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Continuous Third Phase Fruit Monitoring in Olive with Regulated Deficit Irrigation to Set a Quantitative Index of Water Stress

Authors:
Arash Khosravi at Mälardalen University
Arash Khosravi
Matteo Zucchini at Marche Polytechnic University
Matteo Zucchini
Adriano Mancini
Adriano Mancini
Adriano Mancini
  • This person is not on ResearchGate, or hasn't claimed this research yet.
Davide Neri at Marche Polytechnic University
Davide Neri
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Abstract and Figures

The transversal fruit diameter (FD) was monitored continuously by automatic extensimeters (fruit gauges) in order to monitor fruit growth dynamics under deficit irrigation treatments. The daily diameter fluctuation (ΔD, mm), the daily growth (ΔG, mm), the cumulative fruit growth (CFG, mm), and the fruit relative growth rate (RGR, mm mm−1 h−1) of four olive cultivars (Ascolana dura, Piantone di Falerone, Arbequina, and Lea) were studied during the third phase of fruit growth. Two regulated deficit irrigation treatments DI-20 (20% of ETc) and DI-10 (10% of ETc) were applied. The daily hysteretic pattern of FD versus the environmental variable of vapor pressure deficit (VPD) was evaluated using the data of a local weather station. The assessment of fruit growth parameters showed cultivar-specific response to water stress. For instance, after performing deficit irrigation, minimum RGR in different cultivars downsized with various slopes which suggested a very different response of the cultivars to dehydration. On the other hand, the daily hysteretic pattern of FD versus VPD was detected in all the studied cultivars, and a quantitative index (height of hysteresis curves) used for explanation of hysteresis magnitude’s changed according to the deficit irrigation treatments. The results showed a significant reduction of height of hysteresis curves by irrigation treatments which were not cultivar-specific. The quantitative index for hysteresis curve magnitude’s change in the four olive cultivars of Ascolana dura, Piantone di Falerone, Arbequina and Lea can efficiently estimate the plant water response to irrigation treatment in olive orchards. However, further investigation needs to be done to implement precise irrigation systems.
Trend of hourly and daily temperature (T), vapor pressure deficit (VPD), reference evapotranspiration (ET0) and rainfall, during the experiment period (from 224 to 276 days of the year (DOY), obtained by MeteoSense 4.0 weather station.
Trend of hourly and daily temperature (T), vapor pressure deficit (VPD), reference evapotranspiration (ET0) and rainfall, during the experiment period (from 224 to 276 days of the year (DOY), obtained by MeteoSense 4.0 weather station.
… 
Daily fruit relative growth rate (RGR) from 227 to 234 day of the year (DOY) (in correspondence with first and second irrigation days. The olive cultivar Piantone di Falerone (A,B); the olive cultivar Ascolana dura (C,D); the olive cultivar Arbequina (E); the olive cultivar Lea (F). Fal3(DI-0) represents fruit 3 of non-irrigated "Piantone di Falerone". Fal1(DI-20) and Fal2(DI-20) represent fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation, respectively. Asc3(DI-0) represents fruit 3 of non-irrigated "Ascolana dura". Asc2(DI-20) represents fruit 2 of "Ascolana dura" at 20% deficit irrigation. Arb1(DI-10) and Arb2(DI-10) represent fruit 1 and 2 of "Arbequina" at 10% deficit irrigation, respectively. Lea1(DI-10) represents fruit 1 of "Lea" at 10% deficit irrigation.
Daily fruit relative growth rate (RGR) from 227 to 234 day of the year (DOY) (in correspondence with first and second irrigation days. The olive cultivar Piantone di Falerone (A,B); the olive cultivar Ascolana dura (C,D); the olive cultivar Arbequina (E); the olive cultivar Lea (F). Fal3(DI-0) represents fruit 3 of non-irrigated "Piantone di Falerone". Fal1(DI-20) and Fal2(DI-20) represent fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation, respectively. Asc3(DI-0) represents fruit 3 of non-irrigated "Ascolana dura". Asc2(DI-20) represents fruit 2 of "Ascolana dura" at 20% deficit irrigation. Arb1(DI-10) and Arb2(DI-10) represent fruit 1 and 2 of "Arbequina" at 10% deficit irrigation, respectively. Lea1(DI-10) represents fruit 1 of "Lea" at 10% deficit irrigation.
… 
Relative growth rate range (RGRrange) from 227 to 234 day of the year (DOY) (in correspondence with first and second irrigation days: (A) fruit 1 and 2 of "Arbequina" at 10% deficit irrigation (Arb1(DI-10) and Arb2(DI-10), respectively) and fruit 1 of "Lea" at 10% deficit irrigation (Lea1(DI-10)); (B) fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation (Fal1(DI-20) and Fal2(DI-20), respectively) and fruit 2 of "Ascolana dura" at 20% deficit irrigation (Asc2(DI-20)); (C) fruit 3 of non-irrigated "Ascolana dura" (Asc3(DI-0)) and fruit 3 of non-irrigated "Piantone di Falerone" (Fal3(DI-0)).
Relative growth rate range (RGRrange) from 227 to 234 day of the year (DOY) (in correspondence with first and second irrigation days: (A) fruit 1 and 2 of "Arbequina" at 10% deficit irrigation (Arb1(DI-10) and Arb2(DI-10), respectively) and fruit 1 of "Lea" at 10% deficit irrigation (Lea1(DI-10)); (B) fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation (Fal1(DI-20) and Fal2(DI-20), respectively) and fruit 2 of "Ascolana dura" at 20% deficit irrigation (Asc2(DI-20)); (C) fruit 3 of non-irrigated "Ascolana dura" (Asc3(DI-0)) and fruit 3 of non-irrigated "Piantone di Falerone" (Fal3(DI-0)).
… 
Relative growth rate range (RGRrange) from 257 to 262 day of the year (DOY) (in correspondence third irrigation day): (A) fruit 1 and 2 of "Arbequina" at 10% deficit irrigation (Arb1(DI-10) and Arb2(DI-10), respectively) and fruit 1 and 2 of "Lea" at 10% deficit irrigation (Lea1(DI-10) and Lea2(DI-10), respectively); (B) fruit 1 and 2 of "Ascolana dura" at 20% deficit irrigation (Asc1(DI-20) and Asc2(DI-20), respectively) and fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation (Fal1(DI-20) and Fal2(DI-20), respectively); (C) fruit 3 of non-irrigated "Ascolana dura" (Asc3(DI-0)) and fruit 4 of non-irrigated "Piantone di Falerone" (Fal4(DI-0)).
Relative growth rate range (RGRrange) from 257 to 262 day of the year (DOY) (in correspondence third irrigation day): (A) fruit 1 and 2 of "Arbequina" at 10% deficit irrigation (Arb1(DI-10) and Arb2(DI-10), respectively) and fruit 1 and 2 of "Lea" at 10% deficit irrigation (Lea1(DI-10) and Lea2(DI-10), respectively); (B) fruit 1 and 2 of "Ascolana dura" at 20% deficit irrigation (Asc1(DI-20) and Asc2(DI-20), respectively) and fruit 1 and 2 of "Piantone di Falerone" at 20% deficit irrigation (Fal1(DI-20) and Fal2(DI-20), respectively); (C) fruit 3 of non-irrigated "Ascolana dura" (Asc3(DI-0)) and fruit 4 of non-irrigated "Piantone di Falerone" (Fal4(DI-0)).
… 
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Horticulturae2022,8,1221.https://doi.org/10.3390/horticulturae8121221www.mdpi.com/journal/horticulturae
Article
ContinuousThirdPhaseFruitMonitoringinOlivewith
RegulatedDeficitIrrigation
toSetaQuantitativeIndexof
WaterStress
ArashKhosravi
1
,MatteoZucchini
1
,AdrianoMancini
2
andDavideNeri
1,
*
1
DepartmentofAgricultural,FoodandEnvironmentalSciences,MarchePolytechnicUniversity,
60131Ancona,Italy
2
DepartmentofInformationEngineering,MarchePolytechnicUniversity,60131Ancona,Italy
*Correspondence:d.neri@staff.univpm.it
Abstract:Thetransversalfruitdiameter(FD)wasmonitoredcontinuouslybyautomaticextensim‐
eters(fruitgauges)inordertomonitorfruitgrowthdynamicsunderdeficitirrigationtreatments.
