Disclosure of Defensive Enzyme of BRRI dhan29 and IR 64 to Pyricularia oryzae Stress

Abstract

Rice blast disease, caused by Pyricularia oryzae, is a significant threat to global rice production, resulting in substantial yield losses. However, productivity losses due to rice blast disease caused by Pyricularia oryzae are significant, and detailed knowledge of the enzymatic responses linked to physiological resistance remains limited. This study examines the defensive biochemicals and enzymatic responses in two rice cultivars, BRRI dhan29 and IR 64, to Pyricularia oryzae stress. The study was done by using a factorial completely randomized design with three replications. Cultivars were inoculated with a virulent P. oryzae strain (RL-17) at the Plant Protection Laboratory, Khulna University. The results showed a consistent increase in SOD, PAL, and β-1,3-glucanase activities in both cultivars, with IR 64 exhibiting significantly higher SOD activity from 72 to 120 hours post-inoculation, indicating enhanced enzymatic defense and greater stress resilience. LOX and chitinase activities were comparable between the two cultivars, suggesting similar stress responses mediated by these enzymes. Furthermore, IR 64 showed enhanced phenol and flavonoid accumulation, correlating with its elevated antioxidant capacity and reduced oxidative damage. ROS dynamics (superoxide and hydrogen peroxide) varied between the cultivars, with BRRI dhan29 exhibiting excessive ROS accumulation, potentially leading to oxidative stress, whereas IR 64 maintained a balanced ROS-scavenging system. Protein and sugar levels also increased significantly in IR 64, indicating better resource allocation for defense. IR 64 demonstrates superior resilience to Pyricularia oryzae stress, making it a promising resistant benchmark for breeding programs, while targeted improvements are needed to enhance the stress tolerance of the mega variety BRRI dhan29 for food security.