Serratia plymuthica에 의한 인삼 세균뿌리썩음병 발생

First Report of Bacterial Root Rot Caused by Serratia plymuthica on Panax ginseng

Abstract

2011년 8월 경상북도 봉화군 재산면 농가포장 5년생 인삼포장에서 잎이 푸른색을 띈 채 급격하게 마르는 증상이 발견되었다. 잎이 시든 직후 인삼의 뿌리를 채취하였으나, 뿌리나 줄기에서 특별한 병징은 없었으며, 뿌리의 수분이 약간 빠져나간 상태였다. 이러한 증상이 발생된 지 10일이 경과된 뿌리에서는 뿌리가 물러지면서 썩는 증상이 나타났다. 이러한 병징과 건전부의 경계부위에서 세균이 분리되었으며, 이 세균에 의한 뿌리썩음병이 의심되었다. 세균을 배양한 후 건전 인삼에 접종하자, 동일한 썩음 증상이 발현되었으며, 병반으로부터 동일한 세균이 재분리되었다. 이 세균을 BioLog system에 의한 탄소원 이용여부, Vitek 2 system을 이용한 생화학적 반응, GC-MIDI Sherlock system을 이용한 지방산 조성, 16S rRNA 염기서열을 분석한 결과, 모두 Serratia plymuthica로 동정되었다. 이에 따라 인삼 뿌리에 발생하는 이 병을 Serratia plymuthica에 의한 인삼 세균뿌리썩음병으로 명명하여 보고하고자 한다.

In August of 2011, a wilting disease of ginseng was observed at Bongwha, Gyeongbuk province, Korea. Affected plants initially show withering symptoms on leaves of ginseng. As the disease progresses, withering leaves spread downward, eventually encompassing the whole plant. Leaves lose vigor but remain pale green. Symptoms of roots were brown, and soft rots characterized by moist and watery decay of the whole ginseng root, which initiated as small brown, water-soaked lesions of hairy roots and enlarged to the entire roots. The causal organism isolated from the infected roots was identified as Serratia plymuthica based on its physiological and biochemical characteristics, by cellular fatty acid composition (GC-FAME), the utilization of carbon sources (BioLog System), and 16S rRNA sequence of the isolated bacterium were 99% homologous to those of Serratia plymuthica strains. Artificial inoculation of the bacterium produced the same brown or soft rot symptoms on the ginseng roots, from which the same bacterium was isolated. This is the first report of bacterial root rot caused by the Serratia plymuthica in ginseng in Korea. Serratia plymuthica has been used as antagonistic microorganism for biological control on several crop plants. But it was proved pathogen of ginseng at humid condition in this study.

Fig. 1. Wilt symptom of ginseng leaf and stem. The arrow indicates that the disease occurred on water leaking area on shade.

Fig. 2. Symptoms of decayed ginseng root. Symptoms of roots were brown, soft rots characterized by moist and watery decay of the whole ginseng root, which initiated as small brown, watersoaked lesions of hairy roots and enlarged to the entire roots.

Fig. 3. Dark brown lesion and root rot of two years old ginseng root by Serratia plymuthica PG1. Symptoms on ginseng root after 7 days (A and B), 10 days (C), and control (D) caused by artificial inoculation.

Fig. 4. Pathogenicity test on two years old ginseng root by Serratia plymuthica PG1. Symptoms after 50 days on inoculated by S. plymuthica 10⁸ CFU/ml (A and C) and on control (B and D).

Fig. 5. Phylogenetic relationship between Serratia plymuthica and other Serratia species, constructed using the neighbor-joining tree analysis, based on the combined ITS region and β-tubulin gene sequences. The numbers above the branches represent the bootstrap values obtained for 5,000 replicates.

Table 1. Comparison of the bacteriological characteristics of the isolates PG1 isolated from decayed ginseng