Thedailydiameterfluctuation(ΔD,mm),thedailygrowth(ΔG,mm),thecumulativefruitgrowth
(CFG,mm),andthefruitrelativegrowthrate(RGR,mmmm
−1
h
−1
)offourolivecultivars(Ascolana
dura,PiantonediFalerone,Arbequina,andLea)werestudiedduringthethirdphaseoffruit
growth.TworegulateddeficitirrigationtreatmentsDI‐20(20%ofET
c
)andDI‐10(10%ofET
c
)were
applied.ThedailyhystereticpatternofFDversustheenvironmentalvariableofvaporpressure
deficit(VPD)wasevaluatedusingthedataofalocalweatherstation.Theassessmentoffruitgrowth
parametersshowedcultivar‐specificresponsetowaterstress.Forinstance,afterperformingdeficit
irrigation,minimumRGRindifferentcultivarsdownsizedwithvariousslopeswhichsuggesteda
verydifferentresponseofthecultivarstodehydration.Ontheotherhand,thedailyhystereticpat‐
ternofFDversusVPDwasdetectedinallthestudiedcultivars,andaquantitativeindex(heightof
hysteresiscurves)usedforexplanationofhysteresismagnitude’schangedaccordingtothedeficit
irrigationtreatments.Theresultsshowedasignificantreductionofheightofhysteresiscurvesby
irrigationtreatmentswhichwerenotcultivar‐specific.Thequantitativeindexforhysteresiscurve
magnitude’schangeinthefourolivecultivarsofAscolanadura,PiantonediFalerone,Arbequina
andLeacanefficientlyestimatetheplantwaterresponsetoirrigationtreatmentinoliveorchards.
However,furtherinvestigationneedstobedonetoimplementpreciseirrigationsystems.
Keywords:OleaeuropaeaL.;fruitdiameter;hysteresis;deficitirrigation;vaporpressuredeficit
(VPD);waterstressindex;continuousfruit‐basedindex;extensimeter(fruitgauge)
1.Introduction
Theimportanceofolive(OleaeuropaeaL.)asessentialforhumandietandlandscape
managementisundeniableinareaswithMediterraneanclimate.Oliveproductionhas
beenaffectedbyincreasingglobaldemand(tableoliveandoliveoil),whichhasimposed
agreaterneedforagriculturalinputsasweaddressresourcescarcityandclimatechange
[1–3].Oneofthekeyinputsofoliveproductioniswater.Around70%oftheworldsurface
ofolivegrovesisirrigated[4],therefore,thedevelopmentofappropriatemethodsand
strategiesofsustainablewateruseinolivegrovesisfundamental[5].Themostcommon
techniqueforoptimizingwaterefficiencyisRegulatedDeficitIrrigation(RDI),inwhich
waterdeficitsareimposedduringphenologicalperiodswhenthetreeismostinsensitive
towaterstress[6–8],andcomplementaryirrigation[9,10].Furthermore,theresultsof
Goldhamer[11]andGómez‐delCampo[12]showedthatRDIstrategiesresultedinasav‐
ingofabout20%ofthetotalamountofwaterappliedwithoutreducingtheyield,fruit
andoilcontent.Moreover,numerousstudiesshowthatdeficitirrigationavoidsor
Citation:Khosravi,A.;Zucchini,M.;
Mancini,A.;Neri,D.Continuous
ThirdPhaseFruitMonitoringin
OlivewithRegulatedDeficit
IrrigationtoSetaQuantitativeIndex
ofWaterStress.Horticulturae2022,8,
1221.https://doi.org/10.3390/
horticulturae8121221
AcademicEditors:AlessioScalisi,
MarkGlennO’ConnellandIan
Goodwin
Received:21September2022
Accepted:15December2022
Published:19December2022
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2022bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Horticulturae2022,8,12212of28
minimizesthenegativeimpactofirrigationonerosion,inparticularbyreducingsurface
runoffandcontributinglesstotheinfiltrationofpollutants(herbicidesandpesticides)
intogroundwater[13].Intheclassicalmethod,thecalculationofirrigationamountis
basedonmultiplyingreferenceevapotranspiration(ET0)bygrass‐reference‐basedcrop‐
specificcoefficients(Kc).Nevertheless,thetraditionalmethodofestimationofKcforolive
orchardscouldbeinaccurate.Kcisaffectedbysomeaspectssuchascanopyarchitecture,
groundcover,andtheinteractionsofclimaticconditions,soiltype,cultivars,andirriga‐
tionmanagementpractices[6].
Toachievepreciseirrigationresults,somerecentresearchsuggestedcontinuousas‐
sessmentofplantwaterstatusindices[14–17].Infact,inSoilPlantAtmosphereContin‐
uum(SPAC),plantplaysaninterfacerolebetweensoilandtheenvironment,anditsphys‐
iologicalresponseisacombinationofresults[14,18,19].Furthermore,thecontinuous
measurementofplantwaterstatusindiceswouldprovideasolidbaseforprecisionirri‐
gationmanagement,byrealtimeresponsetowaterstress.However,theolivespecies
(Oleaeuropaea)hasaverywidegeneticpool,whichcanrespondtodroughtusingdifferent
leafandfruitphysiologicalandmorphologicalmechanisms[14,20].Itincludesgenotypes
thatcanrespondtodroughtusingdifferenttolerancestoleafdehydrationandmorpho‐
logicalandstructuraladaptationsoftheleaves[14].LoBiancoandScalisi[20]founda
differentleafstomatalregulationamongtheolivecultivars.Duetothisdifficulty,thecor‐
rectchoiceofthewaterstatusindexoftheplantisessential.Themostcommonsuggested
indicesaremiddaystemwaterpotential(ᴪstem),trunkdiametervariation(TDV),sapflow
(SF),leafturgorpressure(LTP),aswellasfruitdiameter(FD),whichcanbeusedaloneor
incombination.Acombinationofindices(sensors)couldproviderobustdata,however,
increasedthecomplexity.Moreover,consideringthedifficultyofreplicatingcontinuous
measurementsonalargenumberoftrees,theneedtoobtainanaccurateindexhasbecome
moreessential.Themiddaystemwaterpotential(ᴪstem)isaccurateandreliable,however,
notonlyitisadestructivemethod,butalsonotsuitableforcontinuousmeasurement
[14,21,22].Thestem/trunkdiametervariation(bytrunkdendrometer)isanotheruseful
index.However,thetrunkdiameterfluctuationsareaffectedbyplantageandsize,crop
load,environmentalvariables,andgrowthpatterns[19].Thesapflow(SF)methodsare
particularlydemandingintermsofinstallation;mostoftheSFmethodssuitableforfruit
treesareinvasive,suchthatsensorsmustbeinstalledwithinthetrunkofthetrees[5].
Moreover,thesapflowratedemonstratestranspirationdynamicsthatdependonsto‐
matalactivityandenvironmentalvariables[22].Theleafturgorpressure(LTP)measure‐
mentmethodiscarriedoutbyprobewhichisacheapandhandymethodbutdoesnot
allowforcontinuousmeasurement[23].TheadvancedLTPmeasurementmethodem‐
ployedleafpatchclamppressure(LPCP)probesisabletocontinuouslymonitorthepres‐
sure,butthedifferentinitialconditionoftheleafrelatedtoage(especiallyinevergreen
species)andexposuretolightinsidethecanopyleadstoobtainingpartialinformation
fromLPCP[15,22].Inaddition,findingsbyJones[24]suggestedthatLTPintheisohydric
speciesisnotveryusefulintheearlydetectionofplantwaterdeficiency.Theotherinno‐
vativeplantwaterstatusindexisfruitdiameter(FD).Thedailyfruitgrowthdynamics
canbeexpoundedaschangesinflowsofwaterintoandoutofthefruit,ratherthancarbon
gains;thus,thedailyfruitdiametervariationrespondstowaterdeficit[15,25–27].Fruits
representtheactualgoalofproductionbutfruitgrowthistheresultofseveralgenetic,
metabolic,hormonal,andenvironmentalinteractions[28],therefore,optimalfruitgrowth
canbedeterminedonlybytheefficientphysiologicalmanipulationoftheconditiontree
[23].Intheolivetree,therootresponsetolocalizedapplicationsystemsoforganicresi‐
dues,nutrients,andwaterrevealanenormousplasticityoftherootsystem[29–31]which
cancompensateforlocalstress.Althougholivetreerootsystemsarehighlycapableand
couldsupplyaconstantwaterflow,fruitdailygrowthtrendisdescribedbyperiodsof
shrinkageandthenafterexpansion,whichusuallyleadtoincreaseinfruitsizeattheend
oftheday[23,27].DuetotheresearchofFernandesetal.[26]andMarinoetal.[15],the
dailyvariationsinfruittransversaldiameterscanbeexpoundedaschangesinflowsof
Horticulturae2022,8,12213of28
waterintoandoutofthefruithence,thesecanbeconnectedtovaporpressuredeficit
(VPD)andtreewaterstatus.Furthermore,Scalisietal.[14]explainedthatfruitgrowth
(measuredbyFD)isstrictlyrelatedtosoilwateravailabilityandplantwaterstatus,itis
alsoinfluencedbyenvironmentalvariables,cropload,geneticfactors,andphenology.
