Light Spectrum Differentially Affects the Yield and Phytochemical Content of Microgreen Vegetables in a Plant Factory

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

Impact of Scion and Rootstock Seedling Quality Selection on the Vigor of Watermelon–Interspecific Squash Grafted Seedlings

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

Optimal LED Wavelength Composition for the Production of High-Quality Watermelon and Interspecific Squash Seedlings Used for Grafting

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

Physiological and Phytochemical Responses of Spinach Baby Leaves Grown in a PFAL System with LEDs and Saline Nutrient Solution

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

Impact of Light on Horticultural Crops

Light is an essential factor for the growth and quality of horticultural plants and its effects depend upon parameters such as duration, intensity and quality [...

The Use of High-Quality Watermelon Seedlings Is Prerequisite to Limit the Transplanting Shock and Achieve Yield Earliness

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

Ascophyllum nodosum and Silicon-Based Biostimulants Differentially Affect the Physiology and Growth of Watermelon Transplants under Abiotic Stress Factors: The Case of Salinity

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

<i>Ascophyllum nodosum</i> and Silicon-Based Biostimulants Differentially Affect the Physiology and Growth of Watermelon Transplants under Abiotic Stress Factors: The Case of Drought

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

Επίδραση τεχνητού φωτισμού διόδων εκπομπής φωτεινής ακτινοβολίας στην αύξηση και ποιότητα εμβολιασμένων σποροφύτων καρπουζιού

