Supplemental Far-red Light Prevents Semidormancy and Enhances Yield and Fruit Quality of Short-day Strawberry in Indoor Production

Seedlings may be grown indoors where environmental conditions can be precisely controlled to ensure consistent and reliable production. The optimal spectrum for production under sole-source lighting is currently unknown. Far-red light (λ = 700–800 nm) typically is not a significant part of the spectrum of light-emitting diode (LED) grow lights. However, far-red light is photosynthetically active and can enhance leaf elongation, which may result in larger leaves and increased light interception. We hypothesized that adding far-red light to sole-source lighting would increase the growth of ‘Dalmatian Peach’ foxglove (Digitalis purpurea) seedlings grown under white LED lights, potentially shortening production times. Our objective was to evaluate the effect of far-red light intensities, ranging from 4.0 to 68.8 µmol·m−2·s−1, on the growth and morphology of foxglove seedlings. Foxglove seedlings were grown in a growth chamber with a photosynthetic photon flux density (PPFD) of 186 ± 6.4 μmol·m−2·s−1 and supplemental far-red light intensities ranging from 4.0 to 68.8 µmol·m−2·s−1. As far-red light increased, shoot dry weight, root dry weight, plant height, and plant height/number of leaves increased by 38% (P = 0.004), 20% (P = 0.029), 38% (P = 0.025), and 34% (P = 0.024), respectively, while root weight fraction decreased 16% (P = 0.034). Although we expected supplemental far-red light to induce leaf and/or stem expansion, specific leaf area and compactness (two measures of morphology) were unaffected. Because a 37% increase in total photon flux density (PPFD plus far-red light) resulted in a 34.5% increase in total plant dry weight, the increased growth likely was due to increased photosynthesis rather than a shade-acclimation response. The growth response was linear across the 4.0 to 68.8 µmol·m−2·s−1 range of far-fed light tested, so we were unable to determine a saturating far-red photon flux density.

In the Mediterranean region, tomato plants are often cultivated in two short cycles per year to avoid the heat of summer and the low solar radiation of winter. Supplementary light (SL) makes it possible to cultivate during the dark season. In this experiment, a tomato F1 hybrid cultivar DRW7723 was cultivated in a greenhouse for a fall-winter cycle. After transplant, light emitting diode (LED) interlighting, with two light spectra (red + blue vs. red + blue + far-red) was applied as SL. Plant growth, yield, gas exchange, nutrient solution (NS) consumption, and fruit quality were analyzed. In general, the effects of adding far-red radiation were not visible on the parameters analyzed, although the yield was 27% higher in plants grown with SL than those grown without. Tomatoes had the same average fresh weight between SL treatments, but the plants grown with SL produced 16% more fruits than control. Fruit quality, gas exchange and NS uptake were not influenced by the addition of far-red light. Interlighting is, therefore, a valid technique to increase fruit production in winter but at our latitude the effects of adding far-red radiation are mitigated by available sunlight.