Consequently,fruitgrowthmonitoring(byFD)couldrepresentasensitiveindicatorof
plantwaterandphysiologicalstatusofthetrees,especiallyduringcellexpansionphase,
whenfruitgrowthrateisconstantandtrulydecisiveforproductiveperformances[23,32].
FDmonitoringhasbeeninvestigatedinseveralstudiesbyresearcherstomeasuredaily
fluctuationinthevolumeofselectedfruits,includingpears[33],sweetcherry[34–36],
mango[37],apple[23],nectarine[22],orange[38],andolive[14,15,26,27].Thecontinuous
FDmonitoringprovidesrobustdatabutwatermanagementprotocolsbasedonFDmeas‐
urementsneedfurtherstudytodevelopfieldapplicablemodels[15,23,27].Acommon
challengewithtree‐basedsensorsistoadjusttheiroutputtophysiologicallymeaningful
parametersinaconsistentmanner[19,27,36].
Inordertotranslateoutputsofplant‐basedsensors,thephenomenonofhysteresis
shouldbefurtherconsidered.Explainingthecausesofhystereticphenomenonappears
fraughtwithcomplexinteractionsbetweenexogenousandendogenousfactorstothe
plantsystem[39].TherootofthewordhysteresisisGreekandmeansto“lagbehind”
[27,40].Hysteresisisnon‐linearloop‐likebehaviorthathasbeenknowninplantsystems
foralongtime[40,41].Inhysteresis,whenthetimeargumentofaninputfunctionis
stretchedorcompressed,thecorrespondingoutputfunctionisnotstretchedinthesame
way,sothehysteresisdoesnotshowaffinesimilaritywithrespecttotime[40,42,43].For
example,adiurnalhysteresisbetweenevapotranspiration(ET)(ortranspiration)andva‐
porpressuredeficit(VPD)hasbeenstudied[40];hysteresisasarelationshipbetweenen‐
vironmentalfactor(e.g.,meteorologicalfactors)andsapflow[40,44,45];hysteresiswas
foundalsointherelationshipbetweencanopyconductanceandtemperature[46];hyste‐
resisbetweenfruitdiameterandleafpressureontwodifferentolivecultivars[14].Fur‐
thermore,inthecherryfruitgrowthrelationshipwithVPD,completehysteresiswas
foundonlyduringthematurationphasewhileduringfruitextensionphasethehysteresis
wasnullorpartial[36].RecentlyKhosravietal.[27]examinedthe“Frantoio”oliveculti‐
varandexplainedthedifferenthysteresiscurvesofthediameterversustheVPDduring
thesecond,third,andfourthphasesofolivefruitdevelopment.Accordingtothisresearch,
monitoringhystereticloopsanddetectingthemagnitudechangecouldbeusedasa
methodfordetectingthegrowthphases.Inthisresearch,theform,magnitude,androta‐
tionalpatternofhysteresiscurve(loop)oftransversaldiameterversusVPDwereinvesti‐
gated.IthasbeenshownthatVPDisespeciallyimportantinwoodyplants,whereitisthe
mainvariableaffectingtheirdiurnalevolutionoftranspiration[47].
Theaimofthisworkwastodescribethirdphaseofolivefruitdevelopmentbycon‐
tinuousmonitoringwithextensimeterunderregulateddeficitirrigationregimes.Further‐
more,wehypothesizedthepresenceofhysteresiscurvesbyexaminingtheolivefruitdi‐
ameter(FD)comparedtoVPD.Weintendedtoprovidesomeindexesforsmartirrigation
inrelationtotheregulateddeficitirrigationinakeyphenologicalstageofthefruit.
2.MaterialsandMethods
2.1.SiteDescriptionandPhenology
Theexperimentwascarriedoutin2021attheexperimentalfarmofthePolytechnic
UniversityofMarche,locatedinAgugliano(Marche,Italy)(latitude43°54′N,longitude
13°36′E,altitude85m),inahigh‐densityoliveorchardinfourself‐rootedolive(Oleaeu‐
ropaeaL.)cultivarsofAscolanadura,PiantonediFalerone,ArbequinaandLea.Thetrees
wereplanted4×2m(1250treeha−1)inMay2012,about9yearsoldatthetimeofexperi‐
ment.Eachcultivarwasdisplayedinaseparaterow.Theolivetreeswereinitiallytrained
asacentralleader,thetreecanopywasafterwardsflattenedaccordingtoahedgerow,
removinglongbranchestowardtheinterrow[48].Integratedagriculturalmethodswere
Horticulturae2022,8,12214of28
adoptedfortheagriculturaloperations,pestcontrol,andfertilizationpracticesaccording
toregionalguidelines[49].Theirrigationwaslocalizedandusedtoperformdifferentir‐
rigationtreatmentsduringexperiment(seeSection2.2.Irrigation).Thesoilwasmanaged
withpermanentgrasscoverintheinter‐rowalley,withmowing3–4timesduringthe
growingseasonandwithtillagealongtherow[27].
2.2.Irrigation
Theolivetreeswereirrigatedbyadripirrigationsystemwithaflowof8(Lh−1)per
tree.Twodeficitirrigationlevelswereperformedandthehigherdose(DI‐20)wassup‐
pliedtobigfruitvarietieswhilethelowerdose(DI‐10)wassuppliedtomedium‐small
fruitvarieties.DI‐20had20%oftheamountofETcandwassuppliedtoAscolanadura
andPiantonediFaleronetrees,whileDI‐10had10%oftheamountofETcandwassup‐
pliedtoLeaandArbequinatrees.ThecropevapotranspirationETcwasestimatedaccord‐
ingtoFAO56equationwhichis:
(ETc=ET0×Kc)(1)
wheretheevapotranspiration(ET0)wascalculatedbythelocalweatherstationautomati‐
callyviaFAOPenman–MonteithequationandKcwasthecropcoefficient[6].Moreover,
effectiverainfall(R)wascalculatedas:
R=(Pp−5)×0.75(2)
wherePp=rainfallobtainedfromthelocalweatherstation[6].Theirrigationtreatment
wasperformedaccordingtotherandomizedblockwiththreereplications,andeachblock
consistedofatleastfiveadjacenttreesonthesamerow.Theirrigationwasdonethree
timesduringtheexperimentperiod,17thAugust(DayoftheYear,DOY,229),19thAu‐
gust(DOY231),and16thSeptember(DOY259).TheDI‐20irrigatedcultivarsreceived62
mmofwaterduringallfruitgrowthphaseswhich17.5mmwasduringthethirdgrowth
phase.FortheDI‐10irrigatedcultivarstheamountofreceivedwaterduringallfruit
growthphasesandthirdgrowthphasewere31and8.75mm,respectively.Forbigfruit
varietiesofAscolanaduraandPiantonediFalerone,thenoirrigatedfruit(DI‐0)wascon‐
sideredasareferencepointfordetectingtheeffectofthedeficitirrigationtreatmenton
fruitgrowth.TherationalebehindusingDI‐0againstfullyirrigatedtreatmentcomesfrom
theideaofanalyzingtheeffectofdeficitirrigationonfruitgrowth(dailyandperiodical
growth)whichshouldbediscoveredincomparisonwithnormalgrowthconditions(with‐
outirrigation).Thechangesinthedailyolivefruitgrowthpatternbyirrigationhasbeen
explainedbysomeresearchpreviously[14,15].
2.3.FruitMaturationMonitoring
From19thSeptember(DOY262)to26thOctober(DOY299)thefruits,whichwere
placedinsidetheextensimeter,werephotographedbyCanonEOS1100DCamera(Canon
Inc.,Tokyo,Japan)weekly.Inthecaseofadverseweatherconditions,takingimageswas
postponedtothenextpossibleday.Theripeningstatusofeacholivefruitwasassessed
accordingtothefirstfive(0–4)classesofJaenindex[50](Table1).UptoDOY276,fruits
insidetheextensimeterwereinthethirdphaseoffruitdevelopment,andmaturityindex
rangedfrom0to2.Consequently,DOY276wasconsideredtheendingdayofthethird
phaseoffruitdevelopment.
Table1.Dataofripeningindexforthefruits,whichweremountedontheextensimeters.Data
werecollectedweeklyfrom262to299daysoftheyear(DOY).Maturationindexeswereper‐
formedaccordingtothefirstfive(0to4)categoriesoftheJaenindex.Arb1(DI‐10)andArb2(DI‐10)
representfruit1and2of“Arbequina”at10%deficitirrigation,respectively.Lea1(DI‐10)and
Lea2(DI‐10)representfruit1and2of“Lea”at10%deficitirrigation,respectively.Asc1(DI‐20)and
Asc2(DI‐20)representfruit1and2of“Ascolanadura”at20%deficitirrigation,respectively.
