Regulation of the drought response of sweet pepper (Capsicum annuum L.) by foliar-applied hormones, in Mediterranean-climate greenhouse conditions

Plant hormones play an important role in regulating stress responses and signaling in plants; many of them act to alleviate environmental stresses. However, the specific effects and physiological changes could be significantly altered according to the crop species, application concentration and frequency, and cultivation conditions. In this study, we investigated the effect of leaf-applied abscisic acid (ABA), gibberellic acid (GA3), and indole-3-acetic acid (IAA) on plant growth before, during, and after water stress. The objective was to determine their effects on pepper plants (Capsicum annuum L.) in commercial greenhouse conditions, specifically their ability to mitigate water stress, through the study of different stress traits—such as plant growth, gas exchange parameters, chlorophyll content and fluorescence, ascorbate peroxidase activity, total phenolic compounds, and lipid peroxidation. While ABA and IAA heightened the water shortage in the leaves along the experiment, GA3 diminished it. The effects of ABA involved short-term responses, such as stomatal closure and decreased transpiration, and long-term changes, affecting the ratios and concentrations of chlorophylls. Moreover, GA3 complicated the crop management since the plants suffered high stress when treated with this hormone. The results obtained represent a first approach to studying the effect of foliar hormone application in sweet pepper and its ability to regulate (mitigate or amplify) the water stress suffered by the plant under greenhouse conditions.