ResearchReport

PotentialYieldIncreasebyGraftingforWatermelonProductioninArizonaAZ1732 January2017

MarkKroggelandChieriKubota

ControlledEnvironmentAgricultureCenter,TheUniversityofArizona

SummaryGraftingcucurbitsontorootstocksresistanttodiseasesandabioticstressescanbeamethodtoovercomelimitedavailabilityofeffectivepre-plantfumigantsorlandtorotateandtoallowearlierplanting.CommonlyusedrootstocksforcucurbitshaveresistancetoFusarium(race1&2)aswellascoldtolerance,amongotherfavorabletraitslikeincreasedvigorofthescion.GraftingofcucurbitswasdevelopedinAsiaprimarilytoallowproductionwithoutrotation,becausearablelandissolimited.IntheUS,croprotationschedulesforseedlesswatermeloncanbe3yearsorlongerreducingtheamountofwatermelonagrowercanproduceinaseason.Wehavebeengrowinggraftedandnon-graftedseedlesswatermelononthesamefield/plotfor4years,withnofumigationoroff-seasonrotationofothercrops.Duringthelast2years,weplantedearly(March1)todetermineifgraftingcouldovercomelownighttemperaturesinadditiontodiseasepressures.Treatmentsincludedgraftedandnon-graftedplants,coveringwithfrostprotectionandnon-covered.Theresultsofthelast2yearsindicatethatgraftedplantsyieldednearlytwiceasmuchasnon-graftedplants,suggestingthatgraftingcanbeapromisingtechnologyforArizonawatermelonproducers.

Introduction

WatermelonisaminorcropinArizonavegetableproduction.However,in2012,atotalof4,876acreswereharvested,beingrankedas8thintheU.S.(USDA,2014).ArizonawatermelonproductionismainlyconcentratedinMaricopa,LaPazandYumacounties.TypicalproductionofmelonsinArizonainvolvestwocropsayearwithappropriatelandrotationprograms.Watermelonisknowntobesensitivetopossibleyielddeclineduetointensivecultivationandrotationisessentialtoavoidsoil-bornediseasesuchasfusarium.Traditionallywatermelonwascultivatedwitharelativelylongrotationprogramsuchas9or10years;however,rotationbecomesmorechallengingduetothelandavailability.Forexample,currently2to3yearsofrotation(withgarbanzobeansorwheat)istypicalinMaricopaandlittleornorotationispracticedinYuma.AnecdotallywatermelonyieldinArizonaisrelativelysmall(20-25ton/acre),presumablyduetovariousfactorsincludinglimitedrotationprograms.

InAsianandEuropeancountries,wherearablelandislimitedandthereforemoreintensivelanduseisperformed,graftinghasbeenusedeffectivelytosustainwatermelonproductionwithoutrelyingonrotationprogramsaswellastoincreasetheyield(Davisetal.,2008;Leeetal.,2010).VegetablegraftingwasintroducedtoArizonainitiallyintheEuropeanbasedgreenhouseindustryinthelate1990sbutalsotofieldproductionintheearly2000s.Whileitbecameastandardtechnologyofincreasingyieldingreenhousetomato(Kubotaetal.,2008)inArizona,evaluationsforwatermelonhavenotbeenperformedyet.Becauseoftheratherhighcostsofseedlings(50-70centsperplant),largeincreasesinyieldorreductionofcostsassociatedwithreducedapplicationofpesticides,reducedmanagement

practicesorreducedfrequencyoflandrotationneedtobeconsideredtogetherasbenefitsofgraftedwatermelonproduction.

