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causes Northern corn leaf blight (NCLB). In this study, 92 isolates of S. turcica were collected from naturally infected corn fields at 57 sites within China to determine physiological race composition and genetic diversity. Based on the reaction of differential hosts, isolates were divided into 14 physiological races (0, 1, 2, 12, 3, 13, 23, N, 1N, 2N, 3N, 13N, 23N, 123N). Races 0 and 1 were dominant, found with frequencies of 34.78% and 28.26%, respectively. This study was the first to identify race 123N in Heilongjiang province, implying possible loss of corn variety resistance to the NCLB pathogen. A total of 64 loci were obtained from eight pairs of primers by sequence-related amplified polymorphism (SRAP), of which 44 were polymorphic, accounting for 68.75% of the loci. Molecular markers showed that 92 isolates could be categorized into four groups with a similarity coefficient of 0.82, indicating abundant genetic diversity. Further analysis of genetic similarity and genetic distance of each geographical population revealed that the populations from Northeast, North, and Northwest China exhibited high similarities to each other, while exhibiting a large genetic distance with those from Southwest China. Analysis of molecular variance indicated that 81.54% of the genetic variation among isolates was derived from individuals within the geographical population (P < 0.001). The cluster analyses suggested that there was no distinct correlation among physiological races, genetic variation and geographic sources. This study provides a basis for understanding trends in S. turcica distribution and control of NCLB in China. [ABSTRACT FROM AUTHOR]