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HORTSCIENCE 53(4):496–503. 2018. https://doi.org/10.21273/HORTSCI12785-17Responses of Sweet Basil to DifferentDaily Light Integrals in Photosynthesis,Morphology, Yield, and NutritionalQualityHaijie DouDepartment of Horticultural Sciences, Texas A&M University, CollegeStation, TX 77843Genhua Niu1Department of Horticultural Sciences, Texas A&M AgriLife Research Centerat El Paso, Texas A&M University System, 1380 A&M Circle, El Paso, TX79927Mengmeng GuDepartment of Horticultural Sciences, Texas A&M AgriLife ExtensionService, College Station, TX 77843Joseph G. MasabniDepartment of Horticultural Sciences, Texas A&M AgriLife Research andExtension Center, Texas A&M University System, 1710 FM 3053 N, Overton,TX 75684Additional index words. Gas exchange rate, Chl a/b, indoor controlled environment, artificiallighting, phenolics, antioxidant capacityAbstract. Consumption of basil (Ocimum basilicum) has been increasing worldwide inrecent years because of its unique aromatic flavor and relatively high concentration ofphenolics. To achieve a stable and reliable supply of basil, more growers are turning toindoor controlled-environment production with artificial lighting due to its highenvironmental controllability and sustainability. However, electricity cost for lightingis a major limiting factor to the commercial application of indoor vertical farming, andlittle information is available on the minimum light requirement to produce uniform andhigh-quality sweet basil. To determine the optimal daily light integral (DLI) for sweetbasil production in indoor vertical farming, this study investigated the effects of fiveDLIs, namely, 9.3, 11.5, 12.9, 16.5, and 17.8 mol·mL2·dL1 on basil growth and quality.‘Improved Genovese Compact’ sweet basil was treated with five DLIs provided by whitefluorescent lamps (FLs) for 21 d after germination, and gas exchange rate, growth, yield,and nutritional quality of basil plants were measured to evaluate the effects of thedifferent DLIs on basil growth and quality. Results indicated that basil plants grownunder higher DLIs of 12.9, 16.5, or 17.8 mol·mL2·dL1 had higher net photosynthesis,transpiration, and stomatal conductance (gS), compared with those under lower DLIs of9.3 and 11.5 mol·mL2·dL1. High DLIs resulted in lower chlorophyll (Chl) a bconcentration per leaf fresh weight (FW), higher Chl a/b ratios, and larger and thickerleaves of basil plants. The shoot FW under DLIs of 12.9, 16.5, and 17.8 mol·mL2·dL1 was54.2%, 78.6%, and 77.9%, respectively, higher than that at a DLI of 9.3 mol·mL2·dL1. Inaddition, higher DLIs led to higher soluble sugar percent and dry matter percent thanlower DLIs. The amounts of total anthocyanin, phenolics, and flavonoids per plant ofsweet basil were also positively correlated to DLIs, and antioxidant capacity at a DLI of17.8 mol·mL2·dL1 was 73% higher than that at a DLI of 9.3 mol·mL2·dL1. Combining theresults of growth, yield, and nutritional quality of sweet basil, we suggest a DLI of 12.9mol·mL2·dL1 for sweet basil commercial production in indoor vertical farming tominimize the energy cost while maintaining a high yield and nutritional quality.Sweet basil (O. basilicum) is often referred as the ‘‘king of herbs’’ or the ‘‘royalherb’’ and is widely used in cooking andmedicinal practices, as well as a fragrant,ornamental plant for gardens and containersbecause of its unique flavor and relativelyhigh content of phenolic compounds (Chianget al., 2005; Kruma et al., 2008; Makri andKintzios, 2008). The United States is both the496largest producer and importer of basil in theworld, with most of its production in openfields (DAFF, 2012). However, the yield andquality of essential oils and phenolics of basilgrown outdoors is hard to