InspringproductionofwatermeloninArizona,seedlingswith2-3leavesaretransplantedbetweenJanuaryandMarch.Duringthistime,somegrowersapplyfloatingrowcoversovernewlytransplantedwatermelonseedlingstoprotectthemfromthecoldnights.Whilethispracticeallowsgrowerstostarttheseedlingsearlyandtherebytargetingtheearlypremiummarket,theadditionalcostaswellastheneedoftemperaturemanagementareconsideredproblematic.Whilewatermelonissensitivetochilling,rootstocks(squashorbottlegourd)widelyusedforgraftingwatermelonareknowntobecoldtolerant(SpalholtzandKubota,2016).Therefore,wehypothesizedthatgraftingmayeliminatetheneedofrowcoverduringearlyspringplantingseasonandconductedasmallscaletrialinanexperimentalfieldattheCampusAgricultureCenter,theUniversityofArizona(Tucson,AZ).Inthisreportwesummarizethecomparisonofgraftedandnon-graftedwatermelonplantsgrownwithandwithoutcover,repeatedovertwoyearsin2015and2016.

ProcedureGraftedandnon-graftedplantswereproducedforthetrials.Thescionwas‘Tri-X313’seedless

watermelon(SyngentaSeeds,Boise,Idaho)androotstockwas‘Strongtosa’interspecifichybridsquash(SyngentaSeeds).Seedsofscionandrootstockwereplantedinto98cellplugtraysonmultipledatesduringfirstweekofFebruaryandgraftedonFebruary16usingthesinglecotyledonmethod.Plantswerehealedfor7daysinhealingchambers,thenacclimatedandgrowningreenhouseuntilMarch1.Non-grafted‘Tri-X313’wasseededonFebruary10andgrowninthesamegreenhouse.PlantswereplantedinafieldatTheUniversityofArizonaCampusAgricultureCenterinsoilcharacterizedasGilafinesandyloamonraisedbedswithbed/rowson80inchcentersandplantsinrowon43inchspacingusingaLatinsquaredesign.Theplantingdensityis1,823plantsperacre.Treatmentswere1)grafted-non-covered,2)grafted-covered,3)non-grafted-non-covered,4)non-grafted-covered.Therewere4replicationsof7plantspertreatment.Pollinizerplants(SP-6,SyngentaSeeds)wereplantedbetweeneverythirdplantintherow.Coveredtreatmentswerecoveredonthedayofplantingwitha0.9ozyd-2spunbondedpolypropylenefabric(AG-30;J&MIndustries,Ponchatoula,LA)followingthepracticeofYumagrowers(K.Nolte,personalcommunication)andventedasnecessarytomoderatetemperatureandcompletelyremovedwhenriskoffrostwaslow(3/21/15and3/16/16).

Plantswereirrigatedbyburieddriptape(Chapinmodel11704420;JainIrrigationSystemsLTD,Maharashtra,India.)basedonplantdemand.Starting3weeksafterplantingfertilizerwasappliedweeklythroughthedrip.Nitrogenwasappliedfor14weeksusingUAN-32toachieveacumulativetotalactualNrateof160lb/acre(180kgha-1)(2015)and110lb/acre(120kgha-1)(2016).Phosphoruswasappliedduringthefirst7weeksusingmono-potassiumphosphate(0-52-34)toachieveacumulativetotalactualPrateof30lb/acre(75kgha-1),andpotassiumwasappliedduringthelast7weeksusingpotassiumsulfate(0-0-50)toachieveacumulativetotalactualKrateof125lb/acre(140kgha-1).ToohighnitrogenmightmakegraftedplantstoovegetativesolimitingNisastandardpracticeinmanaginggraftedwatermelonplants.Therefore,in2016,plant’stissuenitrogenlevelwasmonitoredperiodicallytonotexceedtheupperlimitof1200ppmduringearlydevelopmentstagesand800ppmduringlatedevelopmentstageaccordingtotherecommendationbyBrust(2013).

Plantsweremeasuredforvinegrowth,initialflowering,transplantmortalityandyieldasnumberandweightsoffruit.Fruitqualitywasmeasuredbybrix.Fruitwasconsideredharvestablewhenthe3tendrilsadjacenttothefruithaddried,butbyrecommendation,thegraftedfruitwasharvested5

daysafterthis(R.Hassell,personalcommunication).Fruitwasharvestedfrom5/25/15to7/3/15andfrom6/14/16to7/12/16.Therewasnosignificantinteractionbyyearandsothedatawerecombinedtoanalyzethemainfactorsofthefourtreatments.

