof1000.
theBYDV-PAV-CNisolate(Fig.3),butthenucleotidesofthetwo BYDV-PAVgenewere78%similar(Fig.4).
3.2. Transmissionefficiencyofdifferentaphidclones
Fourteen geographicallyseparateS.avenaeclones were sub-mittedtotransmissionexperiments.Allaphidclonestransmitted theBYDV-PAV-BEisolateandBYDV-PAV-CNisolate(Table1).The average transmissionrate of BYDV-PAV-BE isolatewas 42.06%. A one-way variance analysis of transmission rates revealed a significant effect for the S. avenae clone (df=13, MS= 42.326, F=10.36,P<0.001).TheSTAclonetransmittedat66.67±3.84%, whereas theHDE clone transmitted at only 24.42±2.21%. The most efficient S. avenae clone transmitted BYDV-PAV approxi-matelythreetimesmoreefficientlythantheleastefficientaphid strain.TheaveragetransmissionratefortheBYDV-PAV-CNisolate was35.08%,whichwaslowerthanfortheBYDV-PAV-BEisolate.A significanteffectofthecloneontransmissionratewasobserved (df=13, MS= 8.219,F=23.5, P<0.001). TheSTA clone transmit-tedat56.18±5.22%,whereasetheHDEclonetransmittedatonly 23.55±1.36%.ThemostefficientS.avenaeclonetransmittedthe BYDV-PAVapproximately2.4timesmorethantheleastefficient clone.Thetransmissionefficiencyoftheclonesfromthe middle-lowerreachesoftheYangtzeRiver(AH,HD,HDE,HZ,JZ,JYandSJ) andtheYunnanprovince(YH)werenotsignificantlydifferent,and neitherwerethetransmissionefficienciesoftheclonesfromthe northern(STandSTA)andnorthwestern(QX,SBandXS)regions. Lastly,thetransmissionefficiencyofS.avenaefromthenorthern andnorthwesternregionswashigherthanfromthemiddle-lower reachesoftheYangtzeRiverandtheYunnanprovince.
4. Discussion
BYDVs have been previously demonstrated to display high degreesofvectorspecificityamongdifferentaphidspecies,where each virusistransmittedefficiently byonlyoneorafew aphid species.InChina,Duetal.(2007)reportedthatBYDV-PAVwas effi-cientlytransmittedbyR.padi-LaandS.avenae-LabutpoorlybyS. graminum-La.S.graminum-LaandS.avenae-La.M.dirbodum exhib-itedtransmissionratesof75%withBYDV-GAV,andBYDV-GPVwas transmittedby S.graminum-La andR. padi-Laat approximately 80%and50%,respectively.TheChineseBYDV-PAVandBYDV-GAV isolatesaremembersofLuteovirusanddistinguishablefromtheir relativesisolatedinothercountries.BYDV-GPVisadistinctvirusin China.Itharborsapolerovirus-likecoatproteingeneandisclosest toCYDV-RPVandCYDV-RPSbutlacksaserologicalrelationshipall U.S.isolates(Duetal.,2007).
In thisstudy,theS.avenaecloneswerefromChina,and the BYDV-PAVswerefrom Chinaand Belgium,Europe.The genetic
Fig.4. AlignmentofBYDV-PAV-BEandBYDV-PAV-YL-CN.Upperline:BYDV-PAV-BE,lowerline:BYDV-PAV-YL-CN.Identity=77.93%(392/503),Gap=5.81%(31/534).
distanceanalysisbasedonthecoatproteingenesequences indi-catedthattheBYDV-PAV-BEisolatewasdistinguishablefromthe BYDV-PAV-CNisolate,but thenucleotidesequences ofthe two BYDV-PAVgeneswere78%similar.TheBelgianvirusstrainwas usedtoassessthetransmissibilityofnon-vector-associatedaphid clones.OurresultsdemonstratedthatallChinesecloneswereable totransmitBYDV-PAV-BEatdifferentefficiencyrates.The trans-missionratesvariedfrom24to67%withtheBYDV-PAV-BEisolate andfrom23to56%withtheBYDV-PAV-CNisolate.Theseresults arepartlyconsistentwithpreviousBYDV-PAVtransmission stud-iesusingdifferentS.avenaeclones.GuoandMoreau(1996)and Guoetal.(1997a,1997b)observedatransmissionrange of0to 76% among 21 clones collected from 4 French regions. Papura etal.(2002)tested39F1progenyand observeda0%to88%of viraltransmissionrates.Notably,theBYDV-PAVsdidnotpossess anynon-vectorstrainsinthisstudy.Indeed,allstrains transmit-tedboth BYDV-PAVisolatesatleastat a20%transmissionrate, whereasanextremelylargeareaforaphidstraincollectionwas investigated. Thisfinding providessome context to theresults from Bencharki et al. (2000), who reported that the transmis-sionefficiency of S. avenaewas generally dependent upon the PAVisolate.Considering apool ofaphidclones,thefinal trans-missionratewasextremelysimilarevenfordifferentBYDV-PAV strains.
