HORTSCIENCE 50(5)705ndash713 2015

Comparison of Bedding PlantSeedlings Grown Under Sole-sourceLight-emitting Diodes (LEDs) andGreenhouse Supplemental Lightingfrom LEDs and High-pressureSodium LampsWesley C Randall and Roberto G Lopez12

Department of Horticulture and Landscape Architecture Purdue UniversityWest Lafayette IN 47907

Additional index words annuals daily light integral HPS lamps multilayer production plugs

Abstract To produce uniform compact and high-quality annual bedding plant seedlingsin late winter through early spring growers in northern latitudes must use supple-mental lighting (SL) to achieve a photosynthetic daily light integral (DLI) of 10 to12 molmiddotmL2middotdL1 Alternatively new lighting technologies may be used for sole-sourcephotosynthetic lighting (SSL) to grow seedlings in an indoor high-density multilayercontrolled environment The objective of this study was to compare seedlings grownunder low greenhouse ambient light (AL) to those grown under SL or SSL with a similarDLI On hypocotyl emergence seedlings of vinca (Catharanthus roseus) impatiens(Impatiens walleriana) geranium (Pelargonium3hortorum) petunia (Petunia3hybrida)and French marigold (Tagetes patula) were placed in a greenhouse under AL or AL plusSL delivering a photosynthetic photon flux (PPF) of 70 mmolmiddotmL2middotsndash1 for 16 hours orunder multilayer SSL delivering a PPF of 185 mmolmiddotmL2middotsndash1 for 16 hours in a walk-ingrowth chamber Supplemental lighting consisted of high-pressure sodium (HPS) lampsor high-intensity light-emitting diode (LED) arrays with a redblue light ratio (400ndash700nm) of 8713 and SSL consisted of LED arrays providing a redblue light ratio () of8713 or 7030 Root and shoot dry mass stem diameter relative chlorophyll content andthe quality index (a quantitative measurement of quality) of most species were generallygreater under SSL and SL than under AL In addition height of geranium petunia andmarigold was 5 to 26 62 to 79 and 7 to 19 shorter respectively forseedlings grown under SSL compared with those under AL and SL With the exceptionof impatiens time to flower was similar or hastened for all species grown under SL orSSL compared with AL Seedlings grown under SSL were of similar or greater qualitycompared with those under SL indicating that LED SSL could be used as an alternativeto traditional greenhouse seedling production

Young plants are commonly producedfrom vegetative cuttings or seeds during latewinter and early spring (Klopmeyer et al

2003 Styer 2003) However during peakyoung plant production the average green-house photosynthetic DLI can be as low as 1to 5 molmiddotmndash2middotdndash1 in northern latitudes leadingto decreased quality (Lopez and Runkle2008 Pramuk and Runkle 2005) Previousresearch has determined that a DLI of 10 to12 molmiddotmndash2middotdndash1 is necessary to produce high-quality young plants (Currey et al 2012Hutchinson et al 2012 Lopez and Runkle2008 Oh et al 2010 Pramuk and Runkle2005 Randall and Lopez 2014) The onlyway to appreciably increase DLI duringyoung plant production is through the use ofoverhead SL (Oh et al 2010 Randall andLopez 2014 Sherrard 2003)

High-intensity discharge lamps such asHPS and metal halide lamps have tradition-ally been used for SL to increase greenhouseDLI High-pressure sodium lamps have longbeen the most efficient SL source convert-ing 25 to 30 of their electrical energyinto photosynthetically active radiation [PAR

(400 to 700 nm)] with an operational lifespanof 10000 luminous hours ormore (Spaargaren2001) However as much as 72 of thePAR emitted by HPS lamps is in the 565 to590 nm (yellow) and 590 to 625 nm (orange)wavebands Moreover up to 75 of theelectrical energy used by HPS lamps isemitted as radiant heat and the surface ofthe bulb can reach temperatures as high as450 C thus requiring plants to be separatedfrom the lamps to avoid leaf scorch (Fisherand Both 2004 Sherrard 2003 Spaargaren2001)

In recent years some alternatives to HPSlamps have been introduced includingplasma lamps and high intensity LEDsLight-emitting diodes are solid-state singlejunction semiconductors that are capable ofproducing light wavelengths as short as250 nm and up to greater than 1000 nmThus they are useful for testing specificwavelength combinations for plant growthand morphology (Folta and Childers 2008Randall and Lopez 2014 Stutte 2009)They also radiate minimal heat toward theplant canopy allowing lights to be placedclose to crops Until recently LEDs werelow power (lt1 W) and impractical for SL(Bourget 2008)

Due to their small size wavelength spec-ificity high light output and relatively lowheat output LEDs have been used in envi-ronmental chambers for SSL (Heo et al2006 Wollaeger and Runkle 2013 2014)or in greenhouses as overhead SL (Curreyand Lopez 2013 Randall and Lopez 2014)for ornamental young plants For exampleHeo et al (2006) grew seedlings of Africanmarigold (Tagetes erecta lsquoOrange Boyrsquo)ageratum (Ageratum houstonianum lsquoBlueFieldrsquo) and salvia (Salvia splendens lsquoRedVistarsquo)for 28 d at 25 plusmn 2 C under a 16-h photoperiodfrom SSL LEDs delivering a PPF of 90 plusmn 10mmolmiddotmndash2middotsndash1 (DLI 5 molmiddotmndash2middotdndash1) at a 11ratio of redblue bluefar-red redfar-redlight or under cool-white fluorescent lamps(CWFL) After 28 d leaf area of ageratumand salvia grown under the redblue LEDsincreased by 100 to 122 and 42 to66 respectively compared with the otherLED treatments and was similar to plantsunder CWFL In addition height of agera-tum marigold and salvia was reduced by35 to 69 44 to 56 and 57 to 64respectively under the redblue LEDscompared with the other LED treatmentswhile remaining similar to the plants underthe CWFL (Heo et al 2006) Anotherstudy compared seedlings of impatienslsquoSuperElfin XP Redrsquo petunia lsquoWave Pinkrsquotomato (Solanum lycopersicum lsquoEarly Girlrsquo)and African marigold lsquoDeep Orangersquo grownunder SSLwith an 18-h photoperiod and PPFof 160 mmolmiddotmndash2middotsndash1 (DLI 9 molmiddotmndash2middotdndash1)delivered from LEDs providing 10 blueand 10 green light with the followingcombinations () of orange (peak = 596 nm)red (peak = 634 nm) and hyper-red (peak =664 nm) 203030 0800 06020 0404002060 or 0080 Height of tomato andmarigold was 18 and 13 shorter under

Received for publication 13 Jan 2015 Acceptedfor publication 19 Mar 2015We gratefully acknowledge Rob Eddy GarrettOwen Kristine Adamiec Andrea and AlyssaHilligoss and Bryce Patz for greenhouse and labo-ratory assistance Judy Santini for experimentaldesign and statistical consultation ChristopherCurrey for his helpful review the USDA-NIFASCRI grant no 2010-51181-21369 for fundingPhilips Lighting and Hort Americas for fundingand LEDs and PL Light Systems for HPS lampsWe also thank Ball Horticultural Co for seed Theuse of trade names in this publication does notimply endorsement by Purdue University of prod-ucts named nor criticism of similar ones notmentioned1Associate professor and extension specialist2To whom reprint requests should be addressede-mail rglopezpurdueedu

HORTSCIENCE VOL 50(5) MAY 2015 705

the 04040 than the 0800 orangeredhyper-red LEDs respectively but was similar tothe other light treatments and shoot drymass (SDM) of tomato was 25 to 40greater under the 06020 orangeredhyper-red than under SSL providing 0404002060 or 0080 orangeredhyper-red light(Wollaeger and Runkle 2013) Finally Ran-dall and Lopez (2014) compared seedlings ofsnapdragon (Antirrhinum majus lsquoRocketPinkrsquo) vinca lsquoTitan Punchrsquo celosia (Celosiaargentea lsquoFresh Look Goldrsquo) impatiens lsquoDaz-zler Blue Pearlrsquo geranium lsquoBullseye Scarletrsquopetunia lsquoPlush Bluersquo salvia lsquoVista RedrsquoFrench marigold lsquoBonanza Flamersquo and pansy(Viola middotwittrockiana lsquoMammoth Big Redrsquo)grown under AL supplemented with a PPFof 100 mmolmiddotmndash2middotsndash1 for 16 h from eitherHPS or one of three LED arrays composed of() 1000 8515 or 7030 redblue light After28 d height of all species except snapdragonand geranium was reduced by 9 to 55under 8515 redblue LEDs compared withthose under HPS lamps and stem diameterof geranium marigold and snapdragon was8 to 16 greater under 8515 redblueLEDs compared with seedlings grown underHPS lamps

To our knowledge no studies have com-pared annual bedding plant seedlings grownunder SSL to those grown under SL ina greenhouse providing the same DLI Theobjectives of this study were to 1) quantifythe effects of SL from HPS lamps and LEDarrays compared with a SSL multilayer pro-duction system from LED arrays providingtwo different light qualities on seedlinggrowth morphology and quality and 2) de-termine whether there were any residualeffects of either SL or SSL on subsequentflowering

Materials and Methods

Plant material culture and propagationenvironment Seeds of French marigoldlsquoDurango Yellowrsquo geranium lsquoBullseyeRedrsquo impatiens lsquoSuper Elfin XP Blue Pearlrsquopetunia lsquoDreams Midnightrsquo and vinca lsquoTitanRed Darkrsquo (Ball Horticulture Co WestChicago IL) were sown into 288-cell (6-mL individual cell volume) seed trays filledwith a commercial soilless medium com-posed of (by volume) 65 peat 20 perliteand 15 vermiculite (Fafard Super FineGerminating Mix Sun Gro HorticultureAgawam MA) and placed in a glass-glazedgreenhouse at Purdue University WestLafayette IN (latitude 40N) Exhaust fanand evaporative-pad cooling radiant hotwater heating and retractable shade curtainswere controlled by an environmental controlsystem (Maximizer Precision 10 Priva Com-puters Inc Vineland Station Ontario Can-ada) The DLI and average daily temperatures(ADT) for seasons I II and III from sowing tohypocotyl emergence were 121 plusmn 17 114 plusmn28 and 123 plusmn 18 molmiddotmndash2middotdndash1 and 226 plusmn08 223 plusmn 11 and 224 plusmn 11 C respectivelyOn hypocotyl emergence two trays of eachspecies were moved under either AL AL plus

SL in a glass-glazed greenhouse or SSL ina growth chamber

Greenhouse environment All specieswere placed under a 16-h photoperiod withADTs of 226 plusmn 09 227 plusmn 07 and 227 plusmn28 C for seasons I II and III respectivelyInfrared temperature sensors with an emis-sivity of 095 (OS136 Omega EngineeringInc Stamford CT) recorded seedling can-opy temperatures every 30 s and averageswere logged every 15 min by a data logger(Maximizer Precision 10) Quantum sensors(SQ-110 Apogee Instruments Inc LoganUT) measured solar PPF every 15 s and theaverage was logged every 15 min by a datalogger (WD 2800 Spectrum TechnologiesAurora IL) Environmental data for thegreenhouse environment are reported inTable 1 Seedlings were irrigated with watersupplemented with water-soluble fertilizer(Jackrsquos LX 16Nndash094Pndash123K Plug Formulafor High Alkalinity Water JR Peters IncAllentown PA) providing (in mgmiddotLndash1) 100 N10 P 78 K 18 Ca 94 Mg 010 B 005 Cu050 Fe 025 Mn 005 Mo and 025 Zn

Growth chamber environment All spe-cies were placed under a 16-h photoperiod ina walk-in growth chamber (C5 ControlSystem Environmental Growth ChambersChagrin Falls OH) with ADT of 230 plusmn 01230 plusmn 01 and 230 plusmn 01 C for seasons I IIand III respectively Air temperature rela-tive humidity and carbon dioxide (CO2)were measured and logged every 15 min bya data logger (DL1 Datalogger Environmen-tal Growth Chambers) Environmental datafor the growth chamber environment are

reported in Table 2 Seedlings were irrigatedwith the same fertilizer used in the green-house environment

