Armillaria ostoyae, the cause of Armillaria root rot, is a major problem in cherry orchards in the northwest region of Michigan. One mechanism of resistance to pathogen invasion is the production of antifungal compounds. Prunus maackii was the only Prunus species tested that contained significant antifungal activity based on Thin Layer Chromatography bioassays. The purpose of this research was aimed at understanding the nature of resistance/defense found in P. maackii to Armillaria root rot. A series of additional bioassays were performed to examine the range of antimicrobial activity and the potency of the secondary metabolites contained in the periderm of P. maackii. Periderm-incorporated media was used to screen for growth inhibition of Armillaria species along with a group of non-host pathogens. Prunus maackii periderm amended-media was fungistatic at very low concentrations and also displayed fungitoxic properties. X-ray crystallography was used to determine the structures of two antifungal components of Prunus maackii periderm as 3,5,7-trihydroxy-6 methoxyflavone and 3,5,7-trihydroxy-6-methoxyflavanone. This is the first report of crystallization and antimicrobial activity for both compounds.
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