Alexios A. Alexopoulos

This study aimed to evaluate the effect of two irrigation systems (deficit irrigation (DI)—70% of field capacity—and full irrigation (FI)—100% of field capacity) and a biostimulant formulation (silicon (Si) and calcium (Ca) at four different rates) on the chemical composition and fruit quality of greenhouse-grown tomatoes. Deficit irrigation and biostimulant application influenced the proximate composition of tomato fruits. Fructose and glucose were the main soluble sugars, while malic and citric acids were the predominant organic acids. Free sugar and organic acid content increased under DI and biostimulant applications. In contrast, deficit irrigation combined with biostimulant application decreased α-tocopherol levels. In terms of carotenoids, lycopene and β-carotene concentrations were higher under full irrigation. The main fatty acids were palmitic (C16:0) and linoleic (C18:2n6) acids, with saturated (SFA) and polyunsaturated (PUFA) fatty acids being the main classes. Moreover, biostimulant applications reduced the total phenolic content regardless of the irrigation regime, whereas the flavonoid content increased when biostimulants were applied under FI conditions. Regarding antioxidant activity (assessed by TBARS and OxHLIA assays), a variable response to irrigation and biostimulant application was observed. In conclusion, the application of Si and Ca under DI showed promising results in terms of yield and quality of tomato fruit and it could be considered a sustainable strategy to mitigate adverse effects of climate change on horticultural crops.

Plants of two potato (Solanum tuberosum L.) varieties ‘Spunta’ (mid-early maturity) and ‘Kensa’ (mid-late maturity) were subjected to three nitrogen (N), phosphorus (P), and potassium (K) fertilization regimes, with T1 optimal rates (as recommended by the Tunisian Potato Technical Centre), T2 high rates (+25% of T1), and T3 low rates (−25% of T1). Plant growth, yield components, chlorophyll fluorescence (Fo, Fm, Fv/Fm), photosynthetic active radiation (PAR), real evapotranspiration (RET), and biochemical parameters in mature leaves and tubers (total soluble sugars (TSSs) and starch in both leaves and tubers) were evaluated. Our results showed a significant effect of fertilizer rates on plant growth, physiological, yield, and quality traits, as well as on biochemical contents of leaves and tubers, as well as on the variety. The application of high rates (T2) resulted in increased chlorophyll fluorescence (Fo) and high ratios of Fv/Fm, and it reduced Fm and photosynthetic active radiation (PAR). The highest yield per plant (615.4 g of tubers) and average number of tubers/plant (6.44) were observed in cv. ‘Spunta’ subjected to optimal fertilizer rate (T1), while more than 50% of tubers of this variety were classified as size C1 (>50 mm). On the other hand, high rates (T2) increased the yield per plant (436.74 g; approximately 9.3% compared to T1) and the number of tubers per plant (5.70) in cv. ‘Kensa’, with approximately 56% of tubers being classified in the C1 category. High rates also increased sucrose and starch content in tubers, regardless of the variety, without being significantly different from the other fertilization regimes. In conclusion, our results provide important information regarding the effect of fertilization practice on potato growth and yield parameters and the biochemical composition of leaves and tubers. Therefore, it could be suggested that the application of reduced NPK rates (−25% of optimal rates) in mid-early varieties (namely cv. ‘Spunta’) could reduce the production cost without compromising yield and quality components.

