农病全部英语部分.docx

农病全部英语部分.docx

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农病全部英语部分

APPLESCAB

Applescabexistsworldwidebutismoresevereinareaswithcool,moistspringsandsummers.Similarscabdiseasesaffectpears（Venturiapyrina）andhawthorns（V.inaequalissp.f.pyracanthae）.

Scabisthemostimportantdiseaseofapples.Itsprimaryeffectisreductionofthequalityofinfectedfruit.Scabalsoreducesfruitsizeorresultsinprematurefruitdrop,defoliation,andpoorfruitbuddevelopmentforthenextyear;anditreducesthelengthoftimeinfectedfruitcanbekeptinstorage.Lossesfromapplescabmaybe70%ormoreofthetotalfruitvalue.Inmostapple-producingareas,nomarketablefruitcanbeharvestedifscabcontrolmeasuresarenottaken.

Symptoms

•Atfirst,light,olive-colored,irregularspotsappearonthelowersurfaceofsepals（萼片）oryoungleavesoftheflowerbuds.

Soonafter,thelesionsbecomeolivegreengraywithavelvetysurface.

•Later,thelesion;appearmetallic（金属的）blackincolorandmaybeslightlyraised.

•Lesiononolderleavesgenerallyformontheuppersurfaceoftheleaves.Lesionsmayremaindistinctortheymaycoalesce（联合）.

•Leavesinfectedyoungremainsmallandcurledandmaylaterfalloff.Occasionally,smallscabspotsareproducedontwigsandblossoms.

•Infectedfruitdevelopcircularscablesions,velvetyandolivegreenatfirstbutlaterbecomingdarker,scabby,andsometimescracked.

•Thecuticleofthefruitisruptured（破裂、裂开）atthemarginofthelesions.

•FruitInfectedearlybecomemisshapen（畸形）andcracked,andfrequentlydropprematurely.

•Fruitinfectedwhenapproachingmaturityformonlysmalllesions,which,however,maydevelopintodarkscabspotsduringstorage.

ThePathogen:

Venturiainaequalis

•Themyceliuminlivingtissuesislocatedonlybetweenthecuticleandtheepidermalcells.

•There,itproducesshort,erect,brownishconidiophoresthatgiverisetoseveral,one-ortwo-celled,andspilocaea-type（环痕式）conidiaofrathercharacteristicshape.

•Indeadleavesthemyceliumgrowsthroughtheleaftissuesandproducesascogoniaandantheridia;followingfertilization,pseudotheciaform.Thelatteraredarkbrowntoblackwithaslightbeakandanopening.

•Eachpseudothecium（假囊壳）contains50to100asci,eachwitheightascosporesconsistingoftwocellsofunequalsize.

DevelopmentofDisease

•Thepathogenoverwintersindeadleavesonthegroundasimmaturepseudothecia.Pseudotheciacompletetheirgrowthinlatewinterandspring,andascosporesmatureastheweatherbecomesfavorableforgrowthanddevelopmentofthehost.

•Mostpseudotheciaandascimatureintheperiodduringwhichthefruitbudsopen.

•Whenpseudotheciabecomethoroughlywetinthespring,theasciforciblydischargetheascosporesintotheairwhichcarrythemtosusceptiblegreenappletissues.

•Ascosporedischargemaycontinuefor3to5weeksafterpetalfall.

•Ascosporesgerminateandcauseinfectionwhenkeptwetattemperaturesrangingfrom6to26°C.Forinfectiontooccur,thesporesmustbecontinuouslywetfor28hoursat6°C,for14hoursat10°C,for9hoursat18-24°C,orfor12hoursat26°C.

•Infections,however,aremoreabundantduringcool,wetperiodsofspring,earlysummer,andfall,whiletheyareinfrequentorabsentinthedry,hotsummerweather.

•Afterinfectedleavesfalltotheground,themyceliuminvadestheinterioroftheleafandformspseudothecia,whichcarrythefungusthroughthewinter.

Ongerminationonanappleleaforfruit,theascosporegermtubepierces（穿透）thecuticleandgrowsbetweenthecuticleandtheoutercellwalloftheepidermalcells.Atfirsttheepidermalcellsandlaterthepalisade（栅栏）andthemesophyll（叶肉）cellsshowagradualdepletionoftheircontents,eventuallycollapsinganddying.Thefungus,however,continuestoremainlargelyinthesubcuticularposition.Themyceliumsoonproducesenormousnumbersofconidia,whichpushoutward,rupturethecuticle,and,within8to15daysofinoculation,formtheolive-green,velvetyscablesions.

Conidiagerminateandcauseinfectioninthesamewayascosporesdo.

Control

•Severalapplevarietiesresistanttoscabareavailable,butmanypopularonesaremoderatelytohighlysusceptible.Itappearsthatallapplecultivarsaresusceptibletosomeapplescabfungusisolatesandresistanttoothers.

•Sofar,noeffectivepracticalbiologicalcontrolofapplescabhasbeendeveloped.

•Introducingendochitinasegenesfromfungiintoappleincreasedtheresistanceofappletoscab,butitalsoreducedvigoroftheplant.

•Shreddingofappleleaflitterortreatingthemwithureainthefallreducedtheriskofscabbyabout65%.

•Applescab,however,canbecontrolledthoroughlybytimelysprayswiththeproperfungicides.

