Sclerotium rolfsii causes stem rot on Ixeridium dentatum in Korea

Stem rot was observed on Ixeridium dentatum in Jinan-gun and Dangjin-gun, Korea during the growing seasons of 2016 and 2017. The first symptom was water-soaked lesions on the basal parts of stems. Lower leaves became wilted and blighted before the plants eventually died. White cottony mycelial mats and brown spherical or irregular sclerotia formed on the basal stem and adjacent soil surfaces. The optimal temperature for in vitro colony growth and sclerotia germination were 30 °C and 25 °C, respectively. The in vitro and morphological characteristics of the fungus were identical with those described for Sclerotium rolfsii . Phylogenetic analysis based on the internal transcribed spacer (ITS) region revealed that two isolates isolated from I. dentatum formed a monophyletic group with reference isolates of S. rolfsii . Koch’s postulates were satisfied for the same two S. rolfsii isolates, thereby confirming that the pathogen causes stem rot of I. detatum in Korea.