Diversity and Distribution of Rice Blast (Pyricularia oryzae Cavara) Races in Japan

In total, 310 rice blast (Pyricularia oryzae Cavara) isolates from Japan showed wide variation in virulence. Virulence on rice (Oryza sativa L.) differential varieties (DV) harboring resistance genes Pish, Pia, Pii, Pi3, Pi5(t), Pik-s, and Pi19(t) ranged from 82.9 to 100.0%. In contrast, virulence on DV possessing Pib, Pit, Pik-m, Pil, Pik-h, Pik, Pik-p, Pi7(t), Pi9(t), Piz, Piz-5, Piz-t, Pita-2, Pita, Pi12(t), and Pi20(t) ranged from 0 to 21.6%. Cluster analysis using the reaction patterns of the DV classified isolates into three groups: I, virulent to Pik, Pik-h, Pik-p, Pik-m, Pil, and Pi7(t); Ha, avirulent to the preceding.6 genes and virulent to Pia, Pii, Pi3, and Pi5(t); and lib, avirulent to all 10 genes. Group I was limited to northern Japan and group lib to central Japan, while group ffa was distributed throughout Japan. We estimate that group Ha represents the original population and that groups I and lib arose from it through minor changes in pathogenicity. We classified these isolates into 123 races by a new designation system and conclude that the rice blast races in Japan are less diverse than previously thought.