Unit 3 Fungal Plant Panthogens.docx

Unit 3 Fungal Plant Panthogens.docx

《Unit 3 Fungal Plant Panthogens.docx》由会员分享，可在线阅读，更多相关《Unit 3 Fungal Plant Panthogens.docx（13页珍藏版）》请在冰豆网上搜索。

Unit3FungalPlantPanthogens

FungalPlantPathogens

Introduce

Fungiarespore-forming，non-chlorophytic，eukaryotic（cellshavingtruenuclei）organismsandmostofthetruefungiarefilamentousandbranched．Mostoftheover100，000speciesoffungiaresaprophytes．However，over20，000speciesoffungiareparasitesandcausediseaseincropsandplants．FungalparasitesarebyfarthemostprevalentplantpathogenicorganismAllplantsareattackedbyonespeciesoranotherofphytopathogenicfungi．IndividualspeciesoffungiCanparasitizeoneormanydifferentkindsofplants．

Hyphaemycelium

Thebody，orthallus，ofmostofthehigherfungiiscalledamycelium（pl．mycelia）．Themyceliumismadeupofthread-likestructurescalledhyphae．Hyphaegrowonlyfromtheirtips，andunderfavorableconditionsCangrowindefinitely．Hyphae，mostoften，arepartitionedbycrosswallscalledsepta．Septatehyphaearedividedintoindividualcellsbytheseinternalwalls．Septausuallyhaveacentralporewhichallowssmallorganelles，andinsomecasesnuclei，topassfromonecelltoanother．ThehyphaeoftheclassesAscomycetes，BasidiomycetesandDeuteromycetesareseptateandthehyphaeofclassOomycetesandzygomycetesalenonseptateorcoenocytic．Coencytichyphaehavemultiplenucleiinacommoncytoplasm．

Hyphaeproducespecializedsimpleorbranchedprojectioncalledhaustoria.Haustoriapenetratethehosttissueandactasnutrientabsorbingorgans.．Haustoriacontainnucleiandaconcentratednumberofmitochondria．Thehaustoriadonotrupturethehostcellprotoplasmicmembranebutinvaginatesitselfintothecellthusgreatlyincreasingtheabsorptivesurfaceofthefungus．

Reproductionoffungiisprimarilybymeansofspores．Sporesarereproductivebodiesthatconsistofoneorafewcells．InfunctiontheyareanMogoustotheseedsofgreenplants．Sporesagoproducedbysexualandasexualreproduction．SexualreproductioninvolvestheunionoftWOcompatiblenucleiasproducedbymeiosis．Formanyphytopathogenicfungithesexualcycleoccursonlyonceduringeachgrowingseason．Sexuallyproducedsporesincludeoospores，zygospores，ascosporesandbasidiosporescharacteristicofthephylaOomycota，Zygomycota，AscomycotaandBasidiomycotarespectively．Asexualreproductionusuallyoccursbymeansofmitosiswhichproducemitoticspores，mycelialfragmentation，fissionandbudding．Withasexualreproductiontherepeatingcyclesofinfectioncancontinuethroughoutthegrowingseason．Asexualsporesmaybeclassifiedasoidia（formedbyfragmentationofhyphaeintoindividualcells），conidia（borneontipsorsidesofspecializedbranchesofhyphae）andsporangiospores（anonmotilesporebominasporangiumorcase）．Therearemanytypesanddifferentcharacteristicsoffruitingbodies，sporesandmycelinm．Fungiarebothclassifiedandidentifiedbythesefeatures．

Theclassificationofpathogenicfungiisimportantforidentifyinganddiagnosingplantdisease．Eachkingdom，phylum，class，order，family，genusandspecieshasitsownidentifyingcharacteristics．Manyofthediagnosticfactorsinidentifyingdifferentfungiareverysubtleandwithoutproperlabequipmentandskillaredifficulttoidentifydowntothespecieslevel．Ifwecanidentifythetypeoffruitingbodyand／orsporesthatareassociatedwithaparticularphylum，wecannarrowdownoursearchconsiderably．Mostoften，werelyonvisualsignsandsymptomsfordiagnosisoffungaldisease．

disease．

Theprimaryphyladealtwithinplantpathologyanddiseasediagnosisarelistedbelow．nlisoutlineisverybriefandonlyincludesafewofthemoreimportantpathogensandproblems．Alsoincludedaresomeofthemoreimportantcharacteristicsofeachphylum．Forfurtherclarificationonfungaltaxonomy，youcanrefertoanynumberofresourcesattheExtensionoffice．Also，theinternetisanexcellentsourceofinformationonthissubject.

cellentsourceofinformationonthissubject．

Fungal-likeorganisms（lowerfungi）：

．．

Kingdom：

Protozoa

Phylum：

Plasmodiophoromycota（endoparasiticslimmolds）e．g．，：

Plasmodiophorabrassicae，causingclubrootofcrucifers

Spongosphorasubterranean，causingpowderyscabofpotatotubers．

Kingdom：

Chromista

Phylum：

Oomycota（biflagellatezoospores．Simpleporednonseptatehyphae．Asexual

spores—sporangiospores，motileandnonmotile．Sexualspores—zoospores．）e．g．，：

chrysanthemumwhiterust，Phytophthorassp．diseases，downeymildew.

TrueFungi：

Kingdom：

Fungi

Phylum：

Chytridiomycota（zoospores，lacktruemycelium）e．g．,：

parsiticonrootsof

cabbageandmanyotherplants.

Phylum:

Zygomycota（saprophytesorparasitesofplants,Humansandanimals.Nozoospores.SimpleporednonseptateHyphae.Asexualspores-Sexualnonmotilesporangiispores.）e.g.,:

Rhizopus-breadmolds,rotsoffruitsandvegetables.

