Goldenseal (Hydrastis canadensis L.) Extracts Inhibit the Growth of Fungal Isolates Associated with American Ginseng (Panax quinquefolius L.)

American ginseng, a highly valuable crop in North America, is susceptible to various diseases caused by fungal pathogens, including Alternaria spp., Fusarium spp., and Pestalotiopsis spp. The development of alternative control strategies that use botanicals to control fungal pathogens in American ginseng is desired as it provides multiple benefits. In this study, we isolated and identified three fungal isolates, Alternaria panax, Fusarium sporotrichioides, and Pestalotiopsis nanjingensis, from diseased American ginseng plants. Ethanolic and aqueous extracts from the roots and leaves of goldenseal were prepared, and the major alkaloid constituents were assessed via liquid chromatography–mass spectrometry (LC–MS). Next, the antifungal effects of goldenseal extracts were tested against these three fungal pathogens. Goldenseal root ethanolic extracts exhibited the most potent inhibition against fungal growth, while goldenseal root aqueous extracts and leaf ethanolic extracts showed only moderate inhibition. At 2% (m/v) concentration, goldenseal root ethanolic extracts showed an inhibition rate of 86.0%, 94.9%, and 39.1% against A. panax, F. sporotrichioides, and P. nanjingensis, respectively. The effect of goldenseal root ethanolic extracts on the mycelial morphology of fungal isolates was studied via scanning electron microscopy (SEM). The mycelia of the pathogens treated with the goldenseal root ethanolic extract displayed considerable morphological alterations. This study suggests that goldenseal extracts have the potential to be used as a botanical fungicide to control plant fungal diseases caused by A. panax, F. sporotrichioides, or P. nanjingensis.