Abstract:Pathogenicity of 195 Magnaporthe grisea (Hebert)Barr. single spore isolates from indica rice in Jiangxi during 2006-2008 was measured against 30 rice blast monogenic lines at rice seedling stage. The results showed that most strains were broad-spectrum pathogenic, and the pathogens accounted for 0, 8.72%, 31.28% and 60.00% respectively when the pathogenicity frequency (PF) of the pathogen was divided four sections, i.e. PF＜30%, 30%≤PF＜50%, 50%≤PF＜70% and PF≥70%. The strains population was virulent to all 30 rice blast monogenic lines, virulence frequency (VF) ranged from 17.95%-100%, and resistance genes Pi-zt, Pi-1(1), Pi-z5 and Pi-k received lower VF, i.e.17.95%, 26.67%, 27.46% and 29.23% respectively. The strains population could be divided into 6 groups, 40 physiological races according to 7 Chinese differential cultivars. Most strains belonged to ZA and ZB groups,and the predominant races were ZB13, and ZA1,with the frequency of 17.65% and 11.76% respectively in the 2006 when the rice blast was in epidemic; and the race group and predominant races were similar over the years of 2007-2008 when the disease was moderately-light occurred, most strains belonged to ZB group, the predominant races were ZB15 and ZB13. The different strains of the same predominant race existed obviously pathogenic differentiation. The PF of 28 strains belonging to ZB13 to the 30 rice blast monogenic lines was 50.00% -96.67%, and the PF of 26 strains belonging to ZB15 was 46.67% -86.67%. Cluster analysis also showed that the pathogenic similarity existed in a great difference among the strains with similar PF. All the results revealed the diversity and complexity of the pathogenicity of the fungus in Jiangxi Province.