Biochemical and morpho-physiological responses of rice to Pyricularia oryzae

Rice blast, caused by Pyricularia oryzae, poses a significant threat to global rice production. Understanding biochemical and morpho-physiological defense responses is essential for enzyme profiling and the development of resistant varieties through marker-assisted breeding. Two experiments were conducted to compare the biochemical, morpho-physiological, and yield-related responses of BRRI dhan29 (high-yielding but susceptible variety) and IR 64 (resistant check) against P. oryzae. Biochemical analysis showed lower increases in SOD (9.64 U mg⁻¹ protein) and PAL (4.57 U mg⁻¹ protein) in BRRI dhan29 compared to IR 64 (11.06 and 5.18 U mg⁻¹ protein, respectively) at 120 h after inoculation (HAI), while LOX and CHT activities were statistically similar. BRRI dhan29 accumulated more H₂O₂ (196.72 μmol kg⁻¹ FW), whereas IR 64 exhibited higher levels of total phenolics (15.5 μg mL⁻¹), flavonoids (46.29 μg mL⁻¹), antioxidants (443.21 μg mL⁻¹), soluble sugars (4.75 mg g⁻¹), and proteins (124.44 μg g⁻¹) at 120 HAI. Although both genotypes showed reductions in plant height, tiller number, biomass, leaf area, and yield after inoculation, BRRI dhan29 suffered greater losses, with a 32% yield reduction compared to 10.96% in IR 64. At 20 days after inoculation, BRRI dhan29 showed a higher Percent Disease Index (PDI) of 80%, while IR 64 had a PDI of 50%, indicating partial resistance and superior physiological performance. These results highlight IR 64’s enhanced resistance to P. oryzae and its potential as a donor line in breeding programs. Enhancing blast resistance in BRRI dhan29 is vital for stable yields and food security in affected regions.