Asc3(DI‐0)representsfruit3ofnon‐irrigated“Ascolanadura”.Fal1(DI‐20)andFal2(DI‐20)
Horticulturae2022,8,12215of28
representfruit1and2of“PiantonediFalerone”at20%deficitirrigation,respectively.Fal4(DI‐0)
representsfruit4ofnon‐irrigated“PiantonediFalerone”.
DO
Y
Arb1(DI
‐10)
Arb2(DI
‐10)
Lea1(DI
‐10)
Lea2(DI
‐10)
Asc1(DI
‐20)
Asc2(DI
‐20)
Asc3(DI
‐0)
Fal1(DI
‐20)
Fal2(DI
‐20)
Fal4(DI
‐0)
2620000000000
2690001000002
2760002000212
2840013111322
2911113111333
2991124322433
2.4.FruitMeasurementandExperimentalDesign
Thefruittransversaldiameter(synonymtoequatorialdiameter)oftenfruitswere
monitoredbyautomaticextensimeters(synonymtofruitgauge)from12thAugust(DOY
224)to3rdOctober(DOY276)in2021.Weusedtwokindsofextensimeters;onemodel
wasWinet(Winets.r.l.Cesena,Italy)andanothermodelwasDEX20(DynamaxInc.,Hou‐
ston,TX,USA).TheWinetexperimentalextensimeterconsistedofavariablelinearre‐
sistancetransducersensor(modelMM(R)10‐12)(MegatronElektronikGmbH&Co.,Mu‐
nich,Germany)supportedbyastainlesssteelframe.Theextensimeterswereconnected
tothewirelessdata‐loggersystem(Winets.r.l.Cesena,Italy)whichcollecteddataat10
minintervals.Datahasbeensentthroughthewirelessnodestoacentralnetworknode,
whichtransmitsinformationviageneralpacketradioservice(GPRS)modemtotheserver.
Secondmodelofextensimeter(DEX20)wasacaliperstyledevicewithafullbridgestrain
gageattachedtoaflexiblearm;datawererecordedbyCR1000Xdatalogger(Campbell
scientific,Inc.,Logan,UT,USA)everyhourandsenttoourowncloudservicebasedon
AmazonWebService(AWS)twiceperday.Bothmodelsofextensimeterswereexamined
andshowedaccuratefunctionality[27,51].
ThefullbloomdayoccurredforArbequinaandAscolanaduraonthe24thand28th
ofMay,andforPiantonediFaleroneandLeaonthe31stofMay.So,theexperiment
startedalmost11weeksafterfullbloom(WAFB).Moreover,theBBCHscalewasem‐
ployedtoobtainaphenologicalphase.Inthisscale,theendofthesecondphaseoffruit
development(pit‐hardening)wasdeterminedwhenitwasnolongerpossibletocutthe
fruit[6].Foreachcultivar,15fruitsweresampledrandomly.Samplingwasrepeatedevery
10daysandpitresistancetocuttingwereexaminedbyblade.Theendingdayofthesec‐
ondphaseoffruitdevelopmentwasobservedonthe13thofAugust(DOY225).Conse‐
quently,ourexperimentperiodstartedfromthethirdphase(cellexpansion)offruitde‐
velopment.
EightfruitsweremountedonWi‐netextensimeterwhichconsistedofthreefruitsof
Ascolanadura(twowithDI‐20andoneDI‐0(withoutirrigation)thatfromherecalled
Asc1(DI‐20),Asc2(DI‐20)andAsc3(DI‐0),threefruitsofPiantonediFalerone(twowith
DI‐20andoneDI‐0(withoutirrigation)thatfromherecalledFal1(DI‐20),Fal2(DI‐20)and
Fal3(DI‐0)andtwofruitsofLeawithDI‐10irrigationlevelthatfromherecalledLea1(DI‐
10)andLea2(DI‐10).InthemiddleoftheexperimentthefruitofFal3(DI‐0)feltdownand
wassubstitutedwithFal4(DI‐0).TwofruitsofArbequinawithDI‐10irrigationlevelwere
mountedonDEX20extensimeter(Arb1(DI‐10)andArb2(DI‐10)).Therepresentative
treesaccordingtoirrigationlevelwereselectedinthecenteroftheexperimentalblockto
avoidbordereffect.Moreover,allextensimetersofthesamecultivar‐irrigationlevelwere
installedtogetherononerepresentativetree.
Accordingtotheimportanceandphysiologicaleffectofdaylightonfruitgrowthand
itsroleinphotosynthesis,thegraphicrepresentationofdailyfruitgrowthanditsfluctu‐
ationswerereportedfromthetimeofsunrise[14,27].Infact,thedaystartedfromsunrise
Horticulturae2022,8,12216of28
andcontinuedfor24h.Basedondatafromourweatherstation,sunrisetimefrom12thof
Augustto5thofSeptember(DOY224to248)wasestimatedat6AM,from6thofSeptem‐
berto3rdofOctober(DOY249to276)wasestimatedat7AM.
2.5.FruitGrowthParameters
Incorrespondencewiththedaysinwhichirrigationtreatment(DI‐20andDI‐10)
wereperformed(DOYs229,231and259),6dayintervalswereselectedforassessmentof
deficitirrigationeffectonfruitgrowth.Thementionedwindow(6days)consistedofthe
2daysbeforeirrigationupto3daysafterirrigationday.Theparameterscalculatedfor
eachintervalswere:(1)dailydiameterfluctuation(ΔD,mm)whichwascalculatedasthe
maximumdiameterminustheminimumdiameterofsameday,(2)dailygrowth(ΔG,
mm)whichwascalculatedasthediameterofendingpointofdayminusthediameterof
startingpointofsameday,(3)cumulativefruitgrowth(CFG,mm)asthemaximumdaily
diameterofthefruitsubtractedfrommaximumdiameterofthepreviousday[26],(4)fruit
relativegrowthrate(RGR,mmmm−1h−1)wascalculatedusingthefollowingequation:
RGR=[(lnD2−lnD1)/(t2−t1)](3)
whereD1andD2arefruitdiametersattimest1andt2,respectively[14,15].Andthedaily
rangeofRGR(RGRrange,mmmm−1h−1)wascalculatedasthedifferencebetweenthemini‐
mumvalueandthemaximumvalueofRGRinoneday.
Inaddition,unitless(standardized)datahavebeenusedtoallowcomparisons
amongfruitswithdifferentinitialdiameterwhenextensimeterswereinstalled.Thedata
ofsensorswasstandardizedforeachdaybyusing:
x′=x/x0(4)
wherex′isthestandardizedvalue,xisthevalueoftheexistingdata,andx0istheinitial
valuesofthedataatstartingpointofsameday.
2.6.MeteorologicalData
AccordingtoKöppen–Geigerclimateclassification,AguglianoisclassifiedintheCfa
categoryandthisischaracterizedbywarmtemperature,highlyhumidandwarmsummer
[52]butinrecentyearstheclassificationismovingtowardCsa(hotsummerMediterra‐
nean).MeteorologicaldatawererecordedwithaMeteoSense4.0weatherstation(Net‐
senseS.r.lFlorence,Italy)locatedintheoliveorchard.Forthecalculationofvaporpres‐
suredeficit(VPD),airtemperature(T),andrelativehumidity(RH)datawerecollected
fromourweatherstation.Vaporpressuredeficitwascalculatedas:
VPD=(1−(RH/100))×SVPandSVP(Pascals)=610.7×10(7.5T/(237.3+T))(5)
TheVPDformulawasrecommendedbyMonteithandUnsworth[53];whereRHis
therelativehumidity,SVPissaturatedvaporpressure,andTistemperature(°C).Our
instrumentwassettolegalRometime.
2.7.HysteresisCurves
Toexplorethecircadianpatternofhysteresiscurve(loop),hourlycollecteddataof
transversalfruitdiameter(FD)versusVPDwereconsidered.Fordescriptionofthehyste‐
resisrotationalpattern,thetermsofclockwiseandanticlockwisecurvewereemployed.
