White rot of Panax quinquefolius caused by Sclerotinia nivalis

American ginseng (Panax quinquefolius), one of the most well-known araliaceous perennial herbs, suffered from root rots and mortality in 2020 in Taibai County, Shaanxi Province, China, leading to 40%-60% yield losses. The diseased plants initially showed unevenly yellowing foliage, and yellow-brownish, water-soaked roots with internal softening. Subsequently, white fluffy mycelia manifested on the surface of diseased P. quinquefolius roots, followed by the appearance of black irregular sclerotia-like bodies. In this study, a fungal isolate (SS-TB, GenBank no. MT830866) was obtained from the infected roots. Based on the culture morphology, pathogenicity tests and phylogenetic analysis of the internal transcribed spacer (ITS) region, this isolate was identified as Sclerotinia nivalis. The optimum temperature for mycelial growth and sclerotial production was 20 celcius and 15 celcius, respectively; the optimum pH for mycelial growth and sclerotial production was pH 6.0. This isolate grew faster and produced more sclerotia on potato dextrose agar than on other media. It infected ginseng roots with or without wounds, but inoculation of wounded roots led to more severe disease. S. nivalis also infected 43 of the 48 plant species tested, including vegetables, fruits, oil crops, and flowering plants from Fabaceae, Asteraceae, Solanaceae, Cucurbitaceae, Brassicaceae, Apiaceae, Rosaceae, Liliaceae, Chenopodiaceae, and Orchidaceae. It was nonpathogenic on Triticum aestivum, Zea mays, Anemone vitifolia, Ipomoea batatas, and Vaccinium sp. This study is the first report of S. nivalis causing white rot on P. quinquefolius.