Little is known about why such diversity in transmission ability exists.van den Heuvel etal. (1994, 1997) have demon-stratedthatsymbionin,aGroELhomologousproteinsynthesized byendosymbioticbacteriaandsecretedintotheaphidhemolymph, isessentialforefficientLuteovirustransmission.Additionally,they revealedthatsymbioninfromdifferentaphidspeciescouldbindto Luteoviridaeinvitrowithdifferentaffinities.Bencharkietal.(2000) suggestedthattheobservedintraspecificvariabilityin transmis-sionefficiencymayberelated,atleastinpart,todifferencesinthe movementabilityoftheBYDVvirusthroughouttheepithelialcell barriersatthehindgutand/ortheaccessorysalivaryglandsinthe differentclonesortothestabilityofthevirusinthehemolymph. Symbioninoftheinefficientaphidsub-clonesmaybereleasedat lowconcentrationsorexhibitalowbindingaffinityforthevirus. Althoughendosymbiontsmayparticipateinstabilizingvirus par-ticles,Burrowsetal.(2007)didnotbelievethattheydetermine vectorcompetencebecausetheyobservedthatthehindgutand accessorysalivaryglandbarrierstotransmissionweregenetically controlledandseparatedinF2S.graminumhybrid.Further func-tionalexperimentsusingomicstoolsaremeritedtoelucidatethe molecularmechanismsofthevirus-aphidinteractionsandto char-acterizetheparticipatingproteins.
Takentogether,theresultssuggestthatboththeS.avenaeclone and the BYDV-PAVstrains must beconsidered when assessing
W.Yuetal./JournalofVirologicalMethods194 (2013) 1–6 5
Table1
ComparisonoftransmissionefficiencyofBYDV-PAVbetweenSitobionavenaeclones.
Locality Code TransmissionratesofBYDV-PAV-BE(%) TransmissionratesofBYDV-PAV-CN(%)
Repeat1 Repeat2 Repeat3 Mean±SEb Repeat1 Repeat2 Repeat3 Mean±SEc
Huang-Huaiwinter(autumnsowing)wheatareaandYangtzeRiverwinter(autumnsowing)wheatarea
AnhuiHefei AH 40.00(10d) 33.33(10) 40.00(10) 37.78±2.22CDE 34.19(10) 32.96(10) 30.83(10) 32.66±1.70C
HenanDengzhou HDE 26.67(8) 26.67(8) 20.00(6) 24.42±2.21E 22.89(10) 25.11(10) 22.65(9) 23.55±1.36D
HenanLuoyang HL 40.00(10) 46.67(10) 40.00(10) 42.23±2.23BCDE 31.61(10) 29.32(10) 37.76(10) 32.90±4.36C
HubeiDanjiangkou HD 33.33(10) 26.67(8) 40.00(10) 33.32±3.85DE 27.59(10) 29.36(10) 30.79(10) 29.54±1.60CD
HubeiZaoyang HZ 40.00(10) 33.33(10) 26.67(8) 33.33±3.85DE 30.16(10) 31.08(10) 34.23(10) 31.82±2.13CD
JiangsuYancheng JY 40.00(10) 40.00(10) 33.33(10) 37.78±2.22CDE 37.30(10) 36.82(10) 38.03(10) 37.38±0.61C
JiangsuZhenjiang JZ 26.67(8) 26.67(10) 40.00(10) 31.12±4.44DE 29.61(10) 31.10(10) 33.35(10) 31.35±1.88CD
ShaanxiBaoji SB 66.67(10) 53.33(10) 60.00(10) 60.00±3.87AB 30.61(8) 28.31(10) 36.91(10) 31.94±4.45CDa
ShandongTaian ST 46.67(10) 53.33(10) 46.67(10) 48.89±2.21ABCD 46.46(10) 49.65(10) 42.72(10) 49.61±3.13B
ShanxiTaiyuan STA 73.33(10) 66.67(10) 60.00(10) 66.67±3.84A 50.36(10) 60.45(10) 57.74(10) 56.18±5.22A
Xinjiangwinter-springwheatarea
XinjiangShihezi XS 53.33(10) 46.67(10) 33.33(10) 44.43±5.87BCD 29.39(10) 30.83(10) 36.44(10) 32.22±3.72C
Qinghai-Tibetspring-winterwheatareaandSouthwestwinter(autumnsowing)wheatarea
SichuanJiangyou SJ 46.67(10) 40.00(10) 40.00(10) 42.23±2.23BCDE 36.77(10) 36.81(10) 36.64(10) 36.74±0.09C
QinghaiXining QX 66.67(10) 53.33(10) 46.67(10) 55.56±5.89ABC 38.13(10) 34.12(10) 37.90(10) 36.72±2.25Ca
YunnanHonghe YH 26.67(10) 40.00(10) 26.67(8) 31.12±4.44DE 30.65(10) 28.83(10) 27.73(10) 29.07±1.47CD
Horizontal,Two-samplet-test.
