Incidence and Control of Bottom Rot of Chinese Cabbage Caused by Rhizoctonia solani Kuhn

배추 밑동썩음병 발생과 방제

Bottom rot of Chinese cabbage (Brassica pekinensis Rupr) hitherto undescribed in Korea is caused by Rhizoctonia solani Kuhn. Development of bottom rot in fall crops was observed and the efficiencies of fungiciial control in naturally infested field in Southern region were studied. Bottom rot symptom started to develop 20 days after transplanting 20 day old seedlings, which corresponded to the middle growing stage. At the reading stage, the infection rate increased substantially, which progressed upto an average of $52\%$ at harvesting time. The overall infection rate was about $30\%$ in Chinese cabbage field under plastic film house cultivation. However, disease intensity of fall crops was less severe than that of crops in plastic film house. where plants infested earlier, stunted and their growth was extremely poor. Optimum temperature for mycelial growth of bottom rot isolates of R. solani was $20\~25^{\circ}C$ on potato-sucrose agar. This fungus was highly pathogenic on seedlings of Chinese cabbage, radish, sesame and rape resulting in high percentage of damping-off. For other crops, such as lettuce, tomato the cucumber, the germination was delayed for 2-3 days and the percentage damping-off was lower. Anastomosis group of this fungus was idenlfied as AG II-I. Soil drenching of fungicide pencycr WP., three applications at 10 day interval, was effective; indicating the most promising one with control value $80\%$.

우리나라의 미기록 병인 Rhizoctonia solani Kuhn에 의한 배추 밑동썩음병(Bottom rot)에 대한 남부지방파로재배 시의 발병소장과 방제방법을 검토하였다. 본 병의 발병은 정식 20여일 경과후, 배추의 생육중기부터 발병되기 시작하여 결구기에 증가하는 경향이고, 수확기의 발병주율은 평균 $52\%$ 정도였다. 그 피해는 추파로지재배보다 비닐하우스를 이용한 반촉성재배에서 심하였고, 초기에 심엽까지 감염된 이병주는 위축되어 생육이 극히 불량하여 결구가 되지 않았다. 병주에서 분리한 R. solani의 PDA배지상에서 균사 생육적온은 $20\~25^{\circ}C$였고, 균사융합군은 제II군 제1형으로 분류되었다. 배추, 무, 참깨 및 유채의 유묘에 접종했을 때 입고율이 매우 높았고 상치, 토마토, 오이에서는 입고율은 낮았으나 발아가 $2\~3$일 지연되었다. 방제약제는 발병초기부터 pencycron Wp.를 10일간 3회 처리한 것이 방제가가 $80\%$로 우수하였다.