Watermelon (Citrullus lanatus) is an economically important crop which is mainly propagated through grafting. Grafted watermelon seedlings are produced in three separate stages: growing of scion and rootstock seedlings to-be-grafted (stage I), grafting and healing of grafted seedlings (stage II), and acclimatization of grafted seedlings (stage III). The main objective of the thesis was to investigate whether artificial lighting provided by light-emitting diodes (LEDs) and employed either as sole or as supplemental light source imposes significant positive effect on the quality of scion and rootstock seedlings to-be-grafted, as well as grafted watermelon seedlings. Moreover, the effect of LED spectral composition was tested in the three production stages of grafted watermelon seedlings both under growth chamber and greenhouse conditions. As model plants we used watermelon (Celine F1) scion and interspecific squash (Cucurbita maxima × C. moschata “TZ-148) rootstock. Initially we defined seedling quality categories in the three production stages. We report that shoot and root biomass, stem diameter and leaf area are the most valuable indicators of seedling quality in all production stages. A combination between “high” scions and “optimum” characterized rootstocks is ideal for high-quality grafted seedlings. Moreover, the necessity of artificial lighting was evaluated in all production stages and we concluded that supplemental lighting is necessary in the greenhouse for the growth of watermelon seedlings used as scion as well as for acclimatization of grafted seedlings, while fluorescent lamps are not as efficient as needed during the healing stage. Following, we tested the response of scions and rootstocks under wide spectra LEDs employed in a growth chamber and found that LEDs with relatively high red (53–64%), and low blue (8–14%) light emission enhanced seedling quality. When grown in a greenhouse, watermelon scions showed improved qualitative characteristics under supplemental LED compared to high-pressure sodium (HPS) lamps due to favorable spectral distribution. Healing is a delicate procedure where physiological and histological modifications take place on both segments, thus, we examined the impact of LEDs emitting narrow-band red (R) or blue (B), or red-blue combinations as sole light source during healing. From the results it is evident that R along with red with 12 or 24% blue (12B or 24B) light addition performed greatly in valuable growth and morphological parameters, while B promoted gas exchange parameters. The results were also reaffirmed by the examination of four genotype combination where no significant genotype dependency was detected. Following, we investigated the anatomical and root architecture modifications and we report that blue light proved beneficial for the rapid formation of scion-rootstock vascular bridges and subsequently for a quick start of root formation in the first three days after grafting. In the following days where all vascular bridges were already formed, red light presence enhanced the root system development. Moreover, grafted watermelon seedlings acclimatizing in a greenhouse showed enhanced quality under supplemental LED compared to HPS lamps. In all LED experiments, we also addressed the effects of red and blue light bands on the seedling morphology and physiology and we showed that even small interplays in the light spectra triggers a significant effect in plant behavior.Το καρπούζι (Citrullus lanatus) είναι οικονομικά σημαντικό προϊόν το οποίο πολλαπλασιάζεται κυρίως μέσω εμβολιασμού. Η παραγωγή εμβολιασμένων σποροφύτων καρπουζιού αποτελείται από τρία διακριτά στάδια: την παραγωγή σποροφύτων προς εμβολιασμό (εμβόλιο και υποκείμενο) (στάδιο Ι), τον εμβολιασμό και την επούλωση των τομών εμβολιασμού (στάδιο ΙΙ), και τη σκληραγώγηση των εμβολιασμένων σποροφύτων (στάδιο ΙΙΙ). Ο κύριος στόχος της διατριβής ήταν η διερεύνηση της επίδρασης τεχνητού φωτισμού από διόδους εκπομπής φωτεινής ακτινοβολίας (light-emitting diodes, LEDs) ως συμπληρωματικός ή αποκλειστικός φωτισμός στην ποιότητα εμβολίων και υποκειμένων προς εμβολιασμό, καθώς και εμβολιασμένων σποροφύτων καρπουζιού. Επιπλέον, μελετήθηκε η επίδραση του φάσματος ακτινοβολίας λαμπτήρων LED στα τρία στάδια παραγωγής εμβολιασμένων σποροφύτων σε θάλαμο ανάπτυξης και σε θερμοκήπιο. Μελετώμενα είδη αποτέλεσαν το καρπούζι (εμβόλιο Celine F1) και το διειδικό υβρίδιο κολοκυθιού (υποκείμενο Cucurbita maxima × C. moschata “TZ-148). Αρχικά, καθορίσαμε κατηγορίες ποιότητας σποροφύτων στα τρία στάδια παραγωγής. Αναφέρουμε ότι το ξηρό βάρος υπέργειου τμήματος και ριζικού συστήματος, η διάμετρος ριζικού κόμβου και η φυλλική επιφάνεια είναι οι σημαντικότεροι δείκτες ποιότητας σποροφύτων στα τρία στάδια παραγωγής. Συνδυασμός «high» εμβολίων με «optimum» υποκειμένων είναι ιδανικός για την παραγωγή εμβολιασμένων σποροφύτων υψηλής ποιότητας. Επιπλέον, διερευνήθηκε η ανάγκη χρήσης τεχνητού φωτισμού στα τρία στάδια παραγωγής και καταλήξαμε ότι είναι απαραίτητος ο συμπληρωματικός φωτισμός στο θερμοκήπιο παραγωγής εμβολίων καθώς και σκληραγώγησης εμβολιασμένων σποροφύτων, ενώ οι λαμπτήρες φθορισμού δεν έχουν υψηλή απόδοση κατά το στάδιο επούλωσης. Κατόπιν, μελετήσαμε την επίδραση λαμπτήρων LED με ευρύ φάσμα ακτινοβολίας στην παραγωγή εμβολίων και υποκειμένων σε θάλαμο ανάπτυξης και βρήκαμε ότι LEDs με σχετικά υψηλό ποσοστό ερυθρού φωτός (53-64%) και χαμηλό ποσοστό κυανού φωτός (8-14%) οδήγησε σε ενισχυμένη ποιότητα. Στην περίπτωση του θερμοκηπίου, εμβόλια καρπουζιού παρουσίασαν βελτιωμένα ποιοτικά χαρακτηριστικά κάτω από συμπληρωματικό φωτισμό με LEDs συγκριτικά με λαμπτήρες υψηλής πίεσης νατρίου (HPS) λόγω ευνοϊκότερου φάσματος ακτινοβολίας. Η επούλωση αποτελεί ευαίσθητη διαδικασία κατά την οποία λαμβάνουν χώρα φυσιολογικές και ιστολογικές μεταβολές στα δύο τμήματα. Επομένως, μελετήσαμε την επίδραση φωτισμού με LEDs που εκπέμπουν ακτινοβολία μονοχρωματική ερυθρή (R), κυανή (Β) και συνδυασμούς ερυθρής-κυανής κατά τη διάρκεια της επούλωσης. Από τα αποτελέσματα προέκυψε ότι η R καθώς και ερυθρή με 12 ή 24% επιπρόσθετη κυανή ακτινοβολία (12Β ή 24Β) είχε θετική επίδραση σε σημαντικές μορφολογικές παραμέτρους, ενώ η Β ενίσχυσε παραμέτρους ανταλλαγής αερίων. Τα αποτελέσματα επιβεβαιώθηκαν από τη διερεύνηση τεσσάρων συνδυασμών γενοτύπων όπου δεν εντοπίστηκε σημαντική επίδραση του γενοτύπου. Κατόπιν, μελετήσαμε μεταβολές στην ανατομία της τομής εμβολιασμού και της αρχιτεκτονικής ρίζας και βρήκαμε ότι η κυανή ακτινοβολία είναι ευνοϊκή για την ταχεία ένωση του αγγειακού συστήματος εμβολίου-υποκειμένου και τον σχηματισμού ριζικού συστήματος τρεις μέρες από τον εμβολιασμό. Τις επόμενες ημέρες συνεχίστηκε η ένωση του αγγειακού συστήματος και η παρουσία ερυθρής ακτινοβολίας βελτίωσε την ανάπτυξη του ριζικού συστήματος. Επιπλέον, εμβολιασμένα σπορόφυτα κατά την σκληραγώγηση στο θερμοκήπιο παρουσίασαν αυξημένη ποιότητα κάτω από συμπληρωματικό φωτισμό με LEDs συγκριτικά με λαμπτήρες υψηλής πίεσης νατρίου (HPS). Σε όλα τα πειράματα με λαμπτήρες LED αναδείξαμε την επίδραση του ερυθρού και κυανού φάσματος ακτινοβολίας στη μορφολογία και φυσιολογία σποροφύτων και αποδείξαμε ότι ακόμα και μικρές μεταβολές στο φάσμα ακτινοβολίας ασκεί σημαντική επίδραση στη συμπεριφορά των φυτών

Artificial LED lighting enhances growth characteristics and total phenolic content of Ocimum basilicum, but variably affects transplant success

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±20μmolm-2s-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.</p