Secondary metabolite and antioxidant enzyme dynamics underpin resistance to Magnaporthe oryzae in rice genotypes of the Kashmir Valley

Abstract

Rice blast is one of the most destructive diseases affecting rice cultivation globally, with the Kashmir Valley experiencing significant yield losses due to frequent outbreaks. The disease can reduce rice yields by up to 50 % under favorable conditions, posing a major threat to food security and livelihoods in the region. Despite advances in breeding for blast resistance, the underlying biochemical mechanisms that confer durable resistance remain poorly understood, limiting the effectiveness of resistance breeding programs. This study aimed to elucidate the biochemical basis of blast resistance by comparing the accumulation of key secondary metabolites and antioxidant enzymes in 40 japonica rice genotypes (20 resistant and 20 susceptible) following inoculation with a dominant M. oryzae strain. Quantitative analyses revealed that resistant genotypes exhibited significantly higher levels of phenolic compounds (ranging from 0.235 to 1.807 mg/g), condensed tannins, flavonoids, proteins, and proline compared to their susceptible counterparts. These secondary metabolites are known to strengthen plant cell walls, scavenge reactive oxygen species (ROS), and directly inhibit pathogen growth. Enzymatic assays further demonstrated that resistant lines accumulated greater activities of superoxide dismutase (SOD), guaiacol peroxidase (GPX), and ascorbate peroxidase (APX), enzymes critical for ROS detoxification and signaling during pathogen attack. In contrast, catalase (CAT) activity did not differ significantly between resistant and susceptible genotypes. Correlation analysis indicated strong positive associations between protein and hydrogen peroxide (r = 0.674), as well as phenols and proline (r = 0.408), emphasizing the coordinated activation of biochemical defense in resistant plants. Molecular docking analyses further revealed that predominant rice defense metabolites, particularly phenolics and flavonoids, exhibited strong binding affinities to the MPG1 hydrophobin protein of M. oryzae, a key factor in fungal adhesion and infection. These in silico findings support the experimental results, suggesting that secondary metabolites not only accumulate in resistant genotypes but may also directly interfere with pathogen virulence mechanisms. The integration of biochemical assays and molecular docking provides a comprehensive understanding of the coordinated defense strategies in rice, offering valuable insights for breeding programs aimed at developing cultivars with durable resistance to blast disease.