The use of light-emitting diode (LED) lights in horticulture allows growers to adjust the light spectrum to optimize crop production and quality. However, changes in light quality can also influence plant-arthropod interactions, with possible consequences for pest management. The addition of far-red light has been shown to interfere with plant immunity, thereby increasing plant susceptibility to biotic stress and increasing pest performance. Far-red light also influences plant emission of volatile organic compounds (VOCs) and might thus influence tritrophic interactions with biological control agents. We investigated how far-red light influences the VOC-mediated attraction of the predatory mite Phytoseiulus persimilis to tomato plants infested with Tetranychus urticae, and its ability to control T. urticae populations. Far-red light significantly influences herbivore-induced VOC emissions of tomato plants, characterized by a change in relative abundance of terpenoids, but this did not influence the attraction of P. persimilis to herbivore-induced plants. Supplemental far-red light led to an increased population growth of T. urticae and increased numbers of P. persimilis. This resulted in a stronger suppression of T. urticae populations under supplemental far-red light, to similar T. urticae numbers as in control conditions without supplemental far-red light. We conclude that supplemental far-red light can change herbivore-induced VOC emissions but does not interfere with the attraction of the predator P. persimilis. Moreover, far-red light stimulates biological control of spider mites in glasshouse tomatoes due to increased population build-up of the biocontrol agent. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Understanding crop responses to the light spectrum is critical for optimal indoor production. Far-red light is of particular interest, because it can accelerate growth through both physiological and morphological mechanisms. However, the optimal amount of supplemental far-red light for indoor lettuce production is yet to be quantified. Lettuce ‘Cherokee’, ‘Green SaladBowl’, and ‘Little Gem’ were grown under 204 µmol·m−2·s−1 warm-white light-emitting diodes (LEDs) with supplemental far-red ranging from 5.3 to 75.9 µmol·m−2·s−1. Supplemental far-red light increased canopy light interception 5 days after the start of far-red light treatment (DAT) for ‘Green SaladBowl’ and ‘Little Gem’ and 7 DAT for ‘Cherokee’. The increase in light interception was no longer evident after 12 and 16 DAT for ‘Green SaladBowl’ and ‘Little Gem’, respectively. We did not find evidence that supplemental far-red light increased leaf-level photosynthesis. At the final harvest, shoot dry weights of ‘Cherokee’ and ‘Little Gem’ increased by 39.4% and 19.0%, respectively, while ‘Green SaladBowl’ was not affected. In conclusion, adding far-red light in indoor production increased light interception during early growth and likely increased whole plant photosynthesis thus growth, but those effects were cultivar-specific; the increase in dry weight was linear up to 75.9 µmol·m−2·s−1 far-red light.

Studies have successfully shown that additional far-red (FR) light can induce earlier flowering in strawberries (Fragaria ×ananassa). However, our understanding of the optimal plant growth phase for applying FR light remains incomplete. To optimize the appropriate time of FR light application, the June-bearing strawberry ‘Keepsake’ was irradiated at different growth phases with supplemental FR light at 43.2 µmol·m−2·s−1 at a peak wavelength of 730 nm. The treatments were FR light applied from transplanting to harvest (FR++); FR light applied for the first 40 days after transplanting (FR+−); FR light applied from 40 days after transplanting to harvest (FR−+); and natural light only (FR− −). Supplemental FR light (FR++ and FR+−) elongated the petiole and caused a steep leaf angle, resulting in an extended canopy height. While the dry biomass of the plants remained unaffected, the plants receiving FR light during the initial growth phase (FR++ and FR+−) showed a reduction in leaf area compared with those receiving natural light only or FR light 40 days after transplanting. Far-red light caused early flowering and earlier fruit output; however, this benefit was outweighed by reduced fruit diameter. Plants that received FR light 40 days later produced larger fruits, and they were on par with FR− −. Far-red light timing affected nutrient concentration in plant foliage. Plants subjected to FR light in their early growth phase had lower calcium and magnesium levels while demonstrating elevated iron levels. Manganese concentration was lower in plants exposed to continuous FR light. Therefore, applying FR light during the latter growth phase under natural light conditions may be advantageous in some June-bearing strawberry cultivars.

Overhead supplemental far-red light stimulates tomato growth under intra-canopy lighting with LEDs

Duration of light-emitting diode (LED) supplemental lighting providing far-red radiation during seedling production influences subsequent time to flower of long-day annuals