control and itsphytochemical concentration varies widelywith cultivation location, season, and cultivar(Fischer et al., 2011; Hassanpouraghdamet al., 2010; Pushpangadan and George,2012). To achieve a stable and reliable supplyof basil, more growers are turning to indoorcontrolled-environment production, whichhas proven to be a suitable alternative toopen field and greenhouse production (Liaroset al., 2016; Saha et al., 2016).Indoor vertical farming, also known as‘‘plant factory,’’ is a highly controlled environmental system for plant production thatuses multiple-layer culture shelves with artificial lighting (Despommier, 2010; Kozaiet al., 2015). In consideration of globalclimate change and increasing urban populations, food security is an increasingly pressing matter, especially considering limitedresources such as arable land, clean water,and fuel energy (Dunwoody, 2014; Liaroset al., 2016). Indoor vertical farming emergedas an environmentally sustainable form ofplant production because of its high resourceuse efficiency of both land and water(Despommier, 2013; Kozai, 2013; Kozaiet al., 2015; Touliatos et al., 2016). Theutilization efficiency of land, water, CO2,and light energy in indoor vertical farmingwere 100, 40, 2, and 1.7 times of those ingreenhouses, respectively (Kozai, 2007;Ohyama et al., 2003; Yokoi et al., 2005). Inrecent years, the number of indoor verticalfarming facilities has increased rapidly inJapan, China, and other Asian countries(Kozai et al., 2015). In North America,vertical farming has been built for commercial production of leafy greens, herbs, andtransplants (Kozai et al., 2015). For example,AeroFarms, an enterprise specializing onindoor farming, built its ninth farm inNewark, NJ, and is the world’s largestindoor vertical farm based on annual output (AeroFarms, 2017). As one of the mostpopular herbs in the United States, sweetbasil is a great candidate plant for indoorvertical farming because of its high value anddemand (Liaros et al., 2016).Light is one of the most important environmental factors that affects plant development and regulates plant behavior dependingon light quantity, quality, direction, andduration (Chang et al., 2008; Dou et al.,2017; Figueiredo et al., 2008; ShafieeHajiabad et al., 2016). Daily light integral[the product of photosynthetic photon fluxdensity (PPFD) and photoperiod] representsthe total PPF radiated by a light source in24 h and usually has a linear relationshipwith crop yield and nutrient accumulation(Bochenek and Fallstrom, 2016; Colonnaet al., 2016; Dai et al., 2009). Basil originatesin tropical and subtropical regions and isadapted to moderately high PPFD and longday irradiation (Pushpangadan and George,2012). However, artificial lighting accountsfor 80% of total electricity consumption inan indoor vertical farm, which makes energyconservation one of the biggest concerns forits commercial application (Ohyama et al.,2002). DLIs of 12–17 mol·m–2·d–1 are recommended for vegetables and herbs in vertical farming in terms of energy savings(Albright et al., 2000; Kozai et al., 2015). Afew studies explored the effects of DLIs fromHORTSCIENCE VOL. 53(4) APRIL 2018

13.5 to 34.6 mol·m–2·d–1 on basil growth anddevelopment (Beaman et al., 2009; Changet al., 2008), but no study has determined theoptimum DLI between 12 and 17 mol·m–2·d–1for sweet basil production under indoorcontrolled environment. Between DLIs of17.3 and 23.0 mol·m–2·d–1, no differences inplant height, canopy diameter, or shoot yieldamong ‘Genovese’, ‘Italian Large Leaf’, and‘Nufar’ basil were observed, which werelower than the basil grown under DLIs of28.8 and 34.6 mol·m–2·d–1 in a growth chamber, respectively (Beaman et al., 2009). Ina glasshouse condition, there was no difference in photosynthesis of ‘Genovese’ basilbetween DLIs of 13.5 mol·m–2·d–1 (lightshading in a glasshouse) and 24.9 mol·m–2·d–1(full sunlight), whereas a DLI of 5.3 mol·m–2·d–1(heavy shading) significantly reduced thephotosynthetic rate, leaf area per plant, shootFW per plant, and total essential oils concentration (Chang et al., 2008). The total amountof essential oil of basil ‘Bageco’ increasedsignificantly with supplemental radiationprovided by high-pressure sodium-vaporlamp compared with plants grown undersunlight (Nitz and Schnitzler, 2004). Basedon these circumstances, the objective of thisarticle was to determine the minimum DLIfor sweet basil production with comparablenutritional values in indoor vertical farming.Materials and MethodsPlant materials and culture. The experiment was conducted in a large walk-ingrowth room with multiple ‘‘book-shelfstands’’ each with four vertical layers spaced25 cm apart at the Texas AgriLife Researchand Extension Center at El Paso, TX, from7 Mar. to 26 Apr. 2017 and repeated from17 Apr. to 29 May. ‘Improved GenoveseCompact’ sweet basil (Johnny’s SelectedSeeds, Winslow, ME) was used in bothexperiments. For both experiments, one basilseed per cell was sown in 72 square cell trays(length 3.86 cm, height 5.72 cm, and volume59 mL) with all-purpose commercial mixMetro-Mix 360 (Sun GroÒ Horticulture, Bellevue, WA). All trays were put under mist ina greenhouse for germination. The seedlingswere moved out from mist after germinationand grown in a greenhouse for 2 weeks. Theseedlings were then transplanted to 4 squarepots (length 9.52 cm, height 8.26 cm, andvolume 574 mL) with Metro-Mix 360 whenroots were visible on the outside of the plugReceived for publication 14 Dec. 2017. Acceptedfor publication 23 Feb. 2018.This research is supported partially by the USDANational Institute of Food and Agriculture Hatchproject TEX090450 and Texas A&M AgriLifeResearch.We appreciate the assistance from Youping Sun,Christina Perez, Triston Hooks, and the studentworkers at the Texas A&M AgriLife ResearchCenter at El Paso, TX.1Corresponding author. E-mail: gniu@ag.tamu.edu.HORTSCIENCE VOL. 53(4) APRIL 2018root ball, and uniform plants were selectedand moved to the walk-in growth room fordifferent DLI treatments for 21 d.Treatments. The experiment was conducted as a completely randomized design witha single factor (DLI) at five levels, 9.3, 11.5,12.9, 16.5, and 17.8 mol·m–2·d–1 (hereafter,DLI 9.3, DLI 11.5, DLI 12.9, DLI 16.5, andDLI 17.8, respectively), created by growingbasil plants under five different PPFD of 160,200, 224, 290, or 310 mmol·m–2·s–1, respectively, with the same 16-h photoperiod provided by Cool White Alto Linear FLs (PhilipsLighting, Somerset, NJ). All treatments wererandomly arranged in the growth room and18 uniform plants were randomly assignedfor each treatment (replications). For eachgrowing layer (treatment), mechanical minifans (LS1225A-X; AC Infinity, City of Industry, CA), temperature sensor, and reflective aluminum sheets were installed to keepa uniform growing environment among treatments. To minimize light distribution beingdisproportionate within each treatment, allplants were systematically rearranged every3 d. The PPFD in each treatment was measured at 15 cm from FLs at nine points usingPS-100 spectroradiometer (Apogee Instruments, Logan, UT). All plants were subirrigated with a nutrient solution containing 1.85g·L–1 (277.5 ppm N) 15N–2.2P–12.5K (Peters15–5–15 Ca–Mg Special; The Scotts Company, Marysville, OH) according to plants’water requirement, maintaining an electricalconductivity of 2.0 dS·m–1 and a pH of 6.0 asrecommended (Kiferle et al., 2011; Parket al., 2016; Sgherri et al., 2010; Waltersand Currey, 2015). Plant canopy temperatures in each treatment were recorded andmaintained at 24.5 C/21.3 C day/night. Thebasil