Xylem sap flow of Norway spruce after inoculation with the blue‐stain fungus Ceratocystis polonica

Abstract

In a field experiment, the sap flow of Norway spruce (Picea abies) was measured in response to inoculation with Ceratocystis polonica, a virulent fungal associate of the spruce bark beetle Ips typographus. Four vigorous, mature Norway 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. Sap flow of the six trees was measured by the thermal dissipation method from three weeks prior to inoculation until five months after inoculation. In three trees that had been inoculated with the fungus, sap flow density decreased dramatically within the first weeks after inoculation until no sap flow was measurable 4–6 weeks after inoculation. No marked changes in sap flow density were recorded in the fourth tree that had been inoculated with C. polonica, and this tree survived the inoculation. Inoculation with sterile agar did not have any apparent influence on the sap flow of the control trees. The results confirm the ability of C. polonica to kill mature Norway spruce trees. Sap flow measurements by the thermal dissipation method provided a direct and nondestructive method for monitoring the effects of fungal infection on sapwood functionality. Its application for further studies on vascular wilt and vascular stain diseases of trees is therefore recommended.