Supplemental LED lighting to improve saffron spice quality and corm production

Supplemental LED lighting to improve saffron spice quality and corm production | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Supplemental LED lighting to improve saffron spice quality and corm production Stelluti Stefania, Berruto Francesco, Roberta Paradiso, Scariot Valentina This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8871041/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Saffron is a geophyte grown in open field, but the possibility of year-round greenhouse cultivation is attracting increasing interest. We evaluated the application of supplemental lighting with white light emitting diodes (LEDs) in greenhouse in summer-winter period, in plants grown in pot on two benches, under two lighting treatments: natural light integrated with LEDs (~ 260 µmol m − 2 s − 1 ) and natural light only (NL) as a control. LED lighting delayed flowering by almost a week (72 vs. 66 days after planting) but did not affect the mean number of flowers (4.2 flowers plant − 1 ) or spice yield (29.9 mg plant − 1 ). However, LED treatment increased the phenolic acid content in the spice (+ 52%) compared with NL, indicating an improvement in spice quality. During the subsequent vegetative phase, net photosynthesis was increased by supplemental lighting, while plant leaf area was reduced, since lighted plants developed more leaves but with a lower specific leaf area compared to control. Notably, plants under LED produced more corms (7.5 vs 6.0 corms plant − 1 ), with no differences in mean corm weight (3.4 g plant − 1 ) or starch content (645 mg g − 1 corm dry weight) compared with natural light, suggesting a potential for increasing the yield of propagative material. Overall, supplemental LED lighting may contribute to improve spice phytochemical quality and corm multiplication, which are both agronomically relevant traits for greenhouse soilless saffron cultivation. Crocus sativus L. controlled environment agriculture full-spectrum light soilless cultivation Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Saffron ( Crocus sativus L.) is a sterile geophyte (family Iridaceae) propagated exclusively by vegetative means through underground tuberous-bulb stems, namely the corms. In the Mediterranean climate, flowering, occurs in late autumn (October-November) and lasts from two to three weeks (Molina et al. 2005 ). A vegetative phase follows in the winter, when the leaf photosynthetic activity mainly contributes to the formation of replacement corms, which will take the place of the mother corm (Fig. 1 ). In replacement corms, the growth rate typically increases between late January and early February (Pallotti et al. 2024 ) and are completely formed in spring (April-May), when leaves and roots senesce and enter in dormancy (Molina et al. 2005 ; Renau-Morata et al. 2012). The saffron corm has 2.5–5.5 cm diameter (Kumar et al. 2008 ). Mature corms have one to three apical buds (producing leaves, floral axis, and replacement corms) and many axillary buds, which start dormancy after producing a few leaves. One to three corms per plant are usually produced in a growing season (Rubio-Moraga et al. 2014) and each corm can generate from one to three flowers, (Gresta et al. 2008 ; Kumar et al. 2008 ). The size of the mother corm influences flower formation, vegetative development, and replacement corm production, as larger corms contain sufficient nutrient reserves to support earlier growth and flowering. Corms ≥ 2.5 cm in diameter and ≥ 10 g in weight are usually employed commercially (Gresta et al. 2008 ; Kumar et al. 2008 ; Renau-Morata et al. 2012). The dark red dried stigmas of C. sativus are the precious spice known as saffron, used since ancient times as a condiment and natural dye in traditional foods and as a medicinal plant in folk medicine (Bagur et al. 2017 ; Cardone et al. 2020 ; Mzabri et al. 2019 ; Shahi et al. 2016 ). Organoleptic properties depend mainly on the content of apocarotenoids deriving from zeaxanthin: crocins, conferring colour; picrocrocin, determining bitter flavour; and safranal, responsible for the saffron aroma (Stelluti et al. 2024 ). While safranal, the main aromatic compound, is only at low levels in fresh stigmas, its formation from picrocrocin is aided during the drying process leading to the saffron spice (García-Rodríguez et al. 2014 , 2017 ). Saffron spice is classified into 3 quality categories according to the ISO 3632-1:2011 rules, based on physical features of the dried saffron stigmas, and their colouring capacity, bitterness, and aromatic strength, determined by UV-vis spectrophotometric analysis of 1% w/v aqueous extracts (García-Rodríguez et al. 2014 ; Giupponi et al. 2019 ). The spice also contains phenolic compounds, including anthocyanins, flavonoids, and coumaric, gallic, and ellagic acids (Caser et al. 2020 ). The main apocarotenoids, vitamin C, and phenolic compounds give the spice antioxidant properties, conferring the health beneficial effects to saffron (Bagur et al. 2017 ; Shahi et al. 2016 ). Saffron is mainly cultivated in open fields, under either a perennial cycle of 3–5 years or an annual crop by replanting the largest daughter corms each year (Stelluti and Scariot 2024 ). A major constraint limiting saffron cultivation is the difficulty in obtaining high-quality corms for propagation, with guaranteed levels of purity, homogeneity, and phytosanitary status (Rubio-Morata et al. 2012). The yield of replacement corms is influenced by the size of the mother corm, water availability, fertilization, pedoclimatic conditions, and agronomic practices (Barbieri et al. 2025 ; Caser et al. 2020 ). Indeed, the development of replacement corms depends on the photoassimilates produced by leaf photosynthesis as well as the reserves stored in the mother corms (Pallotti et al. 2024 ). Thus, beyond flowering, light plays a crucial role in sustaining photosynthesis during the subsequent vegetative phase, promoting the development of replacement corms (Moradi et al. 2021 ; Yang et al. 2025 ). In a field experiment, saffron plants grown under low light conditions (50% of natural light intensity using shade cloth) showed a reduced photosynthetic capacity and lower corm yield (Yang et al. 2025 ). Greenhouse cultivation of saffron is gaining increasing interest due to its potential to improve crop management and to enhance both the spice yield and quality (Askari-Khorasgani and Pessarakli 2019 ; Cardone et al. 2020 ; Caser et al. 2019 ; Molina et al. 2005 ). However, although greenhouses provide optimal conditions for producing the spice, yields of high-quality replacement corms are generally lower than in open-field cultivation (Moradi et al. 2021 ; Renau-Morata et al. 2012). As saffron plants often exhibit traits typical of low-light environments under greenhouse conditions, inadequate lighting may be the cause (Rubio-Morata 2012). In this context, supplemental LED lighting in greenhouses represents a promising strategy to enhance the yield of replacement corms, potentially enhancing future yields. In the last decade, innovative lighting systems based on light-emitting diodes (LEDs) have been increasingly adopted to enhance photosynthetic activity, plant productivity, and nutraceutical quality, by promoting the synthesis of bioactive compounds (Alrifai et al. 2019 ; Gao et al. 2023 ; Li et al. 2024 ; Paradiso and Proietti 2022 ). LEDs are solid-state light sources characterized by high energy efficiency, long lifespan, and safe operation. In saffron, it is known that light influences flowering and both spice yield and quality and plants are sensitive to light environment even at the corm stage (Gao et al. 2023 ; Li et al. 2024 ; Zhou et al. 2022 ). Renau-Morata et al. (2012) reported that light saturation during the vegetative phase was reached at 498 µmol m⁻² s⁻¹ for greenhouse-grown plants and at 840 µmol m⁻² s⁻¹ in open-field conditions. Corm treatments with LEDs showed an influence of light spectrum and photoperiod on the flowering process (earliness or delay – Li et al. 2024 ) and of light spectrum and intensity on both the yield and quality of the spice in terms of crocins and picrocrocin content (Zhou et al. 2022 ). To the best of our knowledge, the effects of supplemental white LED lighting applied throughout the entire life cycle of saffron cultivated in greenhouses, particularly on corm yield, have not been previously investigated. In greenhouse systems, light availability is often a limiting factor for saffron growth and development, with direct implications for both spice yield and quality and the production of replacement corms. Therefore, the objective of this study was to evaluate supplemental white LED lighting as a practical strategy to overcome light limitation and enhance saffron productivity, by improving spice yield and quality and corm production under greenhouse conditions. 2. Materials and methods 2.1. Plant material and growing conditions Saffron plants were grown in an unheated greenhouse located at Grugliasco, Italy (45°06′23.21″ N, 7°57′82.83″ E; elevation 300 m ASL). At the end of August 2020, corms with a minimum weight of 19 g were individually potted in 4 L plastic containers (14×14 cm base, 17 cm height), each filled with 1.5 L of sterile perlite (particle size 2–6 mm; Centro Evergreen Turco s.a.s., Moncalieri, Turin, Italy). Plants were placed on two benches: one received supplementary LED lighting (SL), while the other was exposed only to natural light (NL) and served as the control. The experiment employed a randomized block design with 3 blocks per treatment, and 6 pots per block, resulting in a total of 18 pots per treatment. Supplemental lighting was provided by one MIGRO ARAY 4 Full Spectrum LED bars (MIGRO Lighting, Dublin, Ireland) (Fig. 2 ), installed at a fixed height of 80 cm above the pots. The system was dimmed to provide a photosynthetic photon flux density (PPFD) of approximately 260 µmol m⁻² s⁻¹, measured at the plant level using a LI-1000 Data Logger (LI-COR Biosciences, Lincoln, NE, USA). The PPFD level was set to optimize photosynthesis, especially during the vegetative phase, while avoiding light stress and photoinhibition by remaining below the light saturation point (Renau-Morata et al. 2012). Measured PPFD under NL and SL (h 10–16, 1h intervals) were, respectively (Mean ± SD): 277.3 ± 120.25 µmol m⁻² s⁻¹ and 540 ± 120.25 µmol m⁻² s⁻¹ during the flowering phase (October–November), 199.8 ± 79.89 µmol m⁻² s⁻¹ and 462 ± 79.89 µmol m⁻² s⁻¹ during the vegetative phase (December–February), and 465.0 ± 48.16 and 727.8 ± 48.16 µmol m⁻² s⁻¹ during the reproductive phase. The photoperiod followed the natural day-night cycle of Grugliasco (Turin, Italy), based on local sunrise and sunset times ( https://www.calendariando.it/alba-e-tramonto/grugliasco/?anno=2020 ; 2021). LED lighting was provided exclusively during daytime, to supplement natural light without modifying the photoperiod. During the phenological phases, day length ranged from 11 − 9 h (flowering, October-November), 8–10 h (vegetative, December-February), and 10–13 h (reproductive, March-April). The LED lamp used had a power consumption of 250 W. Daily light integral (DLI) was estimated from solar radiation data (W m⁻²) recorded by a NETSENS weather station from October 2020 to April 2021) converted to PPFD (µmol m⁻² s⁻¹) using a factor of 4.57 (Richard and Thimijan, 1983 ), corrected for greenhouse attenuation. The DLI (mol m⁻² d⁻¹) was obtained by integrating corrected PPFD over the photoperiod using the formula: DLI = (PPFD × hours × 3600) ÷ 1,000,000, averaged by phenological phase. Under SL DLI included the LED contribution (~ 260 µmol m⁻² s⁻ 1 ). In NL, DLI was 10.5 ± 5.4 mol m⁻² d⁻¹, 7.0 ± 3.29 mol m⁻² d⁻¹, and 21.2 ± 0.37 mol m⁻² d⁻¹ (Mean ± SD) during flowering (October-November), vegetative (December-February), and reproductive phase (March-April), respectively. Under SL, DLI was 20.3 ± 6.35 mol m⁻² d⁻¹, 16.0 ± 3.98 mol m⁻² d⁻¹, and 33.2 ± 0.67 mol m⁻² d⁻¹ (Mean ± SD) for the same phases. Air temperature and relative humidity in the greenhouse were recorded every 30 minutes using a data logger (EasyLog USB, version 7.6.0.0; Lascar Electronics, UK) throughout the entire experiment. The average monthly day/night temperatures (mean ± SD) were 23.3 ± 4.22/21.0 ± 2.09°C before the flowering phase (September-October), 16.9 ± 4.02/14.9 ± 2.30°C during flowering (November), and 18.7 ± 6.27/14.0 ± 4.05°C during the vegetative phase (December-May), specifically 13.3 ± 4.05/11.4 ± 2.59°C in December-February and 22.5 ± 4.51/17.7 ± 2.54°C in March-May. Plants were fertigated every two weeks with a modified Long-Ashton nutrient solution (Hewitt 1952; Stelluti et al. 2023 ) from the onset of root development until leaf senescence (200 mL per pot; pH 7, EC 979 µS cm − 1 at 22°C). 2.2. Flower production, spice yield, and leaf development At flowering, flower and spice yield per corm were assessed. Saffron spice was produced by initially dehydrating the stigmas in the shade for 48–72 hours, followed by further drying in a cold-air dryer (NWT100, Northwest Technologies, Boves, Italy) at 20°C for 48 hours (Stelluti et al. 2023 ). Leaf production (number of leaves and leaf length per plant) and corm yield (number, weight, and size of replacement corms per plant) were measured toward and at the end of the vegetative phase, respectively. Leaf area (LA, cm² plant -1 ) was estimated using the equation LA = 191.33·e^(L·0.0037), where “L” represents leaf length in millimeters, following the formula proposed by Kumar ( 2009 ). 