PHYTOALEXIN ACCUMULATION AND HYPHAL SPREAD IN JAPANESE CEDAR SAPWOOD INOCULATED WITH A CANKER FUNGUS, GUIGNARDIA CRYPTOMERIAE
T YAMADA and T NAKASHIMA
Forest Biology Division, Forestry and Forest Products Research Institute, Tsukuba, Ibaraki 305-8687, Japan
Background and objectives
Materials and methods
Japanese cedar trees were inoculated with a virulent isolate, MA18, or an avirulent isolate, MA19, of the Guignardia dieback fungus Guignardia cryptomeriae (Botryosphaeria sp.). Spread of wood discoloration and fungal hyphae in the inoculated tree were determined. The boundary of wood discoloration was observed with a light microscope, and methanol extracts of the discolored region were assayed and analysed by thin-layer chromatography and gas chromatography.
Results and conclusions
Within 1 week after inoculation, the moisture content of the discoloured region decreased, and an increase in NAD diaphorase activity, and secretion of oil droplet-like deposits containing norlignans and terpenes, began in the same zone. An antifungal norlignan, hinokiresinol , accumulated quickly, and the concentration of hinokiresinol reached ca 20 and ca 50% of the maximum concentration 1 and 2 weeks after inoculation, respectively. Maximum concentration of hinokiresinol was observed 2-3 months after inoculation. Agatharesinol and sequirin-C, norlignans which have little antifungal activity, and terpenes, accumulated slowly in the reaction zone barrier. These results strongly suggest that accumulation of antimicrobial substances contributes to the restriction of fungal colonization.
Concentrations of norlignans and terpenes in the reaction zone barrier were higher in fungus-inoculated trees than in wounded trees. This fact suggests that the induction of defence responses is enhanced by the presence of pathogenic fungi.