Hydrogen Peroxide Reduces the Effect of Salt Stress on Growth and Postharvest Quality of Hydroponic Mini Watermelon

Hydroponic cultivation of mini watermelon with saline waters can be made possible through the use of substances that can mitigate the deleterious effects of salt stress. In this context, the objective of this study was to evaluate the growth and postharvest quality of mini watermelon as a function of the salinity levels of the nutrient solution and hydrogen peroxide in a hydroponic system. The experiment was conducted in a greenhouse in Pombal, PB, Brazil, using a Nutrient Film Technique (NFT) hydroponic system. The experimental design was completely randomized, in a 4 × 4 factorial scheme, corresponding to four levels of electrical conductivity of the nutrient solution (ECns (2.1, 3.1, 4.1, and 5.1 dS m−1)) and four concentrations of hydrogen peroxide (H2O2 (0, 20, 40, and 60 μM)), with 5 replicates. Foliar spraying of hydrogen peroxide at a concentration of 20 μM improved the postharvest quality of fruits of ‘Sugar Baby’ mini watermelon cultivated in a hydroponic system. Hydrogen peroxide at a concentration of 20 μM associated with ECns of 3.1 dS m−1 promoted the highest values of pH, flavonoids, anthocyanins, reducing sugars, ascorbic acid, and leaf and stem dry mass of mini watermelon. Hydrogen peroxide concentration of 20 μM also promoted an increase in the total soluble solid contents in plants cultivated with ECns of up to 2.6 dS m−1.