2.3. Physiological measurements During the vegetative phase (end of January 2021), the net CO₂ assimilation rate (A, µmol m⁻² s⁻¹) and transpiration rate (E, mmol m⁻² s⁻¹) were measured in 12 plants per treatment using an InfraRed Gas Analyzer (IRGA; LCi-Pro, ADC Hoddesdon, UK). For each measurement, the middle section of three intact, healthy, fully green leaves per plant was enclosed in a 6.25 cm² sealed leaf chamber for approximately one minute. Measurements were conducted between 1:00 and 5:00 pm, at a greenhouse temperature of 15.1 ± 5.9°C (Mean ± SD), a CO₂ concentration of 493.3 ± 17.9 ppm (Mean ± SD), and an air pressure of 99.3 ± 0.52 kPa (mean ± SD). PPFD at canopy level was 394.0 ± 16.0 µmol m⁻² s⁻ 1 (Mean ± SD) under NL and 399.0 ± 55.4 µmol m⁻² s⁻ 1 (Mean ± SD) under SL. Water use efficiency (WUE, µmol CO 2 mmol − 1 H 2 O) was calculated as the ratio A/E. 2.4. Saffron spice quality 2.4.1. Spice extract preparation The aqueous extract of the spice was prepared according to the protocol described by Stelluti et al. ( 2023 ). Briefly, 50 mg of powdered spice was suspended in 5 mL of deionized water and stirred at 1000 rpm for 1 hour at room temperature (~ 21°C) in the dark using a magnetic stirrer. The mixture was then centrifuged at 10,000 rpm for 10 minutes at 4°C using an Eppendorf Centrifuge 5425 R. The supernatant was subsequently filtered using PVDF syringe filters (0.45 µm pore size; CPS Analitica, Milan, Italy). 2.4.2. Spectrophotometric Analysis (ISO 3632) The spice extract was measured using a Cary 60 UV–Vis spectrophotometer (Agilent Technologies, Santa Clara, CA, USA). Absorbance was recorded at wavelengths of 257 nm for picrocrocin, 310 nm for safranal, and 440 nm for crocins (Caser et al. 2020 ; Stelluti et al. 2023 ). Data were normalized to dry matter content and reported as the absorbance of a 1% (w/v) aqueous saffron solution, using a cuvette with a 1 cm optical path length (A₁%¹cm λ_max). The analysis was performed in the dark. Extracts were then stored at 20°C for subsequent evaluations. 2.4.3. HPLC Analysis The concentrations of safranal and phenolic compounds in saffron spice extract were quantified using an Agilent 1200 High-Performance Liquid Chromatography (HPLC) system equipped with a UV-Vis diode array detector (Agilent Technologies, Santa Clara, CA, USA). Separation was performed on a Kinetex C18 column (4.6 × 150 mm, 5 µm particle size; Phenomenex, Torrance, CA, USA). Identification of each compound was achieved by matching retention times and UV spectra with those of reference standards purchased from Sigma-Aldrich (Saint Louis, MO, USA) analysed under identical chromatographic conditions. All analyses were conducted in triplicate. Safranal quantification was performed as described by Stelluti et al. ( 2023 ). Briefly, chromatographic separation was achieved using a water-acetonitrile gradient as the mobile phase: 5% to 95% (v/v) acetonitrile over 30 min, followed by 95% to 5% (v/v) acetonitrile over 5 min, with additional 10 min conditioning period. The flow rate was 0.6 mL min − 1 , and safranal was detected at 310 nm. Results were expressed as mg g − 1 of spice. The phenolic compounds quantified included hydroxycinnamic acids (caffeic, chlorogenic, coumaric, and ferulic acids), hydroxybenzoic acids (ellagic and gallic acids), flavonols (hyperoside, isoquercitrin, quercetin, quercitrin, and rutin), and flavanols (catechin and epicatechin). Total content for each group was calculated by summing the concentrations of individual compounds. Caffeic acid was found in two out of three replicates, while coumaric acid was detected in only one replicate. Phenolic compounds were analysed as described by Stelluti et al. ( 2021 ). Hydroxycinnamic acids and flavonols were separated using a gradient from 5% to 21% acetonitrile (CH₃CN) over 17 min, followed by 21% CH₃CN for 3 min, with a 2 min conditioning period and a flow rate of 1.5 mL min⁻¹. UV detection was performed at 330 nm. Hydroxybenzoic acids and flavanols were separated using a gradient from 3% to 85% methanol/formic acid (CH₃OH/HCOOH, 100:0.1 v/v) over 22 min, followed by 85% CH₃OH/HCOOH for 1 min, with a 2 min conditioning period and a flow rate of 0.6 mL min⁻¹. UV detection was performed at 280 nm. Compound concentrations were expressed as mg g⁻¹ of spice. 2.4.4 Yield and starch content of replacement corms Corms were counted, measured, and weighed. Starch content was determined in three replacement corms with significantly similar fresh and dry weights per treatment (fresh weight: NL 5.5 ± 0.30g, SL 5.4 ± 0.14g; dry weight: NL 1.6 ± 0.02g, SL 1.7 ± 0.03g; Mean ± SE), after drying at 60°C for 120 hours in an oven, using the Megazyme Total Starch Assay Kit (Megazyme International Ireland Ltd, Wicklow, Ireland). The assay followed specific protocols for samples containing resistant starch, D-glucose, and maltodextrins, including the removal of free D-glucose and maltodextrins via alcohol washing, as in Stelluti et al. ( 2023 ). Total starch content per plant was calculated by multiplying the starch concentration (mg g⁻¹ corm) by the total corm dry weight per plant (g). 2.5 Statistical analysis Data normality was assessed using the Shapiro-Wilk test ( p > 0.05), and homoscedasticity was evaluated with Levene’s test ( p > 0.05). When assumptions of normality or homoscedasticity were violated, the non-parametric Wilcoxon rank-sum test was applied. All statistical analyses were performed using RStudio (R Core Team, 2023). Statistically analysed data are expressed as mean ± standard error (SE); climatic data are expressed as mean ± standard deviation (SD). For the ‘number of leaves’, one value from NL (i.e., 79) was discarded due to a z-score ≥ 2. For ‘corm plant⁻¹’, one value from the NL treatment (i.e., 11) and one from the SL treatment (i.e., 10) were also excluded for the same reason. 3. Results 3.1. Plant growth Flowering of saffron plants occurred 6 days later under SL (at 72 days after planting, DAP) compared to NL (66 DAP) and lasted approximately 11 days regardless of lighting conditions (Table 1 ). The 50% of the total number of flowers was reached after 8 days under NL and after 6 days under SL. The number of flowers (ca. 4 per plant) and spice yield (ca. 30 mg per plant) were unaffected by SL (Table 1 ). Table 1 Effects of natural light (NL) and supplemental LED lighting (SL) on flowering, yields, vegetative growth, and starch content of plants. Data are expressed as Mean ± SE. Sample sizes were as follows: flowering onset and flower yield, n = 18; flowering duration and spice yield, n = 3; leaf number, n = 7 (NL) and n = 8 (SL); leaf area, n = 8; corm yield, n = 12 (corms plant⁻¹, n = 11); starch content, n = 3. NL SL Significance p -value Flowers and spice Flowering onset (DAP) 65.6 ± 0.57 71.6 ± 0.92 *** 0.000 Flowering duration in single plants (days plant − 1 ) 4.6 ± 0.47 3.8 ± 0.81 ns 0.155 Flowering period duration (days) 10.7 ± 1.86 11.7 ± 0.33 ns 0.713 Flowers plant − 1 (n.) 3.8 ± 0.20 4.6 ± 0.30 ns 0.051 Days to reach 50% of total flowers 8 6 - - Spice plant − 1 (mg) 29.3 ± 3.70 30.4 ± 2.21 ns 0.819 Leaf number and area Number of leaves (n. plant − 1 ) 38.0 ± 3.38 54.9 ± 3.87 ** 0.006 Leaf length (cm) 38.1 ± 1.08 22.7 ± 0.87 *** 0.000 Individual leaf area (cm 2 ) 7.9 ± 0.29 4.5 ± 0.14 *** 0.000 Plant leaf area (cm 2 ) 330.8 ± 33.75 242.1 ± 19.02 * 0.043 Corm size and starch content Corm plant − 1 (n.) 6.0 ± 0.52 7.5 ± 0.28 * 0.015 Individual corm weight plant − 1 (g) 3.4 ± 0.28 3.3 ± 0.15 ns 0.683 Individual corm size plant − 1 (mm) 19.8 ± 0.67 19.0 ± 0.32 ns 0.671 Total corm fresh weight plant − 1 (g) 20.3 ± 1.04 24.7 ± 0.68 ** 0.002 Starch (mg g − 1 corm dry weight) 603.6 ± 22.96 664.3 ± 21.53 ns 0.126 Total starch per plant (g plant − 1 ) 3.6 ± 0.32 5.2 ± 0.13 * 0.011 During the vegetative phase, SL increased the number of leaves per plant by 45% (from 38.0 to 54.9) compared to NL but led to a 40% reduction in leaf length (from 38.1 to 22.7 cm) and a 43% reduction in individual leaf area (from 7.9 to 4.5 cm 2 ) (Table 1 ). Consequently, the total plant leaf area under SL was 27% lower than that in plants grown under NL (from 330.8 to 242.1 cm 2 ) (Table 1 ). Conversely, plants grown under SL produced 25% more corms (from 6.0 to 7.5), while mean weight (3.4 g per plant), size (19.4 mm per plant), and starch content (634.0 mg g − 1 ) remained unchanged (Table 1 ). Total starch content per plant was estimated to increase by 44% under SL (5.2 g per plant) compared to NL (5.2 vs. 3.6 g per plant). Corm size distribution for the NL and SL treatments is shown in Fig. 3 . 3.2. Spice quality According to the ISO 3632 standard, the saffron spice was qualified as first quality category (I), regardless of lighting conditions (Table 2 ). Compared to natural light, SL did not affect the content of crocins (ca. 228.6–237.0 A1%1cm) and picrocrocin (92.4–97.7 A1%1cm) but resulted in a lower concentration of safranal (31.8–36.9 A1%1cm), thereby reducing the strength of saffron aroma by16% (Table 2 ). However, this reduction was not observed when safranal content (0.01–0.02 mg g⁻¹) was analysed using the more sensitive HPLC-DAD method (Table 2 ). Table 2 Colouring capacity, bitterness, and aromatic strength, determined by UV-vis spectrophotometric analysis according to ISO 3632 (ISO, 2011), of saffron spice collected from plants grown under natural light (NL) and supplemental LED lighting (SL). The quality category is indicated in brackets. Threshold values for Category I quality are: crocins > 200, picrocrocin > 70, and safranal 20 ÷ 50. Data are expressed as Mean ± SE of specific absorbance (A 1 % 1 cm) at 440 nm for crocins, 257 nm for picrocrocin, and 330 nm for safranal. NL SL Significance p -value ISO 3632 Colour/Crocins (A1%, 1cm, λ440) 237.0 ± 7.11 (I) 228.6 ± 2.82 (I) ns 0.306 Flavour/Picrocrocin (A1%, 1cm, λ257) 97.7 ± 2.58 (I) 92.4 ± 1.59 (I) ns 0.113 Aroma/Safranal (A1%, 1cm, λ330) 36.9 ± 0.74 (I) 31.8 ± 0.47 (I) *** 0.000 HPLC-DAD Safranal (mg g − 1 ) 0.01 ± 0.00 0.02 ± 0.01 ns 0.720 Regarding phenolic compounds, SL increased total hydroxycinnamic acid content by 54% (from 4.7 to 7.2 mg g⁻¹) and total phenolic acid content by 52% (from 6.9 to 10.5 mg g⁻¹) (Table 3 ). Table 3 Safranal and phenolic compounds quantified by HPLC-DAD analysis in aqueous extracts of saffron spice from plants grown under NL and supplemental LED lighting (SL). Data are expressed as Mean ± SE (n = 3). Total hydroxycinnamic acids = sum of caffeic, chlorogenic, coumaric, and ferulic acids; n.d. = not detectable. NL SL Significance p -value Hydroxycinnamic acids Caffeic acid 0.18 ± 0.042 0.22 ± 0.052 - Chlorogenic acid 4.54 ± 0.316 4.97 ± 0.356 ns 0.400 Coumaric acid n.d. 0.09 - Ferulic acid n.d. 1.96 ± 0.077 - Total hydroxycinnamic acids (mg g − 1 ) 4.66 ± 0.259 7.18 ± 0.387 * 0.011 Hydroxybenzoic acids Ellagic acid 2.25 ± 0.350 3.31 ± 0.252 ns 0.083 Total phenolic acids (mg g − 1 ) 6.91 ± 0.608 10.49 ± 0.639 * 0.020 Flavonoids (mg g − 1 ) Hyperoside 0.93 ± 0.068 n.d. - Epicatechin 4.25 ± 0.430 4.52 ± 0.361 ns 0.658 Total flavonoids (mg g − 1 ) 5.18 ± 0.433 4.52 ± 0.361 ns 0.309 Total phenolic compounds (mg g − 1 ) 12.09 ± 0.999 15.01 ± 0.284 ns 0.113 No significant differences were observed for chlorogenic and ellagic acids. In contrast, coumaric acid and ferulic acid were detected only under SL. However, coumaric acid was detected in only one sample out of three (0.09 mg g⁻¹). Caffeic acid was found in both NL (0.18 ± 0.042 mg g − 1 ; Mean ± SE, n = 2) and SL (0.22 ± 0.052 mg g − 1 ; Mean ± SE, n = 3) samples. The SL did not affect total flavonoid content, nor did it influence epicatechin specifically. However, hyperoside was found only under NL (Table 3 ). Gallic acid, isoquercitrin, quercetin, quercitrin, rutin, and catechin were not detected under either lighting condition. Overall, total phenolic compound levels tended to be higher under SL, although differences were not statistically significant. 3.4 Gas exchange Physiological parameters of saffron plants under NL and SL are reported in Fig. 4 . The net photosynthetic rate (A) was significantly higher under SL compared to NL (9.9 ± 0.57 vs. 6.1 ± 0.84 µmol m⁻² s⁻¹; p = 0.001). No significant differences were observed in the transpiration rate (E) between SL and NL (3.6 ± 0.30 and 3.3 ± 0.17 mmol m⁻² s⁻¹, respectively). Water use efficiency (WUE) was higher under SL than under NL (2.9 ± 0.17 vs. 2.0 ± 0.34; p = 0.008). 