Salicylic Acid and 24-Epibrassinolide Induced Thermotolerance in Bell Pepper through Enhanced Antioxidant Enzyme System and Heat Shock Proteins

Elevated temperature negatively affects the production of bell pepper (Capsicum annuum L.) especially under North Indian plains where the temperature is above 40°C during summers. In the present study, the effect of exogenous application of Plant Growth Regulators (PGRs) viz. Salicylic Acid (SA) and 24-Epibrassinolide (EBR) on biochemical parameters and antioxidant system of bell pepper cv. Royal Wonder was evaluated. PGRs were applied exogenously 30, 60 and 90 Days After Transplantation (DAT). All the concentrations of PGRs i.e SA (0.10, 0.20, and 0.50 mM) and EBR (0.05, 0.10, and 0.20 μM) were effective in ameliorating the heat shock-induced effects, which enhanced thermotolerance in terms of increased proline content, soluble proteins, total phenols, total soluble sugars and starch content, improved antioxidant system (CAT, APX, POX, SOD and GR) with reduced lipid peroxidation and cellulase enzyme activity at high temperature, and, ultimately, improving total fruit yield. Application of 0.20 mM SA improved thermotolerance most efficiently at all growth stages, specifically when spray was done at 30 and 60 DAT. It resulted in a significant enhancement in biochemical parameters and antioxidant enzyme system as compared to the untreated control.