Identification of Sphaerulina azaleae on Korean Azalea in Korea Based on Morphological Characteristics and Multilocus Sequence Typing

In-Young Choi^1,2 Young-Joon Choi³ Kui-Jae Lee⁴ Ho-Jong Ju^1,2 Seong-Wan Cho⁵ Hyeon-Dong Shin^6,*

¹Department of Agricultural Biology, Jeonbuk National University, Jeonju 54896, Korea
²Institute of Agricultural Science and Technology, Jeonbuk National University, Jeonju 54896, Korea
³Department of Biology, Kunsan National University, Gunsan 54150, Korea
⁴Division of Biotechnology, College of Environmental and Bioresource Sciences, Jeonbuk National University, Iksan 54596, Korea
⁵Department of Pharmaceutics & Biotechnology, Konyang University, Daejeon 35365, Korea
⁶Division of Environmental Science and Ecological Engineering, Korea University, Seoul 02841, Korea

Abstract

From 2008 to 2017, Korean azalea (Rhododendron yedoense f. poukhanense) showing angular, necrotic leaf spots were found in Jeju and Hongcheon, Korea. The lesions occurred frequently, detracting from the beauty of the glossy green leaves of the plant and causing premature defoliation. Therefore, to identify the fungus associated with the lesions, morphological characterization and molecular phylogenetic analysis of actin (Act), translation elongation factor 1-alpha (EF), internal transcribed spacer (ITS), 28S nrDNA (LSU), and RNA polymerase II encoding the second largest subunit (RPB2) of the two representative isolates were performed. The phylogenetic tree inferred from the neighbor-joining method showed the isolates clustering in the Sphaerulina azaleae group. Therefore, the fungus associated with the angular leaf spots on the Korean azalea was identified as Sphaerulina azaleae.

Figures & Tables

Fig. 1. Angular leaf spot of var. infected with . (A) Heavy infections detracting from the beauty of the plant. (B) Close-up symptoms in the later stage of disease development. Note the pycnidial conidiomata showing as small black dots on the lesions. (C) Symptoms of angular leaf spot on current-year leaves. (D) White conidial horns being extruded through the ostioles of pycnidial conidiomata. (E) Close-up of white conidial horns. (F) Conidia. (G) Five-week old colonies of growing on potato dextrose agar. Note plentiful production of conidia on the colonies.