4. Discussions In recent decades, saffron cultivation under controlled conditions has received increasing attention, with the aim of improving crop management, particularly to regulate flowering time, enhance crop yield and produce quality, simplify flower harvesting and stigma separation, and to increase the overall crop profitability (Askari-Khorasgani and Pessarakli 2019 ; Cardone et al. 2020 ; Gresta et al. 2017 ; Molina et al. 2004 ). Saffron is considered a thermo-periodic species and is classified as a short-day plant (Li et al. 2024 ). As in other geophytes such as Tulipa , Freesia , and Iris , temperature represents the main environmental factor regulating both the growth and flowering (Haghighi et al. 2020 ; Khodorova and Boitel-Conti 2013 ; Molina et al. 2005 ; Proietti et al 2022 ). In our study, the average air temperature in greenhouse during the flowering period was 17 ± 1.2°C (Mean ± SD), which is considered the optimal thermal level for reproductive stage in saffron (Haghighi et al. 2020 ; Molina et al. 2005 ). However, previous studies showed that flowering in saffron is influenced also by light, with possible effects of all parameters: intensity, photoperiod, and spectral composition (Gao et al. 2023 ; Li et al. 2024 ; Moradi et al. 2021 ; Zhu et al. 2022 ). In our experiment, under identical temperature conditions, SL delayed the beginning of flowering by 6 days compared to NL. However, flowering lasted approximately 11 days regardless of lighting conditions. In this respect, it is worth noting that most experiments dealing with LED lighting in greenhouse-grown saffron aim at modifying the solar light spectrum by integrating red and/or blue monochromatic light, to trigger targeted photomorphogenetic responses driven by specific wavebands. Differently, the main objective of LED supplemental lighting in our study was to integrate solar radiation with a balanced spectrum artificial light, to guarantee a sufficient light intensity during the winter period, in a geographic area where it can be a limiting factor, particularly in greenhouse, because of the shading effect of structure and cover. To this purpose, LED emission in our study was set at 260 µmol m⁻² s⁻¹ to sustain assimilation, based on the light requirement reported in literature for greenhouse saffron (Renau-Morata et al. 2012). In saffron, a progressive increase in total sugar level (specifically glucose and fructose) was found to be associated with the degradation of starch, from the quiescent stage of corms to the bud break and floral anthesis (Bagri et al. 2017 ). These changes were suggested to initiate sprouting and bud growth in saffron corms. In a “two-segment” cultivation method, during the indoor stage under a greenhouse, saffron corms were treated with five light intensities using LED lamps containing red, blue, green, and white, maintaining a red-to-blue ratio of 3:1. Higher intensity of LED light slowed down the starch degradation in the corms during the flowering phase, with a stronger effect at increasing PPDF (Zhou et al. 2022 ). Accordingly, in a field experiment, during vegetative growth, starch degradation in mother corms was faster under low light conditions (50% of natural light using shading cloth) compared to full solar radiation, with a parallel increase of sucrose and glucose (Yang et al. 2025 ). This reduction in starch content was due to an elevated activity of starch-degrading enzymes (e.g., α-amylase), indicating a mobilization of carbohydrate reserves to support leaf expansion. Besides, in our experimental conditions, the higher light intensity under LED lighting may have sustained a higher photosynthetic assimilation reducing the demand of reserve material for flower and leaf development, hence delaying flowering. Flower production and spice yield were not affected by LED supplemental lighting. This outcome may be due to the influence of the big corm size used in the study, as larger corms already contain sufficient nutrient reserves to promote a proper plant growth and flowering. During flowering, approximately 20–30% of the mother corm’s reserves are mobilized to support the flower formation and the leaf development, which in our case occurred shortly before flowering (Renau-Morata et al. 2012). To the best of our knowledge, no similar studies are currently available for comparison. Under field conditions, where recommended planting density is from 55 to 75 corms m⁻² (Cardone et al. 2020 ), yields generally range from 5 to 15 kg ha⁻¹, though they can vary widely – from 2 kg ha⁻¹ to 30 kg ha⁻¹ – depending on pedoclimatic conditions, agronomic practices, and corm size (Cardone et al. 2020 ; Stelluti and Scariot 2024 ). In particular, planting density affects both spice yield and the development of the corms: while higher densities tend to increase stigma yield, lower densities promote the development of heavier replacement corms (Barbieri et al., 2025 ; Kumar et al., 2008 ). Our results confirm that controlled cultivation conditions can enhance saffron spice yield compared to open-field cultivation, as the spice yield obtained in our study (approximately 15 kg per hectare), at a planting density of 51 corms m⁻², was relatively high compared to typical open-field production. Similarly, our results indicate that controlled cultivation conditions can enhance the yield of replacement corms compared to open-field cultivation. in a previous field experiment, Caser et al. 2020 , using a lower planting density (39 corms m⁻²), obtained an average of 2.1 replacement corms per plant, with a total corm weight per plant of 13.38 g and a corm yield of 422 g m⁻² after one year. These values are lower than those obtained in the present soilless study, conducted at a higher planting density (51 corms m⁻²). Under natural light (NL), we obtained approximately three times more replacement corms per plant, although individual corms weighed about half as much, resulting in a total corm weight per plant of 20.3 g and a corm yield of 1035.3 g m⁻². With supplemental LED lighting, the increase in the number of replacement corms per plant was even greater (about 3.5-fold compared to field conditions), with a comparable individual corm weight, leading to a total corm weight per plant of 24.7 g and a corm yield of 1259.7 g m⁻². However, the average weight of individual corms obtained under field conditions (6.5 g - Caser et al. 2020 ) was higher than that of corms produced in the soilless system, which could reduce flowering performance and, consequently, saffron spice yield in the subsequent growing cycle. In our experiment, the classification of our saffron spice according to ISO 3632 quality categories remained unaffected by lighting conditions and it was consistently classified as first category. Commercial saffron is generally classifiable as first quality category, as demonstrated by Giupponi et al. ( 2019 ) and García-Rodríguez et al. ( 2017 ), who analysed samples from various countries. Specifically, up to 93% of 484 samples collected in Italy over four years were found to be of first category (Giupponi et al. 2019 ). Similarly, 96% of 57 samples from Italy, 94% of 64 samples from Spain, 91% of 115 samples from Greece, and 53% of 154 samples from Iran (for an overall 77.18% of the total number of samples), fell within the first class (García-Rodríguez et al. 2017 ). However, it is known that the ISO 3632 (2011) method lacks accuracy (García-Rodríguez et al. 2017 ). This procedure estimates safranal content via UV-visible spectrophotometry at 330 nm; however, crocins and other compounds also absorb at this wavelength, thus interfering with the analysis. Moreover, the standard assigns the same safranal range (20–50) to all quality grades, making crocins and picrocrocin the main criteria for quality classification; for example, category I requires crocins ≥ 200 and picrocrocin ≥ 70 (García-Rodríguez et al. 2017 ; Stelluti and Scariot 2024 ). Recently proposed analytical methods aim to improve saffron quality classification according to ISO 3632 (Locatelli et al. 2025 ). Although saffron’s colour and bitter taste are highly valued, the distinctive safranal-driven aroma truly reveals the essence of the spice. Previous studies suggested that the more sensitive HPLC-DAD method could be incorporated into or replace the ISO 3632 method (García-Rodríguez et al. 2017 ). Notably, even though the aroma decreased under SL, in our experiment safranal content measured by the HPLC-DAD method was not affected by SL. Light quality is known to influence plant secondary metabolism, particularly the biosynthesis of phenolics and carotenoids (Alrifai et al. 2019 ; Paradiso and Proietti 2022 ). In saffron, light spectrum and photoperiod affects the synthesis and accumulation of apocarotenoids – such as crocins and picrocrocin – and phenolic compounds (Li et al. 2024 ; Moradi et al. 2022; Zhou et al. 2022 ). In our study, SL increased total hydroxycinnamic acids, and consequently the total phenolic acids; notably, coumaric acid and ferulic acid were detected only in SL-treated samples. This effect could be related to a combined effect of both light intensity and spectral composition. Indeed, the higher PPFD at high proportion of R and B could have enhanced the carbon assimilation and carbohydrate production, thereby increasing the amount of carbohydrate allocated to secondary metabolism; besides it is known that B light drives the biosynthesis of several antioxidant compounds, including phenolics (REF). In addition, light perception through specific photoreceptors involved in photomorphogenesis could activate signalling pathways that regulate the expression of enzymes in secondary metabolism, including phenolic biosynthesis, independently of photosynthetic metabolism (Paradiso and Proietti, 2022 ). These mechanisms likely contributed to the observed increase in phenolic acids content under SL. Conversely, SL did not affect the total flavonoids, even if hyperoside was detected only in NL samples. These results indicate that light plays a key role in modulating the phenylpropanoid pathway, as reported in other plant species (Alrifai et al. 2019 ), and may promote the synthesis of specific phenolic compounds in saffron. Overall, our findings suggest that supplemental LED lighting can shape the phenolic composition of saffron, enhancing the accumulation of specific antioxidant compounds, thus improving the nutraceutical profile of the spice. Although these changes do not affect the official quality classification as defined by international standards, they represent an added value in terms of biochemical composition and potential health-related attributes of the spice. During the vegetative phase, following flowering, saffron plants grown under SL exhibited reduced leaf length and area, yet showed an increased photosynthetic activity, as previously observed by Zhou et al. ( 2022 ). Renau-Morata et al. (2012) reported that saffron plants grown in greenhouse exhibited morphological and physiological traits typically associated with low irradiance, e.g., rapid leaf expansion, reduced chlorophyll concentration, and a decline in photosynthetic efficiency. The LED supplemental lighting likely counteracted these traits. After flowering, as leaves and roots reach their maximum development, the contribution of the residual reserves of the mother corm to vegetative growth gradually declines in favour of photosynthetic assimilation. Once these reserves are nearly exhausted, the exponential growth of replacement corms begins, sustained exclusively by photosynthesis (Renau-Morata et al. 2012). The higher net photosynthesis of saffron grown under LED supplemental lighting (+ 62%), together with the unchanged transpiration rate and the increase in water use efficiency (WUE = A/E) indicate that SL-grown plants fixed more CO₂ per unit of transpired water. When estimating the total CO₂ assimilation by multiplying the plant leaf area by the net photosynthesis, plants under SL exhibited approximately 19% higher values compared to those under NL. Accordingly, SL plants produced more replacement corms. While the individual weight of the corms remained unchanged compared to those grown under natural light, the increased number resulted in a higher total weight of corms per plant. As a consequence, although the increase in starch content per corm in SL-grown plants was not statistically significant, the higher number of corms determined that the total accumulation of starch per plant was greater under LED lighting compared to NL. Accordingly, Yang et al. ( 2025 ) found that both starch concentration and corm yield decreased under low light conditions (50% of natural light using shade cloth). This finding is consistent with the observed increase in photosynthetic activity of SL plants, which likely supported both the production of more corms and the greater accumulation of reserve materials. In addition to supplying energy through photosynthesis, light also regulates bud development and shoot branching in plants (Paradiso and Proietti, 2022 ). In saffron, higher proportions of blue light relative to red tend to promote apical dominance and suppress the outgrowth of lateral buds; conversely, an increase in the red-to-blue light ratio tend to stimulate lateral bud production (Moradi et al. 2021 ). Saffron plants cultivated under LED lighting (11 hours photoperiod; 150 ± 10 µmol m⁻² s⁻¹) and exposed to six LED treatments with varying blue-to-red light ratios after flowering, produced fewer but heavier daughter corms under higher proportion of blue light. In contrast, more numerous and lighter daughter corms were produced under full red light (Moradi et al. 2021 ). In our experiment, the higher intensity of white light may have reduced the apical dominance in saffron corm, thereby promoting the development of lateral buds, possibly through the modulation of hormone signalling (Rubio-Moraga et al. 2014). 5. Conclusion Cultivation of saffron in controlled environment offers the opportunity to optimize the crop agronomic management and to improve spice yield and quality and corm multiplication, even if corms produced in soilless systems appear smaller than those obtained in open field. In our experiment, in saffron grown in pot in greenhouse, supplemental LED white light did not improve the spice yield while it enhanced the phenolic acid accumulation, thereby improving the nutraceutical quality of the produce. Besides, LED lighting increased the production of replacement corms. However, quality traits of spice, such as phenolic compound content and antioxidant activity, are not yet widely recognised as factors that could increase the market value of saffron. Conversely, production of replacement corms is an important agronomic aspect to optimize saffron cultivation since propagation represents the most significant variable cost. Indeed, in traditional open-field production, purchased corms of 2.5 ÷ 3.5 cm diameter can account for about 77% of the planting cost, representing about 83% of total yearly direct costs in a 5-year cycle (Barbieri et al. 2025 ). It is known that installing LED systems involves high initial investment and additional energy inputs. In this respect, LED lighting protocols could be optimized by limiting light supplementation to the period of vegetative growth (December–February), when plants could gain the highest advantage from artificial light since light attenuation due to seasonal changes and greenhouse shading can significantly limit the photosynthetic activity. This approach would maximize the cost-effectiveness of LED lighting reducing energy costs while preserving the benefits for propagation and nursery purposes. On this basis, a comprehensive economic evaluation is essential to assess the feasibility of adopting LED technology for greenhouse saffron production, through a trade-off analysis of lamp cost and energy consumption vs. productive outputs, such as energy use per replacement corm produced. Further research is needed to optimise corm yield under supplemental LEDs in greenhouses. In particular, promoting the development of heavier corms may be beneficial, given that corm size significantly influences flower development, spice yield, and daughter corm formation. Declarations Conflict of interest The authors have no relevant financial or non-financial interests to disclose. Funding This research was funded by the program Interreg V-A Francia Italia Alcotra (Grant No. 1139 “ANTEA - Attività innovative per lo sviluppo della filiera transfrontaliera del fiore edule”; and Grant no. 8336 “ANTES - Fiori eduli e piante aromatiche: attività capitalizzazione dei progetti ANTEA ed ESSICA”) and by the program Interreg VI-A Francia Italia Alcotra (Grant No. 21350 “AGRISMART - Soluzioni innovative a basso impatto ambientale per la modernizzazione delle imprese agricole e strutture produttive in aree svantaggiate”). Author Contribution Study conception and design and Funding acquisition: Valentina Scariot; Data collection and analysis: Stefania Stelluti, Francesco Berruto; Writing - original draft preparation: Stefania Stelluti; manuscript integration and revision: all the authors. Acknowledgments The authors thank Alessandro Borrelli and Farzaneh Zamani (Department of Agricultural Sciences - University of Naples Federico II, Portici, Italy), for helping in graphical work. Data Availability The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request. References Alrifai O, Hao X, Marcone MF, Tsao R (2019) Current review of the modulatory effects of LED lights on photosynthesis of secondary metabolites and future perspectives of microgreen vegetables. