Amelioration of heavy metal and nutrient stress in fruit vegetables by grafting

The responseofgraftedvegetablestostressconditionsowingtothenutrientstatus,andthepresenceof heavy metalsintherootenvironmentmaybedifferentthanthatofself-rootedplants,dependingmainly on therootstockgenotype.Severalstudieshaveindicatedthatsomerootstocksarecapableofrestricting the uptakeand/orthetransportofheavymetals(e.g.Cd,Ni,Cr)andmicronutrients(e.g.Cu,BandMn)to the shoot,therebymitigatingthestresscausedbyexcessiveexternalconcentrationsofthem.However, other mechanismsdrivenbytherootsystem,suchasdetoxificationofharmfulelementsorhormonal signals modifyinggeneexpressioninthescion,seemtobeinvolvedinthemitigationofstresscaused by excessiveexternalnutrientorheavymetalconcentrations.Ontheotherhand,theuptakeand/or utilization efficiencyofmacronutrients(N,P,K,CaandMg)byplantsmaybeenhancedbygraftingonto some rootstocks.Thisisascribedmainlytotherootcharacteristicsoftheserootstocks,whicharemore vigorous thanthoseofhighlyproductivecultivatedvarieties.However,othermechanismsimplicatedin the efficiencyofactivenutrientabsorptionbytheroots,aswellassignalsarisingfromthescion,which are mainlygovernedbysinkdemand,mayalsoenhancenutrientuptakeandutilization.Thehigher efficiency ofsomegraftcombinationsoffruitvegetablestotakeupandutilizenutrientsmaymitigate yield lossesowingtoshortagesofthesenutrientsintherootenvironmentofplantsandrestrictnutrient losses duetoleaching.Nevertheless,itisimportanttospecificallytesteachgraftingcombinationand not merelyeachrootstockforitsabilitytoamelioratenutrientorheavymetalstressbecauseinmany instances theresponsesdependontherootstock/scioncombination.Thisreportgivesanoverviewon the prospectsandrestrictionsofgraftingasameanstominimizethenegativeeffectsofheavymetals, excessive nutrientavailability,nutrientdeficiency,andalkalinitystressonvegetablecropperformance taking intoconsiderationagronomical,physiologicalandbiochemicalaspects.