plants in the first experiment weretransplanted 3 d later than the plants in thesecond experiment and basil plants that hada higher yield in the first experiment whenharvest; however, both experiments showeda similar trend, so only data from the secondexperiment are presented.Growth characteristics. The growth characteristics such as plant height, two perpendicular widths, and the number of internodeswere recorded on day 1 (D1) of the treatmentand then weekly. Six plants per treatmentwere randomly selected for measurement.Height and two perpendicular widths of thefirst branch of basil plants were measured onD21, the end of the experiment. Leaf area perplant was measured using a leaf area meter(LI-3100; LI-COR, Lincoln, NE), and shootand root FW per plant were recorded on D21.The shoot and root tissues were dried at 80 Cin a drying oven (Grieve, Round Lake, IL) for3 d to determine the dry weight (DW) perplant.Gas exchange and Chl concentrationanalysis. A portable gas exchange analyzer(CIRAS-3; PP Systems International, Amesbury,MA) was used to measure the gas exchangerate of basil leaves on D20. A PLC3 leafcuvette with an LED light unit was used, andPPFD, relative air humidity, and CO2 concentration inside the leaf chamber were keptconstant at 800 mmol·m–2·s–1, 50%, and 390mmol·mol–1, respectively. The soil plant analysis development (SPAD) index of basil wasrecorded weekly to quantify relative Chlconcentration per leaf area in basil leavesusing a Chl meter SPAD-502 (KonicaMinolta cooperation, Ltd., Osaka, Japan).On D21, 0.2 g of basil leaves were cut intosmall pieces and then extracted in 80%methanol (v/v) for 3 d. The absorbance ofextracts was measured at 663 and 645 nmusing a spectrophotometer (Genesys 10Sultraviolet/Vis; Thermo Fisher Scientific,Madison, WI), and the concentrations ofChl a and Chl b were calculated accordingto Porra et al. (1989) and were used tocalculate Chl a b concentration and Chla/b ratio.Nutritional quality measurement. Sixplants per treatment were randomly selectedfor measurements of soluble sugar percent(%), anthocyanin concentration, total phenolic concentration, total flavonoid concentration, and antioxidant capacity of basil leaveson D21 to evaluate the effects of DLIs onbasil nutritional quality. The soluble sugarpercent of fresh basil leaves was measuredusing a Brix refractometer (Extech Instruments, Nashua, NH). Fresh basil leaveswere collected and stored in a deep freezer at–80 C (IU1786A; Thermo Fisher Scientific,Marietta, OH) until phytochemical analysis.About 2 g of fresh basil leaves were ground inliquid nitrogen and extracted with 15 mL 1%acidified methanol in darkness. After overnight extraction, the mixture was centrifugedat 13,200 rpm for 15 min and the supernatantwas collected for analysis. The absorbance ofextracts was measured at 530 nm using aspectrophotometer mentioned previously andthe anthocyanin concentration was expressedas milligram cyanidin-3-glucoside equivalents using a molar extinction coefficient of29,600.The total phenolic concentration of basilleaves was determined using the modifiedFolin–Ciocalteu reagent method (Xu andMou, 2016) described as follows: a 100-mLextraction sample was added to a mixture of150-mL distilled water and 750 mL 1/10dilution Folin–Ciocalteu reagent; after 6-minreaction, 600 mL 7.5% Na2CO3 was added tothe mixture. The mixture was incubated at45 C in a water bath for 10 min before theabsorbance was measured at 725 nm usinga microplate reader (ELx800; BioTek,Winooski, VT). Results were expressed asmilligram gallic acid equivalent per gram FWof basil leaves. For total flavonoid concentration, a 20-mL extract was mixed with85 mL distilled water and 5 mL 5% NaNO2.After 6 min, 10 mL 10% AlCl3·6H2O wasadded. After another 5 min, 35 mL 1 M NaOHand 20 mL distilled water was added and thenthe absorbance was measured at 520 nmusing the microplate reader mentioned previously. The results were expressed as milligram of ( ) catechin hydrate equivalent pergram FW of basil leaves. The amounts oftotal anthocyanin, phenolic compound, andflavonoid per plant were calculated by497

