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Plant factories with artificial lighting (PFALs) are indoor crop production systems aiming at the growth of high-value products in terms of yield and quality, while maximizing resource use efficiency. The emergence of PFALs opened a new world for crop production and offered an option to tackle problems related to climate change, land availability, and urban/peri-urban farming. This was made possible upon major technological advancements and extensive research in the field of controlled environment agriculture, which paved the way for the establishment of such cost-efficient and climate-unaffected modules of vegetable and other crops' production. In the present review, we have examined the recent research achievements regarding the micro-environmental factors, the principal components, as well as the automated systems used for plant production in PFALs. Ultimately, we provide the reader with a number of future perspectives that can be considered for indoors cultivation in the following years. [ABSTRACT FROM AUTHOR]

The pre-sowing treatment of seeds with an α static magnetic field has been reported in the literature as a means of enhancing plant development. In this work, we have designed, characterized, and constructed a setup for exposing small vegetable seeds to a static magnetic field. In a series of experiments, we have treated the seeds of vegetables that are important for the Mediterranean diet, i.e., tomato, lettuce, and salad rocket. The results show that tomato seedlings significantly benefit from a pre-sowing treatment with a magnetic flux density of 45 mT, for both an exposure time of 60 and 90 min compared to control, while the time of treatment that leads to improved growth is 90 min. In order to improve the growth of salad rocket seedlings the magnetic field had to be 150 mT, whereas the results for lettuce seeds were a bit inconsistent, i.e., it is not clear whether a lower (45 mT) or a higher (300 mT) magnetic flux density should be applied. [ABSTRACT FROM AUTHOR]

One of the most important crops of the Mediterranean, watermelon (Citrullus lanatus), is almost exclusively established through seedlings. For many years, agronomists, nurseries, and farmers have aimed to produce and use high-quality seedlings for better growth in the field. However, seedling quality has not been examined as to what defines the subsequent plant, flower, and fruit development, and to what extent. Our aim was to test whether different seedling qualities labeled as "Optimum", "Acceptable", or "Not Acceptable" for cultivation actually perform variably in terms of vegetative, flowering, and fruit development, as well as fruit quality after a full growing cycle in the field. Vegetative growth (stem diameter, plant area, and leaf number) was evaluated until flowering and was enhanced for Optimum plants. The flowering of Not Acceptable plants started two days later, while Optimum plants retained a greater number of female flowers throughout the two-week blooming evaluation. Most importantly, Optimum plants developed mature fruits four and six days faster than the Acceptable and Not Acceptable ones, respectively, showing considerable yield earliness. The photosynthetic mechanism, as well as fruit morphology and phytochemical content, were not affected by quality categories. Overall, indeed it is important to use high-quality seedlings to achieve yield earliness of watermelon fruits. [ABSTRACT FROM AUTHOR]

Wild rocket is a leafy vegetable with economic interest as a consequence of baby leaf ready-to-eat salads. The climate crisis is expected to influence wild rocket production, but these effects could be confronted with cultivation in greenhouses and plant factories with artificial lighting (PFALs). Climate responses are related to growing seasons. Our objective was to test the impact of two growing seasons, winter and summer, on the growth and physiology of wild rocket baby leaves in different controlled environment systems (greenhouse and PFAL). The growth cycle was reduced by 27% in the PFAL compared to the greenhouse during winter. Summer yield was greater in the greenhouse, but leaf number and area were greater in the PFAL. The lowest water use efficiency was recorded in the greenhouse during summer. Energy use efficiency was lower in PFAL compared to the greenhouse. Land use efficiency was not affected by the growing system, but in PFALs it is able to increase it by growing in vertical layers. Relative chlorophyll content and total soluble solids were enhanced in the greenhouse. The photosynthetic efficiency evaluation showed considerable stress in summer-grown plants in the greenhouse, as shown by PIABS and φP0. In general, the production was similar in the PFAL regardless of seasons. [ABSTRACT FROM AUTHOR]

Overall, red, blue, and far-red wavelengths during the healing of grafted watermelon seedlings improved the growth and accelerated the flowering and fruit production of watermelon crops. Overall, a red/blue ratio of 1.2 and red/far-red ratio of 16, and a photon flux density of 150 mol m SP -2 sp s SP -1 sp were suggested for the production of grafted tomato transplants, taking into account both the seedling quality and the energy consumption. On the other hand, artificial lighting is used as the sole lighting source in plant factories (PFALs) and nurseries (e.g., healing chambers for grafted seedlings). However, solar light strongly differs between winter and summer conditions, with excess light in open field cultivations imposing severe stress on plants, especially during summer months, while supplementary light sources are implemented in greenhouse crop production to complement natural light when it is insufficient. [Extracted from the article]

