Abstract: In order to characterize the dynamics of genetic and pathotypic structures of the rice blast fungus population in Guangdong , three subpopulations each consists of 83 isolates derived from 2000 to 2002，respectively, were used as a experimental population. Genetic structures of the three subpopulations were characterized by the SRAP (sequence related amplified polymorphism) marker-based DNA fingerprinting using the same ten pairs of SRAP primers. Three subpopulations were clustered into 33,25 and 13 genetic lineages, respectively, at the similarity coefficient of 0.92, indicating that genetic diversities of the rice blast fungus populations have been diminished in the recent years. On the other hand, pathotypic structures of the three subpopulations were characterized by the Chinese differentials. Three subpopulations were classified into 20,17 and 15 pathotypes, respectively, indicating that pathotypic diversities of the subpopulations have also decreased in the recent years. Since the genetic diversity of rice cultivars (hybrids) released has decreased in recent years in Guangdong, it, therefore, might be the most important fact to determine the dynamics of genetic and pathotypic structures of the population in Guangdong.

Key words: Pyricularia grisea, Genetic structure, Pathotypic structure, Dynamics