Further Effects of Bark Saprophytes on Hypoxylon Canker

Abstract

Abstract Solutions containing the saprophytes that occurred on the healthy bark of P. trichocarpa were effective in totally inhibiting the growth of H. pruinatum on 1 and 2% water agar and on media containing 1 and 2% agar and 5% malt extract. Solutions sterilized by autoclaving or filtering through Millipore or Fritted glass filters were not effective in preventing the growth of the pathogen. Canker attack by H. pruinatum was delayed considerably when drying cuttings of P. trichocarpa were dipped in test solutions prior to inoculation. Apparently, the solution dips provided a greater coverage of bark saprophytes on the host that, for a period, suppressed the development of the pathogen and, consequently, afforded a measure of biological control of the disease. Cultural studies demonstrated that the degree of antagonism between the bark saprophytes and the pathogen could be modified by environmental change in different substrates, thus opening the way to an analysis of the factors affecting the expression of antagonism in field material.