Supplemental and sole-source lightingtreatments Seedlings in the greenhouse weregrown under AL or AL supplemented with70 mmolmiddotmndash2middotsndash1 PPF at plant height [asmeasured with a spectroradiometer (PS-100Apogee Instruments Inc Logan UT)] from0600 to 2200 HR (Table 1) for 21 d (geraniumand marigold) or 28 d (impatiens petuniaand vinca) Supplemental light was deliveredfrom either two 150-W HPS lamps (PL 2000PL Light Systems Inc Beamsville OntarioCanada) or eight 32-W LED arrays [120-cmlong and 4-cm wide (Philips GreenPowerLED production module KoninklijkePhilips Electronics NV The Netherlands)]spaced on 445-cm centers and 787 cm abovethe bench top providing () 8713 red (664 nm)blue (466 nm) light (SL8713) An automaticwoven shade curtain (OLS 50 LudvigSvensson Inc Charlotte NC) was retractedwhen the outdoor light intensity exceeded1000 mmolmiddotmndash2middotsndash1 throughout the study toachieve a AL DLI of 6 molmiddotmndash2middotdndash1

Seedlings in the growth chamber weregrown under a multilayer production systemwith SSL LEDs providing185 mmolmiddotmndash2middotsndash1

PPF at plant height [as measured witha spectroradiometer (PS-100 StellarNetInc Tampa FL)] from 0600 to 2200 HR

(Table 2) for the same duration as the plantsin the greenhouse Light was delivered fromone of two LED arrays providing 8713 redblue light [SSL8713 (Philips GreenPowerLED production module)] spaced on 204-cm

Table 1 Average day and night plant canopy temperatures relative humidity and total daily light integral(DLI) under ambient solar daylight supplemented with 70 mmolmiddotmndash2

middotsndash1 from high-pressure sodium(HPS) lamps or light-emitting diodes (LEDs 8713 redblue light) from 0600 to 2200 HR Impatiensgeranium marigold petunia and vinca were placed under treatments on 1 Oct 2013 4 Nov 2013 and13 Jan 2014

Treatmentinitiation

Supplementallight source

Supplementallight (mmolmiddotmndash2middotsndash1)

Total DLI(molmiddotmndash2middotdndash1)

Relativehumidity ()

Day canopytemp (C)

Night canopytemp (C)

1 Oct 2013 Ambient mdashz 66 plusmn 14 746 plusmn 220 205 plusmn 24 204 plusmn 19HPS 732 plusmn 346 106 plusmn 17 218 plusmn 17 217 plusmn 16LED 710 plusmn 134 105 plusmn 17 222 plusmn 19 222 plusmn 19

4 Nov 2013 Ambient mdash 63 plusmn 31 718 plusmn 153 191 plusmn 19 189 plusmn 18HPS 709 plusmn 284 104 plusmn 31 206 plusmn 14 204 plusmn 11LED 698 plusmn 126 103 plusmn 31 204 plusmn 14 204 plusmn 14

13 Jan 2014 Ambient mdash 67 plusmn 28 732 plusmn 153 185 plusmn 29 182 plusmn 27HPS 727 plusmn 300 109 plusmn 28 200 plusmn 20 199 plusmn 17LED 730 plusmn 104 109 plusmn 28 204 plusmn 19 203 plusmn 18

zNo supplemental light provided

Table 2 Average growth chamber daily light integral (DLI) relative humidity carbon dioxide (CO2) andsole-source light of 185 mmolmiddotmndash2middotsndash1 delivered from light-emitting diodes (LEDs) with varyingproportions of red (R) and blue (B) light from 0600 to 2200 HR Impatiens geranium marigold petuniaand vinca were placed under treatments on 1 Oct 2013 4 Nov 2013 and 13 Jan 2014

Treatmentinitiation

LED sole-sourcelight

Light intensity(mmolmiddotmndash2

middotsndash1) DLI (molmiddotmndash2middotdndash1)

Relative humidity() CO2 (mmolmiddotmolndash1)

1 Oct 2013 87R13B 1846 plusmn 441 106 705 plusmn 66 4917 plusmn 47370R30B 1857 plusmn 654 107

4 Nov 2013 87R13B 1832 plusmn 406 106 728 plusmn 45 4979 plusmn 12670R30B 1835 plusmn 512 106

13 Jan 2014 87R13B 1841 plusmn 373 106 731 plusmn 46 5076 plusmn 48270R30B 1816 plusmn 493 105

706 HORTSCIENCE VOL 50(5) MAY 2015

centers or 7030 red (660 nm)blue(455 nm) light (SSL7030) [485-cm-longand 33-cm-wide (Philips GreenPower LEDresearch module Koninklijke Philips Elec-tronics NV)] spaced on 76-cm centersThree SSL8713 LEDs or 16 SSL7030 LEDswere mounted to stainless steel shelves(121-cm long and 61-cm wide) The shelveswere composed of three vertical layersspaced 457 and 508 cm apart vertically forthe 8713 and 7030 LEDs respectivelySpectral quality of the SSL and SL wereevaluated in nine positions at the beginningof each replication with a spectroradiometer(PS-100 StellarNet Inc) as shown inFigure 1

Finishing culture and environment Atthe end of greenhouse and growth chamberlighting treatments 10 randomly selectedseedlings from each tray were transplantedinto 114-cm (600 mL) containers (DillenProducts Middlefield OH) filled with a com-mercial soilless medium composed of (byvolume) 65 peat 20 perlite and 15vermiculite (Fafard 2 Sun Gro Horticulture)Plants were placed in a common finish en-vironment with a 16-h photoperiod of AL sup-plemented with a PPF of 70 mmolmndash2sndash1

from HPS lamps to provide a DLI of 112 plusmn19 112 plusmn 26 and 126 plusmn 16 molmndash2middotdndash1

for seasons I II and II respectively Airtemperatures in the finishing environmentwere 193 plusmn 23 192 plusmn 20 and 193 plusmn 18 Cfor seasons I II and III respectively Plantswere irrigated as necessary with acidifiedwater supplemented with a combination oftwo water-soluble fertilizers (31 mixtureof 15Nndash22Pndash125K and 21Nndash22Pndash166KEverris Marysville OH) to provide thefollowing (mgmiddotLndash1) 200 N 26 P 163 K

50 Ca 20 Mg 10 Fe 05 Mn and Zn 024 Cuand B and 01 Mo

Data collection and calculations At21 d (geranium and marigold) or 28 d (im-patiens petunia and vinca) after initiatingSL and SSL treatments 10 plants of eachspecies were randomly selected and mea-sured for height (measured from the baseof the hypocotyl to the shoot apical meri-stem) leaf number and stem diameter(measured above the lowest leaf witha digital caliper) (digiMax Wiha Scho-nach Germany) Total chlorophyll (a + b)content [ie relative chlorophyll content(RCC)] was estimated using a SPAD chlo-rophyll meter (SPAD-502 Konica MinoltaSensing Inc Osaka Japan) After non-destructive measurements were recordedroots and shoots of all seedlings wereseparated and washed All individualleaves were removed at the axil and leafarea was measured using a leaf area meter(LI-3100 LI-COR Inc Lincoln NE)Roots and shoots (leaves and stems) wereplaced in a drying oven at 70 C for at least4 d and then RDM and SDM wererecorded The sturdiness quotient (SQ)was calculated as (stem diameterstemlength) The quality index (QI) an objec-tive integrated and quantitative measure-ment of quality was calculated as the [totaldry mass middot (shootroot ratio + sturdinessquotient)] (Currey et al 2013)

Plants in the finish environment weremonitored daily following transplant Whenthe first flower was fully reflexed the datenumber of nodes beneath the first openflower and plant height from the surfaceof the medium to the top of the plantwere recorded Time to flower (TTF) was

calculated as the time from transplant intothe finish environment to the first openflower

Statistical analysis The experiment useda complete block design replicated overthree seasons for each of the five speciesEffects of light treatments were compared byANOVA using SAS (SAS version 93 SASInstitute Cary NC) PROC MIXED with anadditional program (Arnold M Saxton Uni-versity of Tennessee Knoxville TN) thatprovided pairwise comparisons between treat-ments using Tukeyrsquos honestly significant testat P 005

Results

Morphology Height of all species wassignificantly influenced by both SL and SSL(Fig 2A and B) Vinca and impatiens weregenerally taller under SL and SSL than underAL For instance height of impatiens seed-lings under AL was 29 18 26 and13 shorter compared with those under HPSSL8713 SSL8713 and SSL7030 respec-tively Height of geranium petunia andmarigold seedlings grown under SSL8713and SSL7030 LEDs was suppressed by 21and 26 75 and 79 and 18 and 16respectively compared with those under HPSlamps Stem diameter of all species with theexception of petunia was influenced by SLand SSL (Fig 2C and D) For example underSL and SSL stem diameter of vinca impa-tiens and geranium was 12 to 17 26 to45 and 8 to 15 greater respectivelycompared with those seedlings under ALStem diameter of marigold seedlings was17 and 13 greater under SL from HPSand SL8713 LEDs respectively comparedwith AL Leaf number of all species wassignificantly influenced by SL and SSL (datanot presented) For instance leaf number ofvinca geranium and marigold was 40 to50 9 to 31 and 19 to 21 greaterrespectively for seedlings grown under HPSSL8713 SSL8713 and SSL7030 LEDscompared with AL Leaf number of impa-tiens and petunia was 26 to 34 and 32 to62 greater for seedlings grown under SL orSSL respectively compared with AL Totalleaf area of all species generally increasedunder SL and SSL (Fig 2E and F) Leaf areaof vinca and impatiens seedlings was 20 to134 and 21 to 75 greater for thosegrown under SSL8713 LEDs compared withthe other treatments respectively Leaf areaof geranium was 49 20 and 24 greaterfor seedlings grown under HPS lamps com-pared with those under AL SSL8713 andSSL7030 LEDs respectively

Physiology Relative chlorophyll contentof all species was significantly greater underSL and SSL (Fig 2G and H) The RCC ofimpatiens geranium and petunia seedlingsunder SSL7030 LEDs was 22 to 47 4to 21 and 44 to 85 greater respec-tively compared with those under AL HPSand SL8713 LEDs For marigold RCC wasgreatest under SL and SSL LEDs comparedwith HPS lamps or AL

Fig 1 Spectral quality of 70 mmolmiddotmndash2middotsndash1 delivered from supplemental (SL) high-pressure sodium (HPS)lamps and light-emitting diodes (LEDs) with () 8713 redblue light in the greenhouse or185 mmolmiddotmndash2middotsndash1 delivered from sole-source (SSL) LEDs with 8713 or 7030 redblue light ina growth chamber

HORTSCIENCE VOL 50(5) MAY 2015 707

Fig 2 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on height stem diameter relative chlorophyll content (SPAD) and leaf area of vinca impatiens geranium petunia and marigoldafter 21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test atP 005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

708 HORTSCIENCE VOL 50(5) MAY 2015

Growth Root dry mass (RDM) of allspecies was generally higher under SL andSSL treatments (Fig 3A and B) For exam-ple RDM of vinca impatiens and gera-nium was 104 and 101 81 and 93and 102 and 109 greater for seedlingsgrown under HPS lamps and SSL8713LEDs respectively compared with ALRoot dry mass of petunia was 41 to 57greater under SSL LEDs compared withSL Marigold RDM increased 140 to260 under SL and SSL Shoot dry massof all species was significantly greater un-der SL and SSL (Fig 3C and D) Forexample SDM of vinca impatiens gera-nium petunia and marigold was 74 to154 64 to 164 50 to 82 62 to72 and 59 to 161 greater under SL orSSL respectively compared with AL Ad-ditionally SDM of vinca and impatiensseedlings was 23 to 46 and 21 to61 higher respectively under SSL thanSL

Quality Light treatments significantlyinfluenced the SQ of all species differently(Fig 3E and F) However the SQ ofimpatiens geranium petunia and marigoldwere generally similar when seedlings werepropagated under AL or HPS lamps Forexample the SQ of geranium increased by36 and 30 under SSL7030 LEDs com-pared with seedlings under AL and HPSlamps respectively The SQ of petunia was133 to 306 greater for seedlings grownunder SSL LEDs respectively comparedwith those under AL and SL The QIincreased differently for all species underSL and SSL (Fig 3G and H) For examplethe QI of vinca was 117 higher forseedlings grown under HPS lamps com-pared with AL however for petunia it in-creased by 106 and 129 for seedlingsgrown under SSL8713 and SSL7030 LEDsrespectively compared with AL

