Foliar Ascorbic Acid Enhances Postharvest Quality of Cherry Tomatoes in Saline Hydroponic Substrate System

Ascorbic acid is a non-enzymatic antioxidant compound essential for plant defense under salt stress conditions. It can induce salt stress tolerance and enable the use of saline water in hydroponic cultivation with substrates. This study evaluated the effect of foliar application of ascorbic acid on the yield and postharvest quality of ‘Laranja’ cherry tomatoes grown in saline nutrient solutions under a substrate-based hydroponic system. The experiment was conducted in a greenhouse in Campina Grande, Paraíba, Brazil, in a randomized block design in a 5 × 5 factorial arrangement, corresponding to five levels of electrical conductivity of the saline nutrient solution—SNS (2.1—Control, 2.8, 3.5, 4.2, and 4.9 dS m−1) and five concentrations of ascorbic acid—AA (0, 150, 300, 450, and 600 mg L−1), with four replications. Salinity above 2.1 dS m−1 reduced yield components and phenolic compound content. However, the saline nutrient solution of 4.9 dS m−1 combined with 600 mg L−1 foliar application of AA increased fruit firmness, soluble solids, and titratable acidity. Additionally, SNS of 4.9 dS m−1 enhanced the levels of vitamin C, flavonoids, and anthocyanins. While AA improved postharvest quality of cherry tomatoes, it did not increase production under salt stress. Foliar application is thus a promising approach for enhancing fruit quality of cherry tomatoes grown in hydroponic systems using saline water, supporting sustainable production in semiarid regions.