multiplying the concentration of anthocyanin, phenolic compound, and flavonoid byleaf FW per plant.The total antioxidant capacity of basilleaves was measured using the ferrous ionchelating activity (FICA) method (Xu andMou, 2016) described as follows: a mixtureof 24-mL extracts, 1.20 mL methanol, and16 mL 2 mM ferrous chloride were vortexedvigorously. Thirty-two microliters of 5 mMferrozine was then added and mixed vigorously, and the absorbance of mixture wasmeasured at 562 nm after 4-min reactionusing the spectrophotometer mentioned previously. The total antioxidant capacity wascalculated as the absorbance difference between control (Acontrol) and sample (Asample):total antioxidant capacity (%, FICA) 100 ·(Acontrol – Asample)/Acontrol.Statistical analysis. One-way analysis ofvariance was conducted to test the effects ofDLI on all measured parameters. Mean comparison among treatments was conductedusing Student’s t method. Correlation testwas conducted using the pairwise correlations method. All statistical analyses wereperformed using JMP (version 13; SAS Institute Inc., Cary, NC).ResultsPhotosynthesis and Chl concentration ofbasil leaves under different DLIs. The relative Chl concentration per leaf area andSPAD readings increased significantly asbasil growth stage developed and DLI increased (Fig. 1A). SPAD for treatments DLI9.3, DLI 11.5, and DLI 12.9 increased from30 to 37 after 21 d of treatment, whereasthose in the DLI 16.5 and DLI 17.8 treatments increased to 41, which was 11%higher (Fig. 1A). In contrast, no differencein Chl a concentration per leaf FW wasobserved among the five different DLIs onD21, whereas Chl b concentration was higherfor treatments DLI 9.3 and DLI 11.5, andlower for treatments DLI 12.9, DLI 16.5,and DLI 17.8 (Fig. 1B). Higher levels of Chla/b ratio (Fig. 1C) and lower levels of Chl a bconcentration (Fig. 1B) were observed fortreatments DLI 12.9, DLI 16.5, and DLI 17.8.The Chl a b concentration per leaf FW fortreatments DLI 9.3 and DLI 11.5 were 17%higher than that of basil grown under treatments DLI 12.9, DLI 16.5, and DLI 17.8(Fig. 1B).The leaf net photosynthetic rate per leafarea (Pnleaf), transpiration, and gS of basilleaves increased significantly as DLI increased and were the highest for treatmentsDLI 12.9, DLI 16.5, and DLI 17.8 (11.5, 10.6,and 10.4 mmol·m–2·s–1), followed by treatments DLI 9.3 and DLI 11.5 (6.1 and 7.8mmol·m–2·s–1), respectively (Table 1). Pnleaffor treatments DLI 12.9 was 86% and 47%higher than that for treatments DLI 9.3 andDLI 11.5, respectively, and no differenceamong treatments DLI 12.9, DLI 16.5, orDLI 17.8 was observed (Table 1). Transpiration for treatment DLI 12.9 was 78% and57% higher than that for treatments DLI 9.3498Fig. 1. Relative chlorophyll (Chl) concentration per leaf area (soil plant analysis development) of basilleaves from day 1 to day 21 (A); Chl a, Chl b, and Chl a b concentration per leaf FW (B); and Chla/b ratio (C) of ‘Improved Genovese Compact’ sweet basil grown for 21 d at different daily lightintegrals in indoor controlled environment. Means with the same letters within a group are notsignificantly different according to Student’s t mean comparison (P 0.05). FW fresh weight.Table 1. Net photosynthetic rate per leaf area, transpiration, substomatal CO2 concentration, and stomatalconductance of ‘Improved Genovese Compact’ sweet basil leaves grown for 20 d at different dailylight integrals (DLIs) in indoor controlled environment. A portable