Plant Responses to UV Blocking Greenhouse Covering Materials: A Review

Abstract

Pure polyethylene (PE) is enriched with several additives to make it a smart application material in protected cultivation, as a cover material for either greenhouses or screenhouses. When this material completely or partially absorbs ultraviolet (UV) solar radiation, then it is called UV blocking material. The current work presents a review on the effects of the UV blocking covering materials on crop growth and development. Despite the passage of several years and the evolution of the design technology of plastic greenhouse covers, UV blocking materials have not ceased to be a rather interesting technique for the protection of several vegetable and ornamental species. Much of the research on UV blocking materials focuses on their indisputable effect on reducing the activity of pests and viral-related diseases, rather than on the effects on the crop physiology itself. In the present paper, representative studies dealing with the effect of the UV blocking materials on the agronomic factors of different crops are presented and discussed. The results reveal that UV blocking materials have mainly positive effects on the different plant physiological functions, such as photosynthesis and transpiration rate, and on growth characteristics, while they might have a negative effect on the production and content of secondary compounds, as anthocyanins and total phenolics.

Full text

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Agronomy2020,10,1021;doi:10.3390/agronomy10071021www.mdpi.com/journal/agronomy
Review
PlantResponsestoUVBlockingGreenhouse
CoveringMaterials:AReview
Nikolaos

Katsoulas
1,
*,AnastasiaBari
1
andChrysoulaPapaioannou
2,
*
1
DepartmentofAgricultureCropProductionandRuralEnvironment,SchoolofAgriculturalSciences,
UniversityofThessaly,FytokouStr,38446Volos,Greece;nkatsoul@uth.gr
2
DepartmentofAgrotechnology,SchoolofAgriculturalSciences,UniversityofThessaly,
41500Larisa,Greece
*Correspondence:nkatsoul@uth.gr(N.K.);chpapa@uth.gr(C.P.);
Tel.:+30‐2421093249(N.K.);+30‐2410684524(C.P.)
Received:01June2020;Accepted:12July2020;Published:15July2020
Abstract:Purepolyethylene(PE)isenrichedwithseveraladditivestomakeitasmartapplication
materialinprotectedcultivation,asacovermaterialforeithergreenhousesorscreenhouses.When
thismaterialcompletelyorpartiallyabsorbsultraviolet(UV)solarradiation,thenitiscalledUV
blockingmaterial.ThecurrentworkpresentsareviewontheeffectsoftheUVblockingcovering
materialsoncropgrowthanddevelopment.Despitethepassageofseveralyearsandtheevolution
ofthedesigntechnologyofplasticgreenhousecovers,UVblockingmaterialshavenotceasedtobe
aratherinterestingtechniquefortheprotectionofseveralvegetableandornamentalspecies.Much
oftheresearchonUVblockingmaterialsfocusesontheirindisputableeffectonreducingtheactivity
ofpestsandviral‐relateddiseases,ratherthanontheeffectsonthecropphysiologyitself.Inthe
presentpaper,representativestudiesdealingwiththeeffectoftheUVblockingmaterialsonthe
agronomicfactorsofdifferentcropsarepresentedanddiscussed.TheresultsrevealthatUV
blockingmaterialshavemainlypositiveeffectsonthedifferentplantphysiologicalfunctions,such
asphotosynthesisandtranspirationrate,andongrowthcharacteristics,whiletheymighthavea
negativeeffectontheproductionandcontentofsecondarycompounds,asanthocyaninsandtotal
phenolics.
Keywords:polyethylene;ultravioletradiation;cropresponse;fruitcolorpigmentation;vegetative
growth

1.Introduction
Theconcernforsaferfoodandenvironmentalprotectionisincreasingamongconsumers.
Regulationsonmaximumresiduelimitsincropproductsarebecomingstricter.Growers’/retailers’
commercialcontractsoftendemandminorpesticideusewithincultivationprocedure.Inaddition,
theproductioncostofvegetablescouldbereducedbyadoptingtechniqueswithlimitedchemicaluse
andalternativemethodsforsufficientpestsanddiseasescontrol.Inthisdirection,theuseofUV
blockinggreenhousecoveringmaterialsisalignedwiththecreationofanunfavorableenvironment
forgreenhousecrops’enemies.Manyauthors[1–4]pointedoutthattheuseofUVblockingfilmsas
greenhousecoverleadstodecreasedinsectpopulationandfungaldiseases.Thus,asignificant
numberofgreenhousegrowersindeedusessuchtypeoffilms.However,thesematerialsalsohave
severaleffectsoncropgrowthanddevelopment.PlantresponsestoUVBcanbephotomorphogenetic
andprotective[5].
Growthanddevelopmentofplantsdependsonthepresenceofphotoreceptors(phototropins,
cryptochromeandphytochrome).Phototropinshavetheabilitytomediatelightresponsesand

