Worldwide, rice blast (Pyricularia oryzae) causes more rice crop loss than other diseases. Acid rain has reduced crop yields globally for nearly a century. However, the effects of acid rain on rice-Pyricularia oryzae systems are still far from fully understood. In this study, we conducted a lab cultivation experiment of P. oryzae under a series of acidity conditions as well as a glasshouse cultivation experiment of rice that was inoculated with P. oryzae either before (P. + SAR) or after (SAR + P.) simulated acid rain (SAR) at pH 5.0, 4.0, 3.0 and 2.0. Our results showed that the growth and pathogenicity of P. oryzae was significantly inhibited with decreasing pH treatments in vitro culture. The SAR + P. treatment with a pH of 4.0 was associated with the highest inhibition of P. oryzae expansion. However, regardless of the inoculation time, higher-acidity rain treatments showed a decreased inhibition of P. oryzae via disease-resistance related enzymes and metabolites in rice leaves, thus increasing disease index. The combined effects of high acidity and fungal inoculation were more serious than that of either alone. This study provides novel insights into the effects of acid rain on the plant-pathogen interaction and may also serve as a guide for evaluating disease control and crop health in the context of acid rain.
Keywords: Oryza sativa L.; Pyricularia oryzae; acid rain; antioxidant enzyme activity; disease index; metabolism.