XVI International Botanical Congess

Excised fresh logs of Japanese cedar (Cryptomeria japonica) were inoculated with virulent isolates or avirulent isolates of Guignardia dieback fungus (Guignardia cryptomeriae). Hyphae of virulent isolates grew rapidly, though hyphal spread of avirulent isolates was limited. Concentration of hinokiresinol, an antifungal norlignan, was higher in the reaction zone barrier (RZB) of the logs inoculated with avirulent isolates than those inoculated with virulent isolates. Anatomical observation revealed that a lot of oil droplet-like deposits occluded RZB tracheids of avirulent isolate-inoculated logs, but not of virulent isolate-inoculated logs. These results indicate the reverse correlation between the intensity of defensive responses and virulence of fungus inoculated.