Abstract In previous studies the phenolic acids, p-coumaric, ferulic, syringic, and vanillic, have been quantitatively determined from hydrolyzed extracts of red alder roots, and p-coumaric and vanillic, from Douglas-fir roots. Alder roots resist infection by Poria weirii , whereas Douglas-fir roots are highly susceptible. In the present study, the compounds alone and in all combinations were tested for effects on growth of two genotypes of P. weirii in vitro. The combination of all compounds, as found in alder root hydrolysates, inhibited growth of both Poria isolates. The p-coumaric-vanillic combination associated with Douglas-fir root hydrolysates inhibited one isolate and stimulated the other. The two isolates differed markedly in response to several other combinations of the compounds and in their effects on pH of the medium. Phenolic substances probably participate in the Poria -resistance system of alder. Physiological strains of P. weirii that effectively attack any susceptible host may exist, but not all strains are likely to be equally pathogenic on all hosts or all root parts of a host (bark vs. sapwood vs. heartwood, for example). Biological control of P. weirii , seeming anomalies in behavior of P. weirii in nature, and breeding for host resistance are discussed. Forest Sci. 19:191-196.
Trappe et al. (1973) studied this question.