Morphological and Molecular Characterization of Sclerotium rolfsii(Teleomorph Athelia rolfsii) Associated with Sclerotium Rot of Cucumis melo L. var. makuwa Makino

Abstract

In the present study, a severe outbreak of sclerotium rot on Korean melon(Cucumis melo L. var. makuwa Makino) observed in Jinju, Korea in August of 2014 and 2015 is reported. Thefruit rot disease on the surface of Korean melon fruit appeared as water soaked lesion followedby the development of large rotten areas with abundant white mycelial growth. Abundant whitemycelial mats with globoid and white to brown sclerotia(1-3 mm) were also developed on stemsnear the soil line, and infected plants withered. The fungal pathogen was isolated on potatodextrose agar(PDA) and formed white colonies with numerous sclerotia on PDA. The sclerotiawere globoid in shape, 1-3 mm in size, and white to brown in color. The mycelium formedtypical clamp connection. These measurements and taxonomic characteristics were most similarto those of Sclerotium. DNA sequencing and phylogenetic analysis of the complete internaltranscribed spacer rRNA gene region confirmed that the fungal isolates were Sclerotium rolfsiiSaccardo. Koch's postulates were supported by pathogenicity tests conducted on fruit. Based onmycological characteristics, pathogenicity tests, and molecular identification, the fungus wasidentified as Sclerotium rolfsii. To the best of our knowledge, this is the first report of asclerotium rot caused by S. rolfsii on Korean melon in Korea.