By applying three different LED light treatments, designated as blue (B), red (R)/blue (B), red (R) and white (W) light, as well as the control, the effect on Diplotaxis tenuifolia phenotype (yield and quality), and physiological, biochemical, and molecular status, as well as growing system resource use efficiency, was examined. We observed that basic leaf characteristics, such as leaf area, leaf number, relative chlorophyll content, as well as root characteristics, such as total root length and root architecture, remained unaffected by different LEDs. Yield expressed in fresh weight was slightly lower in LED lights than in the control (1113 g m−2), with R light producing the least (679 g m−2). However, total soluble solids were significantly affected (highest, 5.5° Brix, in R light) and FRAP was improved in all LED lights (highest, 191.8 μg/g FW, in B) in comparison to the control, while the nitrate content was less (lowest, 949.2 μg/g FW, in R). Differential gene expression showed that B LED light affected more genes in comparison to R and R/B lights. Although total phenolic content was improved under all LED lights (highest, 1.05 mg/g FW, in R/B), we did not detect a significant amount of DEGs in the phenylpropanoid pathway. R light positively impacts the expression of the genes encoding for photosynthesis components. On the other hand, the positive impact of R light on SSC was possibly due to the expression of key genes being induced, such as SUS1. In summary, this research is an integrative and innovative study, where the exploration of the effect of different LED lights on rocket growing under protected cultivation, in a closed chamber cultivation system, was performed at multiple levels. [ABSTRACT FROM AUTHOR]

By 2050, the increasing demand for food will put additional pressure on natural resources. Underutilized crops, such as wild vegetables, are an essential component of the Mediterranean diet and are widely correlated with the traditional cuisine of Mediterranean countries. They could be widely associated with resistance to abiotic stress and enhanced genetic diversity, and could provide various ecosystem services. Their cultivation could support the Sustainable Development Goals (SDGs) established by the UN and the current EU policies related to environmentally friendly agriculture. Based on an extensive literature review, the aim of this paper is to summarize the environmental and ecological requirements of specific Mediterranean underutilized vegetables, the provisioning and regulating ecosystem services that could be derived from their cultivation, and their potential use. It is concluded that thorough planning of underutilized crop cultivation could enhance the provisioning and regulating ecosystem services that positively affect Mediterranean agriculture. However, further research should be carried out regarding their environmental and economic impact in order to assess the environmental and socio-economic effects of underutilized crops cultivation. This could lead to designing future policies that support underutilized crop cultivation and consumption. [ABSTRACT FROM AUTHOR]

Salinization of cultivated soils is a global phenomenon mainly caused by agricultural practices and deteriorates plant production. Biostimulants are products which can be applied exogenously to enhance the plants' defense mechanism and improve their developmental characteristics, also under abiotic stresses. We studied the potential of two biostimulants, Ascophyllum nodosum (Asc) seaweed and a silicon-based (Si), to alleviate the saline conditions endured by watermelon transplants. Three salinity (0 mM, 50 mM, and 100 mM NaCl) treatments were applied in watermelon seedlings transplanted in pots, while the two biostimulants were sprayed in the foliar in the beginning of the experiment. Relative water content was improved by Asc in the high salinity level. The plant area, leaf number, and shoot dry weight deteriorated in relation to the salinity level. However, the root system (total root length and surface area) was enhanced by 50 mM salt, as well as Asc in some cases. The OJIP transient of the photosynthetic apparatus was also evaluated. Some OJIP parameters diminished in the high salinity level after Asc application. It is concluded that after salt stress Asc provoked a positive phenotypic response, while Si did not alleviate the salinity stress of transplanted watermelon. [ABSTRACT FROM AUTHOR]

Climate change is an inevitable process characterized by an abrupt increase in global temperature and a decrease in precipitations leading to drought incidents. Biostimulants could be a valuable tool for mitigating these harsh conditions. The objective of our study was to test the efficiency of two biostimulants, a silicon-based seaweed and the seaweed Ascophyllum nodosum, to mitigate the drought stress endured by watermelon transplants during the first few weeks after transplanting. In order to achieve this, three water treatments (100%, 75%, and 50% of field capacity) were applied in pots. Important growth parameters (leaf number, fresh weight, and plant area) deteriorated depending on water availability. This was also the case for the root system development displayed by root dry weight, total length, and surface area. It is the first time the OJIP transient has been evaluated after the application of A. nodosum for drought-stressed plants. Chlorophyll fluorescence parameters showed that the photosynthetic apparatus was more stressed when A. nodosum was applied, especially in the harshest conditions (i.e., 50% field capacity). Overall, the silicon-based biostimulant failed to demonstrate drought-mitigating potential compared to the non-treated counterparts. On the other hand, A. nodosum alleviated the negative effects of water deficit, especially in the harshest conditions. [ABSTRACT FROM AUTHOR]