gas exchange analyzer CIRAS-3was used to measure the gas exchange rate of basil leaves at the end of the experiment.TranspirationSubstomatal CO2Stomatal conductanceNet photosynthetic(mmol·m–2·s–1)concn (mmol·mol–1)(mmol·m–2·s–1)Treatmentrate (mmol·m–2·s–1)1.26 c266 a86 bDLI 9.36.1 czDLI 11.57.8 bc1.43 bc255 a106 bDLI 12.911.5 a2.24 a269 a194 aDLI 16.510.6 a2.01 a273 a172 aDLI 17.810.4 ab1.85 ab252 a142 abzMeans followed by the same letters are not significantly different within a column, according to Student’s tmean comparison (P 0.05).and DLI 11.5, whereas gS for treatments DLI12.9 was 126% and 83% higher than that fortreatments DLI 9.3 and DLI 11.5, respectively(Table 1).Morphological differences of basilinfluenced by DLIs. Basil plants grown underhigher DLIs had a larger canopy because ofincreased height and widths (Table 2) but hadHORTSCIENCE VOL. 53(4) APRIL 2018

Table 2. Plant height and width of ‘Improved Genovese Compact’ sweet basil on 1, 7, 14, and 21 d after transplanting at different daily light integrals (DLIs) inindoor controlled environment.Day 1Day 7Day 14Day 21TreatmentHt (cm)Width (cm)Ht (cm)Width (cm)Ht (cm)Width (cm)Ht (cm)Width (cm)5.1 a5.3 a7.7 b10.1 b10.2 b17.4 c12.5 bDLI 9.33.9 azDLI 11.53.8 a5.4 a5.5 a7.8 b12.1 a10.5 ab20.2 b13.0 abDLI 12.94.0 a5.2 a6.1 a8.3 ab12.7 a10.9 a22.1 a12.8 abDLI 16.53.7 a4.9 a6.0 a8.1 ab12.9 a11.0 a23.3 a13.0 abDLI 17.83.8 a5.1 a6.3 a8.6 a13.0 a10.8 a23.0 a13.4 azMeans followed by the same letters are not significantly different within a column, according to Student’s t mean comparison (P 0.05).Table 3. Leaf area per plant, specific leaf area, and first branch height and width of ‘Improved Genovese Compact’ sweet basil grown for 21 d at different dailylight integrals (DLIs) in indoor controlled environment.Specific leaf areaz (cm2·g–1, DW)Ht of first branch (cm)Width of first branch (cm)TreatmentLeaf area per plant (cm2/plant)518 a2.9 c3.8 bDLI 9.3406 byDLI 11.5454 b480 ab4.5 b5.0 aDLI 12.9560 a462 b5.4 ab5.7 aDLI 16.5609 a389 c6.2 a5.7 aDLI 17.8614 a398 c6.3 a5.9 azSpecific leaf area leaf area per unit leaf dry weight (DW).yMeans followed by the same letters are not significantly different within a column, according to Student’s t mean comparison (P 0.05).similar number of internodes (data not presented). The plant widths responded faster toDLIs than plant height, with visible difference after 1-week DLI treatment, whereas ittook 2 weeks for plant height to showdifference among treatments. On D21, theplant height was the greatest for treatmentsDLI 12.9, DLI 16.5, and DLI 17.8 (22.1, 23.3,and 23.0 cm, respectively), followed by DLI11.5 (20.2 cm), and was the lowest for DLI9.3 (17.4 cm). Although the plant widthsshowed visual differences earlier than theheight, the differences among five DLI treatments were small (Table 2).Basil plants grown under higher DLIs hadlarger and thicker leaves, as well as greaterbranch height and widths (Table 3). With thesame number of leaves, the leaf area per plantfor treatment DLI 17.8 was 51% and 35%higher than that for treatments DLI 9.3 andDLI 11.5, whereas its specific leaf area (leafarea per unit leaf DW) was 30% and 21%lower, respectively. Lower specific leaf areaunder higher DLIs indicated that the thickness of basil leaves increased as DLIs increased. In addition to plant height andwidths, the branching of basil was alsopositively correlated with DLIs. There weretwo pairs of fully expanded leaves for the firstbranch of basil plants grown under treatmentsDLI 12.9, DLI 16.5, and DLI 17.8, whereasonly one pair of fully expanded leaves fortreatment DLI 9.3 (data not presented), whichcontributed to increased branch height andwidths under higher DLIs (Table 3).Plant growth and yield of basil underdifferent DLIs. The highest shoot FW perplant