Flowering Generally TTF was signifi-cantly reduced when seedlings were grownunder SL or SSL for all species with theexception of impatiens (Fig 4A and B) Timeto flower of impatiens seedlings grown underSSL8713 LEDs was delayed by 8 to 11 dcompared with those grown under AL SLand SSL7030 Height at flower of all specieswith the exception of impatiens and marigoldwas significantly influenced by SL and SSLreceived as a seedling (Fig 4C and D) Forexample height at flower of vinca andpetunia was reduced by 50 and 25 whenseedlings were grown under SSL7030 LEDsrespectively compared with those under ALThe number of nodes below the first openflower was affected differently by the light-ing treatment received as a seedling for allspecies with the exception of marigold andpetunia (Fig 4E and F) For instance theaverage number of nodes at flower for im-patiens was reduced by two under ALcompared with the SSL8713 LEDs Addi-tionally vinca and geranium had an aver-age of one less node when seedlings weregrown under SSL7030 LEDs comparedwith AL

Discussion

Without SL young plants are grown un-der a mean DLI of 6 to 8 molmiddotmndash2middotdndash1 atlatitudes of 35 to 45N during peak pro-duction in January and February (Korczynskiet al 2002) To produce high-quality youngplants greenhouse growers try tomaintain therecommended DLI of 10 to 12 molmiddotmndash2middotdndash1

(Runkle 2007) by providing SL witha PPF of 50 to 80 mmolmiddotmndash2middotsndash1 from HPSlamps (Fisher and Runkle 2004) Thereforewe selected 70 mmolmiddotmndash2middotsndash1 as our targetfor SL to achieve a supplemental DLI of4 molmiddotmndash2middotdndash1

Previous research has shown that beddingplant seedlings were generally more compactwith a larger stem diameter higher SQ andhigher RCC under LED SL providing a redblue light ratio () of 8515 and 7030(Randall and Lopez 2014) In additionWollaeger and Runkle (2013) determinedthat there were no consistent differences inplant growth when bedding plant seedlingswere grown under LED SSL providing or-ange red or hyper-red light They alsosuggested that hyper-red LEDs could beselected over red LEDs as they were 7more efficient the efficiency (mmolmiddotJndash1) ofthe orange red or hyper-red LEDs was 072229 and 246 respectively Previous studieshave also reported that high-intensity SL orSSL containing blue light generally inhibitstem elongation when added to red light(Heo et al 2003 Randall and Lopez 2014Wollaeger and Runkle 2014) For exampleblue light and a combination of blue and redlight resulted in a shorter peduncle lengthof cyclamen (Cyclamen persicum lsquoDixieWhitersquo) than red light alone (Heo et al2003) and more compact bedding plant seed-lings with a combination of red and blue light(Randall and Lopez 2014 Wollaeger andRunkle 2014) Thus we selected commer-cially available LED arrays that provideda light ratio of 8713 red (peak = 664 nm)blue (peak = 466 nm) light for our SL andSSL Therefore the primary objective of ourexperiment was to quantify and compare thegrowth morphology quality and subsequentdevelopment of seedlings grown under ALAL plus SL and SSL while all other envi-ronmental characteristics including temper-ature humidity and DLI were constant

In order for young plants to withstandshipping and mechanical transplanting(Latimer 1998) they must be compact (re-duced leaf area and height) and fully rootedwith a large stem diameter and high RDM(Pramuk and Runkle 2005 Wollaeger andRunkle 2014) The QI is a tool that integratesmorphological parameters such as dry massstem length and diameter that contribute toa high-quality seedling Geranium petuniaand marigold seedlings grown under SSLwere generally more compact darker infoliage color (higher RCC) and had a higherRDM and QI than those grown in the green-house under AL or SL Previous studies havedetermined that the QI of young plants in-creases as DLI increases (Currey et al 2012

2013 Randall and Lopez 2014) For ex-ample as the DLI increased from 12 to123 molmiddotmndash2middotdndash1 the QI of diascia (Diasciabarberae lsquoWink Coralrsquo) and lantana (Lantanacamara lsquoLucky Goldrsquo) rooted cuttings in-creased 960 and 53 respectively (Curreyet al 2013) Similarly the QI of all species inthe current study was greater under both SLand SSL with a DLI of 106 molmiddotmndash2middotdndash1

compared with seedlings under ALwith a DLIof 65 molmiddotmndash2middotdndash1 and the QI of im-patiens geranium and petunia was similaror greater for seedlings grown under SSLcompared with SL

Leaf area of all species in the currentstudy was generally similar or greater underSL compared with AL and under SSLtreatments compared with SL Howeverunder SSL as the percentage of blue lightincreased from 13 to 30 leaf area gen-erally decreased Previous studies havereported that plants under red light typicallyhave greater leaf area than those grown under$13 blue or only blue light (Son and Oh2013 Wollaeger and Runkle 2014) Forexample leaf area of lettuce (Lactuca sativalsquoSunmangrsquo and lsquoGrand Rapid TBRrsquo) in-creased by 325 and 324 respectivelyas the () of red light from LED SSLproviding 171 mmolmiddotmndash2middotsndash1 increased froma ratio of 4159 to 1000 redblue light(Son and Oh 2013) Wollaeger and Runkle(2013) reported that total leaf area of impa-tiens lsquoSuperElfin XP Redrsquo and petunialsquoWave Pinkrsquo seedlings grown under SSLLEDs providing a redblue light ratio () of1000 was 55 to 114 and 57 to 130greater respectively than seedlings grownunder 25 or greater blue light Generallya smaller leaf area is desired in ornamentalyoung plant production as seedlings andcuttings are grown under a dense and compet-itive environment that can induce excessivestem extension due to the shade avoidanceresponse

Additionally studies have also reportedleaf anatomical changes with the addition ofblue light (Saeligboslash et al 1995 Schuerger et al1997) For example leaf thickness of pepperplants (Capsicum annuum) increased whengrown under SSL providing blue light fromblue fluorescent lamps providing a redfar-redblue ratio () of 9811 compared withthose providing a redfar-red ratio of 990 or8317 Therefore we can hypothesize thatblue light promotes an increase in leaf thick-ness and a reduction in leaf area Howeverthe extent to which blue light affects plantgrowth and morphology across species is notfully understood

Relative chlorophyll content generallyincreased for all species investigated as theamount of blue light increased from 7 forHPS lamps to 30 for SSL7030 LEDsSimilarly Son and Oh (2013) reported thatRCC of lettuce lsquoSunmangrsquo and lsquoGrand RapidTBRrsquo increased by 140 and 150 asthe percentage of SSL blue light increasedfrom a redblue light ratio () of 1000 to5347 and 1000 to 7426 respectively How-ever chlorophyll concentration of impatiens

HORTSCIENCE VOL 50(5) MAY 2015 709

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

the 04040 than the 0800 orangeredhyper-red LEDs respectively but was similar tothe other light treatments and shoot drymass (SDM) of tomato was 25 to 40greater under the 06020 orangeredhyper-red than under SSL providing 0404002060 or 0080 orangeredhyper-red light(Wollaeger and Runkle 2013) Finally Ran-dall and Lopez (2014) compared seedlings ofsnapdragon (Antirrhinum majus lsquoRocketPinkrsquo) vinca lsquoTitan Punchrsquo celosia (Celosiaargentea lsquoFresh Look Goldrsquo) impatiens lsquoDaz-zler Blue Pearlrsquo geranium lsquoBullseye Scarletrsquopetunia lsquoPlush Bluersquo salvia lsquoVista RedrsquoFrench marigold lsquoBonanza Flamersquo and pansy(Viola middotwittrockiana lsquoMammoth Big Redrsquo)grown under AL supplemented with a PPFof 100 mmolmiddotmndash2middotsndash1 for 16 h from eitherHPS or one of three LED arrays composed of() 1000 8515 or 7030 redblue light After28 d height of all species except snapdragonand geranium was reduced by 9 to 55under 8515 redblue LEDs compared withthose under HPS lamps and stem diameterof geranium marigold and snapdragon was8 to 16 greater under 8515 redblueLEDs compared with seedlings grown underHPS lamps

To our knowledge no studies have com-pared annual bedding plant seedlings grownunder SSL to those grown under SL ina greenhouse providing the same DLI Theobjectives of this study were to 1) quantifythe effects of SL from HPS lamps and LEDarrays compared with a SSL multilayer pro-duction system from LED arrays providingtwo different light qualities on seedlinggrowth morphology and quality and 2) de-termine whether there were any residualeffects of either SL or SSL on subsequentflowering

Materials and Methods

Plant material culture and propagationenvironment Seeds of French marigoldlsquoDurango Yellowrsquo geranium lsquoBullseyeRedrsquo impatiens lsquoSuper Elfin XP Blue Pearlrsquopetunia lsquoDreams Midnightrsquo and vinca lsquoTitanRed Darkrsquo (Ball Horticulture Co WestChicago IL) were sown into 288-cell (6-mL individual cell volume) seed trays filledwith a commercial soilless medium com-posed of (by volume) 65 peat 20 perliteand 15 vermiculite (Fafard Super FineGerminating Mix Sun Gro HorticultureAgawam MA) and placed in a glass-glazedgreenhouse at Purdue University WestLafayette IN (latitude 40N) Exhaust fanand evaporative-pad cooling radiant hotwater heating and retractable shade curtainswere controlled by an environmental controlsystem (Maximizer Precision 10 Priva Com-puters Inc Vineland Station Ontario Can-ada) The DLI and average daily temperatures(ADT) for seasons I II and III from sowing tohypocotyl emergence were 121 plusmn 17 114 plusmn28 and 123 plusmn 18 molmiddotmndash2middotdndash1 and 226 plusmn08 223 plusmn 11 and 224 plusmn 11 C respectivelyOn hypocotyl emergence two trays of eachspecies were moved under either AL AL plus

SL in a glass-glazed greenhouse or SSL ina growth chamber

Greenhouse environment All specieswere placed under a 16-h photoperiod withADTs of 226 plusmn 09 227 plusmn 07 and 227 plusmn28 C for seasons I II and III respectivelyInfrared temperature sensors with an emis-sivity of 095 (OS136 Omega EngineeringInc Stamford CT) recorded seedling can-opy temperatures every 30 s and averageswere logged every 15 min by a data logger(Maximizer Precision 10) Quantum sensors(SQ-110 Apogee Instruments Inc LoganUT) measured solar PPF every 15 s and theaverage was logged every 15 min by a datalogger (WD 2800 Spectrum TechnologiesAurora IL) Environmental data for thegreenhouse environment are reported inTable 1 Seedlings were irrigated with watersupplemented with water-soluble fertilizer(Jackrsquos LX 16Nndash094Pndash123K Plug Formulafor High Alkalinity Water JR Peters IncAllentown PA) providing (in mgmiddotLndash1) 100 N10 P 78 K 18 Ca 94 Mg 010 B 005 Cu050 Fe 025 Mn 005 Mo and 025 Zn

Growth chamber environment All spe-cies were placed under a 16-h photoperiod ina walk-in growth chamber (C5 ControlSystem Environmental Growth ChambersChagrin Falls OH) with ADT of 230 plusmn 01230 plusmn 01 and 230 plusmn 01 C for seasons I IIand III respectively Air temperature rela-tive humidity and carbon dioxide (CO2)were measured and logged every 15 min bya data logger (DL1 Datalogger Environmen-tal Growth Chambers) Environmental datafor the growth chamber environment are

reported in Table 2 Seedlings were irrigatedwith the same fertilizer used in the green-house environment