Results/discussionCoveringaftertransplantingsignificantlyincreasedtheearlyvegetativeandreproductive

developmentofwatermelonplantsregardlessofplanttype(graftedvs.non-grafted).Italsolargelyreducedthelossofprimarilynon-graftedplantsduetotransplantfailure(Table1).However,thesedifferencesinearlyproductionstagedidnotaffectthefruityieldenoughtohaveastatisticallysignificantdifference(Table2).Inthesetrials,wereplacedthetransplantslostduringthefirsttwoweeksoffieldestablishment.Withoutreplacingseedlings,coveringmighthavesignificantlyaffectedtheyield.

Itissuggestedthatseedlesswatermelonseedbeplantedwhenthesoiltemperaturesreaches70F(Shrefleretal.,2015).Thesoiltemperatureintheupper4”didnotreach70Funtil5/25/15and5/11/16(datanotshown),suggestingsuboptimalsoiltemperaturesafterplantingformorethan9weeks.ThecoldtoleranceoftheStrongtosarootstockwouldhaveprovidedanadvantageoverthenon-graftedplantsduringthistime,allowingformorevegetativeplantdevelopment.

GraftedplantsaresensitivetoN,andtoomuchNcanresultinflowerabortion.In2016theapplicationofNwasreducedearlyinthegrowingseasonwiththeintendedeffecttoreducetheamountofearlyflowerabortioningraftedplants,whichitdidasthereweremorefemaleflowersperplantearlyinthecropin2016than2015(4.1±0.21in2016vs2.3±0.38in2015,p=0.001)asmeasuredon54-58daysafterplanting.TherewasnoeffectreducedNonnon-graftedplantsforfemaleflowers(1.35±0.24in2016vs1.32±0.28in2015,p=0.9469).

Nongraftedplantsproducedanaverageof25.8±3.4lbs.perplant,whichisequatedto23.5tonsperacre,asimilarlevelofyieldobservedinArizonawatermelonproduction(S.Martori,personalcommunication).Graftedplantsproduced55.5±6.9lbs.perplantor50.6tonsperacre,twiceasmuchyieldasnon-graftedplants.Thisisduetomorefruitandlargerfruitingraftedplantsthaninnon-graftedplants.Similarresultsofincreasedwatermelonfruitsizebygraftingontointerspecifichybridrootstock(CucurbitamaximaxCucurbitamoschata)havebeenreported(Sakataetal.,2007).

Fruitqualityissometimesreportedasaffectedbyrootstock.Atypicaldifferencebetweengraftedandnon-graftedplantswasthespeedofmaturationoffruit.Forthisreason,wepickedthefruitofgraftedplants5dayspastthefirstindicationofconventionalmaturation.Solublesolidcontentofthefullyripefruitwas10.6±0.11forgraftedplantsand10.7±0.07fornon-graftedplantswithnosignificantdifferencethetwotreatments.

Conclusion

Seedlesswatermelongraftedontoahybridsquashresultedintwicetheyieldofnon-graftedplants,withoutcausinganynegativeinfluenceinfruitquality.Thisyieldincreasewasaresultofmoreandlargerfruit,presumablyduetothemorevigorous,coldtolerantanddiseaseresistantrootsystemoftherootstock.Evenatawholesalepriceof$0.10perlbs.thisaverageyieldincreaseofmorethan25lbs.perplantmorethanpaysforthecostofthegraftedplant($0.50–0.70).Consideringthepossibleeliminationofcovering,fumigationandrepeatedcroppingthisvalueofgraftingisincreased.

Acknowledgements

ThisprojectwasfundedbyUSDANIFASCRI(AwardNumber2011-51181-30963).AuthorswouldliketothankRichardHassellatClemsonUniversityforprovidingtechnicalconsultationinwatermelonproductionandSyngentaSeedsforprovidingwatermelonandrootstockseeds.WearegratefultoKurtNolte,theUniversityofArizona,YumaAgricultureCenterandSteveMartori,MartoriFarms,ArizonafortheirhelpfulconsultationanddiscussionindesigningtheexperimentsrelevanttoArizonamelonproduction.ReferencescitedBrust,D.2013.Usingnitrate-Npetiolesap-testingforbetternitrogenmanagementinvegetablecrops.