was observed in treatments DLI 12.9,DLI 16.5, and DLI 17.8 (20.2, 23.4, and 23.3 g,respectively), followed by DLI 11.5 (15.7 g),whereas DLI 9.3 (13.1 g) exhibited the lowestvalue (Fig. 2A). The fresh leaf and stemweight had the similar trend as fresh shootyield, whereas the root FW per plant was thehighest in treatments DLI 16.5 and DLI 17.8,followed by DLI 12.9, then DLI 11.5, andwas the lowest in DLI 9.3. The leaf DW perplant was more sensitive to DLIs than leafHORTSCIENCE VOL. 53(4) APRIL 2018Fig. 2. Leaf, stem, shoot, and root fresh weight (A) per plant and dry weight (B) per plant of ‘ImprovedGenovese Compact’ sweet basil grown for 21 d at different daily light integrals in indoor controlledenvironment. Means with the same letters within a group are not significantly different according toStudent’s t mean comparison (P 0.05).FW, and significant difference was observedamong treatments DLI 12.9, DLI 16.5, andDLI 17.8 (1.22, 1.58, and 1.55 g, respectively) (Fig. 2B). The shoot DW per plant hada similar pattern with leaf DW, whereas shootDW per plant in DLI 17.8 was more than 2fold than that in DLI 9.3. The shoot FW andDW per plant were both positively correlatedwith DLIs at the time of harvest on D21, withcorrelation coefficients of 0.86 and 0.88,respectively (Fig. 3A). The shoot dry matterpercent of basil was also positively influ-enced by DLIs, ranging from 6.7% to 9.2%(Fig. 3B).Nutritional quality of basil leaves underdifferent DLIs. The soluble sugar percent,total phenolic concentration, and total flavonoid concentration of basil leaves increasedwith DLIs and were 52%, 35%, and 85%higher in treatment DLI 17.8 compared withDLI 9.3, respectively (Table 4). There was nodifference for anthocyanin concentrationamong different DLIs, ranging from 2.60 to2.82 mg·100 g–1 leaf FW (Table 4). The499

increased phenolic compound and flavonoidconcentration of basil leaves led to higherantioxidant capacities with increasing DLIs,which was 73% higher in treatment DLI 17.8than DLI 9.3 (Table 4). Because of higherleaf FW per plant under higher DLIs, theamounts of total anthocyanin, phenolic, andflavonoid per plant were positively correlatedwith DLIs with correlation coefficients of0.84, 0.96, and 0.89 respectively (Fig. 4).DiscussionPhotosynthetic capacity, Chl concentration,leaf morphology, growth, and yield of sweetbasil. As the vital factor affecting plantphotosynthesis, DLI or PPFD alters leaf Chlconcentration to maximize photosyntheticefficiency and productivity (Retkute et al.,2015; Wittmann et al., 2001). In this study,the Pnleaf of sweet basil increased from 6.1mmol·m–2·s–1 in treatment DLI 9.3 (relativelylow PPFD of 160 mmol·m–2·s–1) to 10.4mmol·m–2·s–1 in treatment DLI 17.8 (relatively high PPFD of 310 mmol·m–2·s–1)(Table 1), inferring that the light saturationpoint of sweet basil is higher than 310mmol·m–2·s–1 under this environment. Similarly, Polyakova et al. (2015) reported thatthe Pnleaf of ‘Ararat’ basil grown for 30 dFig. 3. Correlation between shoot fresh weight per plant, shoot dry weight per plant (A), and dry matterpercent (B) with daily light integrals of ‘Improved Genovese Compact’ sweet basil grown for 21 d atdifferent DLIs in indoor controlled environment. Correlation test was conducted using pairwisecorrelations method.under 240–260 mmol·m–2·s–1 provided byinduction lamps was more than twice higherthan that of plants grown under 80–85mmol·m–2·s–1 provided by white LEDs. Onereason for the increased Pnleaf of high-lightleaves is their generally higher Chl concentration per leaf area (Lichtenthaler et al.,2007). Pnleaf represents the sum of individualcell CO2 assimilation, and the thinner leavesunder lower DLIs contain significantly lesscells per leaf area as compared with thickerleaves under higher DLIs (Table 