Furthermore,forcharacterizationofhysteresisform,threeconceptsofpartial,incomplete,
andcompletewereused.Whenthehysteresiscurveappearedinsomepartofthedayand
wasnotrepresentativeofthewholeday,itwascalledpartial.Whentheendingpointof
thehysteresisloopreachedthesamelevelofthestartingpointoftheloop,itwasdefined
ascomplete.Lastly,whentheendingpointofthehysteresisloopdidnotreachthesame
levelofthestartingpointoftheloop,sotheloopwasnotcompletelyclosed,itwascalled
incompletehysteresiscurve.Fordetectionofincompleteclockwisehysteresis,normalized
Horticulturae2022,8,12217of28
dataofdiameterwereemployed.Hysteresisloopswereconsideredincompletewhenthe
loop“opening”wasmorethan0.05units.Inthecaseofloopopening,lessthan0.05is
consideredascomplete[27].
ThemeasureddailydatawerenormalizedbyMin‐Maxmethodthroughtheequa‐
tion:
x′=0.9×((x−xmin)/xmax−xmin)+0.05(6)
wherex′isthenormalizedvalue,xisthevalueoftheexistingdata,andxminandxmaxare
theminimumandmaximumvaluesofthedata,respectively[27,36].
2.8.DataAnalysisandPresentation
One‐wayrepeatedmeasuresanalysisofvariance(ANOVA)wasperformedforas‐
sessingsignificantdifferences.Thesignificantdifferencesamongthetreatmentswereas‐
sessedusingStudent–Newman–Keuls’stest(p<0.05).Alldataanalysesandgraphdesign
wereperformedusingSigmaplot14.5(SystatSoftware,Inc.,SanJose,CA,USA).
3.Results
3.1.EnvironmentalDataAnalysisandVPDEvolution
Figure1showsthedataofVPD,temperature(T),ET0,andrainfallduringtheexper‐
iment(DOY224toDOY276).ThehighestmeasuredhourlyVPDwas5.4(kPa)on16thof
August(DOY228)andthelowestwas0.05(kPa)on23rdand24thofAugust(DOYs235
and236).ThehighestdailyaverageofVPDwas3.0(kPa)onthe16thofAugust(DOY228)
andthelowestwas0.12(kPa)onthe27thofSeptember(DOY270).ThedailymeanofVPD
duringtheexperimentwas0.91±0.56(kPa).Thedailymeanoftemperatureduringex‐
perimentwas21.30±3.43(°C),withaminimumdailytemperatureof15.76(°C)onthe1st
ofOctober(DOY274)andmaximumdailytemperatureof32.26(°C)reachedon17thof
August(DOY229).Themaximumandminimumhourlytemperatureswere39.0and9.5
(°C)whichreachedon16thofAugust(DOY228)and1stofOctober(DOY274),respec‐
tively.ThetotalreferenceET0was173.9(mm)fortheexperimentperiod.Themaximum
andminimumdailyET0was6.3(mmday−1)on16thofAugust(DOY228)and0.6(mm
day−1)on27thofSeptember(DOY270),respectively.ThemaximumhourlyET0was0.7
(mmhour−1)whichreachedon14th,15th,16thofAugust(DOYs226,227,and228).During
theexperimentperiod,theaccumulatedrainfallwas96.1(mm),withmaximumhourly
anddailyof17.6(mmhour−1)and39.5(mmday−1)reachedon23rdofAugust(DOY235).
Horticulturae2022,8,12218of28
Figure1.Trendofhourlyanddailytemperature(T),vaporpressuredeficit(VPD),referenceevap‐
otranspiration(ET0)andrainfall,duringtheexperimentperiod(from224to276daysoftheyear
(DOY),obtainedbyMeteoSense4.0weatherstation.
Horticulturae2022,8,12219of28
3.2.FruitGrowth
Figure2reportsthehourlytransversaldiameteroffruitsforthefourdifferentculti‐
varsfromDOY224toDOY276.Thetypicalthirdphaseofthefruitgrowthwasobservable
inallfourcultivars(Lea,Figure2A;Arbequina,Figure2B;PiantonediFalerone,Figure
2C;AscolanaduraFigure2D);however,withdissimilargrowthslopeamongdifferent
cultivarsandafinalrelentlesstowardmaturation(4thphase).Thefruitgrowthshoweda
diameterincreasewithdiurnalfluctuation.Thediurnalfluctuationofolivefruitwasde‐
tectedasashrinkageoffruitdiameterfrommid‐morningtoearlyafternoonfollowedby
expansionoffruitdiameterfromlateafternoontoearlymorning(FigureS1A).Attheend
oftheday,thefruitsreachedasizelargerthantheinitialpointofthesameday.Infact,
Arbequina(DI‐10)in60.4%ofcases(64outof106),Lea(DI‐10)in82.89%ofcases(63out
of76),Ascolanadura(DI‐0)in77.5%ofcases(38outof49),Ascolanadura(DI‐20)in72.4%
ofcases(55outof76),PiantonediFalerone(DI‐0)in82.5%ofcases(32outof39)and
PiantonediFalerone(DI‐20)in87.7%ofcases(86outof98)reachedasizesimilarorlarger
thantheinitialpointofsameday.
Figure2.Continuousmeasurementsofdiameterofolivefruitsduringtheexperimentperiod
(from224to276daysoftheyear(DOY):(A)fruit1and2of“Lea”at10%deficitirrigation
(Lea1(DI‐10)andLea2(DI‐10),respectively);(B)fruit1and2of“Arbequina”at10%deficitirriga‐
tion(Arb1(DI‐10)andArb2(DI‐10),respectively);(C)fruit1and2of“PiantonediFalerone”at20%
deficitirrigation(Fal1(DI‐20)andFal2(DI‐20),respectively)andfruit3and4ofnon‐irrigated“Pi‐
antonediFalerone”(Fal3(DI‐0)andFal4(DI‐0),respectively);(D)fruit1and2of“Ascolanadura”
at20%deficitirrigation(Asc1(DI‐20)andAsc2(DI‐20),respectively)andfruit3ofnon‐irrigated
“Ascolanadura”(Asc3(DI‐0)).MissingdataFrom224to249dayoftheyear(DOY)forLea2(DI‐
10)andAsc1(DI‐20)andfrom246to249dayoftheyear(DOY)forpanel(A,C,D).
Theduration,frombeginningtofinishingdailyfruitshrinkageandexpansion,did
notshowsimilarityamongcultivar‐irrigationlevel(TableS1).Inaddition,therewere
someexceptionaldayswhichshoweddifferentgrowthpatterns(FigureS1B).Therewas
nouniquepatternforexplanationofdiameter(fruitgrowth)fluctuationofthesedays.
3.3.IrrigationResponse
Monitoringthedailyvariationoffruitdiameter at6days’window(fromDOY227to
234)incorrespondencewithfirstandsecondirrigationdaysshowedthatdiameterofArb1
Horticulturae2022,8,122110of28
(DI‐10)downsizedfrom9.91mmto9.81mm,whereasforArb2(DI‐10)downsizedfrom
8.76mmto8.65mm,butforLea1(DI‐10)startedfrom10.7mmandincreasedto11.1mm.
Atthesameperiod,diameterofAsc2(DI‐20)startedfrom20.4mmupto20.9mm,Fal1
(DI‐20)startedfrom13.7mmupto14.4mm,andFal2(DI‐20)startedfrom13.0mmand
reached13.8mm,whereastransversaldiameterofAsc3(DI‐0)andFal3(DI‐0)startedfrom
15.6mmand15.4mmupto15.7mmand15.4mm,respectively(FigureS2A–D).Itshowed
diameterincreaseforbothcultivarwithandwithoutirrigationtreatment,nevertheless,
standardizeddiameter(Table2)showeddifferentratio ofdiametergrowth. Forirrigated
AscolanaduraandPiantonediFalerone,theratioofdiametergrowthwashigherthan
non‐irrigatedtreatment.
Table2.Standardizeddataofdiameterforperiodof227to234dayoftheyear(DOY)and257to
262dayoftheyear(DOY).DataofDOY227and257isrelatedtothestartingpointofdayandfor
DOY234and262isrelatedtotheendingpointofday.Arb1(DI‐10)andArb2(DI‐10)represent
fruit1and2of“Arbequina”at10%deficitirrigation,respectively.Lea1(DI‐10)andLea2(DI‐10)
representfruit1and2of“Lea”at10%deficitirrigation,respectively.Asc1(DI‐20)andAsc2(DI‐20)
representfruit1and2of“Ascolanadura”at20%deficitirrigation,respectively.Asc3(DI‐0)repre‐
sentsfruit3ofnon‐irrigated“Ascolanadura”.Fal1(DI‐20)andFal2(DI‐20)representfruit1and2
of“PiantonediFalerone”at20%deficitirrigation,respectively.Fal3(DI‐0)andFal4(DI‐0)repre‐
sentfruit3and4ofnon‐irrigated“PiantonediFalerone”,respectively.Fal3(DI‐0)felldownand
hasbeensubstitutedwithFal4(DI‐0)for257to262dayoftheyear(DOY).Missingdatafrom227
to234dayoftheyear(DOY)forLea2(DI‐10)andAsc1(DI‐20).
