Exserohilum turcicum is considered serious destructive disease of maize (Zea mays L.) in North Korea. This study aimed to understand genetic inheritance and combining ability of newly bred lines of maize tolerant to E. turcicum by diallel crosses. Three diallel sets for two different ecological regions and one agronomic trait; eastern (E), northern (N) and stay green (SG) involving 29 inbred lines were tested in eight locations of 2000 and 2001. E. turcicum infections were under natural conditions, respectively. Lines used were selected for high yield potential in test crosses with good agronomic traits and tolerance to biotic and abiotic stresses. Selection for race specific high resistance to biotic stresses was avoided to select quantitatively inherited genes. Host plant responses to E. turcicum were rated on a scale of 1 (highly tolerant) to 9 (highly susceptible). Highly significant variations were recorded in all trials. General combining ability (GCA) mean square was roughly twice that of specific combining ability (SCA). The genotype (G) by environment (E) interaction was highly significant. The overall results of genetic studies in three diallel sets show that genetic control for inbred tolerance to E. turcicum is polygenic and quantitatively inherited. New inbreds; E-3, N-1 and SG-4 confer better tolerance to E. turcicum than the widely used inbreds; Mo17, and B73. Proper use of genetic information from this study shall increase of corn production under high E. turcicum infection in the Far Eastern Regions of Korea and China.

Northern corn leaf blight caused by Exserohilum turcicum Pass is considered the most important disease infecting corn (Zea mays L.) in the Peoples' Republic of Korea (North Korea). It contributes to the food shortage in North Korea. The objectives of the current research were to study resistance expression and responses of corn crosses made between ten hybrids from North Korea and inbreeding lines (S3-4 stage) from the Republic of Korea (South Korea). The experiments were conducted in six trials with a total of 184 crosses including two commercial hybrids in each trial. The trials were conducted at two locations in North Korea (Mirim and Eunsan) and one location in South Korea (Gunwi) under natural infestation of E. turcicum. Host plant responses were rated on a scale of 1 (highly tolerant) to 9 (highly susceptible). A total of 111 crosses (62.4%) showed significant tolerant or susceptible response variations among three locations; 42 crosses (22.8%) at two locations and 69 crosses (39.0%) at one location, respectively. At least 8 crosses of high level of tolerance and 12 crosses of high level of susceptibility showed significantly different biotic responses (P = 0.05). The results of the current study and historical reviews of E. turcicum epidemics in both North and South Korea suggest that breeding of tolerance with quantitatively inherited genes should be carried out for a sustainable corn production in North Korea.