Response of ‘Hua-ruea’ Chili Pepper (Capsicum annuum L.) to Salicylic Acid under Heat Stress

Abstract

Environmental stress, especially high air temperature (T_air) and high vapour pressure deficit (VPD) affect photosynthesis which is directly related to productivity. In this study, salicylic acid (SA), at concentrations of 10^-5 and 10^-7 M, was tested for the ability to ameliorate physiological stress, improve the protein profile, and increase chili pepper yield under extreme environmental conditions. Salicylic acid at a concentration of 10^-7 M (SA10^-7) increased the net photosynthetic rate (P_n), stomatal conductance (g_s), intercellular CO₂ concentration, transpiration rate, and maximum quantum efficiency of PSII photochemistry (F_v/F_m) when temperature was lower than 37 °C and VPD was less than 3 kPa. In addition, SA10^-7 could stimulate the synthesis of proteins associated with photosynthesis, such as chloroplast Rubisco activase, which promoted photosynthesis in chili pepper leaves. However, fruit number and fruit quality were not significantly different between the SA treatments (10^-5 and 10^-7 M) and control. Based on the results, SA application can improve photosynthesis of chili pepper plants, if the temperature does not exceed 37°C and VPD is less than 3 kPa.