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8871041","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":599870795,"identity":"06cc1a0d-0be9-4934-8b84-559f0efae098","order_by":0,"name":"Stelluti Stefania","email":"","orcid":"","institution":"University of Torino","correspondingAuthor":false,"prefix":"","firstName":"Stelluti","middleName":"","lastName":"Stefania","suffix":""},{"id":599870798,"identity":"bb8ac8ae-1116-4e83-9d1b-87548dbdb024","order_by":1,"name":"Berruto Francesco","email":"","orcid":"","institution":"University of Torino","correspondingAuthor":false,"prefix":"","firstName":"Berruto","middleName":"","lastName":"Francesco","suffix":""},{"id":599870803,"identity":"95821d70-60dd-4018-9366-3c2f60c84f3f","order_by":2,"name":"Roberta Paradiso","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAvElEQVRIiWNgGAWjYNACNgkGfiB1AIh5iNci2QDVQqQeNgYGgwNQNkEt5rObn334UWZhb3wj9+DhghoGGXtCWmTuHDOe2XNOInHbjbyEwzOOEeEwCYkEYwbeNokEsxs5Bod52IjSkv6Z8W+bhL3xDJCWf0RpyTFmBtrCuEECqIW3jRgtMmeKmWWAfplx5g1QS58ED88BQlqk2zczvimrs+dvzzH+zPPNxp69gaA1eLnEaBkFo2AUjIJRgAkAGqU03qCB8t4AAAAASUVORK5CYII=","orcid":"","institution":"University of Naples Federico II","correspondingAuthor":true,"prefix":"","firstName":"Roberta","middleName":"","lastName":"Paradiso","suffix":""},{"id":599870808,"identity":"fc0f8981-0df7-4f03-95e0-c8b2f9ac4bd9","order_by":3,"name":"Scariot Valentina","email":"","orcid":"","institution":"University of Torino","correspondingAuthor":false,"prefix":"","firstName":"Scariot","middleName":"","lastName":"Valentina","suffix":""}],"badges":[],"createdAt":"2026-02-13 11:08:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8871041/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8871041/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104402192,"identity":"8fa68c62-0fcb-40ae-ac18-3ef3e84780be","added_by":"auto","created_at":"2026-03-11 12:14:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":412214,"visible":true,"origin":"","legend":"\u003cp\u003eDevelopmental stages of saffron (\u003cem\u003eCrocus sativus\u003c/em\u003e L.) during its annual growth cycle. The diagram illustrates the chronological progression from corm dormancy to complete development of replacement corms: (1) mother corm, (2) germination, (3) initial vegetative growth, (4) flowering stage (5) post-flowering development, (6) maximum vegetative growth with the formation of new corms, (7) corm multiplication, (8) onset of leaf and root senescence, and (9) complete corm development (credits to Alessandro Borrelli and Farzaneh Zamani, University of Naples Federico II, Naples, Italy)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8871041/v1/0e6e2c66bc16ab4da2fce4bd.png"},{"id":103979807,"identity":"00716230-91b6-429a-b201-5a0407232410","added_by":"auto","created_at":"2026-03-05 09:18:33","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":529721,"visible":true,"origin":"","legend":"\u003cp\u003eSpectral distribution of MIGRO ARAY 4 Full Spectrum LED bars used in the study (Credits to MIGRO Lighting, Dublin, Ireland)\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8871041/v1/4062975eeafefef8f72a0f4a.jpeg"},{"id":103979804,"identity":"aea6007b-7541-4a6d-91a4-3762a34a3f8b","added_by":"auto","created_at":"2026-03-05 09:18:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":39835,"visible":true,"origin":"","legend":"\u003cp\u003eCorm size distribution for natural light (NL) and supplemental LED lighting (SL). Values are expressed as percentages of replacement corms in each weight range relative to the total per treatment\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8871041/v1/6295a3cddc2ccbb669ba85b1.png"},{"id":103979806,"identity":"ca033f1c-d26c-468d-a054-1edc368563f9","added_by":"auto","created_at":"2026-03-05 09:18:33","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":385347,"visible":true,"origin":"","legend":"\u003cp\u003eNet photosynthesis (A), transpiration rate (E), and water use efficiency (WUE = A/E) of saffron plants grown under greenhouse conditions with natural light (NL) and supplemental LED lighting (SL). Measurements were performed during the vegetative phase on 29 January between 1:00 and 5:00 pm. Data are presented as Mean ± SE (n=12). Differences between treatments were significant for A (p = 0.001) and WUE (p = 0.008)\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-8871041/v1/d2e8cb3a2bfdc9b9e3d7b25c.jpeg"},{"id":104408746,"identity":"d8a8a537-274b-4a66-b488-4da67ee198f6","added_by":"auto","created_at":"2026-03-11 12:43:14","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2080043,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8871041/v1/749c211d-3e1b-453f-9063-e10dc4b0113d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Supplemental LED lighting to improve saffron spice quality and corm production","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eSaffron (\u003cem\u003eCrocus sativus\u003c/em\u003e L.) is a sterile geophyte (family Iridaceae) propagated exclusively by vegetative means through underground tuberous-bulb stems, namely the corms. In the Mediterranean climate, flowering, occurs in late autumn (October-November) and lasts from two to three weeks (Molina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). A vegetative phase follows in the winter, when the leaf photosynthetic activity mainly contributes to the formation of replacement corms, which will take the place of the mother corm (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In replacement corms, the growth rate typically increases between late January and early February (Pallotti et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and are completely formed in spring (April-May), when leaves and roots senesce and enter in dormancy (Molina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Renau-Morata et al. 2012). The saffron corm has 2.5\u0026ndash;5.5 cm diameter (Kumar et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Mature corms have one to three apical buds (producing leaves, floral axis, and replacement corms) and many axillary buds, which start dormancy after producing a few leaves. One to three corms per plant are usually produced in a growing season (Rubio-Moraga et al. 2014) and each corm can generate from one to three flowers, (Gresta et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Kumar et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). The size of the mother corm influences flower formation, vegetative development, and replacement corm production, as larger corms contain sufficient nutrient reserves to support earlier growth and flowering. Corms\u0026thinsp;\u0026ge;\u0026thinsp;2.5 cm in diameter and \u0026ge;\u0026thinsp;10 g in weight are usually employed commercially (Gresta et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Kumar et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Renau-Morata et al. 2012).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe dark red dried stigmas of \u003cem\u003eC. sativus\u003c/em\u003e are the precious spice known as saffron, used since ancient times as a condiment and natural dye in traditional foods and as a medicinal plant in folk medicine (Bagur et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Cardone et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Mzabri et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Shahi et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Organoleptic properties depend mainly on the content of apocarotenoids deriving from zeaxanthin: crocins, conferring colour; picrocrocin, determining bitter flavour; and safranal, responsible for the saffron aroma (Stelluti et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). While safranal, the main aromatic compound, is only at low levels in fresh stigmas, its formation from picrocrocin is aided during the drying process leading to the saffron spice (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSaffron spice is classified into 3 quality categories according to the ISO 3632-1:2011 rules, based on physical features of the dried saffron stigmas, and their colouring capacity, bitterness, and aromatic strength, determined by UV-vis spectrophotometric analysis of 1% w/v aqueous extracts (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Giupponi et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The spice also contains phenolic compounds, including anthocyanins, flavonoids, and coumaric, gallic, and ellagic acids (Caser et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). The main apocarotenoids, vitamin C, and phenolic compounds give the spice antioxidant properties, conferring the health beneficial effects to saffron (Bagur et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Shahi et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSaffron is mainly cultivated in open fields, under either a perennial cycle of 3\u0026ndash;5 years or an annual crop by replanting the largest daughter corms each year (Stelluti and Scariot \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). A major constraint limiting saffron cultivation is the difficulty in obtaining high-quality corms for propagation, with guaranteed levels of purity, homogeneity, and phytosanitary status (Rubio-Morata et al. 2012). The yield of replacement corms is influenced by the size of the mother corm, water availability, fertilization, pedoclimatic conditions, and agronomic practices (Barbieri et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Caser et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Indeed, the development of replacement corms depends on the photoassimilates produced by leaf photosynthesis as well as the reserves stored in the mother corms (Pallotti et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Thus, beyond flowering, light plays a crucial role in sustaining photosynthesis during the subsequent vegetative phase, promoting the development of replacement corms (Moradi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Yang et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In a field experiment, saffron plants grown under low light conditions (50% of natural light intensity using shade cloth) showed a reduced photosynthetic capacity and lower corm yield (Yang et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGreenhouse cultivation of saffron is gaining increasing interest due to its potential to improve crop management and to enhance both the spice yield and quality (Askari-Khorasgani and Pessarakli \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Cardone et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Caser et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Molina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, although greenhouses provide optimal conditions for producing the spice, yields of high-quality replacement corms are generally lower than in open-field cultivation (Moradi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Renau-Morata et al. 2012). As saffron plants often exhibit traits typical of low-light environments under greenhouse conditions, inadequate lighting may be the cause (Rubio-Morata 2012). In this context, supplemental LED lighting in greenhouses represents a promising strategy to enhance the yield of replacement corms, potentially enhancing future yields.\u003c/p\u003e \u003cp\u003eIn the last decade, innovative lighting systems based on light-emitting diodes (LEDs) have been increasingly adopted to enhance photosynthetic activity, plant productivity, and nutraceutical quality, by promoting the synthesis of bioactive compounds (Alrifai et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Gao et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Paradiso and Proietti \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). LEDs are solid-state light sources characterized by high energy efficiency, long lifespan, and safe operation.