3), whichconsequently resulted in lower Chl concentration per leaf area (SPAD) and Pnleaf(Fig. 1A; Table 1). SPAD reading of plantswas mainly associated with a greater amountof nitrogen per leaf area, as well as higherconcentration of RuBisCo enzyme, and subsequently resulted in increased photosynthesis (Lichtenthaler, 1985). Increased SPADreading also led to darker green leaves ofbasil plants under higher DLIs, which play animportant role for consumers making purchasing decisions (Rouphael et al., 2012).Basil plants under higher DLIs exhibitedhigher Pn not only on leaf area basis but alsoon Chl basis and leaf DW basis (Fig. 5),which could be explained by the possessionof chloroplasts adapted to higher PPFD underhigher DLIs. The high-light–adapted chloroplasts had higher photosynthetic quantumconversion rate with adapted ultrastructure,biochemical organization and a special arrangement of Chls, and carotenoids in thethylakoids under higher DLIs, resulting inincreased Pn on Chl basis and leaf DW basis(Lichtenthaler et al., 2007).In contrast to Chl concentration on leafarea basis, basil leaves under lower DLIs hada significantly higher Chl a b concentrationper leaf FW, and treatment DLI 9.3 was up to16% higher than treatment DLI 17.8(Fig. 1B). This result was consistent withthe Chl a b concentration of ‘Ararat’ basiland Glycyrrhiza uralensis grown under different DLIs (Hou et al., 2010; Polyakovaet al., 2015). The increased Chl a b concentrations of basil leaves under lower DLIsresulted from increased Chl b concentrationwith similar Chl a concentration and consequently lower Chl a/b ratios (Fig. 1C). Thedifference in Chl a/b ratios is also a usefulindicator of light conditions, with lower Chla/b ratios in shade leaves and higher Chla/b ratios in sun leaves (Sarijeva et al., 2007).Under lower DLIs, plants maximize lightharvesting capacity by increasing light-harvestingChl–protein complex in photosystem II, whichTable 4. Brix, anthocyanin concentration, total phenolic concentration (gallic acid equivalent, GAE), total flavonoid concentration [( )-catechin hydrateequivalent, CHE], and antioxidant capacity (ferrous ion chelating activity, FICA) of ‘Improved Genovese Compact’ sweet basil leaves grown for 21 d atdifferent daily light integrals (DLIs) in indoor controlled environment.Total phenolic concnTotal flavonoid concnAntioxidant capacityAnthocyanin concn(GAE mg·g–1 FW)(CHE mg·g–1 FW)(%, FICA)TreatmentBrix (%)(mg·100 g–1 FW)2.60 a1.02 b0.34 c1.96 bDLI 9.32.3 czDLI 11.52.7 bc2.76 a1.07 b0.47 b3.46 abDLI 12.92.9 b2.82 a0.99 b0.40 bc3.80 abDLI 16.52.5 bc2.82 a1.61 a0.90 a5.26 aDLI 17.83.5 a2.73 a1.38 a0.63 a3.37 abzMeans followed by the same letters are not significantly different within a column, according to Student’s t mean comparison (P 0.05).FW fresh weight.500HORTSCIENCE VOL. 53(4) APRIL 2018

Fig. 4. Correlation between amount of total anthocyanin per plant (A), amount of total phenolic per plant(gallic acid equivalent), and amount of total flavonoid per plant [( )-catechin hydrate equivalent] (B)with daily light integral of ‘Improved Genovese Compact’ sweet basil grown for 21 d at different DLIsin indoor controlled environment. Correlation test was conducted using pairwise correlations method.contains most of the Chl b, and consequentlya higher Chl b concentration and lower Chl a/b ratio (Kitajima and Hogan, 2003; Sarijevaet al., 2007). The increased Chl

results of growth, yield, and nutritional quality of sweet basil, we suggest a DLI of 12.9 mol·m L2·d 1 for sweet basil commercial production in indoor vertical farming to minimize the energy cost while maintaining a high yield and nutritional quality. Sweet basil (O. basilicum) is often re-ferred as the ''king of herbs'' or the .

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