Hydrogen peroxide to mitigate the effects of salt stress in the mini watermelon under hydroponic cultivation¹

The use of substances that can mitigate the harmful effects of salt stress is a promising alternative for the use of saline water, especially in semi-arid regions. The aim of this study was to evaluate the effect of different concentrations of hydrogen peroxide in mitigating salt stress in the mini watermelon grown in a hydroponic system. The study was carried out in a greenhouse, in an area belonging to the Federal University of Campina Grande, Pombal, Paraiba. The experimental design was completely randomised using a split-plot factorial scheme wit h four levels of electrical conductivity for the nutrient solution-ECns (2.1, 3.1, 4.1, and 5.1 dS m(-1)) considered the plots, and four concentrations of hydrogen peroxide-H2O2 (0, 20, 40, and 60 mu M) the subplots, with five replications. The foliar application of hydrogen peroxide in concentrations of between 17 and 20 mu M mitigated the effects of salt stress on stomatal conductance, the rate of CO2 assimilation, carboxylation efficiency, and carotenoid content in the mini watermelon up to an ECns of 5.1 dS m(-1). Foliar application of hydrogen peroxide in concentrations greater than 20 mu M intensified the effects of salt stress on gas exchange and the synthesis of photosynthetic pigments in the mini watermelon. Furthermore, there was an increase in electrolyte leakage in the leaf blade.