\u003c/p\u003e \u003cp\u003eIn saffron, it is known that light influences flowering and both spice yield and quality and plants are sensitive to light environment even at the corm stage (Gao et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Zhou et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Renau-Morata et al. (2012) reported that light saturation during the vegetative phase was reached at 498 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; for greenhouse-grown plants and at 840 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; in open-field conditions. Corm treatments with LEDs showed an influence of light spectrum and photoperiod on the flowering process (earliness or delay \u0026ndash; Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) and of light spectrum and intensity on both the yield and quality of the spice in terms of crocins and picrocrocin content (Zhou et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo the best of our knowledge, the effects of supplemental white LED lighting applied throughout the entire life cycle of saffron cultivated in greenhouses, particularly on corm yield, have not been previously investigated. In greenhouse systems, light availability is often a limiting factor for saffron growth and development, with direct implications for both spice yield and quality and the production of replacement corms. Therefore, the objective of this study was to evaluate supplemental white LED lighting as a practical strategy to overcome light limitation and enhance saffron productivity, by improving spice yield and quality and corm production under greenhouse conditions.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Plant material and growing conditions\u003c/h2\u003e \u003cp\u003eSaffron plants were grown in an unheated greenhouse located at Grugliasco, Italy (45\u0026deg;06\u0026prime;23.21\u0026Prime; N, 7\u0026deg;57\u0026prime;82.83\u0026Prime; E; elevation 300 m ASL). At the end of August 2020, corms with a minimum weight of 19 g were individually potted in 4 L plastic containers (14\u0026times;14 cm base, 17 cm height), each filled with 1.5 L of sterile perlite (particle size 2\u0026ndash;6 mm; Centro Evergreen Turco s.a.s., Moncalieri, Turin, Italy).\u003c/p\u003e \u003cp\u003ePlants were placed on two benches: one received supplementary LED lighting (SL), while the other was exposed only to natural light (NL) and served as the control. The experiment employed a randomized block design with 3 blocks per treatment, and 6 pots per block, resulting in a total of 18 pots per treatment.\u003c/p\u003e \u003cp\u003eSupplemental lighting was provided by one MIGRO ARAY 4 Full Spectrum LED bars (MIGRO Lighting, Dublin, Ireland) (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e), installed at a fixed height of 80 cm above the pots. The system was dimmed to provide a photosynthetic photon flux density (PPFD) of approximately 260 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1;, measured at the plant level using a LI-1000 Data Logger (LI-COR Biosciences, Lincoln, NE, USA). The PPFD level was set to optimize photosynthesis, especially during the vegetative phase, while avoiding light stress and photoinhibition by remaining below the light saturation point (Renau-Morata et al. 2012).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMeasured PPFD under NL and SL (h 10\u0026ndash;16, 1h intervals) were, respectively (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD): 277.3\u0026thinsp;\u0026plusmn;\u0026thinsp;120.25 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; and 540\u0026thinsp;\u0026plusmn;\u0026thinsp;120.25 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; during the flowering phase (October\u0026ndash;November), 199.8\u0026thinsp;\u0026plusmn;\u0026thinsp;79.89 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; and 462\u0026thinsp;\u0026plusmn;\u0026thinsp;79.89 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; during the vegetative phase (December\u0026ndash;February), and 465.0\u0026thinsp;\u0026plusmn;\u0026thinsp;48.16 and 727.8\u0026thinsp;\u0026plusmn;\u0026thinsp;48.16 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; during the reproductive phase. The photoperiod followed the natural day-night cycle of Grugliasco (Turin, Italy), based on local sunrise and sunset times (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.calendariando.it/alba-e-tramonto/grugliasco/?anno=2020\u003c/span\u003e\u003cspan address=\"https://www.calendariando.it/alba-e-tramonto/grugliasco/?anno=2020\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e; 2021). LED lighting was provided exclusively during daytime, to supplement natural light without modifying the photoperiod. During the phenological phases, day length ranged from 11\u0026thinsp;\u0026minus;\u0026thinsp;9 h (flowering, October-November), 8\u0026ndash;10 h (vegetative, December-February), and 10\u0026ndash;13 h (reproductive, March-April). The LED lamp used had a power consumption of 250 W.\u003c/p\u003e \u003cp\u003eDaily light integral (DLI) was estimated from solar radiation data (W m⁻\u0026sup2;) recorded by a NETSENS weather station from October 2020 to April 2021) converted to PPFD (\u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1;) using a factor of 4.57 (Richard and Thimijan, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1983\u003c/span\u003e), corrected for greenhouse attenuation. The DLI (mol m⁻\u0026sup2; d⁻\u0026sup1;) was obtained by integrating corrected PPFD over the photoperiod using the formula: DLI = (PPFD \u0026times; hours \u0026times; 3600)\u0026thinsp;\u0026divide;\u0026thinsp;1,000,000, averaged by phenological phase. Under SL DLI included the LED contribution (~\u0026thinsp;260 \u0026micro;mol m⁻\u0026sup2; s⁻\u003csup\u003e1\u003c/sup\u003e). In NL, DLI was 10.5\u0026thinsp;\u0026plusmn;\u0026thinsp;5.4 mol m⁻\u0026sup2; d⁻\u0026sup1;, 7.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.29 mol m⁻\u0026sup2; d⁻\u0026sup1;, and 21.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37 mol m⁻\u0026sup2; d⁻\u0026sup1; (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) during flowering (October-November), vegetative (December-February), and reproductive phase (March-April), respectively. Under SL, DLI was 20.3\u0026thinsp;\u0026plusmn;\u0026thinsp;6.35 mol m⁻\u0026sup2; d⁻\u0026sup1;, 16.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.98 mol m⁻\u0026sup2; d⁻\u0026sup1;, and 33.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67 mol m⁻\u0026sup2; d⁻\u0026sup1; (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) for the same phases.\u003c/p\u003e \u003cp\u003eAir temperature and relative humidity in the greenhouse were recorded every 30 minutes using a data logger (EasyLog USB, version 7.6.0.0; Lascar Electronics, UK) throughout the entire experiment. The average monthly day/night temperatures (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) were 23.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.22/21.0\u0026thinsp;\u0026plusmn;\u0026thinsp;2.09\u0026deg;C before the flowering phase (September-October), 16.9\u0026thinsp;\u0026plusmn;\u0026thinsp;4.02/14.9\u0026thinsp;\u0026plusmn;\u0026thinsp;2.30\u0026deg;C during flowering (November), and 18.7\u0026thinsp;\u0026plusmn;\u0026thinsp;6.27/14.0\u0026thinsp;\u0026plusmn;\u0026thinsp;4.05\u0026deg;C during the vegetative phase (December-May), specifically 13.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.05/11.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.59\u0026deg;C in December-February and 22.5\u0026thinsp;\u0026plusmn;\u0026thinsp;4.51/17.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.54\u0026deg;C in March-May.\u003c/p\u003e \u003cp\u003ePlants were fertigated every two weeks with a modified Long-Ashton nutrient solution (Hewitt 1952; Stelluti et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e) from the onset of root development until leaf senescence (200 mL per pot; pH 7, EC 979 \u0026micro;S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 22\u0026deg;C).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Flower production, spice yield, and leaf development\u003c/h2\u003e \u003cp\u003eAt flowering, flower and spice yield per corm were assessed. Saffron spice was produced by initially dehydrating the stigmas in the shade for 48\u0026ndash;72 hours, followed by further drying in a cold-air dryer (NWT100, Northwest Technologies, Boves, Italy) at 20\u0026deg;C for 48 hours (Stelluti et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLeaf production (number of leaves and leaf length per plant) and corm yield (number, weight, and size of replacement corms per plant) were measured toward and at the end of the vegetative phase, respectively. Leaf area (LA, cm\u0026sup2; plant\u003csup\u003e-1\u003c/sup\u003e) was estimated using the equation LA\u0026thinsp;=\u0026thinsp;191.33\u0026middot;e^(L\u0026middot;0.0037), where \u0026ldquo;L\u0026rdquo; represents leaf length in millimeters, following the formula proposed by Kumar (\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Physiological measurements\u003c/h2\u003e \u003cp\u003eDuring the vegetative phase (end of January 2021), the net CO₂ assimilation rate (A, \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1;) and transpiration rate (E, mmol m⁻\u0026sup2; s⁻\u0026sup1;) were measured in 12 plants per treatment using an InfraRed Gas Analyzer (IRGA; LCi-Pro, ADC Hoddesdon, UK). For each measurement, the middle section of three intact, healthy, fully green leaves per plant was enclosed in a 6.25 cm\u0026sup2; sealed leaf chamber for approximately one minute. Measurements were conducted between 1:00 and 5:00 pm, at a greenhouse temperature of 15.1\u0026thinsp;\u0026plusmn;\u0026thinsp;5.9\u0026deg;C (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD), a CO₂ concentration of 493.3\u0026thinsp;\u0026plusmn;\u0026thinsp;17.9 ppm (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD), and an air pressure of 99.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52 kPa (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD). PPFD at canopy level was 394.0\u0026thinsp;\u0026plusmn;\u0026thinsp;16.0 \u0026micro;mol m⁻\u0026sup2; s⁻\u003csup\u003e1\u003c/sup\u003e (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) under NL and 399.0\u0026thinsp;\u0026plusmn;\u0026thinsp;55.4 \u0026micro;mol m⁻\u0026sup2; s⁻\u003csup\u003e1\u003c/sup\u003e (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD) under SL. Water use efficiency (WUE, \u0026micro;mol CO\u003csub\u003e2\u003c/sub\u003e mmol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e H\u003csub\u003e2\u003c/sub\u003eO) was calculated as the ratio A/E.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4. Saffron spice quality\u003c/h2\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.4.1. Spice extract preparation\u003c/h2\u003e \u003cp\u003eThe aqueous extract of the spice was prepared according to the protocol described by Stelluti et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Briefly, 50 mg of powdered spice was suspended in 5 mL of deionized water and stirred at 1000 rpm for 1 hour at room temperature (~\u0026thinsp;21\u0026deg;C) in the dark using a magnetic stirrer. The mixture was then centrifuged at 10,000 rpm for 10 minutes at 4\u0026deg;C using an Eppendorf Centrifuge 5425 R. The supernatant was subsequently filtered using PVDF syringe filters (0.45 \u0026micro;m pore size; CPS Analitica, Milan, Italy).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e \u003ch2\u003e2.4.2. Spectrophotometric Analysis (ISO 3632)\u003c/h2\u003e \u003cp\u003eThe spice extract was measured using a Cary 60 UV\u0026ndash;Vis spectrophotometer (Agilent Technologies, Santa Clara, CA, USA). Absorbance was recorded at wavelengths of 257 nm for picrocrocin, 310 nm for safranal, and 440 nm for crocins (Caser et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Stelluti et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Data were normalized to dry matter content and reported as the absorbance of a 1% (w/v) aqueous saffron solution, using a cuvette with a 1 cm optical path length (A₁%\u0026sup1;cm λ_max). The analysis was performed in the dark. Extracts were then stored at 20\u0026deg;C for subsequent evaluations.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.4.3. HPLC Analysis\u003c/h2\u003e \u003cp\u003eThe concentrations of safranal and phenolic compounds in saffron spice extract were quantified using an Agilent 1200 High-Performance Liquid Chromatography (HPLC) system equipped with a UV-Vis diode array detector (Agilent Technologies, Santa Clara, CA, USA). Separation was performed on a Kinetex C18 column (4.6 \u0026times; 150 mm, 5 \u0026micro;m particle size; Phenomenex, Torrance, CA, USA). Identification of each compound was achieved by matching retention times and UV spectra with those of reference standards purchased from Sigma-Aldrich (Saint Louis, MO, USA) analysed under identical chromatographic conditions. All analyses were conducted in triplicate. Safranal quantification was performed as described by Stelluti et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Briefly, chromatographic separation was achieved using a water-acetonitrile gradient as the mobile phase: 5% to 95% (v/v) acetonitrile over 30 min, followed by 95% to 5% (v/v) acetonitrile over 5 min, with additional 10 min conditioning period. The flow rate was 0.6 mL min\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and safranal was detected at 310 nm. Results were expressed as mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of spice. The phenolic compounds quantified included hydroxycinnamic acids (caffeic, chlorogenic, coumaric, and ferulic acids), hydroxybenzoic acids (ellagic and gallic acids), flavonols (hyperoside, isoquercitrin, quercetin, quercitrin, and rutin), and flavanols (catechin and epicatechin). Total content for each group was calculated by summing the concentrations of individual compounds. Caffeic acid was found in two out of three replicates, while coumaric acid was detected in only one replicate. Phenolic compounds were analysed as described by Stelluti et al. (\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Hydroxycinnamic acids and flavonols were separated using a gradient from 5% to 21% acetonitrile (CH₃CN) over 17 min, followed by 21% CH₃CN for 3 min, with a 2 min conditioning period and a flow rate of 1.5 mL min⁻\u0026sup1;. UV detection was performed at 330 nm. Hydroxybenzoic acids and flavanols were separated using a gradient from 3% to 85% methanol/formic acid (CH₃OH/HCOOH, 100:0.1 v/v) over 22 min, followed by 85% CH₃OH/HCOOH for 1 min, with a 2 min conditioning period and a flow rate of 0.6 mL min⁻\u0026sup1;. UV detection was performed at 280 nm. Compound concentrations were expressed as mg g⁻\u0026sup1; of spice.