Resorcylic acid lactones from the ginseng pathogen Ilyonectria mors-panacis

Ilyonectria mors-panacis, previously Cylindrocarpon destructans, is the main plant pathogen responsible for the fungal disease ginseng root rot. This economically important disease, also called disappearing root rot, reduces crop yields by an average of 30% at harvest. While the disease is well studied from ecological and genomic perspectives, the role of I. mors-panacis secondary metabolites in the disease process is not well understood. Our previous metabolomics study showed Ilyonectria strains that cause ginseng root rot produce mixtures of putative resorcylic acid lactones, whereas avirulent strains did not, and collectively synthesize fewer metabolites. To confirm these metabolomics findings, we isolated and characterized the secondary metabolites from I. mors-panacis DAOMC 251601, a strain that causes ginseng root rot. From its EtOAc soluble culture filtrate extract, eight resorcylic acid lactones (1-8), including chlorinated and non-chlorinated congeners, were characterized by HRMS and spectroscopic approaches (NMR, OR, UV). The structure of one new metabolite, named radicicol E (1), was elucidated and additional spectroscopic data for the known compound nordinonediol (2) are reported. Further, radicicol (9) production was confirmed by comparison to a standard. The roles that resorcylic acid lactones and the siderophore N,N′,N” triacetylfusarine C have in promoting Ilyonectria ginseng root rot are also discussed.