农病全部英语部分.docx
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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
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