Agronomy2020,10,10212of17
optimizethephotosyntheticyield.TheUVA/bluelightsensingcryptochromesandthered/far‐red
sensingphytochromescoordinatelycancontrolseedlingestablishment,entrainmentofthecircadian
clock,andthetransitionfromvegetativetoreproductivegrowth.Moreover,phytochromesarethe
mainphotoreceptorstocontrolseedgerminationandshade‐avoidanceresponses[6].
RedandFarRedlightisabsorbedbyphytochromesthatarerelatedtophoto‐morphogenetic
reactionsoftheplants.However,photo‐morphogeneticresponseshavebeenalsoreportedasplant
reactiontoUVlightregion[7].
Photo‐morphogeneticresponsestoUVradiationaremediatedbythephotoreceptorUV
ResistanceLocus8(UVR8).Transcriptomeanalysesinmanyspecieshavedemonstratedthat
exposuretoUVBradiationdifferentiallyregulatestheexpressionofhundredsofgenesindiverse
functionalcategories.UVradiationcanchangecellmembranecharacteristicsthatmaynotonlyresult
inchangesinmembranepermeabilityandionicbalance,butmayalsobeultimatelyresponsiblefor
thepartialinhibitionofphotosynthesisandrespiratorychanges[8].Respirationdependsprimarily
onphotosynthesis,astherespirationprocessconsumesthecarbonsthatareproducedfrom
photosynthesis[9].
RegardingthegreateraccumulationofsecondarycompoundsinthepresenceofUVradiation,
ithasbeenreportedthatthesecompoundsaccumulateinleavesofhigherplantstoscreenout
harmfulUVradiation[10].UV‐absorbingpigmentssuchasflavonoidsprotecttheplantby
specificallyabsorbinginthe280–340nmwavelengthregion,thusdecreasingUVpenetrationinto
underlyingtissue[11].UVradiationalsohasanindirectdamagingeffectonthechlorophyllaandb
contentsofplants[12],andthusahigherphotosynthesisratemaybeexpectedunderabsenceofUV
light.PlantsecondarymetabolitesthatareaffectedbyUVlight,areimportantduetotheirhealth‐
promotingproperties.UseofUVblockingcoveringmaterialscanleadtoareductioninsecondary
plantcompounds,suchasphenolics,flavonoidsandcarotenoids.
StomatalbehaviorisalsoaffectedbyUVradiation,althoughitisanintegratedresponsetoa
largenumberofenvironmentalfactorsincludingCO2,humidity,radiation,temperatureandwater
supply.IthasbeenfoundthatUVradiationcanaffectstomatalbehaviorinawavelengthdependent
manner.UVAwavelengthsstimulatetheopeningofstomata,whileUVCmayinducestomatal
closure[11].
Whenreviewingtherelevantscientificfindings,itwasobservedthatmostoftheresearchwork
conductedusuallyhadthestudyoftheeffectsofUVblockinggreenhousecoveringmaterialsonpests
anddiseasesasaprimaryobjective,whiletheeffectsonthegreenhouseenvironmentandoncrop
growthanddevelopmentareusuallyasecondaryobjective.
Theaimofthisworkistopresentareviewoftheresearchcarriedoutinrelationtotheeffectsof
UVblockinggreenhousecoveringfilmsoncropgrowthanddevelopment.Thereviewincludessome
definitionsforsolarradiationandapresentationofthedifferenttypesofgreenhousecovering
materialstestedfortheirUVradiationpropertiesaroundtheworld.Itmakesanassessmentofthe
effectsoftheUVblockingcoveringmaterialsonplantfunctions,asphotosynthesis,respiration,
transpiration,germination,seedlingsandpigmentsynthesis.Plantsgrowthcharacteristicsasroots,
leavesandstemsgrowth,floweringandfruitsetting,butalsoplantperformance,yieldandearliness,
havebeenstudied.Moreover,thisreviewpresentstheinstrumentationandthemethodologyneeded
toidentify,quantifyandevaluatetheeffectsoftheUVblockingcoveringmaterialsoncropgrowth
anddevelopment.Finally,adiscussiononthedifferencesobservedbetweenthedifferentregionsand
cropsstudiedisgiven.
Thesolarradiationthatentersinagreenhouseisrangingmainlybetween280nmand3000nm
[13].Takingintoaccounttheeffectsofsolarradiationonplantgrowthanddevelopment,theabove
rangecanbedividedinthreebasicwavebands,namely:Ultravioletradiation(UV:280–400nmthat
isalsodividedinUVB:280–320nmandUVA:320–400nm),PhotosyntheticallyActiveRadiation
(PAR:400–700nm),andNearInfraredRadiation(NIR:700–1400nm)[14].ThepercentageofUV,PAR
andNIRpartsofsolarenergyincidentinopenfieldduringacleardayvariesfrom2.8%to7%,42.7%
to71%,and30%to54%,respectively[15],whiletheUVradiationisfurtherdividedintoUVA(95%)
andUVB(5%)[16].

Agronomy2020,10,10213of17
Sincethecoverisexposedtodifferentambientconditions,itusuallyconsistsofmanylayersin
ordertoimproveitsstrength,durability,anti‐dripping,etc.,aswellasitsradiometricproperties.
Manytypesofplasticareusedinprotectedcultivationascoveringmaterials.Themostcommon
plasticmaterialispolyethylene(PE),butmanyotherssuchaspolyvinylchloride(PVC),ethylene
vinylacetate(EVA),polyester,etc.arealsoused.Therightcoverhastohavemanypropertiesnot
onlytoaddressharshenvironmentalconditionsbutalsotoconserveresources(energy,water,capital,
etc.).Forallthesereasons,differentadditivesareincludedinacovermaterialinordertotransform
ittoaclever‘greenhousecoveringmaterial’.Theseadditivesintendtoleadmainlytooptimallight
transmission,provideUVstabilization(UVadditives),reduceheatlosses(IRadditives)andreduce
condensation(AFadditives)andformationofdroplets(ADadditives).Thedifferenttypesofplastics
usedindifferentresearchstudiesworldwideinrelationtotheUVblockingeffectongreenhouse
coveringmaterialsinclude:
 PEfilms,testedinFinland[17],Israel[18],Spain[19–22],UK[10,23–25],Greece[26–28],Serbia
[29],Germany[30],USA[31]andAustralia[32];
 PolyestertestedinUSA[33],Finland[17],India[34–36],Italy[37]andChina[38];
 PVCfilmstestedinJapan[39];
 PlexiglastestedinBelgium[40]andGermany[41];
 Ethylene‐tetrafluorethylene(ETFE)filmstestedinGermany[42,43];
 EVAfilmstestedinJapan[44]andinEthiopia[45];
 CellulosediacetatetestedinUSA[33],China[38],inJapan[46],andBangladesh[47,48];
 Teflonandpolycarbonate(PC)filmstestedinUSA[49].
Thecountryofstudy,theyearofthestudyandtheUVradiationregionthatisblockedbythe
differentUVblockingmaterialsreferredinthecurrentreview,arepresentedinTable1.
Table1.Country,yearandUVblockingregionofthematerialsstudiedintheliteraturethatisreferred
inthecurrentreview.
ReferenceCountryYearUVBlockingMaterialsStudied
[4]US20022materialsblockingradiation<360and<380nm
[10]UK20086materialsblockingradiation<280nm,<320nm,<350nm,<370nm,
<380nm,<400nm
[17]FI19993materialsblockingradiation<315nm,<360nm,<400nm
[18]IL20031materialblockingradiation<300nm
[19]ES20093materialsblockingradiation<300nm,<315nm,<380nm
[20]ES20045materialsblockingradiation<380nm
[21]ES20134materialsblockingradiation<380nm
[22]ES20091materialblockingradiation<380nm
[23]UK20111materialblockingradiation<380nm
[24]UK20072materialsblockingradiation<380nm
[25]UK20048materialsblockingradiation<400nm,<405nm
[26]GR20043materialsblockingradiation<380nm
[27]GR20063materialsblockingradiation<380nm
[28]GR20123materialsblockingradiation<380nm
[29]RS20121materialblockingradiation<380nm
[30]DE20131materialblockingradiation<380nm
[31]US20061materialblockingradiation<380nm
[32]AU20171materialblockingradiation<380nm
[33]US19993materialsblockingradiation<380nm
[34]IN20153materialsblockingradiation<270nm,<315nm,<395nm
[35]IN20143materialsblockingradiation<270nm,<315nm,<395nm
[36]IN20052materialsblockingradiation<320nm,<400nm
[37]IT20162materialsblockingradiation<312nm,<400nm

