Environmental pollution, increasing CO₂ atmospheric levels and the greenhouse effect are closely associated with the ongoing climate change and the extreme climatic events we are witnessing all over the Earth. Drought, high temperature and salinity are among the main environmental stresses that negatively affect the yield of numerous crops, challenging the world food safety. These effects are more profound in vegetable crops which are generally more susceptible to climate change than field or tree crops. The response to single or combined environmental stressors involves various changes in plant morphology and physiology or in molecular processes. Knowing the mechanisms behind these responses may help towards the creation of more tolerant genotypes in the long-term. However, the imediacy of the problem requires urgently short-term measures such as the use of eco-sustainable agricultural practices which can alleviate the negative effects of environmental pollution and allow vegetable crops to adapt to adverse climatic conditions. In this review, the main abiotic stressors were examined, namely drought, heat and salinity stress, focusing on the mechanisms involved in the most common vegetable crops responses. Moreover, the use of eco-sustainable cultural techniques, such as biostimulants, grafting and genomic sequencing techniques, to increase the quality of tomato crop under adverse environmental conditions are also presented.

Plant biostimulants (PBs) such as protein hydrolysates and seaweed extracts are attracting the increasing interest of scientists and vegetable growers for their potential toenhance yield and nutritional quality. The current study assessed crop productivity, leaf colorimetry, mineral profile and bioactive compounds of greenhouse spinach in response to the foliar application of three PBs: legume-derived protein hydrolysate [PH], extract of seaweed Ecklonia maxima or mixture of vegetal oils, herbal and seaweed Ascophyllum nodosum extracts. Plants were PB-treated at a rate of 3 mL L⁻¹ four times during their growth cycle at weekly intervals. Foliar PB applications enhanced fresh yield, dry biomass and leaf area of spinach in comparison with untreated plants. Improved yield performance with PB applications was associated with improved chlorophyll biosynthesis (higher SPAD index). The three PB treatments elicited an increase in bioactive compounds (total phenols and ascorbic acid), thus raised the functional quality of spinach. The application of PH enhanced K and Mg concentrations and did not result in increased nitrate accumulation as observed with the other two PB treatments. Our findings can assist vegetable farmers and the agro-food industry in adopting innovative and sustainable tools such as PB for complementing a high yield with premium quality.

Plant-derived protein hydrolysates (PHs) are gaining prominence as biostimulants due to their potential to improve yield and nutritional quality even under suboptimal nutrient regimens. In this study, we investigated the effects of foliar application of a legume-derived PH (0 or 4 mL L⁻¹) on greenhouse baby spinach (Spinacia oleracea L.) under four nitrogen (N) fertilization levels (0, 15, 30, or 45 kg ha⁻¹) by evaluating morphological and colorimetric parameters, mineral composition, carbohydrates, proteins, and amino acids. The fresh yield in untreated and biostimulant-treated spinach plants increased in response to an increase in N fertilization from 1 up to 30 kg ha⁻¹, reaching a plateau thereafter indicating the luxury consumption of N at 45 kg ha⁻¹. Increasing N fertilization rate, independently of PH, lead to a significant increase of all amino acids with the exception of alanine, GABA, leucine, lysine, methionine, and ornithine but decreased the polyphenols content. Interestingly, the fresh yield at 0 and 15 kg ha⁻¹ was clearly greater in PH-treated plants compared to untreated plants by 33.3% and 24.9%, respectively. This was associated with the presence in of amino acids and small peptides PH ‘Trainer^®’, which act as signaling molecules eliciting auxin- and/or gibberellin-like activities on both leaves and roots and thus inducing a “nutrient acquisition response” that enhances nutrients acquisition and assimilation (high P, Ca, and Mg accumulation) as well as an increase in the photochemical efficiency and activity of photosystem II (higher SPAD index). Foliar applications of the commercial PH decreased the polyphenols content, but on the other hand strongly increased total amino acid content (+45%, +82%, and +59% at 0, 15, and 30 kg ha⁻¹, respectively) but not at a 45-kg ha⁻¹-rate. Overall, the use of PH could represent a sustainable tool for boosting yield and nitrogen use efficiency and coping with soil fertility problems under low input regimens.

Selenium (Se) is considered essential for human nutrition as it is involved in the metabolic pathway of selenoproteins and relevant biological functions. Microgreens, defined as tender immature greens, constitute an emerging functional food characterized by overall higher levels of phytonutrients than their mature counterparts. The nutraceutical value of microgreens can be further improved through Se biofortification, delivering Se-enriched foods and potentially an enhanced content of bioactive compounds. The current study defined the effect of sodium selenate applications at three concentrations (0, 8, and 16 μM Se) on the bioactive compounds and mineral content of coriander, green basil, purple basil, and tatsoi microgreens grown in soilless cultivation. Analytical emphasis was dedicated to the identification and quantification of polyphenols by UHPLC-Q-Orbitrap-HRMS, major carotenoids by HPLC-DAD, and macro micro-minerals by ICP-OES. Twenty-seven phenolic compounds were quantified, of which the most abundant were: Chlorogenic acid and rutin in coriander, caffeic acid hexoside and kaempferol-3-O(caffeoyl) sophoroside-7-O-glucoside in tatsoi, and cichoric acid and rosmarinic acid in both green and purple basil. In coriander and tatsoi microgreens, the application of 16 μM Se increased the total phenols content by 21% and 95%, respectively; moreover, it improved the yield by 44% and 18%, respectively. At the same Se dose, the bioactive value of coriander and tatsoi was enhanced by a significant increase in rutin (33%) and kaempferol-3-O(feruloyl)sophoroside-7-O-glucoside (157%), respectively, compared to the control. In green and purple basil microgreens, the 8 μM Se application enhanced the lutein concentration by 7% and 19%, respectively. The same application rate also increased the overall macroelements content by 35% and total polyphenols concentration by 32% but only in the green cultivar. The latter actually had a tripled chicoric acid content compared to the untreated control. All microgreen genotypes exhibited an increase in the Se content in response to the biofortification treatments, thereby satisfying the recommended daily allowance for Se (RDA-Se) from 20% to 133%. The optimal Se dose that guarantees the effectiveness of Se biofortification and improves the content of bioactive compounds was 16 μM in coriander and tatsoi, and 8 μM in green and purple basil.