Boron (B) toxicity is a relevant problem in Mediterranean regions, where irrigation water may present high concentrations of this micronutrient. In this study, the potential of aqueous extracts from the brown macroalga Laminaria digitata and the diatom Phaeodactylum tricornutum, applied alone or in combination with metalloids (Se, Si) and micronutrients (Mn, Fe, Zn), was evaluated to improve the tolerance of tomato plants (Solanum lycopersicum L.) grown under excess B (15 mg L⁻¹). The extracts were applied foliarly, and growth parameters, gas exchange, chlorophyll content, mineral composition, B accumulation, oxidative stress, and metabolic profile were analyzed. Excess B significantly reduced root development, net photosynthesis, and metabolic balance, evidencing a strong physiological impact. The application of algal extracts partially mitigated these adverse effects, mainly through improvements in photosynthesis, water use efficiency, and the accumulation of osmoprotective metabolites (proline, tryptophan, glucose). In particular, L. digitata promoted a significant increase in total biomass and greater physiological recovery compared with P. tricornutum. Conversely, formulations enriched with metalloids and micronutrients did not provide consistent additional benefits and even induced metabolic imbalances. Multivariate analysis (PCA) confirmed that relative tolerance was associated with physiological and metabolic variables rather than nutritional changes. Overall, these results highlight the potential of algal extracts, especially L. digitata, as effective biostimulants to mitigate boron toxicity in tomato.

Agro-food sector byproducts are valuable sources of biostimulants. Alperujo, the primary by-product generated during the two-phase centrifugation process of olive oil extraction, is rich in bioactive compounds, particularly phenolic compounds, which could enhance its valorization potential. Among these, hydroxytyrosol-4-glucoside and hydroxytyrosol were the predominant phenolic compounds detected. Despite the well-documented antioxidant and health-promoting properties of hydroxytyrosol, there is a notable lack of studies evaluating its use as a biostimulant in agricultural applications. To address this gap, the present study evaluated the agronomic and qualitative responses of tomato plants to the application of two commercial hydroxytyrosol-rich formulations (formulas A and B) derived from olive oil extraction by-products. Tomato plants were cultivated under greenhouse conditions using a soilless coco peat substrate, and the formulations were applied via the root system at different doses and application times, following the manufacturer's recommendations. Formulae A and B contained hydroxytyrosol at concentrations of 2.8 mg mL−1 and 6.4 mg mL−1, respectively. Key production parameters, including yield, fruit size, and number of fruits, both marketable and nonmarketable, were recorded. Additionally, fruit quality attributes were assessed, including shelf life, firmness, total soluble solids (TSS), antioxidant capacity, and concentrations of lycopene, vitamin C, total polyphenols, and anthocyanins. Formula B also increased fruit Ca, K and N concentrations, suggesting enhanced nutrient partitioning towards fruits. Metabolomic analysis of fruit tissues was performed using NMR spectroscopy to quantify primary metabolites, including sugars, organic acids, and amino acids, in the fruit. The results demonstrated that the application of these biostimulant formulations enhanced crop yield. Formula B increased the total and marketable yields by 15.7% and 21%, respectively, and formula A by 9.6% and 14.5%, respectively. Fruit firmness improved by up to 30%, and shelf life was extended by 37% and 54% with the use of formulas A and B, respectively. In addition, the key antioxidant attributes were improved. Lycopene increased by 36% and 21% under formula A and B, respectively. Total vitamin C increased by 18% with Formula B. Sugar content (glucose and fructose) and malate concentrations were significantly higher in treated fruits, whereas glutamine levels increased by 67% with Formula B. These findings highlight the potential of hydroxytyrosol-rich biostimulants to improve tomato yield, fruit quality, and postharvest longevity while promoting sustainable agriculture and the valorization of agro-industrial waste.

Agro-food processing by-products represent valuable sources of bioactive compounds with potential applications in sustainable crop production. This study evaluated the agronomic and postharvest responses of greenhouse-grown tomato to two commercial formulations enriched in hydroxytyrosol (Formula A and Formula B) and derived from olive oil processing by-products. Plants were grown in a soilless coco-peat system, and the formulations were applied manually to the root system according to their respective manufacturer-recommended regimes. The substrate bag was considered the experimental unit (n = 6 per treatment), with the greenhouse block retained in the statistical model. Formula A and Formula B increased total yield by 9.6% and 15.7%, respectively, and marketable yield by 14.5% and 21.0%. Both formulations increased fruit firmness, whereas total soluble solids remained unaffected. Shelf life increased from 23 days in control fruit to 32 and 38 days following Formula A and Formula B application, respectively. Antioxidant-related responses were treatment-dependent: Formula B increased DPPH radical-scavenging capacity and total and reduced vitamin C, whereas lycopene increased significantly with Formula A and showed an intermediate response with Formula B; total polyphenols and anthocyanins were unaffected. The treatments also modified fruit primary-metabolite profiles, including sugars, organic acids, and amino acids, and both formulations increased fruit Ca, K, and N concentrations at the final sampling. Overall, these findings demonstrate the potential of hydroxytyrosol-enriched commercial formulations to improve tomato productivity and selected postharvest-quality traits while providing a valorization route for olive oil processing by-products. However, because the formulations differed in composition, hydroxytyrosol concentration, dose, and application frequency, the specific contribution of hydroxytyrosol cannot be isolated from that of the complete formulations.