Chitin and chitosan are natural compounds that are biodegradable and nontoxic and have gained noticeable attention due to their effective contribution to increased yield and agro-environmental sustainability. Several effects have been reported for chitosan application in plants. Particularly, it can be used in plant defense systems against biological and environmental stress conditions and as a plant growth promoter—it can increase stomatal conductance and reduce transpiration or be applied as a coating material in seeds. Moreover, it can be effective in promoting chitinolytic microorganisms and prolonging storage life through post-harvest treatments, or benefit nutrient delivery to plants since it may prevent leaching and improve slow release of nutrients in fertilizers. Finally, it can remediate polluted soils through the removal of cationic and anionic heavy metals and the improvement of soil properties. On the other hand, chitin also has many beneficial effects such as plant growth promotion, improved plant nutrition and ability to modulate and improve plants’ resistance to abiotic and biotic stressors. The present review presents a literature overview regarding the effects of chitin, chitosan and derivatives on horticultural crops, highlighting their important role in modern sustainable crop production; the main limitations as well as the future prospects of applications of this particular biostimulant category are also presented.

Biostimulants, are a diverse class of compounds including substances or microorganism which have positive impacts on plant growth, yield and chemical composition as well as boosting effects to biotic and abiotic stress tolerance. The major plant biostimulants are hydrolysates of plant or animal protein and other compounds that contain nitrogen, humic substances, extracts of seaweeds, biopolymers, compounds of microbial origin, phosphite, and silicon, among others. The mechanisms involved in the protective effects of biostimulants are varied depending on the compound and/or crop and mostly related with improved physiological processes and plant morphology aspects such as the enhanced root formation and elongation, increased nutrient uptake, improvement in seed germination rates and better crop establishment, increased cation exchange, decreased leaching, detoxification of heavy metals, mechanisms involved in stomatal conductance and plant transpiration or the stimulation of plant immune systems against stressors. The aim of this review was to provide an overview of the application of plant biostimulants on different crops within the framework of sustainable crop management, aiming to gather critical information regarding their positive effects on plant growth and yield, as well as on the quality of the final product. Moreover, the main limitations of such practice as well as the future prospects of biostimulants research will be presented.

Water shortage can be a restrictive factor for the growth and quality of vegetable crops. Considering the alleviating effects of biostimulant application against water stress, this study aimed to investigate the effect of four biostimulant products (protein and amino acids with carboxylic acids (Tr1); protein and amino acids with seaweed extracts (Tr2); humic and fulvic acids with seaweed extracts (Tr3); SiO2 (Tr4); and control (no biostimulants added)) and two irrigation systems (regulated deficit irrigation (RDI)—65% of field capacity and regular irrigation (RI)—100% of field capacity) on quality parameters of processing tomato fruit. Regulated deficit irrigation and biostimulant application increased the energetic value, carbohydrates, and free sugars content, while organic acids showed a variable response to biostimulant use. In terms of tocopherols (α-, β-, γ-, δ-) and carotenoids (lycopene and β-carotene), regular irrigation and biostimulant application negatively affected their content, while Tr3 treatment had a beneficial impact on these lipophilic compounds under RDI conditions. The main fatty acids were palmitic (C16:0) and linoleic (C18:2n6) acids, which increased when plants were treated with Tr3 and Tr1 biostimulants under a deficit regime. Antioxidant activity (assessed by TBARS and OxHLIA assays) and total phenolic and flavonoids content also showed a variable response to the studied factors. In particular, the application of Tr3 and the control treatment under RDI increased the total phenolic content, while the control and Tr3 treatments under the same irrigation regime recorded the highest antioxidant activity. In conclusion, our results indicate that the adoption of eco-friendly strategies such as regulated deficit irrigation and biostimulant application can beneficially affect the quality traits of processing tomatoes.