MarylandVegetables.Dec.17,2016.<https://extension.umd.edu/learn/using-nitrate-n-petiole-sap-testing-better-nitrogen-management-vegetable-crops>.

Davis,R.,P.Perkins-Veazie,Y.Sakata,S.López-Galarza,M.Vicente,S.Lee,Y.Huh,Z.Sun,A.Miguel,S.King,R.Cohen,andJ.Lee.2008.Cucurbitgrafting.Crit.Rev.PlantSci.27:50-74.

Kubota,C.,M.A.McClure,N.Kokalis-Burelle,M.G.Bausher,andE.N.Rosskopf.2008.Vegetablegrafting:History,use,andcurrenttechnologystatusinNorthAmerica.HortScience43:1664-1669.

Lee,J.-M.,C.Kubota,S.J.Tsao,Z.Bie,P.HoyosEchevarria,L.Morra,andM.Oda.2010.Currentstatusofvegetablegrafting:Diffusion,graftingtechniques,automation.ScientiaHort.127:93-105.

Sakata,Y.,Takayoshi,O.,andS.Mitsuhiro.2007.ThehistoryandpresentstateofthegraftingofcucurbitaceousvegetablesinJapan.ActaHortic.731:159-170.

Spalholtz,H.andC.Kubota.2016.Rootstockaffectedin-andpost-storageperformanceofgraftedwatermelonseedlingsatlowtemperature.HortTechnology(inpress).

USDA2014.CensusofAgriculture2012.UnitedStatesDepartmentofAgriculture,NationalAgriculturalStatisticsService.

Shrefler,J.,E.Rebek,J.Damicone,andM.Taylor.2015.Watermelonproduction.OklahomaCooperativeExtensionServiceHLA-6236.Dec.17,2016.< http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-1110/HLA-6236web2015.pdf>.

Figure1.Acclimatedgraftedplants(a)andnon-graftedplants(b)ondayofplanting.

Figure2.Watermelonatharvesttime(a)andnearingharvest(b).

Table1.Plantcharacteristicsmeasuredfor2015and2016combined.Numberofvinesmeasuredon55daysafterplanting(DAP).Numberoffemaleflowersmeasuredon54–58DAP.Percentofplantsthatwerereplacedduetomortalitywithin14DAP.Valuesaremean±SE.Treatment Numberofvines Numberoffemale

flowers%ofreplacedtransplants

Grafted 11.1±0.9*** 3.2±0.3*** 1.8±1.2***Non-grafted 4.7±0.3 1.3±0.2 24.1±4.7 Covered 9.5±1.1*** 2.7±0.3* 8.0±3.4*Non-covered 6.4±0.7 1.8±0.4 17.9±5.0*0.05,**0,01,***0.001nsNotsignificant

Table2.Yieldresponsesfor2015and2016combinedfortreatmentmaineffectsofgraftedandnon-graftedplants,coveredandnon-coveredplants.Fruitwasharvestedfrom5/25/15to7/3/15andfrom6/14/16to7/12/16.Plantingdensitywas1823plantsperacre.Valuesaremean±SE.

Treatment tons/acre lbs/plant Fruitsize(lbs) #fruit/plantGrafted 50.6±6.3*** 55.5±6.9*** 15.6±0.7* 3.4±0.3***Non-grafted 23.5±3.1 25.8±3.4 12.3±0.9 1.9±0.2 Covered 38.1±6.7ns 41.8±7.3ns 14.1±0.88ns 2.7±0.3nsNon-covered 36.0±5.3ns 39.5±5.8ns 13.9±1.10ns 2.6±0.3ns*0.05,**0,01,***0.001nsNotsignificantDataweretransformedusingSQRT