Colletotrichum kakivorum: A New Pathogen Causing American Ginseng Root Rot in China with Host Range and Fungicide Efficacy Analyses.

American ginseng (Panax quinquefolius L., AG) is a high-value medicinal and edible crop widely utilized in traditional and modern healthcare systems. Root rot disease, induced by a complex of diverse phytopathogens, is a major limiting factor hindering the sustainable cultivation of AG. In July 2024, a pathogenic fungal strain was isolated from symptomatic rotted roots of American ginseng and taxonomically identified as Colletotrichum kakivorum. To our knowledge, this represents the first formal report of C. kakivorum causing infection in American ginseng in China. Host range assays conducted on nine medicinal herb species demonstrated that C. kakivorum could infect seven host plants, including ginseng, radix codonopsis, ladybell, dried rehmannia, platycodon, fragrant solomonseal rhizome, and cochinchinese asparagus, but did not infect white peony or heterophyllous falsestarwort. Two fungicides, pyraclostrobin and difenoconazole, exhibited prominent inhibitory effects against the pathogen. Specifically, pyraclostrobin at 0.1 mg·L⁻¹ and difenoconazole at 0.05 mg·L⁻¹ completely inhibited the germination of C. kakivorum conidia. Field inoculation trials further verified that foliar application of 500 mg·L⁻¹ pyraclostrobin and 200 mg·L⁻¹ difenoconazole reduced the disease incidence of American ginseng root rot (AGRR) by approximately 62%. An integrated management strategy, including crop rotation with non-host medicinal herbs combined with fungicide application, was verified to efficiently control American ginseng root rot induced by C. kakivorum. Collectively, these findings provide a fundamental theoretical basis and practical reference for the prevention and management of C. kakivorum-associated root rot in American ginseng seedlings.