aSignificantlydifferenttransmissionefficiencybetweenthetwoBYDV-PAVisolateareindicated(n=3,P<0.05).Vertical:One-wayANOVA,Tukey’sstrudentizedrange
test(HSD).
bMeanswithincolumnsfollowedbythesameletterarenotsignificantlydifferent(df=13,MS=42.326,F=10.36,P<0.0001).
c Meanswithincolumnsfollowedbythesameletterarenotsignificantlydifferent(df=13,MS=8.219,F=23.5,P<0.0001).
d No.ofviruliferousaphids.
aphid-virusinteractions.Boththeaphidspeciesandtheviralclones shouldbeconsideredforviraltransmissionassessment.Moreover, theheterogeneityofaphidclonesfromacommongivenspecies, suchas S. avenae, is extremely high and thus must be signifi-cantlysampledforthoroughrepresentation.Indeed,ifmostofthe clonesdisplayedextremelysimilarvirustransmissionefficiencies betweentheBYDV-PAV-BEandBYDV-PAV-CNstrains,wherehalf oftheclonesdisplayeda10%orlesschangesinviraltransmission efficiency,andmorethanaquarteroftheclones(4of14clones) exhibiteda20to30%virustransmissionvariationamongthe BYDV-PAVstrains.Moreover,twoclones(fromShaanxiBaojiandQinghai Xining)displayedhighlysignificantchanges(from40to90%rate increases)whenswitchingfromaBYDV-PAVtootherstrain.These resultsweresystematicallyobservedwithBYDV-PAV-BE,whichisa strainthatdoesnotoccurco-geographicallywithothertestedaphid clones.Thisfindingisimportantgiventhataphidsaredispersed regionallyandinternationally.Becauseatwotothreefoldincrease inviraltransmissionisduetoanewefficientaphidcloneina par-ticulararea,extensivedamageandyieldlossescouldoccur.Inthis study,thetransmissionefficiencyofS.avenaefromnorthernand northwesternChinawashigherthanthatfromthemiddle-lower reachesof theYangtze River and Yunnan province. Coinciden-tally,BYDVspredominantlycausedwheatyellowdwarfdiseases throughoutthenorthernandnorthwesternprovincesofChina(Jin etal.,2004).Duetal.(2007)alsodemonstratedthattheclones thatdisplaythehighesttransmissionefficiencywerefromahighly prevalentBYDVarea. Theseresultssuggestthatassessing varia-tionforviraltransmissionbyidentifyingtheaphidspecieswillbe immenselyinterestingforepidemiologicalstudies.
Analysisofaphidtransmissionefficienciesisparticularly sig-nificanceforresearchingitsmigrationpath.Usingmicrosatellite markers,Wang(2007)inferredthat:(i)S.avenaearehighly migra-torythroughoutthemiddle-lower reachesoftheYangtzeRiver wheatgrowingareaofChina;(ii)S.avenaearehighlymigratory throughoutthenorthandnorthwestwheatgrowingareaofChina; (iii)themicrosatellitemarkeranalysesdidnotsupportthe con-clusionthatS.avenaeoverwintersinthesouthandmigratesnorth inthespring.Theaboveconclusioncoincideswiththeresultof ourstudy:(i)thetransmissionefficienciesoftheclonesfromthe
middle-lowerreachesoftheYangtzeRiver(AH,HD,HDE,HZ,JZ,JY andSJ)didnotdiffer;(ii)thetransmissionefficienciesoftheclones fromthenorthern(STandSTA)andnorthwestern(QX,SBandXS) areasofChinadidnotdiffer;(iii)andthetransmissionefficiencyof S.avenaefromthenorthernandnorthwesternregionswashigher thanfromthemiddle-lowerreachesoftheYangtzeRiver.
Inconclusion,furtheranalysisofthevirus-aphidinteractions aremeritedtoelucidatethemechanismsofvirusacquisition, trans-portandavailabilityintheaphidvectorsbyintegratinghighand lowtransmittingefficiencyclonesandcomparingthem.Further researchmayprovidefurthercontextformonitoringthe occur-renceofimportanttransportersand/orreceptorsinefficientaphid vectorsandforidentifyingpotentialinhibitor/competitorsof virus-bindingproteinstocontrolvirusdispersion.Abetterunderstanding ofviraltransmissionefficiencyinaphidsmaychange epidemiolog-icalmodelsthatareappliedtoplantvirusesinregionalareasand mayimprovecontrolstrategiesforaphid-virusassociations. Acknowledgements
This study was supported by the International Cooperation ProjectbetweenChinaandBelgium(2010DFA32810),and Inter-University Targeted Project between Belgium and China (PIC SHANDONG) was funded by the Cooperation universitaire au développement (CUD), and Modern Agro-industry Technology ResearchSystem(2060302).
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