Abstract
Marri (Corymbia calophylla) is an iconic and keystone forest tree in Western Australia. A canker disease caused by the fungus Quambalaria coyrecup has devastated many marri stands. Disease incidence is higher in remnant stands that border cleared land such as road edges and farmland where there is greater anthropogenic disturbance, such as fertiliser, pesticide and herbicide use, and the introduction of plant pathogens. The progression of the decline strongly suggests a breakdown in the ability of the trees to maintain nutrient balance and we hypothesize that mycorrhizal fungi play a role in this process. The aim of this project was to examine the mycorrhizal species associated with marri and how these communities differ between intact and anthropogenically disturbed forest sites and whether pesticide use, changes in soil nutrition and/or soilborne pathogens are responsible for changes in communities of mycorrhizal fungi and hence canker disease incidence and severity. Seventeen sites were surveyed. Each site consisted of a disturbance gradient. Soil was collected from each transect and tested for nutrient composition, mycorrhizal composition and pathogens. Preliminary results demonstrate differences in soil nutrition between the disturbed transect and all intact forest transects. In addition, there are differences among the communities of fungi between the disturbed and intact forest transects. Disturbed transects show a higher proportion of pathogenic fungi particularly Phytophthora species, than in intact forest transects. Currently, the presence of pesticides and herbicides across the transects are being examined to determine their role in marri decline.