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Laboratory of Plant Disease and Biocontrol, Korea University, Seoul 136-713, Korea(Received on March 23, 2011; Accepted on April 17, 2011)During the summer of 2005, specimens of soybean culti-vars (Daepung, Daewon, Hwanggeum and Taegwang)showing frogeye leaf spot (FLS) were obtained fromvarious areas in Korea. Eight isolates identified asCercospora sojina were inoculated on the adaxial leafsurfaces of 63 Korean soybean cultivars; the diseaseresponses to each isolate were evaluated 14 days and 21days after inoculation. Based on the disease responses(resistant or susceptible) of the cultivars by the isolates,a set of cultivars (Anpeong, Bogwang, Cheongdu No. 1,Cheongja No. 3, Dachae, Daemang, Jangwon, Namhae,Sowon, Taegwang) were selected and inoculated withseven isolates for further testing pathogenic variance.Interestingly, 6 out of 7 tested C. sojina isolates revealeddifferential ability in infecting different soybean culti-vars. This result may indicate the possibility of new raceoccurrence or pathogenic variation; this also presentsevidence for prevalent FLS occurrence during humidand hot weather in Korea.Keywords : Cercospora sojina, frogeye leaf spot, soybeancultivarCercospora sojina is the causal agent of frogeye leaf spot(FLS) on soybeans [Glycine max (L.) Merr.]. The pathogencan infect leaves, stems, and seeds of the host plant. Thesymptoms on leaves are circular or angular, and 1−5 mm indiameter. The water soaked and mature symptomatic spotsappear suddenly and develop into brown spots surroundedby a dark reddish brown margin (Hartman et al., 1999).Upon aging of a lesion, the center becomes grey to lightbrown in color and forms conidiophores and conidia.Lesions appear at time intervals and join together to formirregular lesions. When lesions cover about 30% of the totalleaf area, the leaf quickly withers and falls prematurely(Hartman et al., 1999; Phillips and Boerma, 1981), resultingin more than 35% yield loss through a reduction of seedsize during hot, humid weather (Laviolette et al., 1970;Mian et al., 1998; Mwase and Kapooria, 2000; Wrather etal., 2001; Yorinori, 1981). Epidemics and declines of FLS incidence have shownrepeated cycles. New C. sojina races, infecting cultivarsthat are widely grown and resistant to established races,appear; thus, the disease is prevalent. Since a cultivar, that isresistant to a new prevalent race and a previous establishedrace, had been developed, widely grown, the diseaseincidence has been declined (Athow and Probst, 1952;Athow et al., 1962; Phillips and Boerma, 1981; Ross,1968). Many races have been reported worldwide: 12 racesin the USA, 11 races in the People’s Republic of China,more than 20 races in South America and a race in Japan(Hartman et al., 1999). Thus, monitoring C. sojina racesand developing resistant soybean cultivars should beconcerned in widely soybean-producing countries. In Korea, although soybeans have been widely cultivatedand many soybean cultivars are inbred, there has been littleresearch concerning disease response of cultivars against C.sojina. Therefore, the objective of this study was to deter-mine disease responses of ten soybean cultivars to seven C.sojina isolates for race identification in Korea. FLS-diseased leaves of soybean collected from northernGyeonggi, Gangwon, Gyeongsang, and Chungcheong pro-vinces in July to September, 2005 were provided fromGyonggi-do Agricultural Research and Extension Services,Northern Agriculture Research Station, Yeoncheon, Korea.For fungal isolation, single spore was isolated from spotson leaves and cultured on potato dextrose agar (PDA).After incubation of these plates at 25

Differential Responses of Soybean Cultivars to Cercospora sojina Isolates, the Causal Agent of Frogeye Leaf Spot in Korea