Supplemental and sole-source lightingtreatments Seedlings in the greenhouse weregrown under AL or AL supplemented with70 mmolmiddotmndash2middotsndash1 PPF at plant height [asmeasured with a spectroradiometer (PS-100Apogee Instruments Inc Logan UT)] from0600 to 2200 HR (Table 1) for 21 d (geraniumand marigold) or 28 d (impatiens petuniaand vinca) Supplemental light was deliveredfrom either two 150-W HPS lamps (PL 2000PL Light Systems Inc Beamsville OntarioCanada) or eight 32-W LED arrays [120-cmlong and 4-cm wide (Philips GreenPowerLED production module KoninklijkePhilips Electronics NV The Netherlands)]spaced on 445-cm centers and 787 cm abovethe bench top providing () 8713 red (664 nm)blue (466 nm) light (SL8713) An automaticwoven shade curtain (OLS 50 LudvigSvensson Inc Charlotte NC) was retractedwhen the outdoor light intensity exceeded1000 mmolmiddotmndash2middotsndash1 throughout the study toachieve a AL DLI of 6 molmiddotmndash2middotdndash1

Seedlings in the growth chamber weregrown under a multilayer production systemwith SSL LEDs providing185 mmolmiddotmndash2middotsndash1

PPF at plant height [as measured witha spectroradiometer (PS-100 StellarNetInc Tampa FL)] from 0600 to 2200 HR

(Table 2) for the same duration as the plantsin the greenhouse Light was delivered fromone of two LED arrays providing 8713 redblue light [SSL8713 (Philips GreenPowerLED production module)] spaced on 204-cm

Table 1 Average day and night plant canopy temperatures relative humidity and total daily light integral(DLI) under ambient solar daylight supplemented with 70 mmolmiddotmndash2

middotsndash1 from high-pressure sodium(HPS) lamps or light-emitting diodes (LEDs 8713 redblue light) from 0600 to 2200 HR Impatiensgeranium marigold petunia and vinca were placed under treatments on 1 Oct 2013 4 Nov 2013 and13 Jan 2014

Treatmentinitiation

Supplementallight source

Supplementallight (mmolmiddotmndash2middotsndash1)

Total DLI(molmiddotmndash2middotdndash1)

Relativehumidity ()

Day canopytemp (C)

Night canopytemp (C)

1 Oct 2013 Ambient mdashz 66 plusmn 14 746 plusmn 220 205 plusmn 24 204 plusmn 19HPS 732 plusmn 346 106 plusmn 17 218 plusmn 17 217 plusmn 16LED 710 plusmn 134 105 plusmn 17 222 plusmn 19 222 plusmn 19

4 Nov 2013 Ambient mdash 63 plusmn 31 718 plusmn 153 191 plusmn 19 189 plusmn 18HPS 709 plusmn 284 104 plusmn 31 206 plusmn 14 204 plusmn 11LED 698 plusmn 126 103 plusmn 31 204 plusmn 14 204 plusmn 14

13 Jan 2014 Ambient mdash 67 plusmn 28 732 plusmn 153 185 plusmn 29 182 plusmn 27HPS 727 plusmn 300 109 plusmn 28 200 plusmn 20 199 plusmn 17LED 730 plusmn 104 109 plusmn 28 204 plusmn 19 203 plusmn 18

zNo supplemental light provided

Table 2 Average growth chamber daily light integral (DLI) relative humidity carbon dioxide (CO2) andsole-source light of 185 mmolmiddotmndash2middotsndash1 delivered from light-emitting diodes (LEDs) with varyingproportions of red (R) and blue (B) light from 0600 to 2200 HR Impatiens geranium marigold petuniaand vinca were placed under treatments on 1 Oct 2013 4 Nov 2013 and 13 Jan 2014

Treatmentinitiation

LED sole-sourcelight

Light intensity(mmolmiddotmndash2

middotsndash1) DLI (molmiddotmndash2middotdndash1)

Relative humidity() CO2 (mmolmiddotmolndash1)

1 Oct 2013 87R13B 1846 plusmn 441 106 705 plusmn 66 4917 plusmn 47370R30B 1857 plusmn 654 107

4 Nov 2013 87R13B 1832 plusmn 406 106 728 plusmn 45 4979 plusmn 12670R30B 1835 plusmn 512 106

13 Jan 2014 87R13B 1841 plusmn 373 106 731 plusmn 46 5076 plusmn 48270R30B 1816 plusmn 493 105

706 HORTSCIENCE VOL 50(5) MAY 2015

centers or 7030 red (660 nm)blue(455 nm) light (SSL7030) [485-cm-longand 33-cm-wide (Philips GreenPower LEDresearch module Koninklijke Philips Elec-tronics NV)] spaced on 76-cm centersThree SSL8713 LEDs or 16 SSL7030 LEDswere mounted to stainless steel shelves(121-cm long and 61-cm wide) The shelveswere composed of three vertical layersspaced 457 and 508 cm apart vertically forthe 8713 and 7030 LEDs respectivelySpectral quality of the SSL and SL wereevaluated in nine positions at the beginningof each replication with a spectroradiometer(PS-100 StellarNet Inc) as shown inFigure 1

Finishing culture and environment Atthe end of greenhouse and growth chamberlighting treatments 10 randomly selectedseedlings from each tray were transplantedinto 114-cm (600 mL) containers (DillenProducts Middlefield OH) filled with a com-mercial soilless medium composed of (byvolume) 65 peat 20 perlite and 15vermiculite (Fafard 2 Sun Gro Horticulture)Plants were placed in a common finish en-vironment with a 16-h photoperiod of AL sup-plemented with a PPF of 70 mmolmndash2sndash1

from HPS lamps to provide a DLI of 112 plusmn19 112 plusmn 26 and 126 plusmn 16 molmndash2middotdndash1

for seasons I II and II respectively Airtemperatures in the finishing environmentwere 193 plusmn 23 192 plusmn 20 and 193 plusmn 18 Cfor seasons I II and III respectively Plantswere irrigated as necessary with acidifiedwater supplemented with a combination oftwo water-soluble fertilizers (31 mixtureof 15Nndash22Pndash125K and 21Nndash22Pndash166KEverris Marysville OH) to provide thefollowing (mgmiddotLndash1) 200 N 26 P 163 K

50 Ca 20 Mg 10 Fe 05 Mn and Zn 024 Cuand B and 01 Mo

Data collection and calculations At21 d (geranium and marigold) or 28 d (im-patiens petunia and vinca) after initiatingSL and SSL treatments 10 plants of eachspecies were randomly selected and mea-sured for height (measured from the baseof the hypocotyl to the shoot apical meri-stem) leaf number and stem diameter(measured above the lowest leaf witha digital caliper) (digiMax Wiha Scho-nach Germany) Total chlorophyll (a + b)content [ie relative chlorophyll content(RCC)] was estimated using a SPAD chlo-rophyll meter (SPAD-502 Konica MinoltaSensing Inc Osaka Japan) After non-destructive measurements were recordedroots and shoots of all seedlings wereseparated and washed All individualleaves were removed at the axil and leafarea was measured using a leaf area meter(LI-3100 LI-COR Inc Lincoln NE)Roots and shoots (leaves and stems) wereplaced in a drying oven at 70 C for at least4 d and then RDM and SDM wererecorded The sturdiness quotient (SQ)was calculated as (stem diameterstemlength) The quality index (QI) an objec-tive integrated and quantitative measure-ment of quality was calculated as the [totaldry mass middot (shootroot ratio + sturdinessquotient)] (Currey et al 2013)

Plants in the finish environment weremonitored daily following transplant Whenthe first flower was fully reflexed the datenumber of nodes beneath the first openflower and plant height from the surfaceof the medium to the top of the plantwere recorded Time to flower (TTF) was

calculated as the time from transplant intothe finish environment to the first openflower

Statistical analysis The experiment useda complete block design replicated overthree seasons for each of the five speciesEffects of light treatments were compared byANOVA using SAS (SAS version 93 SASInstitute Cary NC) PROC MIXED with anadditional program (Arnold M Saxton Uni-versity of Tennessee Knoxville TN) thatprovided pairwise comparisons between treat-ments using Tukeyrsquos honestly significant testat P 005

Results

Morphology Height of all species wassignificantly influenced by both SL and SSL(Fig 2A and B) Vinca and impatiens weregenerally taller under SL and SSL than underAL For instance height of impatiens seed-lings under AL was 29 18 26 and13 shorter compared with those under HPSSL8713 SSL8713 and SSL7030 respec-tively Height of geranium petunia andmarigold seedlings grown under SSL8713and SSL7030 LEDs was suppressed by 21and 26 75 and 79 and 18 and 16respectively compared with those under HPSlamps Stem diameter of all species with theexception of petunia was influenced by SLand SSL (Fig 2C and D) For example underSL and SSL stem diameter of vinca impa-tiens and geranium was 12 to 17 26 to45 and 8 to 15 greater respectivelycompared with those seedlings under ALStem diameter of marigold seedlings was17 and 13 greater under SL from HPSand SL8713 LEDs respectively comparedwith AL Leaf number of all species wassignificantly influenced by SL and SSL (datanot presented) For instance leaf number ofvinca geranium and marigold was 40 to50 9 to 31 and 19 to 21 greaterrespectively for seedlings grown under HPSSL8713 SSL8713 and SSL7030 LEDscompared with AL Leaf number of impa-tiens and petunia was 26 to 34 and 32 to62 greater for seedlings grown under SL orSSL respectively compared with AL Totalleaf area of all species generally increasedunder SL and SSL (Fig 2E and F) Leaf areaof vinca and impatiens seedlings was 20 to134 and 21 to 75 greater for thosegrown under SSL8713 LEDs compared withthe other treatments respectively Leaf areaof geranium was 49 20 and 24 greaterfor seedlings grown under HPS lamps com-pared with those under AL SSL8713 andSSL7030 LEDs respectively

Physiology Relative chlorophyll contentof all species was significantly greater underSL and SSL (Fig 2G and H) The RCC ofimpatiens geranium and petunia seedlingsunder SSL7030 LEDs was 22 to 47 4to 21 and 44 to 85 greater respec-tively compared with those under AL HPSand SL8713 LEDs For marigold RCC wasgreatest under SL and SSL LEDs comparedwith HPS lamps or AL

Fig 1 Spectral quality of 70 mmolmiddotmndash2middotsndash1 delivered from supplemental (SL) high-pressure sodium (HPS)lamps and light-emitting diodes (LEDs) with () 8713 redblue light in the greenhouse or185 mmolmiddotmndash2middotsndash1 delivered from sole-source (SSL) LEDs with 8713 or 7030 redblue light ina growth chamber

HORTSCIENCE VOL 50(5) MAY 2015 707

Fig 2 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on height stem diameter relative chlorophyll content (SPAD) and leaf area of vinca impatiens geranium petunia and marigoldafter 21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test atP 005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

708 HORTSCIENCE VOL 50(5) MAY 2015

Growth Root dry mass (RDM) of allspecies was generally higher under SL andSSL treatments (Fig 3A and B) For exam-ple RDM of vinca impatiens and gera-nium was 104 and 101 81 and 93and 102 and 109 greater for seedlingsgrown under HPS lamps and SSL8713LEDs respectively compared with ALRoot dry mass of petunia was 41 to 57greater under SSL LEDs compared withSL Marigold RDM increased 140 to260 under SL and SSL Shoot dry massof all species was significantly greater un-der SL and SSL (Fig 3C and D) Forexample SDM of vinca impatiens gera-nium petunia and marigold was 74 to154 64 to 164 50 to 82 62 to72 and 59 to 161 greater under SL orSSL respectively compared with AL Ad-ditionally SDM of vinca and impatiensseedlings was 23 to 46 and 21 to61 higher respectively under SSL thanSL

Quality Light treatments significantlyinfluenced the SQ of all species differently(Fig 3E and F) However the SQ ofimpatiens geranium petunia and marigoldwere generally similar when seedlings werepropagated under AL or HPS lamps Forexample the SQ of geranium increased by36 and 30 under SSL7030 LEDs com-pared with seedlings under AL and HPSlamps respectively The SQ of petunia was133 to 306 greater for seedlings grownunder SSL LEDs respectively comparedwith those under AL and SL The QIincreased differently for all species underSL and SSL (Fig 3G and H) For examplethe QI of vinca was 117 higher forseedlings grown under HPS lamps com-pared with AL however for petunia it in-creased by 106 and 129 for seedlingsgrown under SSL8713 and SSL7030 LEDsrespectively compared with AL