Agronomy2020,10,10214of17
[38]CH20152materialsblockingradiation<315nm
[39]JP19933materialsblockingradiation<290nm,<320nm,<400nm
[40]BE20012materialsblockingradiation<315nm
[41]DE19944materialsblockingradiation<280nm,<305nm,<320nm,<360nm
[42]DE20093materialsblockingradiation<380nm
[43]DE20103materialsblockingradiation<315nm
[44]JP20081materialblockingradiation<350–400nm
[45]ET20161materialblockingradiation<350nm
[46]JP20124materialsblockingradiation<340nm,<350nm,<360nm,<400nm
[47]BD20164materialsblockingradiation<340nm,<350nm,<360nm,<400nm
[48]BD20164materialsblockingradiation<340nm,<350nm,<360nm,<400nm
[49]US20142materialsblockingradiation<315nm,<380nm
[50]IN19972materialsblockingradiation<280nm,<310nm
[51]
J
P19972materialsblockingradiation<290nm,<400nm
[52]EG20183materialsblockingradiation<380nm
[53]UK20123materialsblockingradiation<380nm
[54]ET20141materialblockingradiation<315nm
[55]IT20194materialsblockingradiation<315nm
[56]DE20102materialsblockingradiation<380nm
[57]AR20061materialblockingradiation<310nm
[58]SA20141materialblockingradiation<380nm
[59]ES20101materialblockingradiation<380nm
[60]EG20163materialsblockingradiation<380nm
[61]ES20104materialsblockingradiation<380nm
[62]GR20113materialsblockingradiation<380nm
[63]US2017Nodetails
2.ExperimentalDesign,MethodologyandInstrumentationNeededtoTestUV‐BlockingCovering
Material
2.1.NecessaryEquipmentandInstrumentsonTestingaUVBlockingMaterial
TomeasuretheUVradiationlevels,specificsensorsareneeded,forthedifferentwavebands.
ThelightsensorsunderdifferentUVblockingmaterialscouldbelikethefollowing:
 Globalsolarradiationsensors,
 Photosyntheticallyactiveradiationsensors,
 UVAandUVBradiationsensors.
OncetheUVblockingmaterialeffectistobeinvestigated,itisusefultotestsensors’UVlight
absorbanceeverythreetosixmonthsbecauseitiswellknownthatthisabilityfadeswithtime
(authors’personalexperienceandunpublisheddata).
2.2.Methodology
Themeasurementsthatastudyshouldconductinordertoconfirmthatacladdingcanattenuate
UVsolarradiationincludethestudyofplantagronomiccharacteristicssuchasheight[4,18,36,39,50–
52],internodelengthandnumber[4,34,47],totalleafarea[32,36,39,43,51,52],anddrymattercontent
[34,50,52].Itisalsoknownthatyieldcharacteristics,astotalandmarketableyield,numberoffruits
andtheirmarketabilitycanbeaffectedbyUVblockingcoveringmaterials[18–24].Moreover,the
maindifferencebetweenfruitsthathavebeenproducedunderUVexclusionconditionsisthatthey
haveasignificantlylowercontentofsecondarycompounds,pigmentsandphenolicswhenthey
comparedwiththatcontainedinfruitsproducedunderopenfieldconditions[19,24,25,33,43,47,53].


Agronomy2020,10,10215of17
3.EffectsofUVBlockingGreenhouseCoveringMaterialsonPlantFunctions
3.1.EffectsonPhotosynthesisandRespiration
InJapan,in1993,theeffectofPVCcoveringmaterialswithdifferentUVradiation
transmissivitiesonthephotosyntheticactivityoftomato(SolanumlycopersicumL.)andradish
(RaphanusraphanistrumL.)plantswasstudied[39].Theyfoundthatthecarbonmetabolismwas
alwaysgreaterundertheUVblockingcover,whiledarkrespirationwasfoundnottobepromoted
bytheUVblockingmaterial.Anincreaseinphotosyntheticactivitywasalsofoundinmungbeans
(VignaradiataL.)[50].Moreover,inGermany,theeffectofthreedifferentUVblockingfilmsona
broccoli(BrassicaoleraceaL.)cropwasinvestigated,wherehigherC/Nratiovaluesweredetected
underUVexclusionconditions[42].Moreover,anincreaseingasexchanges,carbonicanhydrase,
Rubisco,nitratereductaseactivitiesandtotalsolubleproteincontentwasfoundinwheat(Triticum
aestivumL.)plants[34].
However,aneutralresponseonphotosyntheticratewasfoundingreenandredlettuce(Lactuca
sativaL.)[10],andinstrawberry(Fragaria×ananassaL.)plants(cvs.CamarosaandVentana)[19].
Adecreaseinthephotosyntheticrateofsoybean(GlycinemaxL.)plantswasobservedunderUV
blockingcoveringmaterials[49].Also,decreasedcarbonmetabolism(asphotosyntheticrate),
nitrogenmetabolismandproteinlevelswereobservedineggplant(SolanummelongenaL.)[51].
MostoftheabovereportsdeclaredthatUVblockingcoveringmaterialsenhanced
photosyntheticrateinplantspeciesliketomato,radish,mungbean,broccoliandwheat,andhadno
effectineggplantandsoybeanplants;whileinstrawberry,greenandredlettuce(LactucasativaL.)
plants,photosynthesiswassuppressed.Thedifferentresultsmayhaveoccurredduetothefactthat
PhotosystemII(PSII)ofsomeplantspeciesismoresensitivetoUVBradiation[7].
AsummaryoftheeffectsofUVblockinggreenhousecoveringmaterialsonphotosynthesisand
respirationispresentedinTable2.
Table2.EffectofUVblockingcoveringmaterialsonthePhotosyntheticActivityofdifferentplant
species.
ReferenceYearCountryPlantPhotosynthesisDarkRespiration
[39]1993
J
apan tomato ↑1↓
[39]1993
J
apanradish↑1
[51]1997Japaneggplant↓1,2
[50]1997Indiamungbean↑1
[10]2008UKlettuceX
[42]2009Germanybroccoli↑3
[19]2009SpainstrawberryX4
[49]2014USAsoybean↓1
[34]2015Indiawheat↑1,5
↑:increase;↓:decrease;X:noeffectsfound;1:carbonmetabolismasphotosyntheticrate;2:nitrogen
metabolismandproteinlevels;3:C/Nratio;4:contentofcarbohydrates;5:gasexchanges,carbonic
anhydrase,Rubisco,nitratereductaseactivitiesandtotalsolubleproteincontent.
3.2.EffectsonTranspiration
InastudycarriedoutinGreece,itwasstatedthattheplantheight,totalleafareaandleafnumber
werepositivelyaffectedbythelackofUVradiation[26].Theyaddedthataplant’stranspirationrate
wasthoroughlyincreasedaspartoftheirresponsetoUVexclusionconditions.
Asfarasthestomatalconductanceisconcerned,itwasfoundthatcutroses(Rosa×hybrida)
stomatalconductancewasunaffectedunderreducedUVlightconditions[54],whileinwheatplants
washigherundertheUVblockingcovers[35].Thedifferencesnoticedinstomatalconductancemay
beattributedtovariationsinUVBimpactratesofdiverseUVsensitivitiesofvariousspecies,butalso
signifythecomplexityofUVeffectsonstomata[5].

