Seedling rot of Panax ginseng caused by Pythium myriotylum in Japan

Sudden wilt and blight developed on ginseng seedlings ( Panax ginseng ) in Ibaraki Prefecture, Japan, in June 2017. Rootlets rotted and fell off. Aseptate hyphae were observed in this trace tissue that detached from main roots, which had orange-yellowish tinges. The white mycelium isolated from the diseased main roots was identified as Pythium myriotylum based on morphology and cox 1 gene sequences. The isolate reproduced the symptoms on healthy ginseng seedlings and was re-isolated from diseased seedlings. This is the first report of seedling rot (naegusare-byo in Japanese) on ginseng caused by P. myriotylum in Japan.