Watermelon is widely propagated through grafting, after which seedlings are subjected to healing under controlled conditions including artificial lighting. Light wavelengths, such as blue, red, and far-red, impose considerable effects on seedlings, which possibly carry on to the mature plants. The aim of the present study is to examine whether different light wavelengths during healing of grafted watermelon seedlings impose variable effects during field cultivation. After grafting, seedlings were healed in an environmentally controlled healing chamber under fluorescent (FL) lamps and light-emitting diodes, providing 100% red (R), 100% blue (B), 88/12% R/B (12B), and 12B including 5% far-red (12B + FR). After acclimatization, seedlings were transplanted in the field. Vegetative growth until floral initiation was enhanced by 12B and 12B + FR, as shown by stem diameter and leaf number measurements. Flowering was mainly accelerated by 12B + FR and considerably decelerated by FL and B. The same pattern was followed by fruit yield, which was similar for all treatments at the end of the experiment. Nevertheless, fruit quality was not affected by any of the light treatments. It is concluded that a light recipe, including red, blue and far-red, wavelengths during healing of grafted seedlings enhances the overall growth, and flowering and yield earliness of watermelon crops. [ABSTRACT FROM AUTHOR]

Tomato, which is mainly established with grafted seedlings, is one of the most popular vegetables worldwide with a high nutritional value,. Market demand for grafted seedlings is high in specific seasons; thus, commercial nurseries face a problem of limited space availability during the healing stage. Light quality is an essential parameter during healing that can adjust seedling development towards desirable traits and lead to time and space saving during seedling production. Moreover, transplant shock constitutes another challenge that could limit crop yield. The objective of this study was to evaluate the overall quality of grafted tomato seedlings and their potential adjustment to transplant shock as affected by different light spectra during healing in a chamber. Evaluations were conducted immediately after exiting the healing chamber and after transplantation into pots. Light wavelengths were used from fluorescent lamps (FL) or light-emitting diodes with red (R), blue (B), red–blue combinations with 12 and 24% blue (12B and 24B), and white (W) emitting 11% blue. W enhanced the dry shoot biomass and the root architecture before and after transplantation. 24B led to an increased stem diameter, root development, and phenolic and antioxidant accumulation at both phases of the experiment. 12B enhanced the leaf area before transplantation and root development after transplantation. FL, R and B induced inferior seedling growth compared to the red–blue-containing LEDs, with B performing poorly in almost all tested parameters. Overall, red, including 11–24% blue, provides the optimum light conditions during the healing stage for the production of high-quality grafted tomato seedlings, with advanced capabilities of abiotic stress adaptation to transplant shock. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal fungi (AMF) are efficient for improving crop production and quality in organic farming systems. Our objective was to examine the effects of two AMF inocula, Rhizophagus intraradices and Diversispora spp., against a non-inoculated control on lettuce and green onion grown organically in an intercropping cropping system. At time of harvest, colonization levels were very low, and not different compared to the control that was colonized by the native mycorrhizal community. The yield of inoculated lettuce and green onion was unchanged, as also observed in the root system architecture analysis parameters. In both crops, color was not affected, limiting the possibility for consumers to reject the product. Nitrate accumulation was well below the limits set by European Commission in all treatments. Sugar, chlorophyll, K, Na and P contents were also quantified, showing no particular variations. In AMF-treated lettuce, important phytochemical characteristics, such as phenol content and ascorbic acid, showed a tendency for reduced values, while antioxidant capacity was significantly reduced by both AMF treatments. The study provides a description about the effect of AMF on two important co-cultivated crops. Research should be continued in order to determine best matches between plant material and AMF inocula that could result in enhanced production and nutritional quality. [ABSTRACT FROM AUTHOR]

Carotenoids are isoprenoids widely distributed in foods that have been always part of the diet of humans. Unlike the other so-called food bioactives, some carotenoids can be converted into retinoids exhibiting vitamin A activity, which is essential for humans. Furthermore, they are much more versatile as they are relevant in foods not only as sources of vitamin A, but also as natural pigments, antioxidants, and health-promoting compounds. Lately, they are also attracting interest in the context of nutricosmetics, as they have been shown to provide cosmetic benefits when ingested in appropriate amounts. In this work, resulting from the collaborative work of participants of the COST Action European network to advance carotenoid research and applications in agro-food and health (EUROCAROTEN, , ) research on carotenoids in foods and feeds is thoroughly reviewed covering aspects such as analysis, carotenoid food sources, carotenoid databases, effect of processing and storage conditions, new trends in carotenoid extraction, daily intakes, use as human, and feed additives are addressed. Furthermore, classical and recent patents regarding the obtaining and formulation of carotenoids for several purposes are pinpointed and briefly discussed. Lastly, emerging research lines as well as research needs are highlighted. [ABSTRACT FROM AUTHOR]