Agronomy2020,10,10216of17
3.3.EffectsonGerminationandonSeedlings
InastudycarriedoutinGermany,aUVopenandaUVblockingplexiglasscoverwere
comparedinordertoinvestigatetheireffectonsunflower(HelianthusannuusL.)growth,anditwas
foundthatthehypocotyllengthwasreducedby50%undertheUVblockingmaterial[41].Hypocotyl
elongationgrowthisanessentialstepintheseedgerminationandakeycharacteristicforplant
emergence,influencedbyenvironmentalconditions,phytohormones,andisvaryingamong
genotypes[64].
Moreover,thetotalcotyledonsareaandfreshweightwerereducedby70%,aswellasdryweight
beingreducedby8%,whileseedlingscumulativestemelongationwasreducedby22%undertheUV
blockingcoveringmaterial.Moreover,therewasa27%decreaseinsunflowergermination.InJapan,
itwasfoundthatradishandwelshonion(AlliumfistulosumL.)germinationfailurewashigherunder
UVlowconditions.Itwasalsofoundthattherewasanegativeeffectonthegerminationand
hypocotyllengthofsunflowerandbluestar(IsotomaaxillarisL.)undertheUVblockingfilm[44].
Thus,accordingtotheabove,UVblockingcoveringmaterialswouldhaveasuppressiveeffect
onthegrowthanddevelopmentofthegerminationprocess,duetothefactthatUVBradiation
photonsaremoreenergeticthanvisiblelightphotonsand,hence,haveastrongereffectonthesurface
ofplantcells,causingtheultimatebreakdownofseedcoatingallowinggerminationtooccur[64].
3.4.EffectsonPigmentSynthesis
Duringtheripeningprocess,fruitchlorophyllcontentdecreaseswhileotherpigmentsare
synthesized.UVambientlightisacrucialfactorforthedevelopmentofmanypigmentssuchas
carotenoids(i.e.,xanthophyll),flavonoids(i.e.,anthocyanin),andphenolics.Inripefruits,
chlorophyllstillexistsbutinasmallproportion[65].IthasbeenreportedthatalackofUVradiation
hasanegativeeffectonpigmentsynthesis[66,67].
Chlorophyllintomatoandradishleaveswasfounddecreased[39],andalsoitwasobservedthat
thetotalcontentofanthocyaninswasreducedineggplantplants[51].Moreover,flavonoids
(kaempferol3‐glucoside)inscotspine(Pinussylvestris)seedlingsinthesubarcticregion[17],andin
arabidopsis(ArabidopsisthalianaL.)plantswerealsofoundreducedunderUVexclusionconditions
[33].Furthermore,itwasobservedthattotalphenolicsandphenolicacidscontentintomatofruit
wereaffectedbycultivarandUVsolarradiation[31].Thetotalamountofphenoliccompoundsin
tomatofruit,ascaffeicacid,aswellasthecontentoftotalphenolics,werereducedby16%forboth
cultivarstested,undertheUVblockingcover.Lastly,adecreasedconcentrationoftotalpolyphenols
includingluteolin,quercetingalactosideandquercetinglucosidewasdetectedinrocketsalad(Eruca
vesicariaL.)plantsgrownunderaUVblockingcover[55].
InastudyintheUK,theeffectoftwopolyethylenefilmswithvarioustransmissivitiesintheUV
radiation,onthephenolcontentandflavonoidconcentrationinaredlettucecropwastested[24].
Moreover,astudycarriedinUKstatedthattotalcontentofflavonoids(anthocyanin)andphenolic
compoundsweredecreasedunderUVblockingfilm(redandgreenlettuce)[10].Thesameresults
werealsofoundforstrawberrycropsunderUVblockingfilms[19].InGermany,acomparativestudy
wasmaderegardingthetotalamountofbioactivecompoundsingreenhousegrownandopenfield
strawberries.Thetotalcontentofflavonoids,anthocyanins,andkaempferolderivatives,underthe
UVblockingcoverwasdecreasedbyapproximately15–35%[43].Moreover,strawberrycultivars
grownunderUVblockingfilmsshowedareductionintotalphenolics(ellagicacid)andflavonoid
content(anthocyanin).Itwasalsofoundthatthemainflavonoidcompounds(quercetinand
cyanidin)detectedinRedOaklettuceleafwereincreasingwiththeincreaseinUVBradiation[56].In
China,itwasreportedthatambientUVBradiationresultsindelayedgrowthanddevelopmentin
rapeseedplants(BrassicanapusL.).UVradiationseemedtoinhibitphoto‐morphogenesisand
chlorophyllproductionwhiletherewasanincreaseoncarotenoidcontent.Moreovertherewasa
reductionintheaccumulationofUVBabsorbingcompoundsintheleavesundertheUVblocking
film[38].
InIndia,apositiveplantresponseinpigmentsynthesisofguarbeans(Cyamopsistetragonoloba
L.),uradbeans(VignamungoL.)andmungbeanswasdetectedunderfilmswithdifferent

