Response of Ornamental Pepper to High-Temperature Stress and Role of Exogenous Salicylic Acid in Mitigating High Temperature

Ornamental pepper (Capsicum annuum L.) is an important economic decorative plant well known for its abundant genetic diversity. However, high-temperature (HT) stress seriously affects its aesthetic and commercial value. In this work, we analyzed the effects of exogenous salicylic acid (SA) on seed germination and seedling growth of ornamental pepper under HT stress. The inherent physiological and biochemical basis of the alleviating effect of salicylic acid was further analyzed. The findings revealed SA with 0.01 mM and 0.1 mM was most effective in enhancing thermotolerance in seeds and seedlings, respectively. SA treatment increased the germination rate and germination potential, and reduced the oxidative damage of seeds under HT stress. For seedlings, spraying SA with 0.1 mM significantly alleviated yellow leaves and dwarfing under HT stress. SA could maintain high root vigor, inhibit water loss, and maintain the integrity of cell structure by regulating osmotic substance content under HT. SA-induced thermotolerance development involved in the activation of antioxidant defense system. SA decreased the production of reactive oxygen species (ROS), increased the activity of protective enzymes, and the content of non-enzymatic ROS scavengers in plants under HT. The changes of chlorophyll fluorescence parameters showed that SA was beneficial to maintain a high level of photosynthetic capacity of ornamental pepper seedlings under HT stress. Moreover, recovery also showed a mitigatory effect on injuries induced by HT stress. Taken together, this study provided evidence for the ability of exogenous SA application to moderate the detrimental effects by HT stress.