Distribution and Impact of Armillaria luteobubalina in the Eucalyptus marginata Forest of South-Western Australia

Abstract

Armillaria luteobubalina is a widespread primary pathogen in the Eucalyptus marginata forest of south-western Australia. Over 200 infection centres were identified during the 5-year period between 1981 and 1985. The fungus sporulated during June and July, usually from roots but sometimes from stems (e.g. E. calophylla). Armillaria luteobubalina basidiomes were found originating from roots of 34 plant species, with greatest incidence on roots of E. marginata. Root systems were excavated and patterns of A . Luteobubalina invasion recorded. Rhizomorphs were not found and fungal spread between hosts was via root to root contacts, Variation in host species' susceptibility to the fungus was reflected in different patterns of xylem compartmentalisation and variable amounts of cambial damage. The degree of resistance expressed at the collar or lower stem determined the fate of individuals of the various species. Lack of resistance in Eucalyptus wandoo to tangential spread of A. luteobubalina often resulted in death by the time columns of decay had advanced into the lower stem or butt. Banksia grandis, E. calophylla, E. gomphocephala, and E. marginata resisted to varying degrees. Inverted V-shaped lesions, often mis- taken for fire scars, were evidence of the ability of E. gomphocephala and E. marginata individuals to resist tangential spread and prevent girdling of stems. In stems of E. calophylla, lesions did not have a definite V shape, decay penetrated deeper and the fungus persisted longer than in those of E. marginata. Host mortality following infection was greater in the intermediate- and low-rainfall zones of the eastern E. marginata forest than in the high-rainfall zone to the west.