Citrus Blight

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Material Information

Title:
Citrus Blight
Physical Description:
Fact sheet
Creator:
Derrick, K.S.
Publisher:
University of Florida Cooperative Extension Service, Institute of Food and Agriculture Sciences, EDIS
Place of Publication:
Gainesville, Fla.
Publication Date:

Notes

Acquisition:
Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Melanie Mercer.
Publication Status:
Published
General Note:
"Publication date: January 1993. Reviewed: October 1994."
General Note:
"PP-151"

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Source Institution:
University of Florida Institutional Repository
Holding Location:
University of Florida
Rights Management:
All rights reserved by the submitter.
System ID:
IR00004633:00001


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FactSheetPP-151 October1994CitrusBlight1 K.S.Derrick2Citrusblightisamajorproblemofcitrusin Floridaandisresponsibleforthelossof approximately650,000producingtreeseachyear. Treeswithblightseldomdie,butshowageneral declinesomewhatsimilartodroughtstress. Frequently,symptomswillfirstdevelopinonesector ofatree.Infectedpartsofthetreeappearunthrifty withadull-greencast.Asthediseaseprogresses,the canopythinsandproducessmallfruit.Infectedtrees haveoffseasonflushandbloompatternsand frequentlyproducetrunkandrootsprouts.Blightis adiseaseofproducingcitrustrees;symptomshave neverbeenobservedontreeslessthanaboutfour yearsold.Allrootstock-scioncombinationsappearto besusceptibletoblight,buttheincidenceofthe diseasevarieswithrootstock.Roughlemon,Rangpur lime,trifoliateorangeandCarrizocitrangerootstocks areverysusceptible.Sweetorange,sourorangeand Cleopatramandarinrootstockshavesomefield resistancetoblight;withtheserootstocksthe incidenceofthediseaseismuchlowerthanthemore susceptiblerootstocksandsymptomsonlyoccuron treesmorethan15yearsold.Apparentlythereareno rootstocksthataretoleranttoblight;affectedtrees showseveresymptomswithoutregardtorootstock. Therearenospecificdiagnosticsymptomsof blightthatdistinguishitfromthevariousother declinesofcitrus.This,alongwiththetotallackof symptomsonyoungtrees,hashamperedeffortsto determinethecauseofthedisease.Therehasbeen considerableprogressinrecentyearsindeveloping diagnostictestsforidentifyingtreeswithblight. Affectedtreesfrequentlyshowzincdeficiencyin leaves,whichindicatesblightinterfereswiththe translocationofzinc.Symptomsofzincdeficiencyon leavescanbeduetoseveralfactorsandarenot exclusivelydiagnosticforblight.Howeverthezinc contentofthewoodandbarkofblightedtreesis higherthanthatfoundintreeswithoutblightfrom thesamegrove.Thisaccumulationofzincinwoodor barkappearstobeacharacteristicoftreeswithblight anddoesnotoccurinhealthytreesortreesaffected withotherdiseasesordroughtstress. Thedrought-likesymptomsoftreeswithblight alsosuggestproblemswithwatertransport.Thishas beenconfirmedbyobservationsthatthexylemof blightedtreesisconstricted,resultinginlowwater uptake.Asyringeinjectiontesthasbeendeveloped thatisusefulindiagnosingtreeswithblight. Examinationoftrunkwoodfromtreeswithblightby lightandelectronmicroscopyrevealsnumerousplugs incellsofthexylemthatappeartoberesponsiblefor thereducedwateruptakeofaffectedtrees.In addition,blightedtreescontainseveralproteinsnot foundinnonblightedtrees.Theseproteins,which appeartobepathogenesisrelated,havebeenusedto produceantiseraforuseinimmuno-spotandwestern blottestsforblight. 1.ThisdocumentisFactSheetPP-151,aseriesofthePlantPathologyDepartment,FloridaCooperativeExtensionService,InstituteofFood andAgriculturalSciences,UniversityofFlorida.Publicationdate:January1993.Reviewed:October1994. 2.ProfessorandPlantPathologist,PlantPathologyDepartment,CitrusResearchandEducationCenter(CREC),LakeAlfred,Florida, InstituteofFoodandAgriculturalSciences,UniversityofFlorida,Gainesville,Florida. Tradenames,whereused,aregivenforthepurposeofprovidingspecificinformation.Theydonotconstituteanendorsementorguaranteeof productsnamed,nordoesitimplycriticismofproductsnotnamed. TheInstituteofFoodandAgriculturalSciencesisanequalopportunity/affirmativeactionemployerauthorizedtoprovideresearch,educational informationandotherservicesonlytoindividualsandinstitutionsthatfunctionwithoutregardtorace,color,sex,age,handicap,ornational origin.Forinformationonobtainingotherextensionpublications,contactyourcountyCooperativeExtensionServiceoffice. FloridaCooperativeExtensionService/InstituteofFoodandAgriculturalSciences/UniversityofFlorida/ChristineTaylorStephens,Dean

