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An infection experimcnt was made to test the pathogenicity of two Ceratocystis species on Norway spruce trees. Water stress in inoculated and control trees was measured by means of xylem water potential, stomatal aperture and transpiration stream velocity. Most trees inoculated with C. polonica, alone or in combination with C. penicillata, became water-stressed. Ten weeks after inoculation almost all sapwood of water-stressed trees was blue-stained at the level of inoculation. Trees inoculated with C. penicillata alone did not become water-stressed, and their sapwood was not blue-stained. The results indicate that C. polonica is a highly qualified accomplice to Ips typographus in its killing of spruce trees.


The spruce bark beetle, Ips typographus, infects Norway spruce trees with blue-stain fungi, amongst which several species of Ceratocystis are found. Artificial inoculation of healthy trees with C. polonica caused in several cases increased water stress of the trees, and complete sapwood staining. The defences of spruce against Ips/Ceratocystis attack appear to depend on 1. the output of constitutive resin from severed resin ducts, and 2. accumulation of secondary resin around the attack sites. Our preliminary studies indicate that the amount of both types of resin may vary considerably between trees, as well as from place to place on the same tree. A dose/response experiment based on artificial inoculation of C. polonica indicated that at a certain dose (i.e. number of infections per unit area), the accumulation of secondary resin decreased, and the fungus was able to overcome the host defence.