Xylem dysfunction in Yezo spruce (Picea jezoensis) after inoculation with the blue‐stain fungus Ceratocystis polonica

Abstract

SummaryThe blue‐stain fungus Ceratocystis polonica is pathogenic to Norway spruce (Picea abies) in Europe, as well as to Yezo spruce (Picea jezoensis) and Sachalin spruce (Picea glehnii) in Japan. The wilting mechanism in P. jezoensis saplings after inoculation with C. polonica was examined based on anatomical studies of the phloem and xylem of periodically harvested trees. In addition, the course of sap ascent in the trunks was traced by injection of acid fuchsin solution at harvest. As an initial external symptom, needle discolouration was observed. In dye conduction tests, xylem dysfunction in the xylem of inoculated trees became obvious. The dehydrated xylem area (dry zone) had extended more than 20 cm above the inoculation wounds, within 1 month after inoculation. When the sap flow to the branches had nearly stopped, the leaves began to discolour. Hyphae of C. polonica colonized the ray tissue around the inoculation wounds, but were absent at the front of the dry zones. Defence reactions occurred in ray parenchyma cells adjacent to the penetrating hyphae. It is suggested that secondary metabolites, which are formed by the ray cells and epithelial cells of resin canals, are involved in the obstruction of sap flow. Limited necrotic lesions of the phloem and cambium were not associated with foliar symptoms. It is proposed that the dry zone formation caused by C. polonica is the main mechanism leading to tree death.