DOYArb1(DI‐
10)
Arb2(DI‐
10)
Lea1(DI‐
10)
Lea2(DI‐
10)
Asc1(DI‐
20)
Asc2(DI‐
20)
Asc3(DI‐
0)
Fal1(DI‐
20)
Fal2(DI‐
20)
Fal3(DI‐
0)
Fal4(DI‐
0)
 Firstandsecondirrigationtreatment(DOYs229
&231)     
2270.40.460.29‐ ‐ 0.410.620.340.320.72‐
2340.130.150.79‐ ‐ 0.910.90.950.950.89‐
 Thirdirrigationtreatment(DOY259)    ‐ 
2570.190.20.230.240.380.950.10.170.08‐ 0.81
2620.950.910.950.830.890.950.950.920.92‐ 0.95
Incorrespondencewiththethirdirrigationday(fromDOY257to262),diameterofArb1
(DI‐10)startedat10.2mmreached10.8mm,andforArb2(DI‐10)startedfrom9.0mmupto
9.6mm.DiameterofLea1(DI‐10)startedfrom12.7mmandreachedto13.3mm,andforLea2
(DI‐10)startedfrom11.3mmupto11.7mm.AboutAsc1(DI‐20)diameterstartedfrom20.3
mmandreached20.7mmandforAsc2(DI‐20)startedfrom21.3mmandremainedthesame
size.AboutFal1(DI‐20),diameterstartedfrom15.7mmandreached16.3,andFal2(DI‐20)
startedfrom15.0mmandreached15.5mm.Inthenon‐irrigatedfruits,thediameterofAsc3
andFal4startedfrom18.77mmand11.4mmupto19.3mmand11.6mm,respectively(Figure
S2E–H).Datashoweddiameterincreaseforallthefourcultivarswithdifferentirrigationlevels
andfortwocultivars(AscolanaduraandPiantonediFalerone)withoutirrigationtreatment.
DataofstandardizeddiameterexplainedthatdiametergrowthratioinirrigatedAscolana
durawaslowerthannon‐irrigatedandforirrigatedPiantonediFaleronewashigherthannon‐
irrigated(Table2).
Thedailygrowth(ΔG)(Table3)providedmoreinformationrelatedtodiameterchange
incorrespondencewithirrigationdays.Onthefirstirrigationday(DOY229),forbothculti‐
varswithDI‐20,notonlyΔGwaspositive,butitwashigherthanΔGofthepreviousday.At
thesametime,ΔGfornon‐irrigatedfruitsdidnotshowanygrowthincomparisonwiththe
previousday.Infact,ΔGofAscolanadura(DI‐0)waspositiveandthesameastheprevious
dayandforPiantonediFalerone(DI‐0)wasnegativeandlowerthanpreviousday.About
cultivarswithDI‐10,ΔGwashigherthanthepreviousdaybutforLeaitwaspositiveandfor
Arbequinaitwasnegative.Inallfourirrigatedcultivars(withDI‐10orDI‐20),inthedayafter
irrigationΔGincreasedincomparisonwiththedaybefore.ThetrendofΔGinthenon‐
Horticulturae2022,8,122111of28
irrigatedfruitsatthedayafterIrrigationforAscolanadurawasdownward,andforPiantone
diFaleronedidnotshowanychanges.
Table3.Standardizeddataofdailyfruitgrowth(ΔG)incorrespondencewithirrigationdays.
Datawasrelatedtothe6dayswindow(2daysbeforeand3daysafterirrigationday).Arb1(DI‐10)
andArb2(DI‐10)representfruit1and2of“Arbequina”at10%deficitirrigation,respectively.
Lea1(DI‐10)andLea2(DI‐10)representfruit1and2of“Lea”at10%deficitirrigation,respectively.
Asc1(DI‐20)andAsc2(DI‐20)representfruit1and2of“Ascolanadura”at20%deficitirrigation,
respectively.Asc3(DI‐0)representsfruit3ofnon‐irrigated“Ascolanadura”.Fal1(DI‐20)and
Fal2(DI‐20)representfruit1and2of“PiantonediFalerone”at20%deficitirrigation,respectively.
Fal3(DI‐0)andFal4(DI‐0)representfruit3and4ofnon‐irrigated“PiantonediFalerone”,respec‐
tively.Fal3(DI‐0)felldownandhasbeensubstitutedwithFal4(DI‐0)for257to262dayofthe
year(DOY).Missingdatafrom227to234dayoftheyear(DOY)forLea2(DI‐10)andAsc1(DI‐20).
DOYArb1(DI‐
10)
Arb2(DI‐
10)
Lea1(DI‐
10)
Lea2(DI‐
10)
Asc1(DI‐
20)
Asc2(DI‐
10)
Asc3(DI‐
0)
Fal1(DI‐
20)
Fal2(DI‐
20)
Fal3(DI‐
0)
Fal4(DI‐
0)
2270.00040.00210.0019‐ ‐ −0.0029 −0.0006 −0.0029 −0.00310.0000‐
228 −0.00050.00210.0028‐ ‐ 0.00000.0013 −0.0044 −0.00540.0006‐
229 −0.0050 −0.00860.0102‐ ‐ 0.00540.00130.01020.0139 −0.0013‐
230 −0.0076 −0.00660.0119‐ ‐ 0.0063 −0.00130.01160.0144 −0.0013‐
231 −0.0034 −0.00290.0073‐ ‐ 0.0048 −0.00060.00860.00970.0000‐
2320.01580.01770.0027‐ ‐ 0.00340.00060.00640.00740.0006‐
2330.01340.0113 −0.0018‐ ‐ 0.00290.00060.00490.00440.0006‐
2340.00290.0029 −0.0090‐ ‐ −0.00100.00000.00210.00220.0000‐
2570.00430.00590.0000 −0.0044 −0.00890.0000 −0.0011 −0.00320.0000‐ −0.0236
2580.00300.0041 −0.00630.0018 −0.0045 −0.00420.0011 −0.0019 −0.0007‐ −0.0170
2590.0008 −0.00170.01740.01160.0145 −0.00050.00480.00890.0100‐ −0.0009
260 −0.0395 −0.04080.01940.01590.0108 −0.00240.00580.00630.0072‐ 0.0027
261 −0.0177 −0.02040.00760.02010.00150.00000.00740.00880.0098‐ 0.0154
262 −0.00220.00200.00530.00090.00680.00710.00840.01370.0052‐ 0.0294
Onthesecondirrigationday(DOY231),ΔGforbothcultivarswithDI‐20wasposi‐
tive,however,itwaslowerthanΔGofthepreviousday.Concurrently,ΔGofnon‐irri‐
gatedfruitswashigherthanthepreviousday.Although,ΔGofAscolanadura(DI‐0)was
negativeandforPiantonediFalerone(DI‐0)waszero.AboutcultivarswithDI‐10,for
ArbequinaΔGwasgreaterthanthepreviousdayandwithanegativeamountandforLea
itwaslowerthanthepreviousdaywithapositiveamount.Inbothirrigatedcultivarswith
DI‐20,inthedayafterirrigation,ΔGdecreasedincomparisonwiththedaybefore,
whereasΔGofnon‐irrigatedfruitsforbothcultivarsincreased.AboutcultivarswithDI‐
10,inthedayafterirrigation,forArbequinaΔGincreasedandforLeaΔGdecreasedin
comparisonwiththepreviousday.
Onthethirdirrigationday(DOY259),ΔGforbothcultivarsofAscolanaduraand
PiantonediFalerone(irrigated(DI‐20)andnon‐irrigated(DI‐0))washigherthanthepre‐
viousday.AboutcultivarswithDI‐10,ΔGofArbequinawaslowerthanthepreviousday
butforLeawashigher.Onthedayafterirrigation,ΔGforbothcultivarswithDI‐20was
lowerthantheirrigationday,whereasΔGofnon‐irrigated(DI‐0)cultivarswashigher
thantheirrigationday.AboutcultivarswithDI‐10,inthedayafterirrigation,forArbe‐
quinaΔGreducedandforLeaΔGenlargedincomparisonwiththepreviousday(Table
3).
