Ammonium enhances rice resistance to Magnaporthe oryzae through H₂O₂ accumulation

Nitrogen (N) is essential for the physiological processes of plants. However, the specific mechanisms by which different nitrogen forms influence rice blast pathogenesis remain poorly understood. This study used hydroponic assays to explore how ammonium (NH₄⁺) and nitrate (NO₃^-) affect rice after inoculation with Magnaporthe oryzae (M. oryzae). The results showed that NH₄⁺, compared to NO₃^-, significantly reduced disease severity, fungal growth, fungal hyphae number, the expansion capacity of infectious hyphae, and disease-related loss of photosynthesis. Additionally, NH₄⁺ enhanced the expression of defense-related genes, including OsPBZ1, OsCHT1, OsPR1a, and OsPR10. NH₄⁺-treated rice also exhibited higher hydrogen peroxide (H₂O₂) accumulation and increased antioxidant enzyme activities. Moreover, susceptibility to rice blast disease increased when H₂O₂ was scavenged, while a reduction in susceptibility was observed with the application of exogenous H₂O₂. These results suggest that ammonium enhances rice resistance to M. oryzae, potentially through H₂O₂ accumulation. The findings provide valuable insights into how different nitrogen forms affect plant immunity in rice, which is crucial for controlling rice blast and ensuring stable food production.