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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（金屬的）blackincolorandmaybeslightlyraised.?Lesiono
4、nolderleavesgenerallyformontheuppersurfaceoftheleaves.Lesionsmayremaindistinctortheymaycoalesce（聯(lián)合）.?Leavesinfectedyoungremainsmallandcurledandmaylaterfalloff.Occasionally,smallscabspotsareproducedontwigsandblossoms.?Infectedfruitdevelopcircularscablesions,velvetyandolivegreena
5、tfirstbutlaterbecomingdarker,scabby,andsometimescracked.?Thecuticleofthefruitisruptured（破裂、裂開）atthemarginofthelesions.?FruitInfectedearlybecomemisshapen（畸形）andcracked,andfrequentlydropprematurely.?Fruitinfectedwhenapproachingmaturityformonlysmalllesions,which,however,maydevelop
6、intodarkscabspotsduringstorage.ThePathogen:Venturiainaequalis?Themyceliuminlivingtissuesislocatedonlybetweenthecuticleandtheepidermalcells.?There,itproducesshort,erect,brownishconidiophoresthatgiverisetoseveral,one-ortwo-celled,andspilocaea-type(環(huán)痕式)conidiaofrathercharacteristi
7、cshape.?Indeadleavesthemyceliumgrowsthroughtheleaftissuesandproducesascogoniaandantheridia;followingfertilization,pseudotheciaform.Thelatteraredarkbrowntoblackwithaslightbeakandanopening.?Eachpseudothecium（假囊殼）contains50to100asci,eachwitheightascosporesconsistingoftwocellsofune
8、qualsize.DevelopmentofDisease?Thepathogenoverwintersin