Flowering Generally TTF was signifi-cantly reduced when seedlings were grownunder SL or SSL for all species with theexception of impatiens (Fig 4A and B) Timeto flower of impatiens seedlings grown underSSL8713 LEDs was delayed by 8 to 11 dcompared with those grown under AL SLand SSL7030 Height at flower of all specieswith the exception of impatiens and marigoldwas significantly influenced by SL and SSLreceived as a seedling (Fig 4C and D) Forexample height at flower of vinca andpetunia was reduced by 50 and 25 whenseedlings were grown under SSL7030 LEDsrespectively compared with those under ALThe number of nodes below the first openflower was affected differently by the light-ing treatment received as a seedling for allspecies with the exception of marigold andpetunia (Fig 4E and F) For instance theaverage number of nodes at flower for im-patiens was reduced by two under ALcompared with the SSL8713 LEDs Addi-tionally vinca and geranium had an aver-age of one less node when seedlings weregrown under SSL7030 LEDs comparedwith AL

Discussion

Without SL young plants are grown un-der a mean DLI of 6 to 8 molmiddotmndash2middotdndash1 atlatitudes of 35 to 45N during peak pro-duction in January and February (Korczynskiet al 2002) To produce high-quality youngplants greenhouse growers try tomaintain therecommended DLI of 10 to 12 molmiddotmndash2middotdndash1

(Runkle 2007) by providing SL witha PPF of 50 to 80 mmolmiddotmndash2middotsndash1 from HPSlamps (Fisher and Runkle 2004) Thereforewe selected 70 mmolmiddotmndash2middotsndash1 as our targetfor SL to achieve a supplemental DLI of4 molmiddotmndash2middotdndash1

Previous research has shown that beddingplant seedlings were generally more compactwith a larger stem diameter higher SQ andhigher RCC under LED SL providing a redblue light ratio () of 8515 and 7030(Randall and Lopez 2014) In additionWollaeger and Runkle (2013) determinedthat there were no consistent differences inplant growth when bedding plant seedlingswere grown under LED SSL providing or-ange red or hyper-red light They alsosuggested that hyper-red LEDs could beselected over red LEDs as they were 7more efficient the efficiency (mmolmiddotJndash1) ofthe orange red or hyper-red LEDs was 072229 and 246 respectively Previous studieshave also reported that high-intensity SL orSSL containing blue light generally inhibitstem elongation when added to red light(Heo et al 2003 Randall and Lopez 2014Wollaeger and Runkle 2014) For exampleblue light and a combination of blue and redlight resulted in a shorter peduncle lengthof cyclamen (Cyclamen persicum lsquoDixieWhitersquo) than red light alone (Heo et al2003) and more compact bedding plant seed-lings with a combination of red and blue light(Randall and Lopez 2014 Wollaeger andRunkle 2014) Thus we selected commer-cially available LED arrays that provideda light ratio of 8713 red (peak = 664 nm)blue (peak = 466 nm) light for our SL andSSL Therefore the primary objective of ourexperiment was to quantify and compare thegrowth morphology quality and subsequentdevelopment of seedlings grown under ALAL plus SL and SSL while all other envi-ronmental characteristics including temper-ature humidity and DLI were constant

In order for young plants to withstandshipping and mechanical transplanting(Latimer 1998) they must be compact (re-duced leaf area and height) and fully rootedwith a large stem diameter and high RDM(Pramuk and Runkle 2005 Wollaeger andRunkle 2014) The QI is a tool that integratesmorphological parameters such as dry massstem length and diameter that contribute toa high-quality seedling Geranium petuniaand marigold seedlings grown under SSLwere generally more compact darker infoliage color (higher RCC) and had a higherRDM and QI than those grown in the green-house under AL or SL Previous studies havedetermined that the QI of young plants in-creases as DLI increases (Currey et al 2012

2013 Randall and Lopez 2014) For ex-ample as the DLI increased from 12 to123 molmiddotmndash2middotdndash1 the QI of diascia (Diasciabarberae lsquoWink Coralrsquo) and lantana (Lantanacamara lsquoLucky Goldrsquo) rooted cuttings in-creased 960 and 53 respectively (Curreyet al 2013) Similarly the QI of all species inthe current study was greater under both SLand SSL with a DLI of 106 molmiddotmndash2middotdndash1

compared with seedlings under ALwith a DLIof 65 molmiddotmndash2middotdndash1 and the QI of im-patiens geranium and petunia was similaror greater for seedlings grown under SSLcompared with SL

Leaf area of all species in the currentstudy was generally similar or greater underSL compared with AL and under SSLtreatments compared with SL Howeverunder SSL as the percentage of blue lightincreased from 13 to 30 leaf area gen-erally decreased Previous studies havereported that plants under red light typicallyhave greater leaf area than those grown under$13 blue or only blue light (Son and Oh2013 Wollaeger and Runkle 2014) Forexample leaf area of lettuce (Lactuca sativalsquoSunmangrsquo and lsquoGrand Rapid TBRrsquo) in-creased by 325 and 324 respectivelyas the () of red light from LED SSLproviding 171 mmolmiddotmndash2middotsndash1 increased froma ratio of 4159 to 1000 redblue light(Son and Oh 2013) Wollaeger and Runkle(2013) reported that total leaf area of impa-tiens lsquoSuperElfin XP Redrsquo and petunialsquoWave Pinkrsquo seedlings grown under SSLLEDs providing a redblue light ratio () of1000 was 55 to 114 and 57 to 130greater respectively than seedlings grownunder 25 or greater blue light Generallya smaller leaf area is desired in ornamentalyoung plant production as seedlings andcuttings are grown under a dense and compet-itive environment that can induce excessivestem extension due to the shade avoidanceresponse

Additionally studies have also reportedleaf anatomical changes with the addition ofblue light (Saeligboslash et al 1995 Schuerger et al1997) For example leaf thickness of pepperplants (Capsicum annuum) increased whengrown under SSL providing blue light fromblue fluorescent lamps providing a redfar-redblue ratio () of 9811 compared withthose providing a redfar-red ratio of 990 or8317 Therefore we can hypothesize thatblue light promotes an increase in leaf thick-ness and a reduction in leaf area Howeverthe extent to which blue light affects plantgrowth and morphology across species is notfully understood

Relative chlorophyll content generallyincreased for all species investigated as theamount of blue light increased from 7 forHPS lamps to 30 for SSL7030 LEDsSimilarly Son and Oh (2013) reported thatRCC of lettuce lsquoSunmangrsquo and lsquoGrand RapidTBRrsquo increased by 140 and 150 asthe percentage of SSL blue light increasedfrom a redblue light ratio () of 1000 to5347 and 1000 to 7426 respectively How-ever chlorophyll concentration of impatiens

HORTSCIENCE VOL 50(5) MAY 2015 709

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

centers or 7030 red (660 nm)blue(455 nm) light (SSL7030) [485-cm-longand 33-cm-wide (Philips GreenPower LEDresearch module Koninklijke Philips Elec-tronics NV)] spaced on 76-cm centersThree SSL8713 LEDs or 16 SSL7030 LEDswere mounted to stainless steel shelves(121-cm long and 61-cm wide) The shelveswere composed of three vertical layersspaced 457 and 508 cm apart vertically forthe 8713 and 7030 LEDs respectivelySpectral quality of the SSL and SL wereevaluated in nine positions at the beginningof each replication with a spectroradiometer(PS-100 StellarNet Inc) as shown inFigure 1

Finishing culture and environment Atthe end of greenhouse and growth chamberlighting treatments 10 randomly selectedseedlings from each tray were transplantedinto 114-cm (600 mL) containers (DillenProducts Middlefield OH) filled with a com-mercial soilless medium composed of (byvolume) 65 peat 20 perlite and 15vermiculite (Fafard 2 Sun Gro Horticulture)Plants were placed in a common finish en-vironment with a 16-h photoperiod of AL sup-plemented with a PPF of 70 mmolmndash2sndash1

from HPS lamps to provide a DLI of 112 plusmn19 112 plusmn 26 and 126 plusmn 16 molmndash2middotdndash1

for seasons I II and II respectively Airtemperatures in the finishing environmentwere 193 plusmn 23 192 plusmn 20 and 193 plusmn 18 Cfor seasons I II and III respectively Plantswere irrigated as necessary with acidifiedwater supplemented with a combination oftwo water-soluble fertilizers (31 mixtureof 15Nndash22Pndash125K and 21Nndash22Pndash166KEverris Marysville OH) to provide thefollowing (mgmiddotLndash1) 200 N 26 P 163 K

50 Ca 20 Mg 10 Fe 05 Mn and Zn 024 Cuand B and 01 Mo

Data collection and calculations At21 d (geranium and marigold) or 28 d (im-patiens petunia and vinca) after initiatingSL and SSL treatments 10 plants of eachspecies were randomly selected and mea-sured for height (measured from the baseof the hypocotyl to the shoot apical meri-stem) leaf number and stem diameter(measured above the lowest leaf witha digital caliper) (digiMax Wiha Scho-nach Germany) Total chlorophyll (a + b)content [ie relative chlorophyll content(RCC)] was estimated using a SPAD chlo-rophyll meter (SPAD-502 Konica MinoltaSensing Inc Osaka Japan) After non-destructive measurements were recordedroots and shoots of all seedlings wereseparated and washed All individualleaves were removed at the axil and leafarea was measured using a leaf area meter(LI-3100 LI-COR Inc Lincoln NE)Roots and shoots (leaves and stems) wereplaced in a drying oven at 70 C for at least4 d and then RDM and SDM wererecorded The sturdiness quotient (SQ)was calculated as (stem diameterstemlength) The quality index (QI) an objec-tive integrated and quantitative measure-ment of quality was calculated as the [totaldry mass middot (shootroot ratio + sturdinessquotient)] (Currey et al 2013)

Plants in the finish environment weremonitored daily following transplant Whenthe first flower was fully reflexed the datenumber of nodes beneath the first openflower and plant height from the surfaceof the medium to the top of the plantwere recorded Time to flower (TTF) was

calculated as the time from transplant intothe finish environment to the first openflower

Statistical analysis The experiment useda complete block design replicated overthree seasons for each of the five speciesEffects of light treatments were compared byANOVA using SAS (SAS version 93 SASInstitute Cary NC) PROC MIXED with anadditional program (Arnold M Saxton Uni-versity of Tennessee Knoxville TN) thatprovided pairwise comparisons between treat-ments using Tukeyrsquos honestly significant testat P 005

Results

Morphology Height of all species wassignificantly influenced by both SL and SSL(Fig 2A and B) Vinca and impatiens weregenerally taller under SL and SSL than underAL For instance height of impatiens seed-lings under AL was 29 18 26 and13 shorter compared with those under HPSSL8713 SSL8713 and SSL7030 respec-tively Height of geranium petunia andmarigold seedlings grown under SSL8713and SSL7030 LEDs was suppressed by 21and 26 75 and 79 and 18 and 16respectively compared with those under HPSlamps Stem diameter of all species with theexception of petunia was influenced by SLand SSL (Fig 2C and D) For example underSL and SSL stem diameter of vinca impa-tiens and geranium was 12 to 17 26 to45 and 8 to 15 greater respectivelycompared with those seedlings under ALStem diameter of marigold seedlings was17 and 13 greater under SL from HPSand SL8713 LEDs respectively comparedwith AL Leaf number of all species wassignificantly influenced by SL and SSL (datanot presented) For instance leaf number ofvinca geranium and marigold was 40 to50 9 to 31 and 19 to 21 greaterrespectively for seedlings grown under HPSSL8713 SSL8713 and SSL7030 LEDscompared with AL Leaf number of impa-tiens and petunia was 26 to 34 and 32 to62 greater for seedlings grown under SL orSSL respectively compared with AL Totalleaf area of all species generally increasedunder SL and SSL (Fig 2E and F) Leaf areaof vinca and impatiens seedlings was 20 to134 and 21 to 75 greater for thosegrown under SSL8713 LEDs compared withthe other treatments respectively Leaf areaof geranium was 49 20 and 24 greaterfor seedlings grown under HPS lamps com-pared with those under AL SSL8713 andSSL7030 LEDs respectively

