Abstract

Three hundred and twenty-four isolates were obtained from rice blast specimens collected from five typical areas —Wujiang , Ganyu , Tongzhou , Gaoyou and Yixing in Jiangsu Province during 1997～1999. The isolates were assessed against 13 Japanese cultivars for which resistance genes have been determined and were divided into 90 pathotypes. This indicated that complex virulence diversity exists in Magnaporthe grisea in Jiangsu Province. The pathotype composition were dissimilar in the five typical areas , and from 1997～1999 , the dissimilarity tended to increase. The analysis of virulence frequency indicated that the resistance genes Pi-k^s , Pi-ta , Pi-ta² and Pi-sh had narrow resistance spect ra to Magnaporthe grisea isolates tested in Jiangsu Province , while the genes Pi-i , Pi-z , Pi-z ^t and Pi-b had wide resistance spect ra to the pathogen and had value in rice breeding as resources of resistance. Inoculation with six st rains that represent six typical pathotypes of Magnaporthe grisea on 80 major cultivars and newly-bred cultivars of Jiangsu Province showed that most of the Indica cultivars and hybrid rice cultivars tested were resistant and the Japonica rice cultivars were susceptible to the pathogen. The results provide a basis for use of resistance diversity of rice cultivars to control rice blast .