Thedailydiameterfluctuation(ΔD)inthefirstirrigationdaywasreducedinboth
cultivarswithDI‐20andreductioncontinueduntilthedayafterirrigation,whereasin
bothcultivarswithDI‐10,ΔDincreasedandthedayafterdecreased.Inthesecondirriga‐
tionday,ΔDinbothcultivarswithDI‐20wasalmostthesameasthepreviousday,andin
thedayafterirrigation,followedbyslightincreaseforcultivarPiantonediFaleroneand
Horticulturae2022,8,122112of28
stabilityforAscolanadura.Inthesecondirrigationday,ΔDforcultivarwithDI‐10fol‐
lowedtheoppositetrend,whichwasareductionforArbequinaandanincreaseforLea;
however,inthedayafterirrigationΔDforbothDI‐10cultivarsincreased.Inthethird
irrigationday,ΔDforPiantonediFaleroneDI‐20increasedandinthedayafterdecreased.
FortheAscolanaduraDI‐20,onefruitshoweddecreasingofΔDfollowedbyincreasing
inthedayafter,andotherfruitshowedincreasingofΔDfollowedbydecreasinginthe
dayafter.AboutcultivarwithDI‐10,ΔDshowedadifferenttrend.Indeed,forArbequina
ΔDdecreasedandinthedayafterirrigationincreased,butforLeaΔDincreasedandin
thedayafterirrigationonefruitshowedΔDreductionandotheroneshowedΔDincrease
(FigureS3A–D).
Thecumulativefruitgrowth(CFG),forallirrigatedcultivars(DI‐20andDI‐10),in
correspondencewiththefirstirrigationdayincreasedandtheupwardtrendhascontin‐
uedinthedayafterirrigation(Figure3A,B).Innon‐irrigatedcultivars,asmallgrowthof
CFGwasobservedwhichwasfollowedbyareductioninthedayafterirrigation(Figure
3B).Inthesecondirrigationday,CFGforallirrigatedcultivars(DI‐20andDI‐10)de‐
creased,thedownwardtrendcontinuedinthedayafterirrigationbutwithaslightslope
(Figure3A,B).Inthesametime,CFGofDI‐0treatmentsdecreasedbutinthedayafter
irrigationitincreased(Figure3B).Onthethirdirrigationday,CFGforallirrigated(DI‐20
andDI‐10)andnon‐irrigatedcultivarsincreased(Figure3C,D).Theonlyexceptionwas
onefruitofAscolanadura(Asc2(DI‐20))whichCFGdecreased(Figure3D).Ontheday
afterirrigation,CFGofbothcultivarswithDI‐20wasthesameasirrigationdayanddid
notshowanychange(Figure3D),neverthelessCFGofbothcultivarswithDI‐10increased
(Figure3C).CFGforAscolanadura(DI‐0)wasthesameasthepreviousdayanddidnot
change,whereas,CFGofPiantonediFalerone(DI‐0)increased(Figure3D).
Figure3.Standardizedcumulativefruitgrowth(CFG).From227to234dayoftheyear(DOY)(in
correspondencewithfirstandsecondirrigationdays)fortheolivecultivarArbequinaandLea(A)
andfortheolivecultivarsAscolanaduraandPiantonediFalerone(B).From257to262dayofthe
year(DOY)(incorrespondencewiththirdirrigationday)fortheolivecultivarArbequinaandLea
(C)andfortheolivecultivarsAscolanaduraandPiantonediFalerone(D).Arb1(DI‐10)and
Arb2(DI‐10)representfruit1and2of“Arbequina”at10%deficitirrigation,respectively.Lea1(DI‐
10)andLea2(DI‐10)representfruit1and2of“Lea”at10%deficitirrigation,respectively.Asc1(DI‐
20)andAsc2(DI‐20)representfruit1and2of“Ascolanadura”at20%deficitirrigation,
Horticulturae2022,8,122113of28
respectively.Asc3(DI‐0)representsfruit3ofnon‐irrigated“Ascolanadura”.Fal1(DI‐20)and
Fal2(DI‐20)representfruit1and2of“PiantonediFalerone”at20%deficitirrigation,respectively.
Fal3(DI‐0)andFal4(DI‐0)representfruit3and4ofnon‐irrigated“PiantonediFalerone”,respec‐
tively.
Afterthefirstandsecondirrigationday,dailyfruitrelativegrowthrate(RGR)
changedsignificantly(Figure4B–F).Afterthefirstirrigationdaytheminimumamountof
RGRwasnearzeroandthendecreasedcontinuously(dashedorangeline).Theminimum
ofRGRdownsizedwithdissimilarslopesindifferentirrigationlevels.Moreover,the
trendofminimumRGRreductionindifferentcultivarswiththesameirrigationlevelwas
diversetoo.ThemaximumamountofRGRforbothcultivarswithDI‐20increasedslightly
(dashedblacklineinFigure4B,D),whereascultivarswithDI‐10didnotshowanycon‐
sistentdecreasingorincreasingofmaximumRGR(Figure4E,F).Atthesametime,mini‐
mumRGRofPiantonediFalerone(DI‐0)andAscolanadura(DI‐0)showedconsistent
decrease(dashedorangelineinFigure4A,C).ThemaximumRGRforPiantonediFale‐
rone(DI‐0)didnotshowanyspecificpatterns,however,forAscolanadura(DI‐0)was
stable(dashedblacklineinFigure4C).
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Figure4.Dailyfruitrelativegrowthrate(RGR)from227to234dayoftheyear(DOY)(incorre‐
spondencewithfirstandsecondirrigationdays.TheolivecultivarPiantonediFalerone(A,B);the
olivecultivarAscolanadura(C,D);theolivecultivarArbequina(E);theolivecultivarLea(F).
Fal3(DI‐0)representsfruit3ofnon‐irrigated“PiantonediFalerone”.Fal1(DI‐20)andFal2(DI‐20)
representfruit1and2of“PiantonediFalerone”at20%deficitirrigation,respectively.Asc3(DI‐0)
representsfruit3ofnon‐irrigated“Ascolanadura”.Asc2(DI‐20)representsfruit2of“Ascolana
dura”at20%deficitirrigation.Arb1(DI‐10)andArb2(DI‐10)representfruit1and2of“Arbe‐
quina”at10%deficitirrigation,respectively.Lea1(DI‐10)representsfruit1of“Lea”at10%deficit
irrigation.
Afterirrigationwithholding,RGRrangeamountoftwocultivars(Ascolanaduraand
PiantonediFalerone)withDI‐20irrigationtreatmentincreased(Figure5B).TheRGRrange
enlargementhasbeenreportedbyotherresearchasawaterstresssignalinolive[14,15,26].
However,thereisnodefinedthresholdforRGRrangeasawaterstressindex.Thetrendof
RGRrangeinthecultivarswithDI‐10irrigationtreatmentwasnotsameaseachother.In‐
deed,thetrendforcultivarLeawasmoresimilartoDI‐20irrigationtreatedcultivars(Fig‐
ure5A),whereas,thetrendofArbequinauptothedayafterfirstirrigationtreatmentwas
closetoLeaandthenafterfolloweddissimilartrend(Figure5A).ThetrendofAsc3(DI‐
0)wasmismatchedwithFal3(DI‐0),besides,bothofthem(DI‐0s)showeddiversepattern
incomparisonwithrelatedirrigatedcultivar(Figure5C).
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Figure5.Relativegrowthraterange(RGRrange)from227to234dayoftheyear(DOY)(incorre‐
spondencewithfirstandsecondirrigationdays:(A)fruit1and2of“Arbequina”at10%deficit
irrigation(Arb1(DI‐10)andArb2(DI‐10),respectively)andfruit1of“Lea”at10%deficitirrigation
(Lea1(DI‐10));(B)fruit1and2of“PiantonediFalerone”at20%deficitirrigation(Fal1(DI‐20)and
Fal2(DI‐20),respectively) andfruit2of“Ascolanadura”at20%deficitirrigation(Asc2(DI‐20));(C)
fruit3ofnon‐irrigated“Ascolanadura”(Asc3(DI‐0))andfruit3ofnon‐irrigated“Piantonedi
Falerone”(Fal3(DI‐0)).
Afterthirdirrigationtreatment,fruitRGRdynamicsdidnotshowsimilaritytofirst
andsecondirrigationtreatment(Figure6A–F).Moreover,thepatternofthefruitwiththe
samecultivar‐irrigationlevelwasdiversetoo.Forinstance,minimumRGRofPiantonedi
Falerone(DI‐20)foronefruit(Fal1)wasstableandalmostzero,butforotherfruit(Fal2)
followedoscillationandwasnegative,whereasmaximumRGRforbothPiantonediFale‐
rone(DI‐20)hadsametrendbutwithoutanyprogressivedecreaseorincrease(Figure6B).
MaximumRGRforAscolanadura(DI‐20)inonefruit(Asc1)showedconsistentreduction
butfortheotheronewasalmoststableandnearzero(Figure6D).
