Pathogenicity, Molecular Identification, and Integrated Disease Management of Nigrospora oryzae on Rice

Abstract

The opportunistic fungal pathogen Nigrospora oryzae poses a growing threat to global rice production, especially given its enhanced virulence in co-infections with other pathogens. This study aimed to characterize the pathogen and identify effective integrated disease management strategies. Isolates from Indonesia were identified using morphological and molecular markers, including the ITS and ACT genes, which confirmed a strong genetic link to a rice-native strain from China, ruling out a recent host jump from oil palm. Pathogenicity assays demonstrated the fungus’s opportunistic nature, as its virulence and disease progression were significantly heightened when co-inoculated with Curvularia lunata. In vitro fungicide tests revealed a high sensitivity to methyl thiophanate (EC₅₀ ~250 ppm ) but a lower sensitivity to azoxystrobin. Furthermore, silicon application effectively suppressed the disease, highlighting that some rice varieties responded better than others; the IPB 3S variety experienced a 30% reduction in disease incidence compared to 16% in Situ Bagendit. These findings establish a comprehensive framework for integrated disease management, combining varietal selection and silicon application with targeted chemical control to combat this emerging threat.