Watermelon (Citrullus lanatus) is a valuable horticultural crop with nutritional benefits grown worldwide. It is almost exclusively cultivated as grafted scions onto interspecific squash rootstock (Cucurbita maxima × Cucurbita moschata) to improve the growth and yield and to address the problems of soilborne diseases and abiotic stress factors. This study aimed to examine the effect of grafting (homo- and hetero-grafting) on the transcriptome level of the seedlings. Therefore, we compared homo-grafted watermelon (WW) with non-grafted watermelon control (W), homo-grafted squash (SS) with non-grafted squash control (S), hetero-grafted watermelon onto squash (WS) with SS, and WS with WW. Different numbers of differentially expressed genes (DEGs) were identified in each comparison. In total, 318 significant DEGs were detected between the transcriptomes of hetero-grafts and homo-grafts at 16 h after grafting. Overall, a significantly higher number of downregulated transcripts was detected among the DEGs. Only one gene showing increased expression related to the cytokinin synthesis was common in three out of four comparisons involving WS, SS, and S. The highest number of differentially expressed (DE) transcripts (433) was detected in the comparison between SS and S, followed by the 127 transcripts between WW and W. The study provides a description of the transcriptomic nature of homo- and hetero-grafted early responses, while the results provide a start point for the elucidation of the molecular mechanisms and candidate genes for the functional analyses of hetero-graft and homo-graft systems in Cucurbitaceae and generally in the plants. [ABSTRACT FROM AUTHOR]

BACKGROUND A floating system is a suitable low‐cost hydroponic method for growing baby leaf vegetables. Among other, an important characteristic of the system is the use of large volume of nutrient solution which is characterized by high heat capacity. The aim of this study was to evaluate the effect of different root‐zone temperatures on baby leaves of lettuce and rocket plants grown in a floating system under mild (spring) or extreme environmental conditions (summer and winter). RESULTS: Root‐zone temperature was recorded in two tanks, one powered by a photovoltaic system and one where root‐zone temperature was not controlled – this was used as a control tank. Photosynthetic parameters, yield, nutritional quality, and mineral composition were determined. In both baby leaf vegetables, during extreme weather conditions, yield was higher in the tanks with controlled root‐zone temperature conditions than the control (+18.9% for rocket, and + 31.4% for baby lettuce), while quality parameters and chemical composition were not significantly affected. Stomatal conductance and net photosynthesis values were positively affected only during summer. On the other hand, control of root‐zone temperature under mild weather conditions had no significant effect on baby lettuce and rocket. CONCLUSION: Control of the root‐zone temperature could be a useful tool to improve productivity for baby lettuce and rocket crops cultivated in floating systems under extreme weather conditions. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Oaks (Quercus spp.) represent the most important broadleaf genus with respect to forest-shaping tree species in the Mediterranean. Considering future climate scenarios (increased drought conditions), the identification of drought tolerant oak species is of great importance for future forest management in this region. The objective of the study was the comparison of physiological status of three economically and ecologically valuable oak species (Quercus ilex, Quercus frainetto and Quercus pubescens) co-existing in natural coppice stands in NE Greece, in response to seasonal drought stress. Measurements were conducted between June and September 2016, every 15–20 days until leaf falling. The parameters studied were predawn leaf water potential and fast chlorophyll fluorescence induction curves (OJIP test), chlorophyll content, and relative water content. Meteorological data from the area were also collected. Photosynthetic parameters such as performance indices (PIabs and PItot) reacted to summer drought conditions, with Q. frainetto showing the lowest values. The discrepancy between species increased with duration of drought period. Q. frainetto revealed the lowest predawn water potential values. The results indicate that Q. frainetto is less suitable for future forestry applications in the studied climate/elevation zone than Q. pubescens and Q. ilex. [ABSTRACT FROM AUTHOR]

