ScholarWorks@경상국립대학교

초록

As consumer preference for tropical fruits expands, the mango (Mangifera indica L.) cultivation area in South Korea has gradually increased from 42.4 ha in 2017 to 76.8 ha in 2021 and continues to expand (KOSIS 2023). In July 2022, mango twig dieback was first observed in Gimhae, Gyeongsangnam-do, South Korea, and ultimately affected approximately 15% of all 85 trees. Cultivar information for field samples was unavailable. Disease symptoms included shoot and twig dieback, defoliation, and internal wood tissue necrosis. Five diseased twigs were sampled. Twig tissues (3 to 5 mm) were taken from the interfaces of symptomatic and healthy tissues of each twig; the pieces were surface disinfected by immersing them in 1% (w/v) sodium hypochlorite solution for 30 s and washed two times in sterilized distilled water. The sterilized twig tissue pieces were transferred onto water agar and incubated at 25°C for 3 days. Mycelial tips of fungal colonies were transferred to potato dextrose agar (PDA). Fungi with the same cultural characteristics were isolated from all five sampled twigs, and three isolates (GNU F138a to GNU F138c) were subcultured using the single-spore method as previously reported (Kim and Park 1988). Fungal isolates grown on PDA produced olive-colored mycelia, which later darkened and formed short aerial hyphae. Pycnidia were semi-immersed, solitary, globose, papillate, and covered by hyphal hairs. Conidia were ellipsoid with rounded apices; smooth, having fine granular content; hyaline; thin-walled; and unicellular, measuring 20 to 25 x 5 to 7.5 μm (n = 30). The morphological characteristics of the fungus isolated were similar to those of previously described Botryosphaeria species (Fang et al. 2024; Slippers et al. 2004). The isolates were further identified by analysis of the small subunit (SSU), large subunit (LSU), and internal transcribed spacer (ITS) regions of ribosomal RNA, and translation elongation factor 1-alpha (TEF1-α) and β-tubulin 2 (TUB2) genes, amplified with NS1/NS4, NL1/NL4, ITS1/ITS4, EF1-688F/EF1-1251R, and T1/Bt2b, respectively (Alves et al. 2008; Glass and Donaldson 1995; O’Donnell 1993). The sequences of the five loci, ITS, LSU, SSU, TEFI-α, and TUB2, of a representative isolate, GNU F138a, deposited in the Korean Agricultural Culture Collection (KACC 410725) were deposited in GenBank (PP784324, PP784327, PP784328, PP784966, and PP784967, respectively). Concatenated sequences of the five loci were used to conduct a maximum parsimony phylogenetic analysis in MEGA11 (Phillips et al. 2013). The three isolates were grouped into a clade with the ex-type of Botryosphaeria dothidea. The pathogenicity of the three fungal isolates was tested on potted 5-month-old mango plants (‘Irwin’). Colonized PDA plugs (5 mm) were placed on wounded twigs, covered with sterile cotton, and sealed with Parafilm. Sterile distilled water was injected into the inoculation site to moisten the cotton. Noncolonized PDA plugs were inoculated as negative controls. Three plants were inoculated with each isolate into three separate twigs. Plants were maintained in a greenhouse at ambient temperature (;26°C) for 15 days. Pathogenicity tests were conducted two times. In pathogenicity tests, necrosis was evident in all nine inoculated mango twigs on day 7; no difference was found between individual isolates, and control branches showed no symptoms. Furthermore, B. dothidea was only reisolated from lesions of the symptomatic twigs. To our knowledge, this is the first report of mango twig dieback caused by B. dothidea in South Korea. Given the rapid expansion of mango cultivation in South Korea, B. dothidea poses a significant threat to yield and orchard sustainability, necessitating urgent management strategies to mitigate future losses.) and β-tubulin 2 (TUB2) genes, amplified with NS1/NS4, NL1/NL4, ITS1/ITS4, EF1-688F/EF1-1251R, and T1/Bt2b, respectively (Alves et al. 2008; Glass and Donaldson 1995; O’Donnell 1993). The sequences of the five loci, ITS, LSU, SSU, TEFI-α, and TUB2, of a representative isolate, GNU F138a, deposited in the Korean Agricultural Culture Collection (KACC 410725) were deposited in GenBank (PP784324, PP784327, PP784328, PP784966, and PP784967, respectively). Concatenated sequences of the five loci were used to conduct a maximum parsimony phylogenetic analysis in MEGA11 (Phillips et al. 2013). The three isolates were grouped into a clade with the ex-type of Botryosphaeria dothidea. The pathogenicity of the three fungal isolates was tested on potted 5-month-old mango plants (‘Irwin’). Colonized PDA plugs (5 mm) were placed on wounded twigs, covered with sterile cotton, and sealed with Parafilm. Sterile distilled water was injected into the inoculation site to moisten the cotton. Noncolonized PDA plugs were inoculated as negative controls. Three plants were inoculated with each isolate into three separate twigs. Plants were maintained in a greenhouse at ambient temperature (;26°C) for 15 days. Pathogenicity tests were conducted two times. In pathogenicity tests, necrosis was evident in all nine inoculated mango twigs on day 7; no difference was found between individual isolates, and control branches showed no symptoms. Furthermore, B. dothidea was only reisolated from lesions of the symptomatic twigs. To our knowledge, this is the first report of mango twig dieback caused by B. dothidea in South Korea. Given the rapid expansion of mango cultivation in South Korea, B. dothidea poses a significant threat to yield and orchard sustainability, necessitating urgent management strategies to mitigate future losses.

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