The aim of the present work is to study the impact of salinity (i.e., 2 dS/m without addition of NaCl (control); 5 dS/m (EC-5); and 10 dS/m (EC-10) with the addition of 30 and 80 mM NaCl, respectively) on yield, organoleptic quality and the content of antioxidant compounds in Plantago coronopus and Hedypnois cretica plants in relation to different cropping systems and environmental conditions during growth (i.e., pots or floating hydroponics systems in the greenhouse and pots in the field (GPs, GH and FPs, respectively)). Almost all the growth parameters of the H. cretica plants in the greenhouse were impaired by both moderate (EC-5) and high (EC-10) salinity levels, especially in the floating hydroponics system, where, compared to EC-2, a reduction was observed of 33% in EC-5 and 76% in EC-10 in leaf area and of 24% and 75%, respectively, in fresh weight. On the contrary, the growth of the P. coronopus plants was negatively affected by salinity only in the GP system. However, salinity had no effect on most growth characteristics of both species grown in the field, suggesting a strong environmental effect on the impact of salinity in the tested species. On the other hand, the content of pigments, proline and total phenolics in the P. coronopus leaves, as well as their antioxidant capacity, were not affected by salinity in most cases, whereas in H. cretica the salinity effect was significant even at moderate levels (EC-5) in relation to the cropping system and growth environment. Moreover, both salinity levels reduced the nitrate content of P. coronopus plants in all cases (up to 61% in GP plants at EC-10) and of H. cretica GH plants (up to 67% in EC-10). Finally, regardless of the salinity level, the field-grown plants of both species showed a considerably higher content of total phenolics (by 59% in H. cretica and 58% in P. coronopus) and antioxidant activity (by 63% in H. cretica and 53% in P. coronopus, FRAP values), compared to the greenhouse ones. In conclusion, our results indicate that the tested combinations of cropping systems and growth environments could be used as an eco-friendly and sustainable agronomic tool to mitigate the negative effects of salinity and to regulate the organoleptic and biochemical properties of the tested species, allowing small-scale farmers in the affected areas to cope with the ongoing climate change and the environmental pressures they currently face through the exploitation of alternative/underexploited species of high added value.

Salinity stress is severely affecting modern horticulture and puts food security under threat for current and future generations. The aim of the present study was to evaluate the effect of saline conditions (three salinity levels: 2.0, 5.0 and 10.0 dS m⁻¹) on the growth, physiological processes and quality of two wild edible species (Urospermum picroides and Reichardia picroides) grown under three different cropping systems (pots indoors (GP) and outdoors (FP); and floating hydroponics (FH)). Our results indicate that high salinity affected growth parameters in all the studied cropping systems in the case of U. picroides, whereas R. picroides was not affected only when grown in pots outdoors. Moreover, total soluble solids content and titratable acidity in both species were not affected by high salinity for any of the cropping systems, except for in the case of FP system. Similarly, carotenoids content decreased under high salinity when both species were grown in the FP system. A varied effect was recorded for total phenolic compounds content in response to salinity levels, although the FP system resulted in considerably higher phenolics accumulation in both species, while proline content increased when plants were subjected to high salinity, regardless of the cropping system. The antioxidant activity also varied among the studied treatments for both assays (TEAC and FRAP), although cultivation outdoors in pots resulted in considerably higher values compared to the other systems. Finally, nitrate content showed decreasing trends with increasing salinity in plants grown in the GP (both species) and FP system (only U. picroides), whereas no significant differences in physiological parameters in comparison to the control treatment were recorded, except for the stomatal conductance (FP and GP system) and transpiration rate (FP) of R. picroides plants. In conclusion, it seems that the tested plant species responded differently to the salinity treatments but they both displayed a lack of severe stress even at high salinity.

