To study the population pathogenicity of pyricularia oryzae the virulence frequence (V. F.) of the pathogenic isolates was examined in the past ten years with the Chinese differentials, some resistant and cultivated varieties of rice. The varieties can be divided into 4 groups accordingly: a) Highly resistant, V. F. 5%; b)Resistant, V. F. 6%~15%; c)Susceptible, V. F.16%~30%; d)Highly susceptible, V. F>30%. Five varieties of each group were selected as monitoring model for the population virulence dynamics of the pathogen. A method involving a...