Agronomy2020,10,10217of17
transmissivitiesinUVAradiation[36].InArgentina,theaccumulationofphenoliccompoundsin
arabidopsiswasgreaterinplantsgrownunderUVblockingconditions[57].
TheredcolorparametersdetectedineggplantsgrownunderUVblockingfilmswerepositively
affected,whilelightness(L*)wasunaffected[27].InUK,strawberryresponsesunderdifferentUV
blockingcoveringfilmswereinvestigated,andfoundthatthefruitproducedunderUVblocking
filmshadhigherchromavalues(by10–23%)thanunderUVopenfilms[25].InGreece,itwasstudied
theeffectofreducedUVradiationontomatocolor[28].Whenthecolormeasurementstookplaceon
harvestedfruits,nosignificantdifferenceswerefound,whilewhenthecolormeasurementswere
heldinvivo,theyobserveddifferencesincolorparametersatthelaterstagesofmaturity(lightred
andredstages).Theseripeningstagesinredcoloredtomatoesarecharacterizedbythesynthesisof
redpigmentation(lycopeneandβ‐carotene),whichisaffectedbythepresenceofUVradiation.As
theauthorsfoundnodifferencesinlycopenecontent,theyassumedpossibledifferencesinother
pigments(β‐carotene,etc.)content.Onthecontrary,otherauthorsshowedthatintomatoesgrown
underpearlshadeUVblockingfilms,thelycopenecontentwasfoundtobedecreased[29].
Furthermore,strawberryfruitcoloriscorrelatedwithUVradiationlevels[53].Thevaluesof
strawberryfruitcolorwereallreportedtobesignificantlyhigherunderaUVblockingcover,
followedbythelowUVblockingandtheUVopenfilm.Moreover,itwasfoundthatwhenpeppers
(CapsicumannuumL.)weregrownunderUVblockingnetstheyhadhigherconcentrationofphenolic
compoundsduringstorage.Moreover,higheramountsofascorbicacidweredetectedunderUV
blockingconditions[58].LackofUVradiationalsoresultedinincreaseintotalchlorophyllcontent
inthreetropicalplants,undertheUVblockingfilms[36].Moreover,L*,a*andb*parametersvalues
(inupperleaves)ofredamaranthwerefoundtobesignificantlyhigherunderUVexclusion
conditions[48],whereL*parametersvaluesvarybetweenlight(L*=100)anddark(L*=0),a*values
mayvaryfromgreen(a*=−50)tored(a*=50)andb*valuesfromblue(b*=−50)toyellow(b*=50)
[28].Rosepetalblackeningandappearanceofbrownspotsonwhitepetalcultivarsarecorrelated
withtheincreaseinUVradiationlevels[54].
Whiteclovershowedaneutralresponseinchlorophyllcontent(TrifoliumrepensL.)[40],while
thesamewasstatedforcocoplum(ChrysobalanusicacoL.)leaves[18].WhileinSpain,acomparative
studyontwostrawberrycultivars(CamarosaandVentana)underacelluloseacetateandaPEUV
blockingfilmshowednosignificantdifferencesontheantioxidantactivity,thecontentof
carbohydratesandanthocyanin[19].Moreover,greenlettuceplants,cv.LolloBiondo,showedno
phytochemicalresponsestodifferentUVradiationlevelsandtotalphenolicsinraspberries(Rubus
idaeusL.),andblueberries(VacciniumCyanococcusR.)werenotaffectedbythecoveringmaterial[56].
Strawberrytree(ArbutusunedoL.)andgrapevine(VitisviniferaL.)leavesshoweddifferent
responseswhencultivatedunderdifferentUVblockingfilms.Onday191,theplantsthatgrown
insidethegreenhousestransferredoutdoors,andatthatday,thetotalcontentofflavonolswaslower.
LaterflavonolindexingrapevineplantsthatgrowundertheUVblockingfilmwasincreased
significantlywhentheseplantsweremovedinUVopenconditions[37].InAustralia,twoplastic
films,aUVopenandaUVblockingweretestedandfoundafreefractionofphenols(caffeicacid),
andflavonoids(cyanidin)undertheUVblockingfilm.Moreover,inalltestedsorghum(Sorghum
bicolorL.)genotypes,theyfoundhigherconcentrationsoftheboundformsofthesecompoundsunder
theUVblockingfilm.Moreover,theantioxidantactivitywaslowerunderUVblockingtreatmentfor
allgenotypes[32].
Basedontheabovestudies,asalsopresentedinTable3,itcanbesummarizedthat:(a)
chlorophyllcontentispositively(in56%ofthestudies)ornegatively(in11%ofthestudies)affected
orisunaffected(in33%ofthestudies)byUVblockingcoveringmaterials,(b)flavonoidconcentration
andphenoliccompoundswerepositively,negativelyornotaffectedbyUVblockingcovering
materials.Thediscrepanciesthathavebeennoticedamongtheresultsinthesamepigmentcategories
concerndifferentplantspecies.However,whendifferencesarenoticedinthesamespecies,thesecan
beattributedtothedifferentenvironmentalconditionsand,morespecifically,tothedifferent
ambientUVradiationlevels.


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Table3.EffectofUVblockingcoveringmaterialsonpigmentsynthesis.
ReferenceYearCountryPlantSpeciesPigments
ChlorophyllFlavonoidPhenolicCarotenoid
[20,21,36,39],1993,2004,2013,2006Japan,Spain,USAtomato↓↓3X7
[29]2012Serbiatomato 
↓
[33]1999USAarabidopsis↑2↓1↓
[25,43,52,53]2004,2012,2010,2010UK,Germanystrawberry↓ 1,4,5↓
[10,22,24]2008,2009,2007UK,Spainlettuce↑↓ 1,5↓
[42]2009Germanybroccoli ↓↓
[47]2016Bangladeshbroccoli↑
[60]2016Egyptcucumber ↑
[52]2018Egyptcucumber ↓↓
[39]1993
J
apanradish↓ 
[51]1997Japaneggplant ↓
[17]1999Finlandpine↓ 1
[40]2001BelgiumwhitecloverX
[18]2003IsraelcocoplumXX 
[36]2005Indiaguarbean↑ 2↑
[36]2005Indiauradbean↑ 2↑
[36]2005Indiamungbean↑ 2↑
[58]2014SApepper 
↑↓
[38]2015Chinarapeseed  X↓
[34]2015Indiawheat↑ 2X
[45]2016EthiopiapeaXX 
[37]2016Italystrawberrytree ↓
[37]2016Italygrapevine ↓
[47]2016Bangladeshturnip
↑
[48]2016Bangladeshredamaranth ↑
[32]2017Australiasorghum ↓ 3,6
[55]2019Italyrocket↑ 1 
↑:increase;↓:decrease;X:noeffectsfound;1:kaempferol3‐glucosideandquercetin;2:Chlorophyll
aandb;3:Caffeic,p‐coumaric,ferulicacid;4:Pelargonidin‐3‐glucoside;5:Cyanidin‐3‐glucoside;6:
Luteolin;7:lycopene.
4.EffectsofUVBlockingGreenhouseCoveringMaterialsonPlantArchitectureandOrgans
4.1.EffectsonPlantRoots,LeavesandStems
InBelgium,itwasreportedthatwhiteclovergrownunderaUVblockingplexiglasscoverthat
blocked88%ofthesolarUVradiationproducedsignificantlyhigherrootbiomass(comparedwitha
UVblockingcoverthatblockedthe82%ofUVambientradiation[40]),andthatsoybeanplantsgrown
underopenfieldhadsignificantlyhigherrootweight,comparedtothosegrownunderaUVdeficient
environment[49].
StemelongationineggplantattheearlystagesofdevelopmentwasenhancedunderUVB
exclusionconditions[51].InUSA,itwasobservedthatchrysanthemum(ChrysanthemumindicumL.)
andgoldenrod(Solidagosp.L.)plantheightwasslightlyincreasedunderUVblockingcovers,dueto
anincreasednumberofinternodes,withoutanyeffectoninternodelength,numberofbranchesand
numberofbudsperbranch[4],aswasalsothecasefortomatoplantsunderUVblockingmaterials
[20,28].Inaddition,eggplant[27]andpeppercropsweretaller,andhadlongerstemswhengrown
underUVblockingfilmsornets[59].Furthermore,theshootlengthofpotrosecultivarswasfound
tobeincreasedby25–35%[54].TheonlyexceptionwhereaneutralresponseofplantstoUVblocking
materialwasmentionedforcucumber(CucumissativusL.)andtomatoplants[46].
CucumberleafareaanddrymatterwereaffectedbyUVblockingmaterial,showinganincrease
whentheyweregrownunderUVexclusionconditions[52,60].Thesamepositivereactionwasalso
evidentintomato[25],guar,uradandmungbeans[36],eggplant[27],radishandwelshonion[44],
broccoliandturnip(BrassicarapaL.)seedlings[47],soybean[49]androses[54].Lastly,aneutral
reactionofplantleafgrowthunderUVblockingmaterialswasonlyfoundinsomewheatvarieties
[34],rapeseed[38],andpea(Pisumsativum)[45],whileanegativeresponsewasstatedforstrawberry
plants;butthisparameterwasnotaffectedbythedifferentUVblockingmaterials[43].Moreover,