Physiology Relative chlorophyll contentof all species was significantly greater underSL and SSL (Fig 2G and H) The RCC ofimpatiens geranium and petunia seedlingsunder SSL7030 LEDs was 22 to 47 4to 21 and 44 to 85 greater respec-tively compared with those under AL HPSand SL8713 LEDs For marigold RCC wasgreatest under SL and SSL LEDs comparedwith HPS lamps or AL

Fig 1 Spectral quality of 70 mmolmiddotmndash2middotsndash1 delivered from supplemental (SL) high-pressure sodium (HPS)lamps and light-emitting diodes (LEDs) with () 8713 redblue light in the greenhouse or185 mmolmiddotmndash2middotsndash1 delivered from sole-source (SSL) LEDs with 8713 or 7030 redblue light ina growth chamber

HORTSCIENCE VOL 50(5) MAY 2015 707

Fig 2 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on height stem diameter relative chlorophyll content (SPAD) and leaf area of vinca impatiens geranium petunia and marigoldafter 21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test atP 005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

708 HORTSCIENCE VOL 50(5) MAY 2015

Growth Root dry mass (RDM) of allspecies was generally higher under SL andSSL treatments (Fig 3A and B) For exam-ple RDM of vinca impatiens and gera-nium was 104 and 101 81 and 93and 102 and 109 greater for seedlingsgrown under HPS lamps and SSL8713LEDs respectively compared with ALRoot dry mass of petunia was 41 to 57greater under SSL LEDs compared withSL Marigold RDM increased 140 to260 under SL and SSL Shoot dry massof all species was significantly greater un-der SL and SSL (Fig 3C and D) Forexample SDM of vinca impatiens gera-nium petunia and marigold was 74 to154 64 to 164 50 to 82 62 to72 and 59 to 161 greater under SL orSSL respectively compared with AL Ad-ditionally SDM of vinca and impatiensseedlings was 23 to 46 and 21 to61 higher respectively under SSL thanSL

Quality Light treatments significantlyinfluenced the SQ of all species differently(Fig 3E and F) However the SQ ofimpatiens geranium petunia and marigoldwere generally similar when seedlings werepropagated under AL or HPS lamps Forexample the SQ of geranium increased by36 and 30 under SSL7030 LEDs com-pared with seedlings under AL and HPSlamps respectively The SQ of petunia was133 to 306 greater for seedlings grownunder SSL LEDs respectively comparedwith those under AL and SL The QIincreased differently for all species underSL and SSL (Fig 3G and H) For examplethe QI of vinca was 117 higher forseedlings grown under HPS lamps com-pared with AL however for petunia it in-creased by 106 and 129 for seedlingsgrown under SSL8713 and SSL7030 LEDsrespectively compared with AL

Flowering Generally TTF was signifi-cantly reduced when seedlings were grownunder SL or SSL for all species with theexception of impatiens (Fig 4A and B) Timeto flower of impatiens seedlings grown underSSL8713 LEDs was delayed by 8 to 11 dcompared with those grown under AL SLand SSL7030 Height at flower of all specieswith the exception of impatiens and marigoldwas significantly influenced by SL and SSLreceived as a seedling (Fig 4C and D) Forexample height at flower of vinca andpetunia was reduced by 50 and 25 whenseedlings were grown under SSL7030 LEDsrespectively compared with those under ALThe number of nodes below the first openflower was affected differently by the light-ing treatment received as a seedling for allspecies with the exception of marigold andpetunia (Fig 4E and F) For instance theaverage number of nodes at flower for im-patiens was reduced by two under ALcompared with the SSL8713 LEDs Addi-tionally vinca and geranium had an aver-age of one less node when seedlings weregrown under SSL7030 LEDs comparedwith AL

Discussion

Without SL young plants are grown un-der a mean DLI of 6 to 8 molmiddotmndash2middotdndash1 atlatitudes of 35 to 45N during peak pro-duction in January and February (Korczynskiet al 2002) To produce high-quality youngplants greenhouse growers try tomaintain therecommended DLI of 10 to 12 molmiddotmndash2middotdndash1

(Runkle 2007) by providing SL witha PPF of 50 to 80 mmolmiddotmndash2middotsndash1 from HPSlamps (Fisher and Runkle 2004) Thereforewe selected 70 mmolmiddotmndash2middotsndash1 as our targetfor SL to achieve a supplemental DLI of4 molmiddotmndash2middotdndash1

Previous research has shown that beddingplant seedlings were generally more compactwith a larger stem diameter higher SQ andhigher RCC under LED SL providing a redblue light ratio () of 8515 and 7030(Randall and Lopez 2014) In additionWollaeger and Runkle (2013) determinedthat there were no consistent differences inplant growth when bedding plant seedlingswere grown under LED SSL providing or-ange red or hyper-red light They alsosuggested that hyper-red LEDs could beselected over red LEDs as they were 7more efficient the efficiency (mmolmiddotJndash1) ofthe orange red or hyper-red LEDs was 072229 and 246 respectively Previous studieshave also reported that high-intensity SL orSSL containing blue light generally inhibitstem elongation when added to red light(Heo et al 2003 Randall and Lopez 2014Wollaeger and Runkle 2014) For exampleblue light and a combination of blue and redlight resulted in a shorter peduncle lengthof cyclamen (Cyclamen persicum lsquoDixieWhitersquo) than red light alone (Heo et al2003) and more compact bedding plant seed-lings with a combination of red and blue light(Randall and Lopez 2014 Wollaeger andRunkle 2014) Thus we selected commer-cially available LED arrays that provideda light ratio of 8713 red (peak = 664 nm)blue (peak = 466 nm) light for our SL andSSL Therefore the primary objective of ourexperiment was to quantify and compare thegrowth morphology quality and subsequentdevelopment of seedlings grown under ALAL plus SL and SSL while all other envi-ronmental characteristics including temper-ature humidity and DLI were constant

In order for young plants to withstandshipping and mechanical transplanting(Latimer 1998) they must be compact (re-duced leaf area and height) and fully rootedwith a large stem diameter and high RDM(Pramuk and Runkle 2005 Wollaeger andRunkle 2014) The QI is a tool that integratesmorphological parameters such as dry massstem length and diameter that contribute toa high-quality seedling Geranium petuniaand marigold seedlings grown under SSLwere generally more compact darker infoliage color (higher RCC) and had a higherRDM and QI than those grown in the green-house under AL or SL Previous studies havedetermined that the QI of young plants in-creases as DLI increases (Currey et al 2012

2013 Randall and Lopez 2014) For ex-ample as the DLI increased from 12 to123 molmiddotmndash2middotdndash1 the QI of diascia (Diasciabarberae lsquoWink Coralrsquo) and lantana (Lantanacamara lsquoLucky Goldrsquo) rooted cuttings in-creased 960 and 53 respectively (Curreyet al 2013) Similarly the QI of all species inthe current study was greater under both SLand SSL with a DLI of 106 molmiddotmndash2middotdndash1

compared with seedlings under ALwith a DLIof 65 molmiddotmndash2middotdndash1 and the QI of im-patiens geranium and petunia was similaror greater for seedlings grown under SSLcompared with SL

Leaf area of all species in the currentstudy was generally similar or greater underSL compared with AL and under SSLtreatments compared with SL Howeverunder SSL as the percentage of blue lightincreased from 13 to 30 leaf area gen-erally decreased Previous studies havereported that plants under red light typicallyhave greater leaf area than those grown under$13 blue or only blue light (Son and Oh2013 Wollaeger and Runkle 2014) Forexample leaf area of lettuce (Lactuca sativalsquoSunmangrsquo and lsquoGrand Rapid TBRrsquo) in-creased by 325 and 324 respectivelyas the () of red light from LED SSLproviding 171 mmolmiddotmndash2middotsndash1 increased froma ratio of 4159 to 1000 redblue light(Son and Oh 2013) Wollaeger and Runkle(2013) reported that total leaf area of impa-tiens lsquoSuperElfin XP Redrsquo and petunialsquoWave Pinkrsquo seedlings grown under SSLLEDs providing a redblue light ratio () of1000 was 55 to 114 and 57 to 130greater respectively than seedlings grownunder 25 or greater blue light Generallya smaller leaf area is desired in ornamentalyoung plant production as seedlings andcuttings are grown under a dense and compet-itive environment that can induce excessivestem extension due to the shade avoidanceresponse

Additionally studies have also reportedleaf anatomical changes with the addition ofblue light (Saeligboslash et al 1995 Schuerger et al1997) For example leaf thickness of pepperplants (Capsicum annuum) increased whengrown under SSL providing blue light fromblue fluorescent lamps providing a redfar-redblue ratio () of 9811 compared withthose providing a redfar-red ratio of 990 or8317 Therefore we can hypothesize thatblue light promotes an increase in leaf thick-ness and a reduction in leaf area Howeverthe extent to which blue light affects plantgrowth and morphology across species is notfully understood

Relative chlorophyll content generallyincreased for all species investigated as theamount of blue light increased from 7 forHPS lamps to 30 for SSL7030 LEDsSimilarly Son and Oh (2013) reported thatRCC of lettuce lsquoSunmangrsquo and lsquoGrand RapidTBRrsquo increased by 140 and 150 asthe percentage of SSL blue light increasedfrom a redblue light ratio () of 1000 to5347 and 1000 to 7426 respectively How-ever chlorophyll concentration of impatiens

HORTSCIENCE VOL 50(5) MAY 2015 709

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

Fig 2 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on height stem diameter relative chlorophyll content (SPAD) and leaf area of vinca impatiens geranium petunia and marigoldafter 21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test atP 005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

708 HORTSCIENCE VOL 50(5) MAY 2015

Growth Root dry mass (RDM) of allspecies was generally higher under SL andSSL treatments (Fig 3A and B) For exam-ple RDM of vinca impatiens and gera-nium was 104 and 101 81 and 93and 102 and 109 greater for seedlingsgrown under HPS lamps and SSL8713LEDs respectively compared with ALRoot dry mass of petunia was 41 to 57greater under SSL LEDs compared withSL Marigold RDM increased 140 to260 under SL and SSL Shoot dry massof all species was significantly greater un-der SL and SSL (Fig 3C and D) Forexample SDM of vinca impatiens gera-nium petunia and marigold was 74 to154 64 to 164 50 to 82 62 to72 and 59 to 161 greater under SL orSSL respectively compared with AL Ad-ditionally SDM of vinca and impatiensseedlings was 23 to 46 and 21 to61 higher respectively under SSL thanSL

Quality Light treatments significantlyinfluenced the SQ of all species differently(Fig 3E and F) However the SQ ofimpatiens geranium petunia and marigoldwere generally similar when seedlings werepropagated under AL or HPS lamps Forexample the SQ of geranium increased by36 and 30 under SSL7030 LEDs com-pared with seedlings under AL and HPSlamps respectively The SQ of petunia was133 to 306 greater for seedlings grownunder SSL LEDs respectively comparedwith those under AL and SL The QIincreased differently for all species underSL and SSL (Fig 3G and H) For examplethe QI of vinca was 117 higher forseedlings grown under HPS lamps com-pared with AL however for petunia it in-creased by 106 and 129 for seedlingsgrown under SSL8713 and SSL7030 LEDsrespectively compared with AL

Flowering Generally TTF was signifi-cantly reduced when seedlings were grownunder SL or SSL for all species with theexception of impatiens (Fig 4A and B) Timeto flower of impatiens seedlings grown underSSL8713 LEDs was delayed by 8 to 11 dcompared with those grown under AL SLand SSL7030 Height at flower of all specieswith the exception of impatiens and marigoldwas significantly influenced by SL and SSLreceived as a seedling (Fig 4C and D) Forexample height at flower of vinca andpetunia was reduced by 50 and 25 whenseedlings were grown under SSL7030 LEDsrespectively compared with those under ALThe number of nodes below the first openflower was affected differently by the light-ing treatment received as a seedling for allspecies with the exception of marigold andpetunia (Fig 4E and F) For instance theaverage number of nodes at flower for im-patiens was reduced by two under ALcompared with the SSL8713 LEDs Addi-tionally vinca and geranium had an aver-age of one less node when seedlings weregrown under SSL7030 LEDs comparedwith AL

