Sclerotium Rot of Mungbean (Phaseolus radiatus L.) Caused by Sclerotium rolfsii in South Korea

Sclerotium rot was observed on mungbean (Phaseolus radiatus L.) plants cultivated in the exhibition field of Gyeongsangnam-do Agricultural Research and Extension Services in September 2015. The progression of rot was initially observed as water-soaked lesions on several parts of the affected plant. Severely infected plants were blighted and eventually died. White mycelial mats spread over the lesions and numerous sclerotia formed on stems near the soil line. The sclerotia were globoid in shape, 1~3 mm in size, and white to brown in color. The optimum temperature for mycelial growth and sclerotia formation on potato dextrose agar (PDA) was $30^{\circ}C$ and the hyphal width was $4{\sim}8{\mu}m$. Typical clamp connections were observed on the hyphae of fungus grown on PDA. For molecular identification, the complete internal transcribed spacer (ITS) ribosomal DNA (rDNA) of the causal fungus was sequenced and analyzed. Based on the mycological characteristics, ITS rDNA sequence analysis, and pathogenicity to host plants, the fungus was identified as Sclerotium rolfsii. This is the first report of Sclerotium rot on mungbean caused by S. rolfsii in Korea.

Sclerotium rolfsii에 의한 녹두 흰비단병

2015년 9월 경상남도농업기술원 시험연구포장에 재배중인 녹두에서 흰비단병 증상이 발생하였다. 병징은 녹두의 줄기 지제 부위가 수침상으로 물러지고 부패되어 서서히 시들면서 포기 전체가 말라 죽었다. 줄기의 병반부와 토양 표면에 흰색의 곰팡이가 발생하며 갈색의 작은 둥근 균핵을 많이 형성하였다. 감자한천배지에서 균총은 흰색이고 잘 자라며 배양기간이 경과됨에 따라 갈색의 작은 둥근 균핵을 많이 형성하였다. 균핵의 크기는 1~3 mm이며 균사의 폭은 $4{\sim}9{\mu}m$였다. 균사 생육과 균핵 형성 적온은 $30^{\circ}C$이었다. 균사 특유의 clamp connection이 관찰되었다. 녹두에서 발생한 병징과 병원균의 균학적 특징, internal transcribed spacer rDNA 염기서열 비교분석 결과를 토대로 이 병을 Sclerotium rolfsii Saccardo에 의한 녹두 흰비단병으로 명명하고자 제안한다.