The effect of light-emitting diodes (LED) with broad radiation spectra on developmental, physiological, and phytochemical characteristics of Greek sage (Salvia fruticosa L.) seedlings was assessed. Fluorescent (FL - control) tubes and four LED lights [AP67 (moderate blue, red and far-red), L20AP67 (moderate blue, red and far-red, high green), AP673L (moderate blue, high red) and NS1 (high blue and green, low red, high red : far-red, 1% ultraviolet)] were used in a growth chamber. Seedlings grown under FL, L20AP67 and AP673L exhibited the best morphological and developmental characteristics. FL led to inferior root biomass formation compared to all LEDs. AP67 promoted greater root-to-shoot dry weight ratio and dry-to-fresh overground and root weight ratios, but induced the least morphological and developmental characteristics. NS1 performed well regarding the root biomass production. Total phenolic content and the root growth capacity were not significantly affected. The present study demonstrates that L20AP67 and AP673L LEDs performed equally to FL light regarding the developmental characteristics. AP67 and NS1 may have the potential to be used for compact seedling production. [ABSTRACT FROM AUTHOR]

Light-emitting diode (LED) technology has rapidly advanced the past years and it is nowadays irrevocably linked with controlled-environment agriculture (CEA). We provide here an amalgamation of the recent research achievements in the horticulture and floriculture industry, ranging from greenhouse applications to climate rooms and vertical farming. We hope this overview bestows ample examples for researchers and growers in the selection of the appropriate LED light solution for amending crop yield, phytochemical content, nutritional value, flowering control, transplant success, pre-harvest and postharvest product quality, and production of regeneration material. We leave the reader with some future prospects and directions that need to be taken into account in this ever-growing field. [ABSTRACT FROM AUTHOR]

The objective of the present study was to investigate the impact of light-emitting diodes (LEDs) on the morphological and developmental characteristics of wild cherry (Prunus avium) and common dogwood (Cornus sanguinea). The LEDs used were L20AP67 (moderate blue, red and far-red, high green), AP673L (moderate blue, high red), G2 (low blue, high red and far-red), AP67 (moderate blue, red and far-red), and NS1 (high blue and green, low red, high red:far-red, 1% ultraviolet). Fluorescent light [FL (high blue and green, low red)] tubes served as the control treatment. The growth rate and subsequently the shoot height of Cornus sanguinea were greater under FL. Root length of Prunus avium was longer under NS1. Prunus avium produced more biomass under NS1 and AP67, while Cornus sanguinea was favored under G2 and AP67. Greater root:shoot ratio was found under NS1 for Prunus avium and under NS1, AP67, G2, and AP673L for Cornus sanguinea. Root growth capacity (RGC) was also assessed in order to evaluate the transplanting response. RGC of Prunus avium and Cornus sanguinea was favored after precultivation under G2 and AP67, and under NS1 and AP67, respectively. Our study demonstrated that LEDs were more efficient in promoting a number of morphological characteristics than conventional FL in Prunus avium and Cornus sanguinea. [ABSTRACT FROM AUTHOR]

The morphological and phytochemical characteristics of two Ocimum basilicum cultivars (Lettuce Leaf, and Red Rubin-mountain Athos hybrid) under artificial lighting were investigated. Four LED light treatments [AP673L (high red and high red:far-red), G2 (high red and low red:far-red), AP67 (moderate blue and red and low red:far-red), and NS1 (high blue and green, high red:far-red and 1% ultraviolet)] with different colors mixing UV, blue, green, red and far-red, and fluorescent tubes (FL, high blue, green and red:far-red) as Control were used in the growth chambers for 28 days under PPFD of 200 ± 20 μmol m −2 s −1 for all treatments at plant height. G2, Control and AP67 treatments for Lettuce Leaf, and G2 for Red Rubin hybrid had higher growth rate. Roots of Lettuce Leaf were significantly longer under AP673L compared to NS1, while Red Rubin hybrid showed no significant differences. Total biomass was significantly greater under NS1, AP67 and G2 compared to the Control, for both cultivars. For both Lettuce Leaf and Red Rubin hybrid, root:shoot ratio (R/S) was favored under NS1, whereas the Control had the lowest impact. Leaf area of both cultivars was greater under the Control. Root growth capacity evaluation was also assessed. Seedlings of Lettuce Leaf cultivated under the effect of the Control and AP673L, and seedlings of Red Rubin hybrid grown under AP673L (mainly) quickly developed new root system. This could offer the advantage of fast exploitation of larger soil volume after transplanting. Total phenolic content of Lettuce Leaf was significantly higher under NS1 compared to the rest of the treatments, while in Red Rubin hybrid, NS1 had significantly higher total phenolic content compared to the Control and G2. Our study demonstrates that LEDs variably affected growth characteristics and increased total phenolic content compared to conventional fluorescent light for these two O. basilicum cultivars. [ABSTRACT FROM AUTHOR]