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.4.4 Yield and starch content of replacement corms\u003c/h2\u003e \u003cp\u003eCorms were counted, measured, and weighed. Starch content was determined in three replacement corms with significantly similar fresh and dry weights per treatment (fresh weight: NL 5.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30g, SL 5.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14g; dry weight: NL 1.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02g, SL 1.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03g; Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE), after drying at 60\u0026deg;C for 120 hours in an oven, using the Megazyme Total Starch Assay Kit (Megazyme International Ireland Ltd, Wicklow, Ireland). The assay followed specific protocols for samples containing resistant starch, D-glucose, and maltodextrins, including the removal of free D-glucose and maltodextrins via alcohol washing, as in Stelluti et al. (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Total starch content per plant was calculated by multiplying the starch concentration (mg g⁻\u0026sup1; corm) by the total corm dry weight per plant (g).\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e2.5 Statistical analysis\u003c/h2\u003e \u003cp\u003eData normality was assessed using the Shapiro-Wilk test (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), and homoscedasticity was evaluated with Levene\u0026rsquo;s test (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). When assumptions of normality or homoscedasticity were violated, the non-parametric Wilcoxon rank-sum test was applied. All statistical analyses were performed using RStudio (R Core Team, 2023).\u003c/p\u003e \u003cp\u003eStatistically analysed data are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error (SE); climatic data are expressed as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard deviation (SD).\u003c/p\u003e \u003cp\u003eFor the \u0026lsquo;number of leaves\u0026rsquo;, one value from NL (i.e., 79) was discarded due to a z-score\u0026thinsp;\u0026ge;\u0026thinsp;2. For \u0026lsquo;corm plant⁻\u0026sup1;\u0026rsquo;, one value from the NL treatment (i.e., 11) and one from the SL treatment (i.e., 10) were also excluded for the same reason.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e3.1. Plant growth\u003c/h2\u003e \u003cp\u003eFlowering of saffron plants occurred 6 days later under SL (at 72 days after planting, DAP) compared to NL (66 DAP) and lasted approximately 11 days regardless of lighting conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The 50% of the total number of flowers was reached after 8 days under NL and after 6 days under SL. The number of flowers (ca. 4 per plant) and spice yield (ca. 30 mg per plant) were unaffected by SL (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of natural light (NL) and supplemental LED lighting (SL) on flowering, yields, vegetative growth, and starch content of plants. Data are expressed as Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE. Sample sizes were as follows: flowering onset and flower yield, n\u0026thinsp;=\u0026thinsp;18; flowering duration and spice yield, n\u0026thinsp;=\u0026thinsp;3; leaf number, n\u0026thinsp;=\u0026thinsp;7 (NL) and n\u0026thinsp;=\u0026thinsp;8 (SL); leaf area, n\u0026thinsp;=\u0026thinsp;8; corm yield, n\u0026thinsp;=\u0026thinsp;12 (corms plant⁻\u0026sup1;, n\u0026thinsp;=\u0026thinsp;11); starch content, n\u0026thinsp;=\u0026thinsp;3.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSignificance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowers and spice\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowering onset (DAP)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e65.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e71.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowering duration in single plants (days plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.155\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowering period duration (days)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10.7\u0026thinsp;\u0026plusmn;\u0026thinsp;1.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.713\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlowers plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (n.)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.051\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDays to reach 50% of total flowers\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpice plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (mg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.3\u0026thinsp;\u0026plusmn;\u0026thinsp;3.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e30.4\u0026thinsp;\u0026plusmn;\u0026thinsp;2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.819\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeaf number and area\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNumber of leaves (n. plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.0\u0026thinsp;\u0026plusmn;\u0026thinsp;3.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e54.9\u0026thinsp;\u0026plusmn;\u0026thinsp;3.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.006\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLeaf length (cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.1\u0026thinsp;\u0026plusmn;\u0026thinsp;1.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndividual leaf area (cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlant leaf area (cm\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e330.8\u0026thinsp;\u0026plusmn;\u0026thinsp;33.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e242.1\u0026thinsp;\u0026plusmn;\u0026thinsp;19.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.043\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCorm size and starch content\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCorm plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (n.)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndividual corm weight plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.683\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndividual corm size plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.671\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal corm fresh weight plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (g)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20.3\u0026thinsp;\u0026plusmn;\u0026thinsp;1.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStarch (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corm dry weight)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e603.6\u0026thinsp;\u0026plusmn;\u0026thinsp;22.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e664.3\u0026thinsp;\u0026plusmn;\u0026thinsp;21.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.126\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal starch per plant (g plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cem\u003e*\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.011\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eDuring the vegetative phase, SL increased the number of leaves per plant by 45% (from 38.0 to 54.9) compared to NL but led to a 40% reduction in leaf length (from 38.1 to 22.7 cm) and a 43% reduction in individual leaf area (from 7.9 to 4.5 cm\u003csup\u003e2\u003c/sup\u003e) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Consequently, the total plant leaf area under SL was 27% lower than that in plants grown under NL (from 330.8 to 242.1 cm\u003csup\u003e2\u003c/sup\u003e) (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eConversely, plants grown under SL produced 25% more corms (from 6.0 to 7.5), while mean weight (3.4 g per plant), size (19.4 mm per plant), and starch content (634.0 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) remained unchanged (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Total starch content per plant was estimated to increase by 44% under SL (5.2 g per plant) compared to NL (5.2 vs. 3.6 g per plant). Corm size distribution for the NL and SL treatments is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e3.2. Spice quality\u003c/h2\u003e \u003cp\u003eAccording to the ISO 3632 standard, the saffron spice was qualified as first quality category (I), regardless of lighting conditions (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Compared to natural light, SL did not affect the content of crocins (ca. 228.6\u0026ndash;237.0 A1%1cm) and picrocrocin (92.4\u0026ndash;97.7 A1%1cm) but resulted in a lower concentration of safranal (31.8\u0026ndash;36.9 A1%1cm), thereby reducing the strength of saffron aroma by16% (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). However, this reduction was not observed when safranal content (0.01\u0026ndash;0.02 mg g⁻\u0026sup1;) was analysed using the more sensitive HPLC-DAD method (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eColouring capacity, bitterness, and aromatic strength, determined by UV-vis spectrophotometric analysis according to ISO 3632 (ISO, 2011), of saffron spice collected from plants grown under natural light (NL) and supplemental LED lighting (SL). The quality category is indicated in brackets. Threshold values for Category I quality are: crocins\u0026thinsp;\u0026gt;\u0026thinsp;200, picrocrocin\u0026thinsp;\u0026gt;\u0026thinsp;70, and safranal 20\u0026thinsp;\u0026divide;\u0026thinsp;50. Data are expressed as Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE of specific absorbance (A\u003csub\u003e1\u003c/sub\u003e%\u003csup\u003e1\u003c/sup\u003ecm) at 440 nm for crocins, 257 nm for picrocrocin, and 330 nm for safranal.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSignificance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eISO 3632\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eColour/Crocins (A1%, 1cm, λ440)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e237.0\u0026thinsp;\u0026plusmn;\u0026thinsp;7.11 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e228.6\u0026thinsp;\u0026plusmn;\u0026thinsp;2.82 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.306\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlavour/Picrocrocin (A1%, 1cm, λ257)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e97.7\u0026thinsp;\u0026plusmn;\u0026thinsp;2.58 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e92.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.59 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAroma/Safranal (A1%, 1cm, λ330)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e36.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e31.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47 (I)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e***\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.000\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHPLC-DAD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSafranal (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.720\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eRegarding phenolic compounds, SL increased total hydroxycinnamic acid content by 54% (from 4.7 to 7.2 mg g⁻\u0026sup1;) and total phenolic acid content by 52% (from 6.9 to 10.5 mg g⁻\u0026sup1;) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSafranal and phenolic compounds quantified by HPLC-DAD analysis in aqueous extracts of saffron spice from plants grown under NL and supplemental LED lighting (SL). Data are expressed as Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE (n\u0026thinsp;=\u0026thinsp;3). Total hydroxycinnamic acids\u0026thinsp;=\u0026thinsp;sum of caffeic, chlorogenic, coumaric, and ferulic acids; n.d. = not detectable.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSL\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSignificance\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydroxycinnamic acids\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCaffeic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.042\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChlorogenic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.316\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.356\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.400\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCoumaric acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.09\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFerulic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.077\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal hydroxycinnamic acids (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.259\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.387\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.011\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHydroxybenzoic acids\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEllagic acid\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.350\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.252\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.083\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal phenolic acids (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.608\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.639\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.020\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlavonoids (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHyperoside\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.068\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEpicatechin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.658\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal flavonoids (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.433\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.361\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.309\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTotal phenolic compounds (mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.999\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.284\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.113\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNo significant differences were observed for chlorogenic and ellagic acids. In contrast, coumaric acid and ferulic acid were detected only under SL. However, coumaric acid was detected in only one sample out of three (0.09 mg g⁻\u0026sup1;). Caffeic acid was found in both NL (0.