Characterization and distribution of black rot disease causing pathogen-Xanthomonas campestris pv. campestris races of the Jeju Island, South Korea

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc) is the most devastating cabbage disease and causes substantial economic losses worldwide. Among the eleven known Xcc races, races 1 and 4 are the most devastating to Brassica oleracea. Therefore, the deployment of regional race-specific resistant cultivars could be an effective way to safeguard cabbage production. Unfortunately, the racial diversity and distribution of black rot pathogens are not well understood in many countries, including South Korea. This study aimed to investigate the Xcc races and their distribution in the northwestern region of Jeju Island, a major cabbage-growing region in South Korea. Black rot-infected cabbage and broccoli leaves were collected from 19 locations across 5 different regions of Jeju Island. Pathogens (Xcc) were isolated and cultured from the infected leaves, and distinct individual colonies of Xcc (10 colonies per location) were selected for further experimentation. Using Xcc pathovar-specific PCR-based markers, 183 colonies were confirmed as Xcc. Race-typing was performed using race 1 to race 6 specific markers which identified race 1 in 12 locations and race 4 in two locations. In addition, both races were present in one location, indicating the prevalence of races 1 and 4 on Jeju Island. This is the first study to demonstrate the uses of the race-specific molecular markers to identify the Xcc races. The races of the remaining colonies were determined. Similarly, a nationwide survey of Xcc races is necessary to develop regional and race-specific resistant varieties.