In many countries of Europe and Eastern Asia, watermelon production is mainly based on the use of grafted seedlings. Upon grafting, seedlings undergo a period of healing where artificial lighting is provided by light-emitting diodes in controlled chambers in order to accelerate and improve the healing process. The objective of our study was to test the effect of light quality on the final product (i.e., seedlings ready for transplanting) in the nursery, as well as to evaluate the possible implications on fruit quality after field cultivation. Narrow-band blue (B) and red (R) wavelengths, 64–36% R-B (36B), 76–24% R-B (24B), 88–12% R-B (12B), and 83–12% R-B plus 5% far-red (12B+FR) wavelengths were tested. 12B+FR enhanced the root dry weight, root architecture, and maximum photosynthetic rate, while RB combinations generally showed better root system development with increased blue portion. R light induced inferior root dry weight and quality indices (root/shoot and shoot–dry–weight/length ratios), lower gas exchange parameters, and chlorophyll content, but high shoot length and leaf area. B light led to inferior root architecture, lower stem diameter, leaf area, and maximum photosynthetic rate. Both R and B wavelengths showed decreased concentration of macronutrients and trace elements. After field cultivation, fruit quality (i.e., morphology and color), and valuable nutritive characteristics (i.e., phenolics, carotenoids, lycopene, antioxidants) maintained high quality irrespective of light treatments. Overall, 12B+FR performed well in almost all qualitative parameters including the morphology, the root development, and photosynthesis, while also maintaining high fruit quality. [ABSTRACT FROM AUTHOR]

Sustainable agriculture relies on replacing fossil-based mineral fertilizers, which are highly cost-energetic to produce, and demand extensive use of scarce natural resources. Today, agronomic practices within the concept of circular economy are emerging and, as such, the exploitation of digestate as a biofertilizer and soil amender is extensively investigated. This study aimed at evaluating the agronomic potential of liquid digestate as the sole nutrient source for hydroponic cultivation of baby lettuce in greenhouses. Growth rate, physiological responses, concentration of secondary metabolites, and nutrient uptake were compared between baby leaf lettuce grown in digestate in concentrations of 5, 10, and 20% diluted in water (either with or without pH adjustment) and in Hoagland solution (control). Results showed that the production yield was negatively correlated with the concentration of the added digestate. Nevertheless, the antioxidant capacity was significantly enhanced in 5 and 10% liquid digestate treatments compared to the control. Additionally, the nutrient composition in the baby leaf lettuce and the reduction in nutrient concentrations in the growth media demonstrated efficient mineral uptake by the plants. Thus, the application of liquid digestate as a fertilizer in hydroponic systems is a promising practice to recover residual resources, leading to the transition towards more sustainable greenhouse production. [ABSTRACT FROM AUTHOR]

Light quality exerts considerable effects on crop development and phytochemical content. Moreover, crops grown as microgreens are ideal for plant factories with artificial lighting, since they contain greater amounts of bioactive compounds compared to fully-grown plants. The aim of the present study was to evaluate the effect of broad-spectra light with different red/blue ratios on the yield, morphology, and phytochemical content of seven microgreens. Mustard, radish, green basil, red amaranth, garlic chives, borage, and pea shoots were grown in a vertical farming system under three light sources emitting red/blue ratios of about 2, 5, and 9 units (RB2, RB5, and RB9, respectively). Mustard exhibited the most profound color responses. The yield was enhanced in three microgreens under RB9 and in garlic under RB2. Both the hypocotyl length and the leaf and cotyledon area were significantly enhanced by increasing the red light in three microgreens each. Total soluble solids (Brix) were reduced in 4 microgreens under RB2. The total phenolic content and antioxidant capacity were reduced under RB2 in 6 and 5 microgreens, respectively. The chlorophylls were variably affected but total the carotenoid content was reduced in RB9 in three microgreens. Overall, light wavelength differentially affected the microgreens' quality, while small interplays in spectral bands enhanced their phytochemical content. [ABSTRACT FROM AUTHOR]

Climate change imposes severe stress on European forests, with forest degradation already visible in several parts of Europe. Thus adaptation of forestry applications in Mediterranean areas and central Europe is necessary. Proactive forestry management may include the planting of Mediterranean oak species in oak-bearing Central European regions. Five replicate common gardens of Greek and Italian provenances of Quercus ilex, Q. pubescens and Q. frainetto seedlings (210 each per plantation) were established in Central Italy, NE Greece (two) and Southern Germany (two, including Q. robur) to assess their performance under different climate conditions. Climate and soil data of the plantation sites are given and seedling establishment was monitored for survival and morphological parameters. After 3 years (2019) survival rates were satisfactory in the German and Italian sites, whereas the Greek sites exerted extremely harsh conditions for the seedlings, including extreme frost and drought events. In Germany, seedlings suffered extreme heat and drought periods in 2018 and 2019 but responded well. Provenances were ranked for each country for their performance after plantation. In Greece and Italy, Q. pubescens was the best performing species. In Germany, Q. pubescens and Q. robur performed best. We suggest that Greek or Italian provenances of Q. pubescens may be effectively used for future forestation purposes in Central Europe. For the establishment of Quercus plantations in Northern Greece, irrigation appears to be a crucial factor in seedling establishment. [ABSTRACT FROM AUTHOR]