Agronomy2020,10,10219of17
redamaranth(AmaranthustricolorL.)showedadecreaseinthetotalnumberofleaves,totalleafarea
andleafbrixwhengrownunderUVexclusionconditions[48].
TheabovestudiesregardingtheeffectofUVblockingmaterialonplantheight,leafnumberand
leafareapresentedapositiveorneutralresponseinmostoftheplantspeciestested,becauseofthe
factthatplantsexposedtoUVradiationshowtypicallylesselongatedleaves,stems,andhypocotyls,
increasedbranchingofstemsandroots,andthickerleaves[7].
AsummaryoftheeffectsofUVblockinggreenhousecoveringmaterialsonplantgrowthare
presentedinTable4.
Table4.EffectofUVblockingmaterialonStemandLeafcharacteristics.
ReferenceYearCountryPlantSpeciesStemLeaf
HeightInter‐NodesDryMatterNumberAreaDryMatter
[39]1993Japantomato↑
↑↓ 1
[46]2012JapantomatoX  
[39]1993Japanradish   ↓ 1
[44]2008Japanradish  ↑↑ 3
[51]1997Japaneggplant↑
↑
[60]2018Egyptcucumber↑
↑↑
[46]2012JapancucumberX  
[50]1997Indiamungbean↑↑X↑↑
[36]2005Indiaguarbean↑↑↑
[36]2005Indiauradbean↑↑↑
[33]1999USAarabidopsis   ↓ 2
[40]2001Belgiumwhiteclover    X
[4]2002USAchrysanthemum↑X 
[18]2003Israelcocoplum↑
[44]2008Japanwelshonion  ↑↑ 3
[59]2010Spainpepper↑
[54]2014Ethiopiarose↑1  ↑↑
[49]2014USASoybean↑
↑↑
[38]2015Chinarapeseed↑X
[34]2015Indiawheat↑↑ 2X
[45]2016Ethiopiapea↑XX
[47]2016Bangladbroccoli↑
↑
[47]2016Bangladturnip   
↑
[48]2016Bangladredamaranth↑↑ 3
↑
↑:increase;↓:decrease;X:noeffectsfound.
4.2.EffectsonFlowering
TheeffectofUVblockingcoveringmaterialsonfloweringhasnotbeenstudiedextensively.In
thecaseofwhiteclover,itwasfoundthattherewasanincreaseinnumberandbiomassallocationin
flowers[40].Thesameresultswerealsofoundintomatoplants[20].
4.3.EffectsonFruitSetting
ThepositiveeffectofUVblockingmaterialsonfruitsettinghasbeenstatedinmanystudies
(Table5).InSpain,itwasfoundthatthenumberofsetfruitsintomatoplantswasgreaterunderthe
UVblockingcoveringmaterial[20].InGreece,ahighernumberofmarketablefruitsandmeanfruit
weightwereobservedunderUVblockingcoveringmaterials,whiletotalfruitnumberandshape,
totalsolublesolids,ascorbicacid,lycopenecontent,pHandtitratableaciditywerefoundtobe
unaffected,andfinallyinjuriescausedbyinsectsweresuppressed[28].InSpain,alowernumberof
fruitsperm2werefoundintomatoplantsgrownunderUVexclusionconditions[21].
Cropssuchaseggplant[27],strawberries[25]andpeppers[58]grownunderUVblocking
coveringmaterialsshowedhighermarketableyieldandsignificantlylowerweightandfirmnessloss
inpostharveststorage.Inthecaseofstrawberryplants,positiveeffectsarepresentinmostcases
[19,25,43,53],whileneutralreactionswerefoundonlyinveryfewstudies[43,53].

Agronomy2020,10,102110of17
EvaluatingtheresultsofdifferentreportsrelevanttotheeffectofaUVblockingmaterialonfruit
setting,the78%ofreportsreportedpositiveeffect,the11%ofthemnegativeandtheremain11%
neutralresponse,respectively.Mostofthediscrepanciesfoundontheaboveresultsareduetothe
differentenvironmentalconditionsduringtheconductoftheexperiments.
Table5.EffectofUVblockingcoveringmaterialonfruit.
ReferenceYearCountryPlantSpeciesFruit
NumberFreshWeightMarketability
[20,21]2004,2013Spaintomato↑ 1↑↑
[19
,
25]2004Spain,UKstrawberry↑↑ 2↑
[43,56]2010Germanystrawberry↑ 4X3
[53]2012UKstrawberryX↑X
[27]2006Greeceeggplant↑
[58]2014SApeppers↑↑
↑:increase;↓:decrease;X:noeffectsfound;1:fruitsetperplant;2:totalfruitfreshweightperplant;
3:fruitdrymattersize;4:meanfruit.
5.EffectsofUVBlockingGreenhouseCoveringMaterialsPlantPerformance
5.1.EffectsonYield
ThepositiveeffectofUVblockingcoveringmaterialsonplantyieldwasfirstreportedintomato
plantsinJapan,wherethefreshanddryweightoftomatofruitwasfoundtobegreaterundertheUV
blockingcover[39].InSpain,a14–19%increaseintomatototalyieldanda37%increaseinmarketable
yieldperplant,whentomatoesgrownundertheUVblockingfilm[21].
Furthermore,anupto60%increaseinthetotalyieldofguar,uradamdmungbeanswas
reported[36].Thesametrendwasalsoobservedinthecaseofaneggplantcropwherefruitweight
washigherunderUVblockingconditions[27].Asimilartrendwasalsonoticedinlettucecrop(cv.
Constance)wherefreshanddryweightincreasedundertheUVblockingfilm[24].Redlettuce(cv.
Revolution)produced40%moredryweightundercompleteUVexclusionconditions[22].Thesame
resultswereobservedforstrawberry[19]andbroccoliplants[42].StrawberriesgrownunderUV
blockingcoversshoweda20–40%higheryield[19],whiletheoppositewasreportedformelon
(CucumismeloL.)andwatermelon(CitrulluslanatusL.)plants,areductioninyieldunderUVblocking
filmduetoadecreaseininsectactivity[68].
ItwasreportedthattomatototalyieldwasincreasedunderpearlshadeUVblockingnets[29].
OntheQinghai‐Tibetanplateau,rapeseedbiomassincreasedabout12–20%underUVblockingfilms
[38].InIndia,itwasfoundthatwheatplantshadagreatergrainyieldundertheUVblockingfilms
[34].RelativeresultswerealsoobtainedinEthiopiawhereinopenfieldconditionspeaproduced
morebranchescomparedtotheotherUVblockingtreatmentsandforbothtestedaltitudesshoot
elongationwasaffectedsimilarlybyUVradiation[45].
InBangladesh,broccoliandturnipseedlingsfreshweightwasincreasedby50–70%,whiledry
weightdidnotfollowasimilartrendandinbroccoliseedlings,thehighestamountsofdrymatter
wererecordedinsidethetunnelsthatwerecoveredwiththeUVblockingfilmthatblocked
wavelengthsshorterthan340nm,whileturnipseedlings’drymatterwashigherinplantsthatgrew
outdoors[47].Inthecaseofredamaranth,freshanddryweightweregreaterunderUV‐blocking
filmsthanunderUVopenfilmsorinopenfield[48].
Inthecaseofornamentalplants,theshootlengthandnumberofleavesofthreepotrosecultivars
wereincreased(25–35%and15–19%,respectively)undertheUVblockingfilms,andthecolorofthe
marketablecutflowerswasalsooptimized[54].
NodifferenceswerefoundonBrusselssprouts’averageweightandtotalyield,butthequality
ofsproutswassignificantlylowerundertheUVblockingcover[30].AneutralresponsetoUV
radiationlevelswasalsoreportedforstrawberry[43]andtomatoplantswhereonlythetotalyield
wasunaffectedwhilemarketableyieldwasincreased[28].InEgypt,therearetworeportsconcerning

