Occurrence and Race Distribution of Frogeye leaf spot, Cercospora sojina on Soybean in Korea

Frogeye leaf spot(FLS) is an important foliar disease in many soybean(Glycine max) production areas of the world including the region of northern part of Gyeonggi-do. This study was conducted to investigate the occurrence patterns and the distribution of FLS races. The results are summarized as follows. The pathogen of FLS is Cercospora sojina Hara. The conidia are 2 ~ 8 sepates, and are 6.0 ~ 7.7 micrometer x 38.4 ~ 91.2 micrometer. The optimal temperature for the growth of C. sojina was at 25 Celsius on PDA medium, and for the conidia formation was at 28 Celsius on V8 medium. FLS occurs from the middle of July to the middle of September in the northern part of Gyeonggi-do, and the amount of occurrence increase at the middle of August. It occurred severely when the temperature and humidity were continued at 24 ~ 26 Celsius, 83~87% from the late of July to the early of August. The organ of soybean in the order of frequency in occurrence was leaves (75% ), petioles (20% ), and pods (5%). The occurrence of FLS might be related with soil condition. Probably FLS occur more frequently in the continuous soybean culture plot than discontinuous soybean cultured plot. And cropping patterns also affected on the occurrence of FLS that the mobility rate were double cropping(with Cruciferae) 22.6% double cropping(with Graminae) 14.4% pady-upland rotation 4.4%. The average mobility rate of FLS in 2006 to 2007 were 68% 2006 64% 2005 43% in the region of northern part of Gyeonggi-do, and were Gangwon-do 78%, Gyeonggi-do 62%, Chungcheongbuk-do 54%, Gyeongsangbuk-do 43%, Jeonlabuk-do 36%, Chungcheongnam-do 33%, respectively. We isolated six C. sojina races from the infected plant collected from 52 areas. The selection of race were based on the cultivation area and variety which we had collected pathogen from 2005 to 2007, especially based on the pathogenicity against 63 soybean varieties in Korea.