Rocket and spinach baby leaves are valuable commodities since they are basic components of popular ready-made salads. Two methods may follow after harvesting: establishment of new cultivations or successive revegetations and harvests. This study aimed to investigate the yield and nutritional value of rocket and spinach baby leaves after individual cultivations or successive revegetations in a floating system to improve their production strategy. The crops were cultivated in a greenhouse for seven weeks using a floating system with an adjusted nutrient solution. The leaves were either harvested and immediately replaced with a new set of plants (control) or harvested and placed again in the same tank in order to revegetate (revegetation). Revegetated rocket baby leaves in five cuts produced similar yield, with greater antioxidant capacity (DPPH scavenging activity) and total phenolic content, and greater nitrate content (eight times below the maximum allowed by EU) compared to control. Revegetated spinach produced more yield with enhanced antioxidant activity and total phenolic content and the same nitrate content compared to the control. Colour was not affected in either crop, thus eliminating the possibility for market rejection. Production efficiency was increased, as shown by the yields and the reduced resources provided in the revegetation tank. Thus, successive harvesting and revegetation are suggested for increased production efficiency and quality of rocket and spinach baby leaves. [ABSTRACT FROM AUTHOR]

Grafting is the main means of propagation for watermelon crops. The aim of the present study was to evaluate whether light quality during graft healing variably affects different scion × rootstock genotype combinations. Two watermelon hybrid scions (Sunny Florida F1 and Celine F1) and two interspecific squash rootstocks (Radik and TZ-148) were used, and four scion × rootstock genotype combinations derived. After grafting, we tested seven light-emitting diodes (LEDs), which provided narrow-band red (R) and blue (B); R-B with 36% (36B), 24% (24B), and 12% (12B) blue; 12B with additional far-red (12B+FR); and white (W), in a healing chamber. In three genotype combinations, shoot length, leaf area, and shoot biomass were mainly enhanced under red-blue LEDs, while stem diameter was greater under R. In contrast, dry weight of roots, Dickson's quality index, and ratio of shoot dry weight/length were variably affected in each genotype combination. From the results, it is concluded that light treatments differentially affected each genotype combination, but some parameters involving biomass production show genotypic dependency. [ABSTRACT FROM AUTHOR]

Spinach is a leafy vegetable containing a plethora of bioactive compounds. Our study aimed to evaluate the physiological (i.e., JIP-test) and phytochemical response of spinach baby leaves grown with regular or mildly saline (40 mM NaCl) nutrient solution and irradiated by four light-emitting diodes (LEDs) with broad spectra. T1 (highest red and far-red, low blue) and T3 (high red, balanced blue, green and far-red) led to a better developed photosynthetic apparatus compared to T2 (red peak in 631 nm) and T4 (highest blue and green), highlighted by PIABS and its structural components: RC/ABS, φP0, ψE0, and ΔVIP. Elevated salinity only affected the latter parameter. T1 induced the maximum yield production but also the highest nitrate content which was far below the maximum level permitted by European legislation. Regardless of salinity level, T3 enhanced total phenol, chlorophyll, and carotenoid content. T2 and T4 led to inferior nutritional quality. Non-saline nutrient solution promoted the chlorophyll and carotenoid contents and the antioxidant potential, regardless of light treatment. By contrast, soluble sugar content was enhanced by saline nutrient solution. Our study shows that physiology and nutritional quality of spinach baby leaves can be manipulated by small interplays in the light spectra and salinity level. [ABSTRACT FROM AUTHOR]

Watermelon is mainly grafted onto interspecific squash, and during the season of high demand, seedlings of variable quality are used to cover grafting needs. The objective was to combine watermelon and interspecific squash of different seedling quality categories in order to obtain the optimal combination for the production of high-quality grafted watermelon seedlings. Acceptable seedlings of both species were grouped into quality categories, namely "low", "optimum", and "high". Seedlings of each quality category were combined with each other and grafted seedlings from the nine derived categories were evaluated at two time intervals, at 7 (exit from the healing chamber) and 14 (final product) days after grafting. At both time intervals, watermelon "high" combined with interspecific squash "optimum" exhibited relatively higher shoot length, stem diameter, leaf area, and shoot and root dry weight, as well as shoot dry weight-to-length ratio, which is a quality index. The study shows that watermelon scions should have "high" quality, while interspecific squash rootstocks should have "optimum" quality during grafting for the production of high-quality grafted plants. If possible, "low" to-be-grafted watermelon seedlings should be avoided because the grafted derived seedlings are considered low quality. [ABSTRACT FROM AUTHOR]