Agronomy2020,10,102111of17
cucumbercultivationunderUVblockingmaterialswhereaneutralresponseofthecropwasfound
[52,60].
Welshonionandradishshootfreshweightunderphotoselectiveredandbluefilms(lowUV
levels)wasfoundtobegreaterthaninUVopenfilms.Shootdryweightwashigherunderredfilms
followedbyblue(UVblocking)andclearfilm,respectively[44].
IntheUSA,itwasreportedthatsoybeantotalpoddryweightwaslowerunderUVexclusion
conditions,whilenodifferenceswereobservedintotalseedweightperplant,individualseedweight,
numberofnodes,orstemweight[49].InSpain,itwasreportedadecreaseinlettuceaverageweight
grownunderUVblockingnets[22].
Moreover,whiteclover[40],chrysanthemumandgoldenrodplantsyieldwasdecreasedunder
UVminusconditions[4].
TheeffectofUVblockingcoveringmaterialsonplantyieldwasthoroughlyinvestigated(28
relativepapers).The61%ofthemreportedinapositive,11%negativeand28%neutralreaction,
respectively,concerningdifferentplantspecies.Moreover,itwasreportedthatthe86%ofthestudies
revisedshowedanincreaseinshoots’freshanddryweight—resultsthatcanbeexplainedbythefact
thathigherexposuretoUVradiationleadstotheincreasedbranchingofstems[5](Table6).
Table6.EffectofUVblockingcoveringmaterialsontheyieldofdifferentcrops.
ReferenceYearCountryPlantSpecies
Yield
FreshWeightDryWeightShootsNo
Detail
[40]2001Belgiumwhiteclover ↑ 1↑ 2
[4]2002USAchrysanthemum
↑ 3
[4]2002USAgoldenrods ↑ 3
[21,39]2012,1993Spain,Japantomato↑↑↑ 4,6
[28]2012Greecetomato↑ 12X
[36]2005Indiaguarbean↑↑ 7
[36]2005Indiauradbean↑↑ 7
[36]2005Indiamungbean↑↑ 7
[22]2009Spainlettuce↓
[27]2006Greeceeggplant ↑ 8
[44]2008Japanwelshonion ↓ 8↑ 9
[19]2009Spainstrawberry↑
↑
[43]2010Germanystrawberry↓X
[42,47]2009,2016Germany,Bangladeshbroccoli↑↑↑ 10
[68]2010Spainmelon ↓ 11
[68]2010Spainwatermelon  ↓ 11
[30]2013Germanybrusselssprouts  X
[54]2014Ethiopiarose
↑
[49]2014USAsoybean ↓ 13X1,4
[38]2015Chinarapeseed ↑ 15
[34]2015Indiawheat 
↑
[45]2016Ethiopiapea↓ 16
[60]2016Egyptcucumber X
[47]2016Bangladeshturnip↑↑
↑:increase;↓:decrease;X:noeffectsfound;1:totalbiomass;2:increasedyield;3:numberofbranches;
budsperbranch;4:marketableyieldperplant;5:greaterfinalsize;6:increasedfruit#andmeanfruit
weight;7:sizeofthepod;8:shootdryweight;9:shootfreshweight;10:increasedabove‐ground
biomassaccumulation;11:disturbanceinpollinationactivity;12:Nodifferencesintotalyield;fruit
number;marketablemeanfruitweightbutsignificantlyhighermarketableyieldoughttolessinsect
injuries;13:totalpoddryweight;14:nodifferencesinseedweightperplant;individualseedweight;
nodespermainstem;orstem);weightperplant;15:plantbiomass;16:decreasednumberofbranches
andshootelongation;17:yieldremainedunaffectedevenwithpronounceddifferencesintheir
vegetativeresponses.


