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Damping-off of indigenous jarrah forest plant species by Phytophthora cinnamomi and Phytophthora citricola in bauxite pit rehabilitation in the northern jarrah forest

Woodman, Gregory (1993) Damping-off of indigenous jarrah forest plant species by Phytophthora cinnamomi and Phytophthora citricola in bauxite pit rehabilitation in the northern jarrah forest. Honours thesis, Murdoch University.


Alcoa of Australia Limited mines bauxite from the Darling Range in south-west Western Australia. They have a goal to replace >80% of plant species indigenous to the surrounding jarrah (Eucalyptus marginata Donn ex Smith) forest in their 15 month old rehabilitation by 1997.

Annual monitoring of the 15 month old rehabilitation has identified some plant species that germinate well in glasshouse and laboratory trials but were not returning to the rehabilitated areas m expected numbers. It was hypothesized that Phytophthora cinnamomi Rands and Phytophthora citricola Sawada, which had been recovered from soil and diseased vegetation in the pits may have been reducing establishment of these species. This project aimed to determine whether P . cinnamomi and P. citricola could cause damping-off of native plant species in bauxite pit rehabilitation.

To achieve this aim five preliminary experiments, followed by a glasshouse experiment and an experiment based in a rehabilitated bauxite pit, were undertaken. The preliminary glasshouse and laboratory experiments determined mean percentage germination, as well as isolating seed testa fungi, for six native plant species identified as not returning in expected numbers to the rehabilitation. The plant species chosen were Clematis pubescens Huegel ex Endl., Cyathochaeta avenacea Benth., E. marginata. H akea lissocarpha R.Br., H ovea chorizemifolia (Sweet) DC. and Xanthorrhoea preissii Endl.

Soil from rehabilitated pits was also shown to not cause suppression of P. cinnamomi and P. citricola. An appropriate density of millet seed for use in the main glasshouse experiment was determined and the process of soil solarization was investigated to determine whether it could be used to eradicate phytophthora species from soil in rehabilitated bauxite pits. The method of soil solarization used in this project was found to not be effective in eradicating Phytophthora species from the rehabilitated areas.

The two main experiments tested the pathogenicity of P . cinnamomi and P. citricola on seed and seedlings of the six native plant species chosen for this study, in the glasshouse and rehabilitated bauxite pit environments. Both P. cinnamomi and P. citricola were found to cause post-emergent damping-off of E. rna r gina ta in the glasshouse, with P. cinnamomi also causing damping-off of X. preissii seedlings in this environment. An introduced isolate, as well as indigenous isolates of P. citricola caused pre and post-emergent damping-off of E. marginata in the field. P. citricola also caused pre-emergent damping-off of H. lissocarpha in the rehabilitated trial areas.

The P. cinnamomi inoculum did not cause disease in the field due to sub-optimum ambient temperatures which inhibited sporangia! formation and mycelial growth (Shearer and Tippett, 1989). However, P. cinnamomi has been shown to cause damping-off in regenerating areas (Mwanza and Kellas, 1987) and probably causes damping-off in Alcoa's rehabilitated areas when conditions are more favourable, in autumn and spring. P. cinnamomi and P. citricola therefore probably reduce the biodiversity of Alcoa's rehabilitated pits by reducing the establishment of susceptible species.

Topics requiring further research are discussed.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Biological and Environmental Sciences
United Nations SDGs: Goal 15: Life on Land
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor(s): Hardy, Giles and Colquhoun, I.
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