• R or RB favored growth and morphological parameters of grafted watermelon seedlings. • Shoot and root biomass accumulated faster under R and B containing LEDs. • Monochromatic R light led to lower gas exchange and photosynthetic efficiency. • DW/L quality index showed that FL and B led to inferior development. Watermelon is an economically important crop that is exclusively established through the use of grafted seedlings. Grafting procedure and the period of healing are critical for the production of high quality seedlings. During healing, grafted seedlings are grown in a chamber with controlled conditions, including supplementary lighting. The aim of the present study was to evaluate the impact of commonly used fluorescent (FL, control) lamps or light-emitting diodes (LEDs) with varying red (R) and blue (B) proportions [100 % R (R), 12 % B and 88 % R (12B), 24 % B and 76 % R (24B), 36 % B and 64 % R (36B) or 100 % B (B)] employed in the healing chamber on the quality of grafted watermelon seedlings. Seedlings under FL and B performed poorly in almost all tested parameters compared to the other LEDs. However, monochromatic B led to the greatest rates of photosynthesis (P max), stomatal conductance (g) and transpiration (E). On the contrary, R promoted the seedling length, fresh and dry weight (FW and DW) of shoots and roots, and root-to-shoot ratio (R/S) but led to inferior gas exchange and photosynthetic efficiency (F v /F m). B addition to R light (12B and 24B) enhanced the morphological and growth characteristics tested at least as much as R light or even more (leaf area, shoot DW). It should be noted that the entire root system of the seedlings was cut off during the grafting procedure and its re-growth was highly promoted by dichromatic LEDs (R plus B). Altogether, the above results demonstrate that R light with addition of low proportion of B light (12–24%) enhances the production of high quality grafted watermelon seedlings. [ABSTRACT FROM AUTHOR]

Shelf life of horticultural commodities is dependent on postharvest handling but also on a wide range of pre-harvest factors, which include genetic and environmental parameters. This study was conducted to explore the influence of cultivar, leaf position, and piece position on the leaf on visual quality of fresh-cut butterhead lettuce as well as the effect of a wide range of cultivation seasons on the postharvest quality and shelf life of baby leaves (spinach and 'wild' rocket). Six butterhead lettuce cultivars were used (cultivated soilless in an unheated plastic greenhouse) while the effect of leaf position on the plant (outer and inner leaves) and the piece position on the leaf (piece one close to the leaf base and piece four close to the top) were also evaluated. Baby leaves were cultivated under an unheated plastic greenhouse for winter production and under a nethouse for the rest of the growing season, with a total of five and seven sampling dates for spinach and 'wild' rocket respectively. The cultivar of butterhead lettuce had a significant effect on postharvest quality of fresh-cut product but more important was the piece position on the leaf. When this was closer to the base of the leaf, there was more browning on cut edges and limited shelf life for the fresh-cut lettuce. The result was associated in one tested cultivar with PAL activity, which was higher by 106% for piece one compared to piece four as an average for the whole storage period. The growing season of baby leaves had a great impact on their shelf life, with the season of mild environmental conditions achieving the highest marketability. [ABSTRACT FROM AUTHOR]

Watermelon is cultivated worldwide and is mainly grafted onto interspecific squash rootstocks. Light-emitting diodes (LEDs) can be implemented as light sources during indoor production of both species and their spectral quality is of great importance. The objective of the present study was to determine the optimal emission of LEDs with wide wavelength for the production of watermelon and interspecific squash seedlings in a growth chamber. Conditions were set at 22/20 °C temperature (day/night), 16 h photoperiod, and 85 ± 5 μmol m−2 s−1 photosynthetic photon flux density. Illumination was provided by fluorescent (FL, T0) lamps or four LEDs (T1, T2, T3, and T4) emitting varying wide spectra. Watermelon seedlings had greater shoot length, stem diameter, cotyledon area, shoot dry weight-to-length (DW/L) ratio, and Dickson's quality index (DQI) under T1 and T3, while leaf area and shoot dry weight (DW) had higher values under T1. Interspecific squash seedlings had greater stem diameter, and shoot and root DW under T1 and T3, while leaf and cotyledon areas were favored under T1. In both species, T0 showed inferior development. It could be concluded that a light source with high red emission, relatively low blue emission, and a red:far-red ratio of about 3 units seems ideal for the production of high-quality watermelon (scion) and interspecific squash (rootstock) seedlings. [ABSTRACT FROM AUTHOR]