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The effect of deficit irrigation and biostimulant application on chemical composition and nutritional value of processing tomato.
Climate change has resulted in the reduction of available irrigation water required to meet the needs of crops, while it has also degraded the quality of irrigation water. The aim of the present study was to evaluate the effects of deficit irrigation and biostimulant application on the chemical composition and nutritional value of processing tomatoe (Lycopersicum esculentum L. cv. Heinz 1162). For this purpose, five biostimulant formulations were implemented (Μ1: Vegetal proteins and amino acids + Carboxylic Acids; Μ2: Vegetal proteins and amino acids + Seaweed extracts (Laminaria digitata + Ascophyllum nodosum); Μ3: Humic & Fulvic Acids + Seaweed extracts (Laminaria digitata + Ascophyllum nodosum); Μ4: SiO2; Μ5: Seaweed extracts (Ascophyllum nodosum) + water soluble nitrogen (0.5%) + soluble potash (17% K2O); including the untreated control), while at the same time two levels of irrigation were applied (100%, 65-70% of maximum field capacity). The results showed a significant effect of the tested factors on all the tested parameters. In particular, fruit obtained from normally irrigated plants had a higher moisture content than the ones treated with deficit irrigation. On the other hand, a varied effect was recorded on proximate composition with deficit irrigation resulting in higher protein, ash, carbohydrates and energy content in the case of M3 and M5, M2, M2 and M3 and M3 treatments, respectively, whereas the highest ash content was recorded for deficit irrigation and the M5 treatment. Similarly, deficit irrigation increased free sugars content (e.g. fructose, glucose, sucrose and total sugars) for M4, M1, Control and M1 treatments, respectively, while the same trend was recorded for organic acids content (malic, ascorbic and total organic acids increased for M2, and citric acid for control treatment), except the case of oxalic acid where the highest content was detected in normally irrigated plants treated with the M4 treatment. A-tocopherol was the most abundant vitamin E isomer, while the highest content was recorded for M3 and deficit irrigation conditions. The same conditions were also the most beneficial for lycopene and carotene contents. The main fatty acids detected were palmitic, linoleic and oleic acid which increased under deficit irrigation and for M3 in the case of palmitic acid, as well as for M1 treatments in the case of the other two fatty acids. The highest total phenolic compounds content was recorded for deficit and the M3 treatment, whereas total flavonoids were benefited by normal irrigation and the M1 treatment. Antioxidant activity was determined with TBARS and OxHLIA assays, where in both cases deficit irrigation resulted in lower EC50 values (higher antioxidant activity) for the control and M3 treatments, respectively. In conclusion, our results indicate a positive effect of deficit irrigation on most of the tested parameters, while specific biostimulants such as M3 significantly improved tocopherols, lycopene, carotene and total phenolic compounds content, resulting in higher antioxidant activity, as determined by OxHLIA assay. Therefore, it could be suggested that both agronomic tools studied could be implemented and mitigate water stress effects while improving the overall nutritional value and bioactivity of the final product.