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Figure6.Dailyfruitrelativegrowthrate(RGR)from257to262dayoftheyear(DOY)(incorre‐
spondencewiththethirdirrigationday).TheolivecultivarPiantonediFalerone(A,B);theolive
cultivarAscolanadura(C,D);theolivecultivarArbequina(E);theolivecultivarLea(F).Fal4(DI‐0)
representsfruit4ofnon‐irrigated“PiantonediFalerone”.Fal1(DI‐20)andFal2(DI‐20)represent
fruit1and2of“PiantonediFalerone”at20%deficitirrigation,respectively.Asc3(DI‐0)represents
fruit3ofnon‐irrigated“Ascolanadura”.Asc1(DI‐20)andAsc2(DI‐20)representfruit1and2of
“Ascolanadura”at20%deficitirrigation,respectively.Arb1(DI‐10)andArb2(DI‐10)represent
fruit1and2of“Arbequina”at10%deficitirrigation,respectively.Lea1(DI‐10)andLea2(DI‐10)
representfruit1and2of“Lea”at10%deficitirrigation,respectively.
Horticulturae2022,8,122117of28
Afterirrigationwithholdinguptofirstrainyday(DOY260),RGRrangeamountofAs‐
colanadurawithDI‐20irrigationtreatmentincreased(Figure7B),whereas,inthePian‐
tonediFaleronewithDI‐20irrigationtreatment,RGRrangeamountintheonefruitin‐
creasedandinotheronedecreased(Figure7B).Inaddition,onthedayafterfirstrainthe
RGRrangeamountofAscolanadurawithDI‐20irrigationtreatmentdecreasedandforPi‐
antonediFaleroneincreased(Figure7B).Finally,theincreaseofRGRrangeinAscolanadura
andPiantonediFalerone(Figure7B)in2rainydays(DOYs260and262)wasincontrast
withourexpectation.Nevertheless,itresultedfromthetimeofrainfall.Datashowedthat
rainfallinDOY260and262startedat16:00and15:00,respectively.Consequently,the
fruitexperiencedwaterstressbeforerainfall,andRGRrangeincreased.RGRrangeofAsc3(DI‐
0)andFal4(DI‐0)incorrespondencewithtworainydaysshowedthesameresultsofDI‐
20treatedandconfirmedtheeffectoftimeofrainfallhappening(Figure7C).
Figure7.Relativegrowthraterange(RGRrange)from257to262dayoftheyear(DOY)(incorre‐
spondencethirdirrigationday):(A)fruit1and2of“Arbequina”at10%deficitirrigation
(Arb1(DI‐10)andArb2(DI‐10),respectively)andfruit1and2of“Lea”at10%deficitirrigation
(Lea1(DI‐10)andLea2(DI‐10),respectively);(B)fruit1and2of“Ascolanadura”at20%deficit
irrigation(Asc1(DI‐20)andAsc2(DI‐20),respectively)andfruit1and2of“PiantonediFalerone”
at20%deficitirrigation(Fal1(DI‐20)andFal2(DI‐20),respectively);(C)fruit3ofnon‐irrigated“As‐
colanadura”(Asc3(DI‐0))andfruit4ofnon‐irrigated“PiantonediFalerone”(Fal4(DI‐0)).
TheRGRrangeinthecultivarswithDI‐10irrigationtreatmentdidnotshowsimilarity
toeachother(Figure7A).Ontheirrigationday,theRGRrangeofArbequinaincreasedbut
forLeainLea1increasedandinLea2decreased(Figure7A).Fromirrigationdayupto
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theendof6dayswindow(DOY262),theRGRrangetrendofArbequina(DI‐10)wassimilar
toAscolanadura(DI‐20)(includingpatternin2rainydays(DOYs260and262)).Whereas,
LeashoweddissimilartrendincomparisonwithArbequina.Inaddition,RGRrangetrend
ofLea1andLea2wasdiversetoo(Figure7A).
3.4.HysteresisCurvesofFruitGrowthversusVPD
Thehysteresisphenomenonisanindirectresponseofvegetationtodiurnalchanges
intheexternalenvironmentandthetimelagisamajorcharacteristicofhysteresis[54].In
ourcasehysteresisisformedbythetimelagbetweenVPDandfruitgrowth.Tobetter
capturethetimelagbetweendailydiameterandVPD,thenormalizeddataofdiameter
andVPDhavebeenused. Theblueboxshowedatimelagbetweensomeexamplefruits
diameterandVPD(Figure8).
Figure8.Normalizeddiameterofexamplefruitsversusnormalizedvaporpressuredeficit(VPD)
in228dayoftheyear(DOY).TheblueboxshowsdailytimelagbetweenVPDandfruitdiameter.
Intheblueboxdarknessofcolorshowsincreasingtimelag.Tobetterdemonstratetimelag,aneg‐
ativenormalizedamountofVPDhasbeenemployed.Lea1(DI‐10)representsfruit1of“Lea”at
10%deficitirrigation.Arb1(DI‐10)representsfruit1of“Arbequina”at10%deficitirrigation.
Fal1(DI‐20)representsfruit1of“PiantonediFalerone”at20%deficitirrigation.Fal3(DI‐0)repre‐
sentsfruit3ofnon‐irrigated“PiantonediFalerone”.Asc2(DI‐20)representsfruit2of“Ascolana
dura”at20%deficitirrigation.Asc3(DI‐0)representsfruit3ofnon‐irrigated“Ascolanadura”.
Inmostperiodsofexperiment,thedailygrowthoffruittransversaldiameterversus
VPDformedclockwisecurves.Thementionedcurves,accordingtotheirshape,wereex‐
plainableascompletehysteresis(Figure9A),incompletehysteresis(Figure9B),orpartial
hysteresis(Figure9C).Although,differentkindsofhysteresiscurveshaveappearedby
dissimilarfrequency,shape,andmagnitudeineachcultivar‐irrigationlevel(Table4).
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Figure9.Hysteresisloopsofdiameterversusvaporpressuredeficit(VPD)inoneexampleday
(232dayoftheyear(DOY)).(A)Completeclockwisehysteresis;(B)incompleteclockwisehystere‐
sis;(C)partialclockwisehysteresis.Dottedblacklineshowstherotationalpatternandstarting
andendingpointofhysteresisloops.Arb1(DI‐10)andArb2(DI‐10)representfruit1and2of“Ar‐
bequina”at10%deficitirrigation,respectively.Lea1(DI‐10)representsfruit1of“Lea”at10%defi‐
citirrigation.Asc2(DI‐20)representsfruit2of“Ascolanadura”at20%deficitirrigation.Asc3(DI‐
0)representsfruit3ofnon‐irrigated“Ascolanadura”.Fal1(DI‐20)andFal2(DI‐20)representfruit1
and2of“PiantonediFalerone”at20%deficitirrigation,respectively.Fal3(DI‐0)representsfruit3
ofnon‐irrigated“PiantonediFalerone”.
Table4.Dataofpercentageofappearanceofdifferenthysteresiscurves.Invaliddatawereex‐
cludedfromthetable.Arb1(DI‐10)andArb2(DI‐10)representfruit1and2of“Arbequina”at10%
deficitirrigation,respectively.Lea1(DI‐10)andLea2(DI‐10)representfruit1and2of“Lea”at10%
deficitirrigation,respectively.Asc1(DI‐20)andAsc2(DI‐20)representfruit1and2of“Ascolana
dura”at20%deficitirrigation,respectively.Asc3(DI‐0)representsfruit3ofnon‐irrigated“As‐
colanadura”.Fal1(DI‐20)andFal2(DI‐20)representfruit1and2of“PiantonediFalerone”at20%
deficitirrigation,respectively.Fal3(DI‐0)andFal4(DI‐0)representfruit3and4ofnon‐irrigated
“PiantonediFalerone”,respectively.
Typeof
hysteresis
Arb1(DI‐
10)
Arb2(DI‐
10)
Lea1(DI‐
10)
Lea2(DI‐
10)
Asc1(DI‐
20)
Asc2(DI‐
20)
Asc3(DI‐
0)
Fal1(DI‐
20)
Fal2(DI‐
20)
Fal3(DI‐
0)
Fal4(DI‐
0)
Complete27.4515.6919.0512.5015.0012.8227.666.6710.2635.290.00
Incomplete41.1850.9823.8162.5050.0025.6419.1542.2215.3817.6533.33
Partial23.5325.4942.8616.6715.0030.7734.0426.6748.7223.5350.00
No
hysteresis7.847.8414.298.3320.0030.7719.1524.4425.6423.5316.67
Thetrendofhysteresiscurvesincorrespondencewithirrigationdayshasbeen
showninTable5.Inthefirstandsecondirrigationday,inallirrigatedcultivars(withDI‐
10andDI‐20),a