Research in Plant Disease (식물병연구)

The Korean Society of Plant Pathology (한국식물병리학회)
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First Report of Black Rot Caused by Diplodia seriata on Apple

Diplodia seriata에 의한 사과 검은썩음병 발생보고

  • Kim, Young Soo (Department of Plant Medicals, Andong National University) ;
  • Yun, Yun Joo (Department of Plant Medicals, Andong National University) ;
  • Jeon, Yongho (Department of Plant Medicals, Andong National University)
  • 김영수 (국립안동대학교식물의학과) ;
  • 윤윤주 (국립안동대학교식물의학과) ;
  • 전용호 (국립안동대학교식물의학과)
  • Received : 2018.09.20
  • Accepted : 2018.10.29
  • Published : 2018.12.31
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Abstract

In 2018, symptoms of black rot on apple (Malus pumila var. dulcissima KOIDZ) cv. Fuji were observed in Yeongcheon-si, Korea. The fruit decay symptoms consisted of purple pimples spots, black rot around the seed cavity (calyx end), mummified fruit. To isolate the causal agent, small fragment (2 to 3 mm) of decayed tissue from the lesion margin were placed on WA or PDA. Fungal colonies on PDA produced dense white aerial mycelium, becoming dark gray with age. Pycnidia and conidia were observed under a light microscopy. The shapes of conidia were aseptate, ovoid, rounded at both ends, and $21.7-28.3{\times}9.9-15.3{\mu}m$. Based on morphological and cultural characteristics, this fungus was identified as Diplodia seriata. To confirm its identity, two loci (ITS and ${\beta}$-tubulin) were sequenced for molecular identification. BLAST searches indicated 100% identity with D. seriata. A pathogenicity test was conducted with isolates on Fuji apples. The apples were inoculated with mycelial plugs (5 mm) from 7-day-old cultures of the putative pathogens. All inoculated apples developed rot symptoms identical to the original symptoms, from which D. seriata were reisolated, fulfilling Koch's postulates. This study is the first report of black rot caused Diplodia seriata on apple.

2018년 경북 영천지역 사과과수원에서 미이라화 된 과실, 배꼽이 썩어 들어간 과실과 점무늬를 형성한 과실의 증상을 관찰하였다. 이 증상의 원인균을 증명하기 위해 이병체에서 균사체를 분리하여 병원성 검정을 수행한 결과 건전한 사과 과실이 급격히 썩으면서 발견 시의 병징과 일치하였다. 곰팡이의 특성은 흰색의 균사로 자라다가 시간이 지나면서 암회색으로 변하였다. 병자각 안에서 분생포자가 형성되고 분생포자는 갈색의 타원 형태였으며 격막이 없고 끝이 둥근 형태이다. 분생포자 크기는 $21.7-28.3{\times}9.9-15.3{\mu}m$이다. 병원균의 ITS, ${\beta}$-tubulin 유전자의 염기서열을 이용하여 유연관계를 분석한 결과 Diplodia seriata로 동정되었다. Diplodia seriata는 국내에서 식물병원균으로 보고된 바 없다. 사과에서 Diplodia seriata에 의한 Black rot은 우리나라에서 처음 보고되는 것이며 사과 검은썩음병으로 명명하여 보고하고자 한다.

Keywords

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Fig. 1. Symptoms of black rot caused by Diplodia seriata on apple cv. Fuji. Mummified apple (A-C), black to brown spot symptoms (D-E) and black rot symptoms at the calyx end (F).

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Fig. 2. Pathogenicity tests. Symptoms at 3 days (B, C) and 5 days (F, G) after inoculation of the isolate AM1 with wound. Control is no symptoms (A, D). Spot symptoms 7 days after spraying of the conidial suspension (isolate AS1) without wounding (D, H).

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Fig. 3. Cultural and morphological characteristics of the present isolate. Colony growth at 25oC on PDA after 7 days (A) and 14 days (B) of incubation. Aerial hyphae on PDA after 14 days of incubation (C-D).

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Fig. 4. Diplodia seriata. Longitudinal section of conidiomata (A, B), conidiogenous cells with developing conidia (C, D). Conidiogenous cells and conidia, which become pale brown soon after formation (E)-(J). Conidia developing on conidiogenous cells, one conidium in I and J is starting to become coloured. Pale brown aseptate conidia (K, L). Conidia germinationg on a glass slide (M, N). Scale bars: A, B=100 μm, C, D, K, L=20 μm, E-J, M, N=10 μm

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

Table 1. Morphological characteristics of Diplodia seriata

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