Genetic Variation and Pathogenic Aggressiveness of Pyricularia oryzae Isolates Causing Rice Blast Disease

Abstract

Rice blast caused by Pyricularia oryzae is one of the most destructive diseases of rice, responsible for severe yield losses across major rice-growing regions. The present study investigates the genetic variation and pathogenic aggressiveness of P. oryzae isolates collected from diverse rice-growing ecosystems. Diseased leaf and panicle samples showing typical blast lesions were collected, and fungal isolates were obtained and purified for further analysis. Pathogenicity tests were conducted on susceptible rice cultivars under controlled conditions to assess virulence variability among isolates. Results revealed significant differences in lesion size, disease severity, and infection efficiency, indicating wide variation in pathogenic aggressiveness. Molecular characterization using ITS and gene-specific markers demonstrated considerable genetic diversity among isolates, suggesting the presence of multiple lineages within the pathogen population. Phylogenetic analysis grouped isolates into distinct clusters that were partially associated with geographic origin and host cultivar, indicating both regional differentiation and gene flow. Highly aggressive isolates were genetically distinct from less virulent ones, suggesting a possible correlation between genetic makeup and pathogenicity. Environmental conditions such as humidity and temperature strongly influenced disease development and expression of virulence. The study highlights the dynamic nature of P. oryzae populations and their ability to evolve rapidly under field conditions. These findings emphasize the importance of continuous monitoring of pathogen variability for effective disease management. Overall, the results provide important insights into the genetic structure and pathogenic behavior of P. oryzae, supporting the development of resistant rice varieties and integrated disease management strategies to mitigate rice blast impact in diverse agroecosystems.