The scarcity of water is limiting crop production and is one of the most important stressors that severely affects crop yield, and it may also decrease the quality of the final products. Most of the medicinal and aromatic plants are considered resilient to water stress and constitute a sustainable choice for crop production in arid and semiarid conditions. In the present study, we examined the effect of scheduled deficit irrigation (e.g., I1: 40% of field capacity); I2: 70% of field capacity; and I3: 100% of field capacity) combined with biostimulant application (four different products that consisted of nitrogenous compounds and carboxylic acids (M1); nitrogenous compounds and seaweed extracts (M2); humic and fulvic acids and seaweed extracts (M3); and CaO, SiO₂, calcium mobilization and translocation factor and microminerals (M4)) on crop performance and essential oil production of mint plants (Mentha arvensis L.). Our aim was to define an irrigation regime that increases water-use efficiency and the biostimulant products that alleviate water stress effects. Our results indicate that moderate deficit irrigation (I2 treatment) and biostimulants that contained seaweed extracts and nitrogenous compounds and humic and fulvic acids (M2 and M3 treatments, respectively) significantly improved yield parameters in terms of fresh and dry herb yield and essential oil production. Moreover, the same biostimulant treatments significantly increased water-use efficiency of mint crops based on the various yield parameters tested in this study. In conclusion, our results indicate that selection of proper biostimulatory products may allow to apply deficit irrigation regimes in mint cultivation without compromising the crop performance in terms of both biomass production and essential oil yield. Therefore, the combination of these agronomic tools could facilitate water saving strategies in arid and semiarid regions and contribute to the sustainable management of water resources.

The aim of the study was to develop an efficient micropropagation protocol of Origanum scabrum, which will allow its commercial exploitation in the pharmaceutical and horticultural industries. First, the effect of the date of the explant collection (20 April, 20 May, 20 June, 20 July, 20 August) and the position of the explant on the plant stem (shoot apex, 1st node, 3rd node, 5th node) on the establishment of in vitro cultures was studied (1st experiment: Stage I). Next, the effect of temperature (15 °C, 25 °C) and the node position (microshoot apex, 1st node, 5th node) on the microplant production and ex vitro survival of plantlets was studied (2nd experiment: Stage II). The optimum season to collect explants from wild plants was shown to be during the vegetative growth of the plants (April to May), while the shoot apex and the 1st node were the most suitable explants. For the proliferation and production of rooted microplants, the best results were obtained from single-node explants excised from microshoots produced from 1st node-explants collected on 20th of May. Temperature did not affect microshoot number, leaf number and the percentage of rooted microplants, while microshoot length was higher at 25 °C. Moreover, microshoot length and the percentage of rooted microplants were higher in those derived from apex explants, while the survival of plantlets was not affected by treatments and ranged between 67% and 100%.

The cultivation of tolerant species with low-quality irrigation water is one of the main strategies to address the lack of availability of irrigation water. In this work, the effect of salinity on plant growth, nutritional composition, and quality features of Hedypnois cretica and Urospermum picroides was tested. Fresh yield of leaves and roots of both species were severely decreased under high salinity, while the mineral profile of leaves and roots also showed a decrease in most minerals. The recorded values of K/Na and Ca/Na ratios indicate that H. cretica has a higher susceptibility to salt stress due to a higher decrease in the values of the respective ratios compared to U. picroides. Leaf pigments and total phenolic compounds content were not significantly affected by salinity, while total soluble solids and titratable acidity increased under increasing salinity in most cases. Moreover, free proline content increased with increasing salinity, while the opposite trend was recorded for nitrates’ content. In conclusion, our findings indicate that tailor-made nutrient solutions could allow the use of irrigation water of a low quality for the commercial cultivation of H. cretica and U. picroides, thus allowing their domestication and integration in cropping systems where the cultivation of conventional crops is compromised.

