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Range expansion of Phytophthora, particularly Phytophthora cinnamomi into colder environments: adaptation, a changing environment or both?

Khaliq, Ihsanul (2019) Range expansion of Phytophthora, particularly Phytophthora cinnamomi into colder environments: adaptation, a changing environment or both? PhD thesis, Murdoch University.

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Abstract

Alpine and sub-alpine regions were long considered free of Phytophthora species, especially Phytophthora cinnamomi due to restrictions on their growth from low temperatures. However, P. cinnamomi was isolated from a sub-alpine area ‘Barrington Tops National Park’ in the 1990s. Subsequent Australia wide surveys detected 68 Phytophthora species in Australia. Of these, 33 Phytophthora species, including P. cinnamomi, were detected in the alpine and sub-alpine areas on Kosciuszko National Park (KNP) alone. This suggested that Phytophthora species had adapted to cold environments. This project investigated the ability of Phytophthora species to produce infective propagules (zoospores) and cause disease at increasingly lower temperatures. Phytophthora cinnamomi was selected as a ‘test’ species due to its national and international significance. Initially, preliminary surveys were conducted in the sub-alpine and alpine areas of KNP and Tasmania to obtain living Phytophthora isolates. The lower temperature limit for growth and sporulation of Mediterranean (one isolate was from a sub-alpine area) P. cinnamomi isolates was determined and phenotypic plasticity experiments were established in an attempt to ‘train’ them to produce infective propagules and cause disease at increasingly lower temperatures. Finally, the distribution patterns of Phytophthora and vascular plants species in relation to disturbance and elevation were determined across elevation gradients in KNP. Preliminary surveys resulted in the isolation of eight Phytophthora species, including two new species that were formally described. Phytophthora cinnamomi was shown to produce infective propagules at temperatures lower (7.5 °C) than originally established (10 °C), and in a shorter time compared to original isolates when ‘trained’ under cold conditions. This suggests that P. cinnamomi responds rapidly to selection pressure and adapts to new environments. Although P. cinnamomi produced infective propagules at 7.5 °C, the pathogen could not be isolated from plants grown at 7.5 °C after three months. Therefore, more work is required to establish disease development at 7.5 °C and below. Results of surveys along elevation gradients showed Phytophthora and vascular plant species exhibited a linearly monotonic decline with increasing elevation on roads, but not in native vegetation. However, the elevation range of Phytophthora species was higher than vascular plants on both roads and in native vegetation. Phytophthora species did not show any habitat preference and exhibited similar composition and frequency on roads and in native vegetation; vascular plants showed the opposite trend with greater frequency in native vegetation. This suggests that Phytophthora richness at the plot level mimics that of vascular plants. A changing climate may permit invasion by other Phytophthora species not yet present.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Veterinary and Life Sciences
Supervisor(s): Burgess, Treena, Hardy, Giles and McDougall, Keith
URI: http://researchrepository.murdoch.edu.au/id/eprint/43119
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