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CitrusBlight Page2Properidentificationofatreewithblightshould includeseveral,ifnotall,ofthefollowing observationsandtests:(1)visualobservationofa generaldecline,(2)knowledgeoftherootstock involved(fortreesonsourorangetristezamustbe considered,declineonsweetorangecouldberootrot, etc.),(3)comparisonofthezinccontentoftrunk woodfromaffectedandadjacenthealthyappearing trees,(4)ratesofwateruptakebythesyringe injectiontestofthesametreesselectedforzinc analysis,and(5)analysisforblightproteinsby immuno-spotandwesternblotanalysis. Repeatedattemptstotransmitorpropagateblight bybudgraftingorreproducethediseaseby reconstitutingblightedtreesfromrootsproutsand budsfromdiseasedtreeshavefailed.These observationshaveledtosuggestionsthatthecauseof blightis"abiotic".ThepHofthesoil,soiltypeand ratesoffertilizationhavebeensuggestedascausing blight.Butblightoccursontreesonavarietyofsoil types,andthedistributionoftheinitialaffectedtrees inagroveareusuallyrandomlydistributed;further developmentofthediseasemaybeintreesclumped aroundtheoriginalinfectedtreesorinarandom pattern.Inanygrovewhereblightisfoundtherewill beseverelyaffectedtreesadjacenttohealthytrees. Therateofspreadofblightisfortunatelyquiteslow. Datatakenovertwentyormoreyearstendtoshow constantrateofincreaseindiseasedtrees.Thisleads someresearcherstosuggestthatthecauseofblightis "abiotic".Therepeateddemonstrationsthatallofthe symptomsandcharacteristicsassociatedwithcitrus blightcanbereproducedbyrootgraftinoculations suggestthatthediseaseiscausedbyasystemic pathogen. Priortothediscoveriesthatmycoplasmas,xylem limitedbacteria,andviroidscauseplantdiseases, pathogensthatmovedsystematicallyinplantswerein generalassumedtobeviruses.Tocoverallthese possibilitiesanuncharacterizedpathogenthatisgraft transmittedisnowreferredtoasbeingviruslike.The onehundredplusyearsthatcitrusblighthasbeenin Floridapredatesanunderstandingofanyofthevirus likeagentsthatinfectplants.Overtheyears,as virusesandviruslikeagentswerecharacterizedand methodsdevelopedfortheirdetection,experiments weredonetodetermineifanyoftheseagentswere associatedwithblight.Todatenoviroid,xylem limitedbacteriumormycoplasmahasbeenshownto bethecauseofthedisease.Therehavebeenreports associatingxylemlimitedbacteriawithblightandthat tetracyclinetreatmentsreversedthesymptomsofthe disease,whichsuggestabacteriumormycoplasmais causingthedisease.However,studiesusingthinsectionmicroscopyhavefailedtoassociatexylem limitedbacteriaormycoplasmaswithblightand additionalexperimentsusingtetracyclinetreatments didnotshowaconsistentremissionofsymptoms. Bacteriawerenotfoundinanexaminationof numeroussamplesofxylemfluidfromrootsof blightedandhealthytreeswiththeelectron microscope.However,largenumbersofunusual filamentousstructureswerefoundinxylemfluidfrom blightedtrees.Thenatureandfunctionofthese structuresareunknown,buttheyseemtobe constantlyassociatedwithdiseasedtrees. Currentresearchoncitrusblightplacesmajor emphasisonidentificationandcharacterizationofthe pathogenthatcausesthedisease.Grafttransmission experimentsindicatethepathogenmayberestricted totherootsandisrarely,ifever,presentinabove groundpartsofthetree.Examinationsofextracts fromrootsofblightedandhealthytreeshave associatedseveralproteinsandsomeunusual filamentousstructureswithblight,butnospecific viruslikeagentshavebeenfound.Inaddition, serologicalassaysforblightspecificproteinsare currentlybeingusedinepidemiologystudieswhich includedeterminationifyoungpresymptomatictrees canbeidentifiedandremovedfromgrovesbefore symptomsdevelop.