IntroductionThe regeneration of roots is crucial for the survival and healthy development of double-root-cutting (DRC) grafted watermelon seedlings. However, methods to effectively enhance root regeneration in the rootstock of DRC grafted watermelons remain unclear.MethodsIn this study, supplementary far-red (FR) light was applied to DRC grafted watermelon seedlings to evaluate its impact on seedling growth and rooting, using dark (CK) as the control.Results and discussionsIt was discovered that supplementary FR light substantially promoted root development in the rootstock, reducing the time required for root regeneration and boosting root biomass. Transcriptome profiling indicated that genes associated with sugar catabolism, oxidative stress, and auxin signaling were markedly upregulated in roots by FR light at 4 d post-grafting. FR0.3 (red/far-red ratio = 0.3) light significantly enhanced the expression of genes involved in hyperoxide scavenging (CmAPX1, CmPOD1, CmCAT1), sugar transportation (CmSWEET12, CmBST2, CmSCP1), and auxin response (CmAUX28, CmIAA11, CmSAUR20) compared with the control. Moreover, FR0.3 light treatment notably decreased reactive oxygen species content and improved antioxidant enzyme activities in roots compared with the control. However, despite increased gene expression, peroxidase and catalase did not contribute substantially to reactive oxygen species scavenging at the protein activity level under FR0.3 compared with other light qualities. In addition, sugar content and hexokinase activity responded differently to light quality: starch, sucrose, and hexokinase activity were significantly increased by FR0.3 light at 4 d post-grafting, while glucose content in the FR0.3 treatment was significantly higher than that in other treatments only at 8 d post-grafting. These results demonstrate that supplementary FR light significantly promotes rooting and growth of DRC grafted watermelon seedlings. Specifically, FR light can induce root regeneration in the rootstock, potentially by alleviating oxidative stress during grafting and providing a relatively stable plant environment through the synergistic effects of sugar metabolism, the antioxidant enzyme system, and auxin accumulation in the roots via the regulation of antioxidants, sugar metabolism, and auxin-related gene transcription. The findings from this study present a practical method to enhance the quality of grafted watermelon seedlings.

Strawberries (Fragaria ×ananassa) are being produced increasingly in indoor vertical farms, where the light quality of sole-source lighting is a primary factor that influences the outcomes of crop production. Far-red (FR) light (700–750 nm) has been shown to promote plant responses such as leaf expansion, biomass accumulation, and flowering in some long-day plant species. However, the impacts of including FR light in sole-source lighting on strawberries have not been fully understood. This study investigated the impacts of FR light on the growth and development of long-day strawberries ‘Albion’ and ‘Monterey’ in an indoor vertical farm. We hypothesized that the addition of FR light under a long photoperiod would promote leaf expansion, biomass accumulation, flowering, and fruit production in long-day strawberries. Bare-root strawberry plants were grown in a deep-water-culture hydroponic system at an air temperature of 22 °C and an 18-hour photoperiod using 90 μmol⋅m–2⋅s–1 of blue (peak = 455 nm) + 250 μmol⋅m–2⋅s–1 of red (peak = 660 nm) light-emitting diodes (LEDs) with or without adding 50 μmol⋅m–2⋅s–1 of FR (peak = 730 nm) LEDs. After 5 weeks of lighting treatments, additional FR light increased the leaf area and shoot dry mass of strawberry ‘Monterey’ by 74% and 73%, respectively, and the number of crowns per plant of strawberry ‘Albion’ by 33%. However, FR light did not influence flowering time in either cultivar. Adding FR light increased the number of fruit harvested per plant by 36%, the total fruit yield by 48%, and the total soluble solids of fruit by 12% in strawberry ‘Albion’, but not in ‘Monterey’. In both cultivars, FR light did not affect the individual fruit mass. Our results suggest that the addition of FR light in sole-source lighting can promote leaf expansion, biomass accumulation, fruit yield, and fruit quality in at least some long-day strawberry cultivars.

The contributions of cell division and cell elongation and the potential role of gibberellins in the far-red light stimulation of bean internode elongation were investigated. When bean plants, Phaseolus vulgaris cv. Kentucky Wonder, were grown in white light supplemented with far-red light a significant increase, up to threefold, in internode elongation was observed. Microscopic examination revealed that cell lengths were also increased but by a lower magnitude than internode length. Cell-labeling studies with [3H]thymidine showed that nuclei labeling was increased in internodes receiving supplemental far-red light. Thus far-red light induced increased internode elongation is a result of both increased cell elongation and increased cell division. Gibberellins A1, A20, A19, A44, and A4 and kaurenoic acid were identified in extracts of internode tissue by gas chromatography – mass spectroscopy using [2H2]-labeled internal standards for quantification. It thus appears that the early C-13 hydroxylation pathway is operative in the elongating internode. Endogenous GA1 and GA20 were approximately twofold higher in the first internodes of plants receiving supplemental far-red light. A comparison of the metabolism of exogenously supplied [2H2]GA19 suggested that GA turnover was greater in tissues exposed to supplemental far-red light. These results indicate that both cell division and elongation contribute to the enhanced elongation response of bean internodes to far-red light and that these processes are correlated with an increase in GA levels and (or) metabolism. Keywords: Phaseolus, gibberellins, phytochrome, far-red light.

