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1、APPLESCABApplescabexistsworldwidebutismoresevereinareaswithcool,moistspringsandsummers.Similarscabdiseasesaffectpears(Venturiapyrina)andhawthorns(V.inaequalissp.f.pyracanthae).Scabisthemostimportantdiseaseofapples.Itsprimaryeffectisreductionofthequalityofinfectedfruit.Scabalsor
2、educesfruitsizeorresultsinprematurefruitdrop,defoliation,andpoorfruitbuddevelopmentforthenextyear;anditreducesthelengthoftimeinfectedfruitcanbekeptinstorage.Lossesfromapplescabmaybe70%ormoreofthetotalfruitvalue.Inmostapple-producingareas,nomarketablefruitcanbeharvestedifscabcon
3、trolmeasuresarenottaken.Symptoms•Atfirst,light,olive-colored,irregularspotsappearonthelowersurfaceofsepals（萼片）oryoungleavesoftheflowerbuds.Soonafter,thelesionsbecomeolivegreengraywithavelvetysurface.•Later,thelesion;appearmetallic（金属的）blackincolorandmaybeslightlyraised.•Lesiono
4、nolderleavesgenerallyformontheuppersurfaceoftheleaves.Lesionsmayremaindistinctortheymaycoalesce（联合）.•Leavesinfectedyoungremainsmallandcurledandmaylaterfalloff.Occasionally,smallscabspotsareproducedontwigsandblossoms.•Infectedfruitdevelopcircularscablesions,velvetyandolivegreena
5、tfirstbutlaterbecomingdarker,scabby,andsometimescracked.•Thecuticleofthefruitisruptured（破裂、裂开）atthemarginofthelesions.•FruitInfectedearlybecomemisshapen（畸形）andcracked,andfrequentlydropprematurely.•Fruitinfectedwhenapproachingmaturityformonlysmalllesions,which,however,maydevelop
6、intodarkscabspotsduringstorage.ThePathogen:Venturiainaequalis•Themyceliuminlivingtissuesislocatedonlybetweenthecuticleandtheepidermalcells.•There,itproducesshort,erect,brownishconidiophoresthatgiverisetoseveral,one-ortwo-celled,andspilocaea-type(环痕式)conidiaofrathercharacteristi
7、cshape.•Indeadleavesthemyceliumgrowsthroughtheleaftissuesandproducesascogoniaandantheridia;followingfertilization,pseudotheciaform.Thelatteraredarkbrowntoblackwithaslightbeakandanopening.•Eachpseudothecium（假囊壳）contains50to100asci,eachwitheightascosporesconsistingoftwocellsofune
8、qualsize.DevelopmentofDisease•Thepathogenoverwintersin