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.042 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE, n\u0026thinsp;=\u0026thinsp;2) and SL (0.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.052 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SE, n\u0026thinsp;=\u0026thinsp;3) samples. The SL did not affect total flavonoid content, nor did it influence epicatechin specifically. However, hyperoside was found only under NL (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Gallic acid, isoquercitrin, quercetin, quercitrin, rutin, and catechin were not detected under either lighting condition.\u003c/p\u003e \u003cp\u003eOverall, total phenolic compound levels tended to be higher under SL, although differences were not statistically significant.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Gas exchange\u003c/h2\u003e \u003cp\u003ePhysiological parameters of saffron plants under NL and SL are reported in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The net photosynthetic rate (A) was significantly higher under SL compared to NL (9.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.57 vs. 6.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.84 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1;; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001). No significant differences were observed in the transpiration rate (E) between SL and NL (3.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30 and 3.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17 mmol m⁻\u0026sup2; s⁻\u0026sup1;, respectively). Water use efficiency (WUE) was higher under SL than under NL (2.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17 vs. 2.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.008).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussions","content":"\u003cp\u003eIn recent decades, saffron cultivation under controlled conditions has received increasing attention, with the aim of improving crop management, particularly to regulate flowering time, enhance crop yield and produce quality, simplify flower harvesting and stigma separation, and to increase the overall crop profitability (Askari-Khorasgani and Pessarakli \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Cardone et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Gresta et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Molina et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSaffron is considered a thermo-periodic species and is classified as a short-day plant (Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). As in other geophytes such as \u003cem\u003eTulipa\u003c/em\u003e, \u003cem\u003eFreesia\u003c/em\u003e, and \u003cem\u003eIris\u003c/em\u003e, temperature represents the main environmental factor regulating both the growth and flowering (Haghighi et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Khodorova and Boitel-Conti \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Molina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e; Proietti et al \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In our study, the average air temperature in greenhouse during the flowering period was 17\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2\u0026deg;C (Mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD), which is considered the optimal thermal level for reproductive stage in saffron (Haghighi et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Molina et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). However, previous studies showed that flowering in saffron is influenced also by light, with possible effects of all parameters: intensity, photoperiod, and spectral composition (Gao et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Moradi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Zhu et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In our experiment, under identical temperature conditions, SL delayed the beginning of flowering by 6 days compared to NL. However, flowering lasted approximately 11 days regardless of lighting conditions. In this respect, it is worth noting that most experiments dealing with LED lighting in greenhouse-grown saffron aim at modifying the solar light spectrum by integrating red and/or blue monochromatic light, to trigger targeted photomorphogenetic responses driven by specific wavebands. Differently, the main objective of LED supplemental lighting in our study was to integrate solar radiation with a balanced spectrum artificial light, to guarantee a sufficient light intensity during the winter period, in a geographic area where it can be a limiting factor, particularly in greenhouse, because of the shading effect of structure and cover. To this purpose, LED emission in our study was set at 260 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1; to sustain assimilation, based on the light requirement reported in literature for greenhouse saffron (Renau-Morata et al. 2012).\u003c/p\u003e \u003cp\u003eIn saffron, a progressive increase in total sugar level (specifically glucose and fructose) was found to be associated with the degradation of starch, from the quiescent stage of corms to the bud break and floral anthesis (Bagri et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). These changes were suggested to initiate sprouting and bud growth in saffron corms. In a \u0026ldquo;two-segment\u0026rdquo; cultivation method, during the indoor stage under a greenhouse, saffron corms were treated with five light intensities using LED lamps containing red, blue, green, and white, maintaining a red-to-blue ratio of 3:1. Higher intensity of LED light slowed down the starch degradation in the corms during the flowering phase, with a stronger effect at increasing PPDF (Zhou et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Accordingly, in a field experiment, during vegetative growth, starch degradation in mother corms was faster under low light conditions (50% of natural light using shading cloth) compared to full solar radiation, with a parallel increase of sucrose and glucose (Yang et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). This reduction in starch content was due to an elevated activity of starch-degrading enzymes (e.g., α-amylase), indicating a mobilization of carbohydrate reserves to support leaf expansion. Besides, in our experimental conditions, the higher light intensity under LED lighting may have sustained a higher photosynthetic assimilation reducing the demand of reserve material for flower and leaf development, hence delaying flowering.\u003c/p\u003e \u003cp\u003eFlower production and spice yield were not affected by LED supplemental lighting. This outcome may be due to the influence of the big corm size used in the study, as larger corms already contain sufficient nutrient reserves to promote a proper plant growth and flowering. During flowering, approximately 20\u0026ndash;30% of the mother corm\u0026rsquo;s reserves are mobilized to support the flower formation and the leaf development, which in our case occurred shortly before flowering (Renau-Morata et al. 2012). To the best of our knowledge, no similar studies are currently available for comparison.\u003c/p\u003e \u003cp\u003eUnder field conditions, where recommended planting density is from 55 to 75 corms m⁻\u0026sup2; (Cardone et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), yields generally range from 5 to 15 kg ha⁻\u0026sup1;, though they can vary widely \u0026ndash; from 2 kg ha⁻\u0026sup1; to 30 kg ha⁻\u0026sup1; \u0026ndash; depending on pedoclimatic conditions, agronomic practices, and corm size (Cardone et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Stelluti and Scariot \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In particular, planting density affects both spice yield and the development of the corms: while higher densities tend to increase stigma yield, lower densities promote the development of heavier replacement corms (Barbieri et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Kumar et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Our results confirm that controlled cultivation conditions can enhance saffron spice yield compared to open-field cultivation, as the spice yield obtained in our study (approximately 15 kg per hectare), at a planting density of 51 corms m⁻\u0026sup2;, was relatively high compared to typical open-field production.\u003c/p\u003e \u003cp\u003eSimilarly, our results indicate that controlled cultivation conditions can enhance the yield of replacement corms compared to open-field cultivation. in a previous field experiment, Caser et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, using a lower planting density (39 corms m⁻\u0026sup2;), obtained an average of 2.1 replacement corms per plant, with a total corm weight per plant of 13.38 g and a corm yield of 422 g m⁻\u0026sup2; after one year. These values are lower than those obtained in the present soilless study, conducted at a higher planting density (51 corms m⁻\u0026sup2;). Under natural light (NL), we obtained approximately three times more replacement corms per plant, although individual corms weighed about half as much, resulting in a total corm weight per plant of 20.3 g and a corm yield of 1035.3 g m⁻\u0026sup2;. With supplemental LED lighting, the increase in the number of replacement corms per plant was even greater (about 3.5-fold compared to field conditions), with a comparable individual corm weight, leading to a total corm weight per plant of 24.7 g and a corm yield of 1259.7 g m⁻\u0026sup2;. However, the average weight of individual corms obtained under field conditions (6.5 g - Caser et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) was higher than that of corms produced in the soilless system, which could reduce flowering performance and, consequently, saffron spice yield in the subsequent growing cycle.\u003c/p\u003e \u003cp\u003eIn our experiment, the classification of our saffron spice according to ISO 3632 quality categories remained unaffected by lighting conditions and it was consistently classified as first category. Commercial saffron is generally classifiable as first quality category, as demonstrated by Giupponi et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) and Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), who analysed samples from various countries. Specifically, up to 93% of 484 samples collected in Italy over four years were found to be of first category (Giupponi et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Similarly, 96% of 57 samples from Italy, 94% of 64 samples from Spain, 91% of 115 samples from Greece, and 53% of 154 samples from Iran (for an overall 77.18% of the total number of samples), fell within the first class (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, it is known that the ISO 3632 (2011) method lacks accuracy (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). This procedure estimates safranal content via UV-visible spectrophotometry at 330 nm; however, crocins and other compounds also absorb at this wavelength, thus interfering with the analysis. Moreover, the standard assigns the same safranal range (20\u0026ndash;50) to all quality grades, making crocins and picrocrocin the main criteria for quality classification; for example, category I requires crocins\u0026thinsp;\u0026ge;\u0026thinsp;200 and picrocrocin\u0026thinsp;\u0026ge;\u0026thinsp;70 (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Stelluti and Scariot \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Recently proposed analytical methods aim to improve saffron quality classification according to ISO 3632 (Locatelli et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). Although saffron\u0026rsquo;s colour and bitter taste are highly valued, the distinctive safranal-driven aroma truly reveals the essence of the spice. Previous studies suggested that the more sensitive HPLC-DAD method could be incorporated into or replace the ISO 3632 method (Garc\u0026iacute;a-Rodr\u0026iacute;guez et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Notably, even though the aroma decreased under SL, in our experiment safranal content measured by the HPLC-DAD method was not affected by SL.