Control of flowering in the perennial model, the woodland strawberry (Fragaria vesca L.), involves distinct molecular mechanisms that result in contrasting photoperiodic flowering responses and growth cycles in different accessions. The F. vesca homolog of TERMINAL FLOWER1 (FvTFL1) functions as a key floral repressor that causes short-day (SD) requirement of flowering and seasonal flowering habit in the SD strawberry. In contrast, perpetual flowering F. vesca accessions lacking functional FvTFL1 show FLOWERING LOCUS T (FvFT1)-dependent early flowering specifically under long-days (LD). We show here that the end-of-day far-red (FR) and blue (B) light activate the expression of FvFT1 and the F. vesca homolog of SUPPRESSOR OF THE OVEREXPRESSION OF CONSTANS (FvSOC1) in both SD and LD strawberries, whereas low expression levels are detected in red (R) and SD treatments. By using transgenic lines, we demonstrate that FvFT1 advances flowering under FR and B treatments compared to R and SD treatments in the LD strawberry, and that FvSOC1 is specifically needed for the B light response. In the SD strawberry, flowering responses to these light quality treatments are reversed due to up-regulation of the floral repressor FvTFL1 in parallel with FvFT1 and FvSOC1. Our data highlights the central role of FvFT1 in the light quality dependent flower induction in the LD strawberry and demonstrates that FvTFL1 reverses not only photoperiodic requirements but also light quality effects on flower induction in the SD strawberry.

It has been reported that PSI photoinhibition is induced even in wild-type plants of Arabidopsis thaliana, rice and other species by exposure of leaves to fluctuating light (FL) for a few hours. Because plants are exposed to FL in nature, they must possess protective mechanisms against the FL-induced photodamage. Here, using A. thaliana grown at various irradiances, we examined PSI photoprotection by far-red (FR) light at intensities comparable with those observed in nature. Dark-treated leaves were illuminated by red FL alternating high/low light at 1,200/30 µmol m-2 s-1 for 800 ms/10 s. By this FL treatment without FR light for 120 min, the level of photo-oxidizable P700 was decreased by 30% even in the plants grown at high irradiances. The addition of continuous FR light during the FL suppressed this damage almost completely. With FR light, P700 was kept in a more oxidized state in both low- and high-light phases. The protective effect of FR light was diminished more in mutants of the NADH dehydrogenase-like complex (NDH)-mediated cyclic electron flow around PSI (CEF-PSI) than in the PGR5 (proton gradient regulation 5)-mediated CEF-PSI, indicating that the NDH-mediated CEF-PSI would be a major contributor to PSI photoprotection in the presence of FR light. We also confirmed that PSI photoinhibition decreased with the increase in growth irradiance in A. thaliana and field-grown plants, and that this PSI photodamage was largely suppressed by addition of FR light. These results clearly indicate that the most effective PSI protection is realized in the presence of FR light.