Phylum:

Ascomycota[thesacfungi-mosthavebothteleomorphic（sexual）andanamophic（asexual）stages.Simpleseptatehyphae.Producesexualspores（ascospores）orasexualspores（conidia）onfreehyphaeorinasexualfruitingbodiessuchasCleistothecium,Perithecium,ApotheciumandPycnidium.]Thisphylumisresponsibleformostofourphytopathogenicfungaldiseases.

Class:

Deuteropmycetes（Mitosporicorimperfectfungi-alsoknownasFungiImperfecti.Sexualreproductionandstructuresarerare,lackingorunknown.Simpleseptatehyphaewithsomeexceptions.Asexualspores-condiaproducedinpycnidiaandacervuli）.Thisclassisresponsibleformanyrots,wilts,molds,leaf,spotsandothersymptoms.

Phylum:

Basidiomycota（clubandmushroomfungi）-complexseptatehyphae,clampconnections.Asexualspore-conidia,oidia.Sexualspores-basidiosporesproducedexternallyonclub-likesporeproducingstructurecalledbasidium.

DiagnosticSignsandSymptomsofFungalInfection

Fungicancausegeneralorlocalizedsignsand／orsymptoms．Inthemajorityofcases，fungalinfectionscausegeneralnecrosisofhosttissueandoftencausestunting，distortionsandabnormalchangesinplanttissueandorgans．

Themostdistinctiveandeasilyidentifiablecharacteristicsoffungalinfectionsarethephysicalpresenceofsignsofthepathogen．Signsincludehypha，mycelia，fruitings，bodiesandsporesofthefungalpathogenaresignificantcluestoproperidentificationanddiagnosisofadisease．Thefruitingbodiesoffungirangefrommicroscopictomacroscopic．Theycomeinmanyshapesandconfigurationsandhavetheirindividualcharacteristics．Thefruitingbodies，alongwithspores，andmycelium，inmostcasescanleadtoanaccurateidentificationofthedisease．Thefollowingsymptomsarecommoninfhngalinfectionswhetheraloneorincombinationwithotherfungalpathogens．

Leafspotsareverycommoninbothbioticandabioticplantdisorders．Fungalleafspotsoftentaketheformoflocahzedlesionsconsistingofnecroticandcollapsedtissue．Leafspotscanvaryinsizeandaregenerallyroundandconcentric，butcanbeovoidorelongatedonbothleavesandstemsofthehost．Thetypicalfungalleafspotwillhavea“bulls-eye-like”appearanceconsistingofroughlyconcentrictingsthatmaydisplayzonesofdifferentcolorssuchasyellow，redorpurple，andwilloftenhaveatancenter．Asthespotsdevelop，theyarenotrestrictedbytheleafveinsascanbethecaseinbacterial1eafspots．Fungalleafspotswillusuallyhaveadrytexturebutarenotdryandpapery．

Bullhusseyebull’seye

beaty’seye

Othercommonsymptomsoffungalinfectionscanbe：

Anthracnose：

anulcer-likelesionthatcanbenecroticandsunken．Theselesionscanappearonthefruit，flowersandstemsofthehost-e.g.，Appleanthracnoseofstemsandorleaves（Cryptosporiopsissp．formallyPeziculasp．），ordogwoodanthracnose（Disculadistructiva）．

Canker：

alocalizednecroticlesiononwoodytissue，oftensunken-e．g．，AppleEuropeancanker（Nectriagalligena），Douglasfir，upperTwigCanker（phomopsissp．），andmanymore．

Dampingoff：

arapidcollapseanddeathofveryyoungseedling．Eithertheseedrotsbefore

emergenceortheseedlingrotsatthesoillineandfallsoveranddies．Severalsoil-bornfungicausethisdisease．ThemostcommongenerainvolvedaleFusarium，RhizoctoniaandPythium．

Scab：

localizedlesiononhostfruitleavestubersandotherplantparts．Theseinfectionsusuallyresultinaroughened，crust-likealeaonthesurfaceofthehost-e。

g．，Applescab（Venturiainaequalis）andpealscab（Venturiapirina）．

Scabofpotato

Softanddryrootrots：

rotanddisintegrationoffleshyleaves，roots，tubersandfruit-e．g．，

Dampingoffofseedlings，Rhododendron，PhytophthoraRootrot（P．cinnamomi），Armaillariaspp．Rootrotoftreesandhundredsofotherplants．

Blight:

rapidgeneralizedbrowninganddeathofleaves，floralorgans，stemsandbranches．BlightsCanrefertobothbioticandabioticdisorders-e．g．，Cherrybrownrot，blossomblight（MoniliniafructcolaandM.laxa），tomatoearlyblight（Alternariatomatophilai，formally，A．solani）andtomatoandpotatolateblight（Phytophthorainfastans）．P.infestanswasresponsibleforthegreatpotatofamineinIrelandin1845．

Dieback：

progressivedeathofshootsandtwigsgenerallystartingatthetipoftheinfectedplantpart-e-g·，Shootdiebackofappleduetocherrybrownrot（Moniliniasp.）andpoplarshootdieback（Venturiapopulina）·Bacteriaareprobablymorecommonlyassociatedwithdiebacks（Pseudomonassynngae）．

Decline：

progressivelossofvigoroveraperiodoftime．Generaldeclinecanbecausedbymanyfactorsincludingfungal，bacterial，environmentalandotherfactors，usuallyincombination．

Othersymptomsassociatedwithexcessivegrowth（hyperplasia）orenlargement（hypertrophy）

anddistortionofplantpartscanbedemonstratebythefollowing:

anddistortionofplantpartsCanbedemonstratedbythefollowing：

Galls：

enlargedpartsofplantorgans，usuallycausedbyexcessivemulti