Abstract:

The blue-stain fungus Ceratocystis polonica, a virulent fungal associate of the spruce bark beetle Ips typographus, is pathogenic to European spruce (Picea abies) in Europe. The wilting mechanism in P. abies after inoculation with C. polonica was examined based on anatomical studies of the phloem and xylem of periodically harvested trees. In a field experiment, the blue-stained sapwood area of European spruce was measured in response to inoculation with C. polonica, four vigorous, mature European spruce trees were mass-inoculated with C. polonica at a density of four inoculations per dm² within a 120-cm-wide band on the lower bole. Two other trees were inoculated with sterile agar and served as controls. In four trees that had been inoculated with the fungus, blue-stained sapwood area increased dramatically within the first weeks after inoculation until no blue-stained sapwood area was measurable 4～6 weeks after inoculation. No obvious blue-stained sapwood area were recorded in the two control trees. Biochemical analysis and histochemical localization techniques were used to assess changes and distribution of cellulase in the xylem fraction. It was shown that, in maturing xylem tissue that inoculated with sterile agar for two weeks, a small amount of the cellulase activity signal was found. However, high cellulase activity was detected in the xylem tissue of four trees that had been inoculated with C. polonica after two weeks. An isoelectric-focusing electrophoresis of the extracted protein displayed obvious isozyme bands of cellulose for the inoculation treatment. This proved that C. polonica can secrete cellulase to utilize cellulose of xylem in host trees. The results confirm the ability of C. polonica to kill mature European spruce trees in the Alps.

Key words: anatomical characteristics, Ceratocystis polonica, cellulose activity, European spruce, isoelectric-focusing electrophoresis