第八讲TrainingandPruningofShoot/Root枝条与根系整形修剪吴树敬园艺科学与工程学院Training-controloftheshape,sizeanddirectionofplantgrowthOrientationoftheplantinspacePruning-JudiciousremovalofplantpartsControlsshape,size,fruitloadI.TerminologyII.TheprinciplesconcerningpruningandtrainingRoot:shootratioThereisaninnatebalancebetweenthedrymatterpartitionedtotheshootanditsroot.Thisbalancedefinesandco-ordinatestherelationshipsbetweenprocessestakingplacewithintheshootandroot.Theingredientscontrollingroot/shootbalance1.WaterRegulationofwatersupplythroughtheuseoftechniquessuchaspartialrootdrying(PRD)andregulateddeficitirrigation(RDI)canprovideeffectivemeansofreducingwateruseandenhancingplantwaterefficiencyaswellasawaytoinfluencevegetativeandreproductivegrowth.2.Hormonal2.1TheinfluenceofrootonshootCytokininsaresynthesisedintherootsandtransportedtotheshootviathexylem,inthetranspirationstream.Intheshoot,cytokininscaninfluencegrowth,photosynthesisandleafsenescence.Inapple,rootpruningreducesshootcytokininlevelsthatinturninfluenceflowering,pre-harvestdropandshootgrowth.Cytokininconcentrationinxylemsapcouldincreaseasthevigourofrootstockincrease.Droughtstressresultedinalargereductioninshootcytokininwhichwascausedbytheinhibitionoftransportalthoughcytokinproductioninrootwasincreased.Rootsalsoserveasthesiteforthesynthesisofgibberellins(GA);theymayalsobesitesinvolvedintheinter-conversionofshoot-derivedGA.GAactivityrelatedwithdwarfingphenotypeofrootstock.AdverseconditionsintherhizospherehavebeenshowntoaffecttheamountofGAexportedfromtheroot.Forexample,lowtemperaturesreduceGAinrootsapandthis,inturn,reducesshootlength.Auxincanalsobederivedfromroots;therootcapappearstobethemostlikelysiteofsynthesis.IAAlevelshavebeenshowntochangewiththedevelopmentalageofrootsandwithotherfactorssuchashighmechanicalsoilimpedance.Rootsrespondtotheamountofavailablesoilwater,andcommunicatewiththeshoottoaffectaco-ordinatedresponse,usingabscisicacid(ABA)inthetranspirationstream.WhentheABAsignalarrivesintheleaf,theaer...