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5.2.EffectsonPlantEarliness/Senescence
FloweringearlinessandrateoffruitandcropdevelopmentseemstobeaffectedbyUVblocking
materials.StudieshaveshownthattheuseofUVblockingcoverscandelaytomatoandradishleaf
senescence[39].Thesamewasobservedforeggplantplants[51].
RelativeresultsinUKandSpainreportedquickerestablishmentanddevelopmentofstrawberry
crops[25]aswellasadelayinripeningprocess[19],whentheplantsweregrownunderUVblocking
covers.Inadditionfruitcolordevelopmentofthesameplantwasalsodelayed[53].
Moreover,UVblockingmaterialhadanegativeeffectonfloweringprocessofpeaplant[45].
RegardingtheeffectofUVblockingmaterialonplantdevelopment,variedresultshavebeen
emerged.Asitconcernsleafaging,33%oftherelativereportsshowedapositiveresponsewhilea
67%showedanegative.Regardingripening,50%ofthestudiesreportedpositiveresponsewhilean
equalnegativeresponsewasalsopublished.Colordevelopmentandflowerdelaywereboth
depressed(underUVblockingmaterial)inalltheexaminedcases,duetothelimitedactivityof
cryptochromes,whichareresponsiblefortheplantdevelopmentprocess[6],asshowninTable7.
Table7.EffectofUVblockingcoveringmaterialonplantDevelopment/Earliness.
ReferenceYearCountryPlantSpeciesDevelopment
[39]1993
J
apantomato↓ 1
[39]1993Japanradish↓ 1
[51]1997Japaneggplant↑ 1
[25]2004UKstrawberry↑ 2,3
[19]2009Spainstrawberry↓ 3,4
[45]2016Ethiopiapea↓ 5
↑:increase,↓:decrease,X:nodifferencesfound,1Leafaging,2Establishment,3Ripening,4Color
development,5Flowering.
6.VariationsofUVAmbientRadiationLevelsonEvaluatingDataRegardingUVBlocking
Material
UVradiationlevelsandspatialdistributionofsolarUVradiationmustbetakeninto
considerationduringtheevaluationoftheresults,includingtheeffectoftheUVblockingcovering
materialonthecrop.Specifically,UVradiationlevelsexhibitaseasonalvariationpatternwithinthe
year(Table8).
Forallthesereasons,theestablishmentofageneralruleabouttheresponseofplantsinseveral
levelsofUVradiationmustberelatedtotheplaceandthemonth.Itmustbementionedthathigher
UVradiationlevelshavebeenreportedincountriesnearequatorwherethelatitudeisnearzero,such
asEthiopia(Lat.=6)(Table8).
Besidesthat,UVradiationlevelsvarywiththepresenceofclouds,haze,snow,sunpositionand
altitude.ThehighestUVradiationlevelsonEarthcanbefoundin:Peru,Bolivia,ChileandArgentina,
wheretheUVindexexceeds24[69]inhighaltitudes(alpine).
Accordingtosomerepresentativestudies,differentresponseswerefoundforthesamespecies
whentheexperiments,heldindifferentworldareas.Specifically,differenceshavebeenfoundonthe
plantheightofcucumbercropsgrowninEgypt[52]andJapan[46],althoughbothcountriesexhibit
equalUVradiationlevels(Table9).Indetail,inEgypt,plantheightwasenhancedbytheexclusion
ofUVradiation,whilenodifferenceswherenoticedinJapan.Thiscanbeattributedtodifferent
responsesofspeciesandcultivarstoUVradiationlevels,duetodifferencesinthegenetic
background.
Insomeplantspecies,responsescouldbeproportionaltoUVradiationlevels.Forexample,in
Germany[42],whereUVradiationlevelsarelow,flavonoidindexinbroccoliplantswasfoundtobe
lower,incontrastwithbroccoliplantsgrowninBangladesh[47],whereUVradiationishigher.
Similarresponseswerenoticedinthecaseofstrawberryplants’freshweight,inexperiments

Agronomy2020,10,102113of17
conductedinSpain[19]andGermany[43],andinripeningprocessdelaysofthesameplant,
comparingthefindingsinSpainandtheUK[23].
Accordingly,thecountriesexaminedinthispaperaregatheredinfivecategoriesregardingUV
radiationlevels(Table9).
Table8.UVIndexvariationinthesameplacewithintheyearinplacesregardingUVblockingstudies
reviewedinthiswork.DifferentbackgroundcolorsindicatedifferentUVlevels.
Country(City) Latitude J F M A M J J A S O N D
Argentine(BuenosAires)35°S9974322457910
Australia(Perth)32°S1211964334681012
Germany(Berlin)52°N112457753110
Greece(Volos)39°N3458991097432
J
apan(Tokyo)36°N2458991097422
Africa(Ethiopia)6°S121212121212121212121211
Brazil(RiodeJaneiro)23°S12119755579101212
Cuba(Havana)23°N689101011121110865
Vietnam(Hanoi),(≈India)21°N6810111111121210866
Spain(Mallorca)39°N234689986421
USA(LosAngeles)34°N34689101097532
Table9.LevelsofambientsolarUVradiationincountriesmentionedinthiswork.
Continent1÷2
LOW
3÷5
MODERATE
6÷7
HIGH
8÷10
VERY
HIGH
11
EXTREME
Europe
UK
Germany
Belgium
Italy
Serbia
Spain
Italy
Greece
 
Asia
Japan
ChinaIndia
Bangladesh
N.AmericaS.
America
North
CarolinaCalifornia
Florida
Argentina
AfricaEgyptSouthAfricaEthiopia
Oceania  Perth
7.ConcludingRemarks
SummarizingtheresultsconcerningplantresponsesonUVblockingmaterialworldwide,itwas
foundthatthemostexaminedparameteristheeffectofthesematerialsonplantpigments(32papers),
followedbyyield(28papers)andleafarea(25),whiletheleastexaminedplantorgansarerootsand
flowers(2papers).
Basedontheseresults,astrongpositiveornegativeeffectemergedinchlorophyllorphenolic
compounds,respectively,underUVblockingmaterials,whileamoredimresponsewasalsoreported
forflavonoidandcarotenoidcompounds.

Agronomy2020,10,102114of17
TheplantfunctionsthataremostaffectedbyUVblockingmaterialsareeitherenhancedincases
ofphotosynthesis(foundinmorethan50%of9relevantreports)inplantspeciessuchastomato,
radish,mungbean,broccoliandwheat,orincasesofstomatalconductance(wheat),ortranspiration.
PlantheightandleafareaseemtobepositivelyaffectedbyUVblockingcladdingmaterials.Thesame
isevidentalsoforyieldandgrowthcharacteristics.However,UVblockingmaterialssuppressthe
totalantioxidantcontentandotherhealthrelatedphytochemicals,andthisisconsideredbymany
researchersasthebasicdisadvantageofthismaterial.
Eventhoughthereisadecreaseininsecticideuse,adecreasedpestpopulationentersinto
greenhousesornethouses[62].Ifotherchemicalsareappliedtoplantsduringthegrowingseason,
thentheseresiduesonfruitsthathavebeenproducedunderUVblockingconditionsare
characterizedbyamoreconsistentretention[63]afterharvest.Lastly,theapplicationofUVblocking
materialscreatesaparticularlightmodificationintheplantenvironmentwhichleadstoabetter
canopylightuseefficiency[69].
Abbreviations
SYMBOLNAMEWAVEBAND(nm)
UVUltraviolet280–400
UVA UltravioletradiationtypeA320–400
UVB UltravioletradiationtypeB280–320
PARPhotosynteticallyActiveRadiation400–700
IRInfraRedradiation700–100,000
NIR(orIRA)NearInfraRedradiation750–1400
FRFarRed700–780
AuthorContributions:Conceptualization,N.K.andC.P.;datacuration,A.B.andC.P.;writing—originaldraft
preparation,A.B.andC.P.;writing—reviewandediting,N.K.andC.P.;supervision,N.K.;project
administration,N.K.;fundingacquisition,N.K.Allauthorshavereadandagreedtothepublishedversionofthe
manuscript.
Funding:Thisresearchhasbeenco‐financedbytheEuropeanUnionandGreeknationalfundsthroughthe
OperationalProgramCompetitiveness,EntrepreneurshipandInnovation,underthecallRESEARCH—
CREATE—INNOVATE(projectcode:T1EDK‐01499).
ConflictsofInterest:Theauthorsdeclarenoconflictofinterest.
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