Discussion

Without SL young plants are grown un-der a mean DLI of 6 to 8 molmiddotmndash2middotdndash1 atlatitudes of 35 to 45N during peak pro-duction in January and February (Korczynskiet al 2002) To produce high-quality youngplants greenhouse growers try tomaintain therecommended DLI of 10 to 12 molmiddotmndash2middotdndash1

(Runkle 2007) by providing SL witha PPF of 50 to 80 mmolmiddotmndash2middotsndash1 from HPSlamps (Fisher and Runkle 2004) Thereforewe selected 70 mmolmiddotmndash2middotsndash1 as our targetfor SL to achieve a supplemental DLI of4 molmiddotmndash2middotdndash1

Previous research has shown that beddingplant seedlings were generally more compactwith a larger stem diameter higher SQ andhigher RCC under LED SL providing a redblue light ratio () of 8515 and 7030(Randall and Lopez 2014) In additionWollaeger and Runkle (2013) determinedthat there were no consistent differences inplant growth when bedding plant seedlingswere grown under LED SSL providing or-ange red or hyper-red light They alsosuggested that hyper-red LEDs could beselected over red LEDs as they were 7more efficient the efficiency (mmolmiddotJndash1) ofthe orange red or hyper-red LEDs was 072229 and 246 respectively Previous studieshave also reported that high-intensity SL orSSL containing blue light generally inhibitstem elongation when added to red light(Heo et al 2003 Randall and Lopez 2014Wollaeger and Runkle 2014) For exampleblue light and a combination of blue and redlight resulted in a shorter peduncle lengthof cyclamen (Cyclamen persicum lsquoDixieWhitersquo) than red light alone (Heo et al2003) and more compact bedding plant seed-lings with a combination of red and blue light(Randall and Lopez 2014 Wollaeger andRunkle 2014) Thus we selected commer-cially available LED arrays that provideda light ratio of 8713 red (peak = 664 nm)blue (peak = 466 nm) light for our SL andSSL Therefore the primary objective of ourexperiment was to quantify and compare thegrowth morphology quality and subsequentdevelopment of seedlings grown under ALAL plus SL and SSL while all other envi-ronmental characteristics including temper-ature humidity and DLI were constant

In order for young plants to withstandshipping and mechanical transplanting(Latimer 1998) they must be compact (re-duced leaf area and height) and fully rootedwith a large stem diameter and high RDM(Pramuk and Runkle 2005 Wollaeger andRunkle 2014) The QI is a tool that integratesmorphological parameters such as dry massstem length and diameter that contribute toa high-quality seedling Geranium petuniaand marigold seedlings grown under SSLwere generally more compact darker infoliage color (higher RCC) and had a higherRDM and QI than those grown in the green-house under AL or SL Previous studies havedetermined that the QI of young plants in-creases as DLI increases (Currey et al 2012

2013 Randall and Lopez 2014) For ex-ample as the DLI increased from 12 to123 molmiddotmndash2middotdndash1 the QI of diascia (Diasciabarberae lsquoWink Coralrsquo) and lantana (Lantanacamara lsquoLucky Goldrsquo) rooted cuttings in-creased 960 and 53 respectively (Curreyet al 2013) Similarly the QI of all species inthe current study was greater under both SLand SSL with a DLI of 106 molmiddotmndash2middotdndash1

compared with seedlings under ALwith a DLIof 65 molmiddotmndash2middotdndash1 and the QI of im-patiens geranium and petunia was similaror greater for seedlings grown under SSLcompared with SL

Leaf area of all species in the currentstudy was generally similar or greater underSL compared with AL and under SSLtreatments compared with SL Howeverunder SSL as the percentage of blue lightincreased from 13 to 30 leaf area gen-erally decreased Previous studies havereported that plants under red light typicallyhave greater leaf area than those grown under$13 blue or only blue light (Son and Oh2013 Wollaeger and Runkle 2014) Forexample leaf area of lettuce (Lactuca sativalsquoSunmangrsquo and lsquoGrand Rapid TBRrsquo) in-creased by 325 and 324 respectivelyas the () of red light from LED SSLproviding 171 mmolmiddotmndash2middotsndash1 increased froma ratio of 4159 to 1000 redblue light(Son and Oh 2013) Wollaeger and Runkle(2013) reported that total leaf area of impa-tiens lsquoSuperElfin XP Redrsquo and petunialsquoWave Pinkrsquo seedlings grown under SSLLEDs providing a redblue light ratio () of1000 was 55 to 114 and 57 to 130greater respectively than seedlings grownunder 25 or greater blue light Generallya smaller leaf area is desired in ornamentalyoung plant production as seedlings andcuttings are grown under a dense and compet-itive environment that can induce excessivestem extension due to the shade avoidanceresponse

Additionally studies have also reportedleaf anatomical changes with the addition ofblue light (Saeligboslash et al 1995 Schuerger et al1997) For example leaf thickness of pepperplants (Capsicum annuum) increased whengrown under SSL providing blue light fromblue fluorescent lamps providing a redfar-redblue ratio () of 9811 compared withthose providing a redfar-red ratio of 990 or8317 Therefore we can hypothesize thatblue light promotes an increase in leaf thick-ness and a reduction in leaf area Howeverthe extent to which blue light affects plantgrowth and morphology across species is notfully understood

Relative chlorophyll content generallyincreased for all species investigated as theamount of blue light increased from 7 forHPS lamps to 30 for SSL7030 LEDsSimilarly Son and Oh (2013) reported thatRCC of lettuce lsquoSunmangrsquo and lsquoGrand RapidTBRrsquo increased by 140 and 150 asthe percentage of SSL blue light increasedfrom a redblue light ratio () of 1000 to5347 and 1000 to 7426 respectively How-ever chlorophyll concentration of impatiens

HORTSCIENCE VOL 50(5) MAY 2015 709

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

Growth Root dry mass (RDM) of allspecies was generally higher under SL andSSL treatments (Fig 3A and B) For exam-ple RDM of vinca impatiens and gera-nium was 104 and 101 81 and 93and 102 and 109 greater for seedlingsgrown under HPS lamps and SSL8713LEDs respectively compared with ALRoot dry mass of petunia was 41 to 57greater under SSL LEDs compared withSL Marigold RDM increased 140 to260 under SL and SSL Shoot dry massof all species was significantly greater un-der SL and SSL (Fig 3C and D) Forexample SDM of vinca impatiens gera-nium petunia and marigold was 74 to154 64 to 164 50 to 82 62 to72 and 59 to 161 greater under SL orSSL respectively compared with AL Ad-ditionally SDM of vinca and impatiensseedlings was 23 to 46 and 21 to61 higher respectively under SSL thanSL

Quality Light treatments significantlyinfluenced the SQ of all species differently(Fig 3E and F) However the SQ ofimpatiens geranium petunia and marigoldwere generally similar when seedlings werepropagated under AL or HPS lamps Forexample the SQ of geranium increased by36 and 30 under SSL7030 LEDs com-pared with seedlings under AL and HPSlamps respectively The SQ of petunia was133 to 306 greater for seedlings grownunder SSL LEDs respectively comparedwith those under AL and SL The QIincreased differently for all species underSL and SSL (Fig 3G and H) For examplethe QI of vinca was 117 higher forseedlings grown under HPS lamps com-pared with AL however for petunia it in-creased by 106 and 129 for seedlingsgrown under SSL8713 and SSL7030 LEDsrespectively compared with AL

Flowering Generally TTF was signifi-cantly reduced when seedlings were grownunder SL or SSL for all species with theexception of impatiens (Fig 4A and B) Timeto flower of impatiens seedlings grown underSSL8713 LEDs was delayed by 8 to 11 dcompared with those grown under AL SLand SSL7030 Height at flower of all specieswith the exception of impatiens and marigoldwas significantly influenced by SL and SSLreceived as a seedling (Fig 4C and D) Forexample height at flower of vinca andpetunia was reduced by 50 and 25 whenseedlings were grown under SSL7030 LEDsrespectively compared with those under ALThe number of nodes below the first openflower was affected differently by the light-ing treatment received as a seedling for allspecies with the exception of marigold andpetunia (Fig 4E and F) For instance theaverage number of nodes at flower for im-patiens was reduced by two under ALcompared with the SSL8713 LEDs Addi-tionally vinca and geranium had an aver-age of one less node when seedlings weregrown under SSL7030 LEDs comparedwith AL

Discussion

Without SL young plants are grown un-der a mean DLI of 6 to 8 molmiddotmndash2middotdndash1 atlatitudes of 35 to 45N during peak pro-duction in January and February (Korczynskiet al 2002) To produce high-quality youngplants greenhouse growers try tomaintain therecommended DLI of 10 to 12 molmiddotmndash2middotdndash1

(Runkle 2007) by providing SL witha PPF of 50 to 80 mmolmiddotmndash2middotsndash1 from HPSlamps (Fisher and Runkle 2004) Thereforewe selected 70 mmolmiddotmndash2middotsndash1 as our targetfor SL to achieve a supplemental DLI of4 molmiddotmndash2middotdndash1

Previous research has shown that beddingplant seedlings were generally more compactwith a larger stem diameter higher SQ andhigher RCC under LED SL providing a redblue light ratio () of 8515 and 7030(Randall and Lopez 2014) In additionWollaeger and Runkle (2013) determinedthat there were no consistent differences inplant growth when bedding plant seedlingswere grown under LED SSL providing or-ange red or hyper-red light They alsosuggested that hyper-red LEDs could beselected over red LEDs as they were 7more efficient the efficiency (mmolmiddotJndash1) ofthe orange red or hyper-red LEDs was 072229 and 246 respectively Previous studieshave also reported that high-intensity SL orSSL containing blue light generally inhibitstem elongation when added to red light(Heo et al 2003 Randall and Lopez 2014Wollaeger and Runkle 2014) For exampleblue light and a combination of blue and redlight resulted in a shorter peduncle lengthof cyclamen (Cyclamen persicum lsquoDixieWhitersquo) than red light alone (Heo et al2003) and more compact bedding plant seed-lings with a combination of red and blue light(Randall and Lopez 2014 Wollaeger andRunkle 2014) Thus we selected commer-cially available LED arrays that provideda light ratio of 8713 red (peak = 664 nm)blue (peak = 466 nm) light for our SL andSSL Therefore the primary objective of ourexperiment was to quantify and compare thegrowth morphology quality and subsequentdevelopment of seedlings grown under ALAL plus SL and SSL while all other envi-ronmental characteristics including temper-ature humidity and DLI were constant

In order for young plants to withstandshipping and mechanical transplanting(Latimer 1998) they must be compact (re-duced leaf area and height) and fully rootedwith a large stem diameter and high RDM(Pramuk and Runkle 2005 Wollaeger andRunkle 2014) The QI is a tool that integratesmorphological parameters such as dry massstem length and diameter that contribute toa high-quality seedling Geranium petuniaand marigold seedlings grown under SSLwere generally more compact darker infoliage color (higher RCC) and had a higherRDM and QI than those grown in the green-house under AL or SL Previous studies havedetermined that the QI of young plants in-creases as DLI increases (Currey et al 2012

2013 Randall and Lopez 2014) For ex-ample as the DLI increased from 12 to123 molmiddotmndash2middotdndash1 the QI of diascia (Diasciabarberae lsquoWink Coralrsquo) and lantana (Lantanacamara lsquoLucky Goldrsquo) rooted cuttings in-creased 960 and 53 respectively (Curreyet al 2013) Similarly the QI of all species inthe current study was greater under both SLand SSL with a DLI of 106 molmiddotmndash2middotdndash1

compared with seedlings under ALwith a DLIof 65 molmiddotmndash2middotdndash1 and the QI of im-patiens geranium and petunia was similaror greater for seedlings grown under SSLcompared with SL