Sea daffodil is a perennial medicinal plant with several beneficial health properties that is enlisted as an endangered and protected species. For the exploitation and conservation of such valuable species, sustainable propagation is a key factor. For this purpose, the establishment of in vitro cultures using botanical seeds is an effective way to produce a large number of microplants which can be used as propagating material and/or bulblets with further uses for the isolation–production of biocactive substances. In this work, we performed two separate experiments where we studied (a) the effect of temperature (10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) on seed germination in vitro and (b) the effect of temperature (10 °C, 20 °C, and 30 °C) and sucrose concentration (40 and 80 g/L) in growth medium on microplant development and the production of bulblets. Seed germination rates were high (over 70%) at a wide range of temperatures (15–30 °C), although the fastest and the most uniform germination was observed at 20–25 °C. Regarding the effect of temperature on microplant development and bulblet production, low temperatures (10 °C) had a negative effect on the number of leaves, bulb diameter, and fresh weight (F.W.) and dry weight (D.W.) of leaves, roots, and bulblets. The best growth of microplants (number of leaves, F.W. and D.W. of leaves, roots) and bulblet production (diameter, F.W., and D.W.) were observed in culture media with sucrose concentration 40 g/L and temperature of 30 °C. In culture medium with a sucrose concentration of 80 g/L the production of bulbs (diameter, F.W., and D.W.) was not inferior to culture media with a sucrose concentration of 40 g/L, although microplants had less root growth. It is concluded that the best treatment for the production of well-rooted microplants with large bulblets that could be used as propagating material or for the production of bulblets as a source for twin scales explants or pharmaceutical substances was the culture at 30 °C in culture medium with sucrose concentration 40 g/L. On the other hand, culture medium with a sucrose concentration of 80 g/L at 30 °C or 20 °C could be also used for the production of bulblets.

Soil salinization is one of the major environmental factors responsible for limited crop production throughout the world. Therefore, there is urgent need to find tolerant/resistant species to exploit in commercial cultivation systems. In this context, the valorization of wild edible greens for human consumption and/or medicinal purposes is gaining more and more interest. The aim of the present work was to study the effect of salinity, e.g., electrical conductivity: 2 mS cm⁻¹ (nutrient solution EC), 6 mS cm⁻¹ and 10 mS cm⁻¹ on plant growth and chemical composition of Reichardia picroides and Taraxacum officinale plants grown in a floating hydroponic system. The results showed that R. picroides is a moderately salt-tolerant species, as the majority of plant growth parameters determined were not negatively affected under the treatment of 6 mS cm⁻¹. On the other hand, the growth parameters of T. officinale plants were severely affected under the same conditions. Moreover, high salinity levels (EC at 10 mS cm⁻¹) impaired the growth of both species. The content of leaves in chlorophylls (a, b and total), carotenoids+xanthophylls and total soluble solids was not significantly affected by the tested EC levels in both species, whereas the titratable acidity increased under the treatment of 10 mS cm⁻¹. Moreover, R. picroides exhibited a more effective adaptation mechanism against saline conditions than T. officinale, as evidenced by the higher accumulation of osmolytes such as proline and the higher shoot K content, probably through a more efficient K/Na selectivity. In conclusion, both species were severely affected by high salinity; however, R. picroides showed promising results regarding its commercial cultivation under moderate salinity levels, especially in regions where resources of high-quality irrigation water are limited.

Given the important medicinal and nutritional value of wild edible greens, the last few years there is an increasing interest for their domestication and commercial exploitation. However, information concerning their adaptation to environmental conditions and their response to modern agricultural systems are scarce. In the present study, the effect of nutrient solution pH (4.0, 5.5 and 7.0) on the growth, chemical composition and inorganic nutrition of Taraxacum officinale and Reichardia picroides plants grown indoors in a floating hydroponic system was evaluated. Both species performed better at pH 5.5 and were slightly affected by pH 7.0, whereas pH 4.0 was not prohibitive for growth for both species, although R. picroides was less tolerant than T. officinale at low pH. Moreover, pH 4.0 did not severely affect nutrients uptake and transport within the plant tissues, suggesting that R. picroides susceptibility to low pH should not be attributed to nutrients imbalance. Nevertheless, low pH positively enhanced the content in total soluble solids, total phenolics, chlorophylls (a, b and total) and carotenoids, and decreased nitrates in both species. In conclusion, the studied species could be successfully grown in soilless systems with nutrient solutions of varied pH. Moreover, low pH levels (pH = 4.0) seemed to be beneficial to nutritional and dietary value in both species highlighting the potential of commercial cultivation under adverse conditions, especially in sustainable farming systems.