•Sincetheearly1990s,considerableprogresshasbeenmadeindevelopingsimpleorcomputerizedapplescabpredictionsystemsofsporereleaseandinfectionforschedulingfungicideapplicationsforscabcontrol.

Thetobaccomosaicviruscanattackawiderangeofplants,includingtomato,pepper,eggplant,tobacco,spinach,petunia,andmarigold.

Ontomato,virusinfectioncauseslightanddarkgreenmottledareasontheleaves.Stuntingofyoungplantsiscommon,andoftenisaccompaniedbyadistortionandfern（蕨类植物）-likeappearanceoftheleaves.Olderleavescurldownwardandmaybeslightlydistorted.Certainstrainsoftheviruscancauseamottling,streaking,andnecrosisofthefruits.Infectedplantsarenotkilled,buttheyproducepoorqualityfruitandlowyields.

Thecucumbermosaicvirushasoneofthebroadesthostrangesofanyoftheviruses.Thediseaseaffectsanumberofimportantvegetablesandornamentalsincludingtomato,pepper,cucumber,melons,squash,spinach,celery,beets,andpetunia.

Tomatoesinfectedwiththecucumbermosaicvirusdevelopaslightyellowingandmottlingoftheolderleaves.Expandingleavestypicallybecometwisted,curldownward,anddevelopa'shoestring'appearanceasaresultofarestrictionoftheleafsurfacetoanarrowbandaroundthemidriboftheleaf.Diseasedplantsarestuntedandproducesmallquantitiesoffruit.

Thetomatospottedwiltvirusalsohasawidehostrangeandcanaffectanumberofornamentalplantsaswellastomato.Earlysymptomsofspottedwiltontomatoaredifficulttodiagnose.Young,infectedplantsmayshowaninwardcuppingofleaves,andthefoliagemayappearoff-colororhaveaslightbronzecast.Insomecases,leaveswithexhibitdarkpurpleflecksorsmallnecroticconcentricrings.

DevelopmentofDisease

Thetobaccomosaicvirusisverystableandcanpersistindrycontaminatedsoil,ininfectedtomatodebris,onorintheseedcoat.Thevirusistransmittedreadilyfromplanttoplantbymechanicalmeans.Thismaysimplyinvolvepickinguptheviruswhileworkingwithinfectedplantmaterial,theninoculatinghealthyplantsbyrubbingorbrushingagainstthemwithcontaminatedtools,clothing,orhands.Aphidsarenotvectorsofthetomatomosaicvirus,althoughcertainchewinginsectsmaytransmitthepathogen.

Thecucumbermosaicvirusoverwintersinperennialweedsandmaybetransmittedtohealthyplantsbyaphidvectors（althoughtomatoesarenotthepreferredhostofaphids）orbymechanicalmeans.

Thecucumbermosaicviruscannotwithstanddrying,orpersistinthesoil.Italsoismoredifficultthantobaccomosaictotransmitmechanically.Thus,cucumbermosaictendstoprogressmoreslowlythantobaccomosaicinafieldorgarden.

Thespottedwiltvirusistransmittedfromplanttoplantbyseveralspeciesofsmallinsectscalledthrips.Thripsarelessthanone-quarterinchinlength,lightgreentobrown,andareextremelydifficulttofindontheplants.Severalweedyhostsandornamentalplantsmayserveasalternatehostsforthevirus.

Control

Virusdiseasescannotbecontrolledoncetheplantisinfected.Therefore,everyeffortshouldbemadetopreventintroductionofvirusdiseasesintothegarden.

Manyvarietiesoftomatoareavailablewithresistancetotobaccomosaicvirus.

Sanitationistheprimarymeansofcontrollingtheothertwovirusdiseases.Infectedplantsshouldberemovedimmediatelytopreventspreadofthepathogens.

Perennialweeds,whichmayserveasalternatehosts,shouldbecontrolledinandadjacenttothegarden.

Avoidplantingtomatoesnexttocucurbits,spinach,orothervegetablesandflowerssusceptibletothesediseases.

Controlofinsects,especiallyaphidsandthrips,willhelpreducethelikelihoodofcucumbermosaicandspottedwilt.

TomatoLeafMould

ØLeafmouldisadiseaseoftomatoesonly.

ØLeafmoldisprimarilyaproblemongreenhousetomatoes.

ØThediseaseismostdestructiveinthegreenhouseduringthefall,earlywinter,andspringwhentherelativehumidityismostlikelytobehigh,andairtemperaturesaresuchthatheatingisnotcontinuous.

Whenhumidityishigh,thefungusdevelopsrapidlyonthefoliage,usuallystartingonthelowerleavesandprogressingupward.

Ifthediseaseisnotcontrolled,largeportionsofthefoliagecanbekilled,resultinginsignificantyieldreductions.Earlyinfectionsaremostthreatening.

Symptoms

Majorsymptomsoccuronthefoliagebuttheymayalsooccuronpetioles（叶柄）,stems,andfruitpeduncles（果梗）.

Allstagesofgrowthareattacked.

Thefirstleafsymptomistheappearanceofsmall,white,palegreen,oryellowishspotswithindefinitemarginsontheupperleafsurface.Onthecorrespondingareasofthelowerleafsurfacethefungusbeginstosporulate.Thefungusappearsasanolivegreentograyishpurplevelvetygrowthcomposedmostlyofspores（conidia）oftheleafmoldfungus.

Diseasedevelopmentisslowandseveresymptomsareusuallypresentonl