Insufficient light supply for canopies is a constant issue during greenhouse production in most areas of Northern China. Applying supplemental lighting to plant canopies is an efficient method of solving this problem. Several studies were conducted to identify the optimal, economically efficient abaxial leafy supplemental lighting mode to produce high-quality greenhouse tomatoes. In this experiment, no supplemental treatment was used as a blank control (CK), while three supplemental lighting modes were used as treatments: T1, continuous supplemental lighting from 8:00–9:00 (at GMT+8, which is 6:00–7:00 local time, before the thermal insulation covers, abbreviated as TIC below, opening), and 20:00–22:00 (after TIC closing) with photosynthetic photon fluxion density (PPFD) of 200 μmol·m−2·s−1; T2, dynamic altered supplemental lighting with PPFD rising from 100 μmol·m−2·s−1 to 200 μmol·m−2·s−1 before TIC opening and falling from 200 μmol·m−2·s−1 to 100 μmol·m−2·s−1 after TIC closing; and T3, intermittent supplemental lighting which was automatically conducted with PPFD of 100 μmol·m−2·s−1 when indoor PPFD below 150 μmol·m−2·s−1 from 8:00–22:00. The results demonstrated that abaxial leafy supplemental lighting treatment could improve both fruit yield and quality. The total yield in the T1 and T2 treatments was higher than in other treatments, though there was no significant difference. Differences in leaf carbon exportation showed the possibility of determining fruit yield from the 3rd leaf under the fruit. The overall appearance, flavor quality, nutrient indicators, and aroma of cherry tomato fruits under T1 and T2 treatments were generally higher than in other treatments. Correlation analysis of fruit yield and quality parameters suggested that they produce relatively high yield and fruit quality. Combined with a cost-performance analysis, dynamic altered supplemental lighting (T2) is more suitable for high-valued greenhouse cherry tomato production.

Supplementary far-red light may increase fruit yield in greenhouse tomato cultivation. Apart from end-of-day applications, research has focussed on the effects of far-red light during the entire photoperiod, while few studies focused on the timing of far-red application. In this study, we assessed the impact of timing and duration of far-red application on fruit yield and quality in a high-wire tomato crop. Two commercial tomato cultivars were grown under 226 μmol m−2 s−1 of red and white supplementary LED lighting. Far-red light (63 μmol m−2 s−1) was additionally supplied during either the first or the second half of the photoperiod. These treatments were compared to a negative control, where no far-red light was supplied, and a positive control, where far-red light was supplied during the whole photoperiod. A yield component analysis was conducted to identify the parameters responsible for changes in fruit yield. We determined that fruit yield, total fruit dry weight and fruit production per unit of supplementary PAR light (400–700 nm) increased linearly with the duration of far-red application. Fruit yield was increased to a similar extent whether far-red was supplemented in the first or in the second half of the photoperiod. While different light treatments included 0, 14, or 28 % far-red in their cumulative supplementary photon flux density, there were no significant differences in their fruit production per unit of supplementary radiation (400–800 nm). Supplementary far-red increased fruit dry weight per unit of cultivation area by 23 % to 25 % as a result of increasing both plant dry weight (10 % to 12 %) and dry weight partitioning to the fruits (10 % to 14 %). The increase in fruit yield was less than the corresponding increase in total fruit dry weight due to a simultaneous increase in fruit dry matter content. Total soluble solids and pH of the fruits were hardly affected by far-red application. We concluded that supplementary far-red increased tomato fruit yield without compromising fruit quality, with this increase being determined by the duration of far-red application, not by its timing during the photoperiod.

Chenopodium album seedlings were grown in light environments in which supplementary far-red light was mixed with white fluorescent light during various parts of the photoperiod. Both the logarithmic rate constant of stem extension and the leaf dry weight: stem dry weight ratio were linearly related to estimated phytochrome photoequilibrium (ϕ) in each treatment regime. These data are taken to be indicative of a functional link between phytochrome and development in the green plant. A layer of chlorophyllous tissue only affected the linearity between calculated ϕ and the logarithmic stem extension rate at high chlorophyll concentrations, whilst even low concentrations-equivalent to the levels found in stem tissue-caused a significant shift in measured ϕ. End-of-day supplementary far-red (FR) light induced between 0-35 per cent of the response elicited by all-day supplementary FR, whilst daytime supplementary FR (with a white fluorescent light end-of-day treatment) induced approximately 90 per cent. The ecological significance of this difference is discussed with respect to shade detection.