\u003c/p\u003e \u003cp\u003eLight quality is known to influence plant secondary metabolism, particularly the biosynthesis of phenolics and carotenoids (Alrifai et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Paradiso and Proietti \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In saffron, light spectrum and photoperiod affects the synthesis and accumulation of apocarotenoids \u0026ndash; such as crocins and picrocrocin \u0026ndash; and phenolic compounds (Li et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Moradi et al. 2022; Zhou et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In our study, SL increased total hydroxycinnamic acids, and consequently the total phenolic acids; notably, coumaric acid and ferulic acid were detected only in SL-treated samples. This effect could be related to a combined effect of both light intensity and spectral composition. Indeed, the higher PPFD at high proportion of R and B could have enhanced the carbon assimilation and carbohydrate production, thereby increasing the amount of carbohydrate allocated to secondary metabolism; besides it is known that B light drives the biosynthesis of several antioxidant compounds, including phenolics (REF). In addition, light perception through specific photoreceptors involved in photomorphogenesis could activate signalling pathways that regulate the expression of enzymes in secondary metabolism, including phenolic biosynthesis, independently of photosynthetic metabolism (Paradiso and Proietti, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These mechanisms likely contributed to the observed increase in phenolic acids content under SL.\u003c/p\u003e \u003cp\u003eConversely, SL did not affect the total flavonoids, even if hyperoside was detected only in NL samples. These results indicate that light plays a key role in modulating the phenylpropanoid pathway, as reported in other plant species (Alrifai et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), and may promote the synthesis of specific phenolic compounds in saffron. Overall, our findings suggest that supplemental LED lighting can shape the phenolic composition of saffron, enhancing the accumulation of specific antioxidant compounds, thus improving the nutraceutical profile of the spice. Although these changes do not affect the official quality classification as defined by international standards, they represent an added value in terms of biochemical composition and potential health-related attributes of the spice.\u003c/p\u003e \u003cp\u003eDuring the vegetative phase, following flowering, saffron plants grown under SL exhibited reduced leaf length and area, yet showed an increased photosynthetic activity, as previously observed by Zhou et al. (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Renau-Morata et al. (2012) reported that saffron plants grown in greenhouse exhibited morphological and physiological traits typically associated with low irradiance, e.g., rapid leaf expansion, reduced chlorophyll concentration, and a decline in photosynthetic efficiency. The LED supplemental lighting likely counteracted these traits.\u003c/p\u003e \u003cp\u003eAfter flowering, as leaves and roots reach their maximum development, the contribution of the residual reserves of the mother corm to vegetative growth gradually declines in favour of photosynthetic assimilation. Once these reserves are nearly exhausted, the exponential growth of replacement corms begins, sustained exclusively by photosynthesis (Renau-Morata et al. 2012). The higher net photosynthesis of saffron grown under LED supplemental lighting (+\u0026thinsp;62%), together with the unchanged transpiration rate and the increase in water use efficiency (WUE\u0026thinsp;=\u0026thinsp;A/E) indicate that SL-grown plants fixed more CO₂ per unit of transpired water.\u003c/p\u003e \u003cp\u003eWhen estimating the total CO₂ assimilation by multiplying the plant leaf area by the net photosynthesis, plants under SL exhibited approximately 19% higher values compared to those under NL. Accordingly, SL plants produced more replacement corms. While the individual weight of the corms remained unchanged compared to those grown under natural light, the increased number resulted in a higher total weight of corms per plant. As a consequence, although the increase in starch content per corm in SL-grown plants was not statistically significant, the higher number of corms determined that the total accumulation of starch per plant was greater under LED lighting compared to NL. Accordingly, Yang et al. (\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2025\u003c/span\u003e) found that both starch concentration and corm yield decreased under low light conditions (50% of natural light using shade cloth). This finding is consistent with the observed increase in photosynthetic activity of SL plants, which likely supported both the production of more corms and the greater accumulation of reserve materials.\u003c/p\u003e \u003cp\u003eIn addition to supplying energy through photosynthesis, light also regulates bud development and shoot branching in plants (Paradiso and Proietti, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In saffron, higher proportions of blue light relative to red tend to promote apical dominance and suppress the outgrowth of lateral buds; conversely, an increase in the red-to-blue light ratio tend to stimulate lateral bud production (Moradi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Saffron plants cultivated under LED lighting (11 hours photoperiod; 150\u0026thinsp;\u0026plusmn;\u0026thinsp;10 \u0026micro;mol m⁻\u0026sup2; s⁻\u0026sup1;) and exposed to six LED treatments with varying blue-to-red light ratios after flowering, produced fewer but heavier daughter corms under higher proportion of blue light. In contrast, more numerous and lighter daughter corms were produced under full red light (Moradi et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn our experiment, the higher intensity of white light may have reduced the apical dominance in saffron corm, thereby promoting the development of lateral buds, possibly through the modulation of hormone signalling (Rubio-Moraga et al. 2014).\u003c/p\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eCultivation of saffron in controlled environment offers the opportunity to optimize the crop agronomic management and to improve spice yield and quality and corm multiplication, even if corms produced in soilless systems appear smaller than those obtained in open field.\u003c/p\u003e \u003cp\u003eIn our experiment, in saffron grown in pot in greenhouse, supplemental LED white light did not improve the spice yield while it enhanced the phenolic acid accumulation, thereby improving the nutraceutical quality of the produce. Besides, LED lighting increased the production of replacement corms. However, quality traits of spice, such as phenolic compound content and antioxidant activity, are not yet widely recognised as factors that could increase the market value of saffron. Conversely, production of replacement corms is an important agronomic aspect to optimize saffron cultivation since propagation represents the most significant variable cost. Indeed, in traditional open-field production, purchased corms of 2.5\u0026thinsp;\u0026divide;\u0026thinsp;3.5 cm diameter can account for about 77% of the planting cost, representing about 83% of total yearly direct costs in a 5-year cycle (Barbieri et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIt is known that installing LED systems involves high initial investment and additional energy inputs. In this respect, LED lighting protocols could be optimized by limiting light supplementation to the period of vegetative growth (December\u0026ndash;February), when plants could gain the highest advantage from artificial light since light attenuation due to seasonal changes and greenhouse shading can significantly limit the photosynthetic activity. This approach would maximize the cost-effectiveness of LED lighting reducing energy costs while preserving the benefits for propagation and nursery purposes.\u003c/p\u003e \u003cp\u003eOn this basis, a comprehensive economic evaluation is essential to assess the feasibility of adopting LED technology for greenhouse saffron production, through a trade-off analysis of lamp cost and energy consumption vs. productive outputs, such as energy use per replacement corm produced.\u003c/p\u003e \u003cp\u003eFurther research is needed to optimise corm yield under supplemental LEDs in greenhouses. In particular, promoting the development of heavier corms may be beneficial, given that corm size significantly influences flower development, spice yield, and daughter corm formation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eConflict of interest\u003c/strong\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis research was funded by the program Interreg V-A Francia Italia Alcotra (Grant No. 1139 \u0026ldquo;ANTEA - Attivit\u0026agrave; innovative per lo sviluppo della filiera transfrontaliera del fiore edule\u0026rdquo;; and Grant no. 8336 \u0026ldquo;ANTES - Fiori eduli e piante aromatiche: attivit\u0026agrave; capitalizzazione dei progetti ANTEA ed ESSICA\u0026rdquo;) and by the program Interreg VI-A Francia Italia Alcotra (Grant No. 21350 \u0026ldquo;AGRISMART - Soluzioni innovative a basso impatto ambientale per la modernizzazione delle imprese agricole e strutture produttive in aree svantaggiate\u0026rdquo;).\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eStudy conception and design and Funding acquisition: Valentina Scariot; Data collection and analysis: Stefania Stelluti, Francesco Berruto; Writing - original draft preparation: Stefania Stelluti; manuscript integration and revision: all the authors.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors thank Alessandro Borrelli and Farzaneh Zamani (Department of Agricultural Sciences - University of Naples Federico II, Portici, Italy), for helping in graphical work.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlrifai O, Hao X, Marcone MF, Tsao R (2019) Current review of the modulatory effects of LED lights on photosynthesis of secondary metabolites and future perspectives of microgreen vegetables. 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Sci Hortic 303:111202. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scienta.2022.111202\u003c/span\u003e\u003cspan address=\"10.1016/j.scienta.2022.111202\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"plant-growth-regulation","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"grow","sideBox":"Learn more about [Plant Growth Regulation](https://www.springer.com/journal/10725)","snPcode":"10725","submissionUrl":"https://submission.nature.com/new-submission/10725/3","title":"Plant Growth Regulation","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Crocus sativus L., controlled environment agriculture, full-spectrum light, soilless cultivation","lastPublishedDoi":"10.21203/rs.3.rs-8871041/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8871041/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSaffron is a geophyte grown in open field, but the possibility of year-round greenhouse cultivation is attracting increasing interest. We evaluated the application of supplemental lighting with white light emitting diodes (LEDs) in greenhouse in summer-winter period, in plants grown in pot on two benches, under two lighting treatments: natural light integrated with LEDs (~\u0026thinsp;260 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and natural light only (NL) as a control. LED lighting delayed flowering by almost a week (72 vs. 66 days after planting) but did not affect the mean number of flowers (4.2 flowers plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) or spice yield (29.9 mg plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). However, LED treatment increased the phenolic acid content in the spice (+\u0026thinsp;52%) compared with NL, indicating an improvement in spice quality. During the subsequent vegetative phase, net photosynthesis was increased by supplemental lighting, while plant leaf area was reduced, since lighted plants developed more leaves but with a lower specific leaf area compared to control. Notably, plants under LED produced more corms (7.5 \u003cem\u003evs\u003c/em\u003e 6.0 corms plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), with no differences in mean corm weight (3.4 g plant\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) or starch content (645 mg g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corm dry weight) compared with natural light, suggesting a potential for increasing the yield of propagative material. Overall, supplemental LED lighting may contribute to improve spice phytochemical quality and corm multiplication, which are both agronomically relevant traits for greenhouse soilless saffron cultivation.\u003c/p\u003e","manuscriptTitle":"Supplemental LED lighting to improve saffron spice quality and corm production","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-05 09:18:28","doi":"10.21203/rs.3.rs-8871041/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-03-18T15:06:28+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-16T03:45:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"293312014835328068098007903006922716415","date":"2026-03-02T16:57:28+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-02T16:08:35+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"181789625581222614285329016557567439212","date":"2026-03-02T12:17:02+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-02T11:51:14+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-02-14T07:54:54+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-02-14T07:54:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"Plant Growth Regulation","date":"2026-02-13T10:52:20+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"plant-growth-regulation","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"grow","sideBox":"Learn more about [Plant Growth Regulation](https://www.springer.com/journal/10725)","snPcode":"10725","submissionUrl":"https://submission.nature.com/new-submission/10725/3","title":"Plant Growth Regulation","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"30c2c737-0760-4f32-81b6-4e6b09a048da","owner":[],"postedDate":"March 5th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-08T07:53:49+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-05 09:18:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8871041","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8871041","identity":"rs-8871041","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}