The aim of the present study was to evaluate the effects of three biostimulant products (Nomoren (N), Twin Antistress (TW), x-Stress (XS) and control treatment (C: no biostimulants added)) on the nutritional value, chemical composition and bioactive properties of greenhouse tomato fruit grown under full (W+: 100% of field capacity) and deficit irrigation (W–: 70% of field capacity) conditions. Fat content was the highest for the fully irrigated plants that received no biostimulants (CW+), while proteins and carbohydrates and energetic value were the highest in the XSW+ treatment. The content of the main detected sugars (fructose, glucose and trehalose) varied depending on the irrigation and biostimulant treatment. The highest amounts of individual and total organic acids and tocopherols were recorded in fully irrigated plants treated with Twin Antistress (TW), whereas the lowest overall values were observed under deficit irrigation for plants that received the XS treatment. The most abundant fatty acids were palmitic (27.5–36.0%) and linoleic acid (27.4–35.4%), followed by oleic (9.2–21.2%), linolenic (5.4–13.1%) and stearic acid (5.3–6.8%). Moreover, the highest values of β-carotene and lycopene were recorded for the CW- and NW+ treatments, respectively. The TWW+ showed the highest antioxidant activity for both assays tested (TBARS and OxHLIA). Most of the tested extracts showed lower antibacterial activity against the tested bacteria compared to the positive controls. On the other hand, CW+, XSW+ and XSW- treatments showed higher antifungal activity (MIC values) than positive controls. In conclusion, each biostimulant product had a different effect on the determined characteristics depending on the level of irrigation. Therefore, more research is needed to better identify the mechanisms of action and the physiological processes, after which the tested biostimulants may be used to standardize the application of such products in tomato cultivation.

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.

Climate change necessitates direct measures in horticultural crop production, including the adoption of sustainable agronomic practices, such as the use of biostimulants and the inclusion of alternative species in agroecosystems. The aim of the present study was to evaluate the effect of two biostimulant formulations, one based on beneficial bacteria and fungi and the other based on seaweed extracts, on the growth, nutritional value, and bioactive properties of three wild edible species, namely, Sonchus oleraceus, Cichorium spinosum, and Scolymus hispanicus, grown in a greenhouse under optimal conditions. Our results indicate that biostimulant application had a variable effect on crop performance depending on the biostimulant formulation and species, with Bactiva showing a clear beneficial effect on the fresh weight, number of leaves, and leaf area of S. oleraceus (increased by 63.2%, 32.4%, and 51.1%, respectively, compared to the control), while seaweed extracts mostly improved the crop performance of S. hispanicus and the number of leaves and the Soil Plant Analysis Development (SPAD) index of C. spinosum (increased by 1.1% and 24.8%, respectively, compared to the control). Moreover, Bactiva significantly increased the leaf protein content of all the studied species (increased by 2.1%, 5.2%, and 6.9% for S. oleraceus, C. spinosum, and S. hispanicus, respectively, compared to the control), whereas a varied response was observed for the rest of the macronutrients, depending on the species and biostimulant. Similarly, the macromineral content (N, P, and K) increased for the application of Bactiva and/or seaweed extracts in S. oleraceus (increased by 2.1%, 22.4%, and 14.0% for N, P and K, respectively, compared to the control) and C. spinosum (increased by 5.2%, 19.3%, and 14.7% for N, P, and K, respectively, compared to the control) leaves, while for S. hispanicus leaves, only N and K increased for Bactiva (increase by 7.0% and 17.9% for N and K, respectively, compared to the control). Finally, the use of the studied biostimulants had a varied effect on the polyphenol content of the three species, and the antioxidant activity also varied among the three assays implemented. In conclusion, the use of biostimulants on these underexplored species showed promising results in terms of crop performance and chemical composition/. However, considering that the plants were subjected to optimal conditions, further research is needed to reveal the stress-mitigating effects of these biostimulant formulations for their integration as a sustainable agronomic tool for the commercial exploitation of wild edible greens.