Abstract
To obtain the information about the effect of nitrogen application to rice plants on severity of blast disease epidemics, sporulation capacity of the disease lesions, a component of the epidemic, at various application timing was examined. Nitrogen topdressing applied from 9 days before to 4 days after infection of a blast fungus to rice plants increased the potential sporulating ability of the leaf lesions. The sporulating ratio of the lesions on treated/untreated rice plant is represented as y=-0.018t+1.88, where y is the ratio and t the infection time (days) after nitrogen topdressing, respectively.
