First Report of Anthracnose Caused by Colletotrichum nymphaeae on Kiwiberry in Korea

The fruit of Actinidia arguta, named kiwiberry or hardy kiwi, can be eaten without peeling its skin and for this reason, the popularity and the production of kiwiberry has been increasing in Korea (Kim et al. 2017). In August 2016, typical anthracnose symptoms were observed on kiwiberries at two orchards at Gwangyang, Jeonnam Province in Korea. Initial small specks developed into larger brown or black lesions on fruits. Later, white to gray mycelial mats were observed on the lesions. Based on field survey, the disease incidences at the two orchards were 5 and 8%, respectively. A total of 35 isolates cultured from typical anthracnose lesions were identified by morphological examination and molecular analysis. Their colonies initially produced white mycelia with pinkish-orange conidial masses, which turned gray after 5 days. Conidia were cylindrical, one-celled, aseptate, hyaline, and 10.6 to 15.9 μm (avg. 12.8 μm) × 4.0 to 5.8 μm (avg. 4.9 μm, n = 100) in size. Appressoria were circular to slightly irregularly shaped, smooth walled, light brown, and 7.4 to 17.8 μm (avg. 14.7 μm) × 5.5 to 9.3 μm (avg. 7.3 μm, n = 100) in size. A sexual stage has not been observed in cultural condition. These morphological characteristics are consistent with those of Colletotrichum nymphaeae (Damm et al. 2012). Because all isolates showed identical morphological characteristics, we randomly selected four isolates, named CC, OC, GC, and GNC, for further investigation. The ITS (MG515032-35), TUB2 (MG515024-27), and ACT (MG515016-19) gene sequences matched with C. nymphaeae strain CDMF-1 (MF187553, MF278015, and MF278014, respectively). The CHS-1 (MG515020-23) gene matched with C. nymphaeae culture-collection CBS:100064 (JQ948885). The GAPDH (MG515028-31) sequences matched with C. acutatum strain CPPL1501 (KT321123). Results from maximum likelihood phylogenetic analyses, based on concatenated ITS, TUB2, CHS-1, ACT, and GAPDH DNA sequences, placed the representative isolates within a clade comprising the holotype of C. nymphaeae SA-01. A mycelial plug (5 mm diameter) was inoculated onto three freshly harvested fruits that were surface sterilized with 70% ethyl alcohol for 2 min and wounded by piercing with or without a sterilized needle. Another six control fruits were inoculated with sterile agar plugs of the same medium with or without wounding. Inoculated fruits were maintained in a plastic bags in growth chamber at 25°C. Initial symptoms were observed at 3 days postinoculation (dpi) and typical anthracnose symptoms were appeared at 5 dpi. The pathogen was successfully reisolated and the reisolated fungus was confirmed with sequence analysis of the five mentioned genes with morphological characteristics, thus fulfilling Koch’s postulates. To our knowledge, this is the first report of C. nymphaeae as an anthracnose pathogen on kiwiberry.