Effect of phenolic and other compounds on growth of Poria weirii in vitro

Twenty-five compounds, widely occurring in nature, were tested individually in vitro at 0 . 5 and 2 . 0 mM concentrations for effects on two isolates of Poria weirii Murr., a serious root pathogen of conifers in western North America. Growth of both isolates was strongly inhibited in media containing coumarin, 4-hydroxycoumarin, or 7-hydroxycoumarin at either concentration, but o-catechol, salicylic acid, benzoic acid, ferulic acid, o-coumaric acid, and phenylacetic acid were inhibitory only at the higher concentration. The remaining compounds either inhibited only one isolate, had no effect, or stimulated growth of the fungus. Presence of significant amounts of the inhibitory compounds in host tissue could account for resistance to P. weirii by plants such asAlnusrubra Bong.