Leaf area of all species in the currentstudy was generally similar or greater underSL compared with AL and under SSLtreatments compared with SL Howeverunder SSL as the percentage of blue lightincreased from 13 to 30 leaf area gen-erally decreased Previous studies havereported that plants under red light typicallyhave greater leaf area than those grown under$13 blue or only blue light (Son and Oh2013 Wollaeger and Runkle 2014) Forexample leaf area of lettuce (Lactuca sativalsquoSunmangrsquo and lsquoGrand Rapid TBRrsquo) in-creased by 325 and 324 respectivelyas the () of red light from LED SSLproviding 171 mmolmiddotmndash2middotsndash1 increased froma ratio of 4159 to 1000 redblue light(Son and Oh 2013) Wollaeger and Runkle(2013) reported that total leaf area of impa-tiens lsquoSuperElfin XP Redrsquo and petunialsquoWave Pinkrsquo seedlings grown under SSLLEDs providing a redblue light ratio () of1000 was 55 to 114 and 57 to 130greater respectively than seedlings grownunder 25 or greater blue light Generallya smaller leaf area is desired in ornamentalyoung plant production as seedlings andcuttings are grown under a dense and compet-itive environment that can induce excessivestem extension due to the shade avoidanceresponse

Additionally studies have also reportedleaf anatomical changes with the addition ofblue light (Saeligboslash et al 1995 Schuerger et al1997) For example leaf thickness of pepperplants (Capsicum annuum) increased whengrown under SSL providing blue light fromblue fluorescent lamps providing a redfar-redblue ratio () of 9811 compared withthose providing a redfar-red ratio of 990 or8317 Therefore we can hypothesize thatblue light promotes an increase in leaf thick-ness and a reduction in leaf area Howeverthe extent to which blue light affects plantgrowth and morphology across species is notfully understood

Relative chlorophyll content generallyincreased for all species investigated as theamount of blue light increased from 7 forHPS lamps to 30 for SSL7030 LEDsSimilarly Son and Oh (2013) reported thatRCC of lettuce lsquoSunmangrsquo and lsquoGrand RapidTBRrsquo increased by 140 and 150 asthe percentage of SSL blue light increasedfrom a redblue light ratio () of 1000 to5347 and 1000 to 7426 respectively How-ever chlorophyll concentration of impatiens

HORTSCIENCE VOL 50(5) MAY 2015 709

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

Fig 3 (AndashH) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on root dry mass shoot dry mass sturdiness quotient and quality index of vinca impatiens geranium petunia and marigold after21 or 28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P005 Each bar represents a mean of 10 plants and error bars represent SEs of the mean

710 HORTSCIENCE VOL 50(5) MAY 2015

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

and petunia seedlings was not influenced bySSL treatments providing anywhere froma redblue light ratio () of 0100 to 1000(Wollaeger and Runkle 2014) Although wedid not determine anthocyanin content visu-ally geranium seedling leaves under SSLhad much darker patterns especially underSSL7030 LEDs (Fig 5A and C) Marigoldunder SSL developed dark-purple spotting on

the adaxial and abaxial surface of leaves andthe severity appeared to increase as thepercentage of blue light increased from13 to 30 (Fig 5B) Similarly whenmarigold lsquoDeep Orangersquo was grown underSSL providing a bluegreen light ratio ()1010 with the remaining percentages oforangeredhyper-red light 203030 080006020 04040 02060 and 0080 seedlings

developed a similar leaf disorder on theabaxial surface of the leaves (Wollaegerand Runkle 2013) Previous studies havereported that certain crops grown underultraviolet radiation blue light or far-redlight deficient environments or red dominantenvironments have developed leaf disorderssuch as edema or intumescence Furtherresearch would have to be conducted to

Fig 4 (AndashF) Effect of ambient light (AL) or 70 mmolmiddotmndash2middotsndash1 of supplemental light (SL) delivered from high-pressure sodium (HPS) lamps or light-emittingdiodes [LEDs SL8713 () redblue light] or 185 mmolmiddotmndash2middotsndash1 of sole-source (SSL) light delivered from LEDs [SSL8713 and SSL7030 () redblue light]during seedling production on finish time to flower height at flower and nodes below flower of vinca impatiens geranium petunia and marigold after 21 or28 d Different lowercase letters above each light source within a species are significantly different by Tukeyrsquos honestly significant difference test at P 005Each bar represents a mean of 10 plants and error bars represent SEs of the mean

HORTSCIENCE VOL 50(5) MAY 2015 711

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

determine the exact cause of the purplespotting

Previous studies have reported that as DLIincreases during the young plant stage sub-sequent TTF decreases (Currey et al 2012Lopez and Runkle 2008 Oh et al 2010) Inthe current study vinca and geranium werethe only species that flowered faster whengrown as a seedling under either SL or SSLproviding a higher DLI compared with ALInterestingly TTF of impatiens (day neutralflowering response) seedlings grown underSSL8713 LEDs was delayed up to 11 dcompared with those grown under AL SLor SSL3070 LEDs When the amountof blue light was increased by 17(31 mmolmiddotmndash2middotsndash1) in the SSL3070 LEDsTTFwas reduced by 8 d Similarly Wollaegerand Runkle (2014) reported that impatiens

lsquoSuperElfin XP Redrsquo grown under LEDSSL without blue light had the fewest flowerbuds after 4 weeks and thus a delay in TTFThey postulated that an accelerated flower-ing response such as an increase in flowerbuds with increasing blue light could beattributed to CRY2 cryptochrome activityFor example CRY2 degradation regulatesphotoperiodic flowering response and actson downstream genes including CO and FT(Chaves et al 2011 El-Assal et al 2003)Additionally Meng (2014) reported thatnight interruption lighting with high inten-sity blue light alone and when added to redand far-red light can regulate flowering ofphotoperiodic crops

Conclusions

Supplemental and SSL with blue lightsuppress extension growth and leaf expan-sion resulting in compact young plantswhich is often a desirable characteristic forgreenhouse growers (Randall and Lopez2014 Wollaeger and Runkle 2013 2014)In addition LEDs could be used for SSL inhigh-density multilayer production systemsas an effective alternative to greenhouseproduction systems for annual bedding plantseedling production From the results of ourstudy and that of Wollaeger and Runkle(2014) a general recommendation for SSLof bedding plant seedlings would be to in-clude anywhere from 10 to 30 blue lightdepending on the desired crop-specific attri-butes and costs Further research is necessaryto determine the effects of far-red light inaddition to sole-source red and blue light ongrowth morphology quality and subsequentflowering of day neutral and photoperiodicbedding plant seedlings

Literature Cited

Bourget MC 2008 An introduction to light-emitting diodes HortScience 431944ndash1946

Chaves I R Pokorny M Byrdin N HoangT Ritz K Brettel L-O Essen GTJ vander Horst A Batschauer and M Ahmad2011 The cryptochromes Blue light photore-ceptors in plants and animals Annu Rev PlantBiol 62335ndash364

Currey CJ VA Hutchinson and RG Lopez2012 Growth morphology and quality ofrooted cuttings of several herbaceous annualbedding plants are influenced by photosyn-thetic daily light integral during root develop-ment HortScience 4725ndash30

Currey CJ and RG Lopez 2013 Cuttings ofImpatiens Pelargonium and Petunia propagatedunder light-emitting diodes and high-pressuresodium lamps have comparable growth mor-phology gas exchange and post-transplant per-formance HortScience 48428ndash434

Currey CJ AP Torres RG Lopez and DFJacobs 2013 The quality index A new tool forintegrating quantitativemeasurements to assessquality of young floriculture plants Acta Hort1000385ndash391

El-Assal SED C Alonso-Blanco AJM PeetersC Wagemaker JL Weller and M Koornneef2003 The role of cryptochrome 2 in flowering inArabidopisis Plant Physiol 1331504ndash1516

Fisher P and AJ Both 2004 Supplementallighting technology and costs p 43ndash46 InP Fisher and E Runkle (eds) Lightingup profits Understanding greenhouse light-ing 1st ed Meister Media WorldwideWilloughby OH

Fisher P and E Runkle 2004 Managing light-ing in the greenhouse ndash Why is it importantp 9ndash17 In P Fisher and E Runkle (eds)Lighting up profits Understanding green-house lighting Meister Media WorldwideWilloughby OH

Folta KM and KS Childers 2008 Light asa growth regulator Controlling plant biologywith narrow-bandwidth solid-state lighting sys-tems HortScience 431957ndash1964

Heo JW CW Lee and KY Paek 2006 In-fluence of mixed LED radiation on the growthof annuals J Plant Biol 49286ndash290

Heo JW CW Lee HN Murthy and KY Paek2003 Influence of light quality and photope-riod on flowering of Cyclamen persicum Millcv lsquoDixie Whitersquo Plant Growth Regulat407ndash10

Hutchinson VA CJ Currey and RG Lopez2012 Photosynthetic daily light integral dur-ing root development influences subsequentgrowth and development of several herba-ceous annual bedding plants HortScience47856ndash860

Klopmeyer M M Wilson and CA Whealy2003 Propagating vegetative crops p 165ndash180 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Korczynski PM J Logan and JE Faust 2002Mapping monthly distribution of daily lightintegrals across the contiguous United StatesHortTechnology 1212ndash16

Latimer JG 1998 Mechanical conditioning tocontrol height HortTechnology 8529ndash534

Lopez RG and ES Runkle 2008 Photosyn-thetic daily light integral during propagationinfluences rooting and growth of cuttingand subsequent development of NewGuinea impatiens and petunia HortScience432052ndash2059

Meng Q 2014 Investigating use of blue red far-red light from light-emitting diodes to regulateflowering of photoperiodic ornamental cropsMich State Univ East Landing MS ThesisAbstr 1560317

Oh W ES Runkle and RM Warner 2010Timing and duration of supplemental lightingduring the seedling stage influence quality andflowering in petunia and pansy HortScience451332ndash1337

Pramuk LA and ES Runkle 2005 Photosyn-thetic daily light integral during the seedlingstage influences subsequent growth and flower-ing of Celosia Impatiens Salvia Tagetes andViola HortScience 401336ndash1339

Randall WC and RG Lopez 2014 Comparisonof supplemental lighting from high-pressuresodium lamps and light-emitting diodes duringbedding plant seedling production Hort-Science 49589ndash595

Runkle ES 2007 Maximizing supplementallighting Greenhouse Product News 17(11)66

Saeligboslash A T Krekling and M Appelgren 1995Light quality affects photosynthesis and leafanatomy of birch plantlets in vitro Plant CellTissue Organ Cult 41177ndash185

Schuerger AC CS Brown and EC Stryjewski1997 Anatomical features of pepper plants(Capsicum annuum L) grown under red light-emitting diodes supplemented with blue or far-red light Ann Bot (Lond) 79273ndash282

Fig 5 (A) Plug trays of geranium seedlings grownunder ambient light 70 mmolmiddotmndash2middotsndash1 of SLdelivered from high-pressure sodium (HPS)lamps light-emitting diodes (LEDs) provid-ing a redblue light ratio () of 8713 sole-source LEDs providing a redblue light ratio() of 8713 and 7030 from left to right(B) Dark-purple pattern on geranium leavesunder LED sole-source lighting (SSL) providinga redblue light ratio () of 7030 (C) Dark-purple spotting on the adaxial and abaxial surfaceof French marigold leaves under SSL

712 HORTSCIENCE VOL 50(5) MAY 2015

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713

Sherrard T 2003 Supplemental lighting p 137ndash

140 In C Beytes (ed) Ball redbook green-

houses and equipment Volume two 17th ed

Ball Publishing Batavia ILSon K-H and M Oh 2013 Leaf shape growth

and antioxidant phenolic compounds of two

lettuce cultivars grown under various combi-

nations of blue and red light-emitting diodes

HortScience 48988ndash995

Spaargaren IJJ 2001 Supplemental lighting forgreenhouse crops 2nd ed PL Light SystemsInc Beamsville Ontario Canada

Stutte GW 2009 Light-emitting diodes for ma-nipulating the phytochrome apparatus Hort-Science 44231ndash234

Styer C 2003 Propagating seed crops p 151ndash163 In D Hamrick (ed) Ball redbook cropproduction Volume two 17th ed Ball Pub-lishing Batavia IL

Wollaeger HM and ES Runkle 2013 Growth

responses of ornamental annual seedlings

under different wavelengths of red light pro-

vided by light-emitting diodes HortScience

481478ndash1483Wollaeger HM and ES Runkle 2014 Growth of

impatiens petunia salvia and tomato seed-

lings under blue green and red light-emitting

diodes HortScience 49734ndash740

HORTSCIENCE VOL 50(5) MAY 2015 713