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The genetic diversity of Teratosphaeria cryptica in Australia

Lazar, Katherine (2016) The genetic diversity of Teratosphaeria cryptica in Australia. PhD thesis, Murdoch University.

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Teratosphaeria cryptica is one of the most important causal agents of Teratosphaeria leaf disease in plantations in Australia, the others being Teratosphaeria nubilosa and T. pseudonubilosa. While T. nubilosa has been distributed globally, T. cryptica and T. pseudonubilosa are only found in Australia and New Zealand. Teratosphaeria cryptica has a very broad distribution and host range within Australia. In this thesis the population genetics of T. cryptica was examined in order to determine its mode of reproduction, origin and patterns of movement within Australia, to look for evidence of cryptic speciation, and determine whether there is evidence for host preferences or spatial structure within and between populations.

Eleven primer sets were designed for polymorphic microsatellites regions for T. cryptica. These were then used on over 1000 samples of T. cryptica collected throughout its range within Australia; Western Australia (WA), Victoria (VIC), Tasmania (TAS), New South Wales (NSW) and into far north Queensland (QLD). Several aspects of the overall Australian population were revealed. The pathogen most likely originated in south eastern Australia (VIC, TAS and Southern NSW). In the eastern states there appears to be a division between the north (northern NSW and QLD) and the south (VIC, TAS and southern NSW) from which very different populations were found.

Within both the northern and southern areas of eastern Australia there was evidence of linkage disequilibrium in populations. Analysis with the program STRUCTURE found two clusters in the north and four clusters in the south. These clusters do not appear to represent cryptic species as there was evidence of admixture. Although QLD was not thoroughly sampled, the two northern clusters were not closely related and it is therefore proposed that they represent two separate migration events from the south. In vi the south, there was correlation (although also many exceptions) between clusters and host species (two clusters were associated mainly with E. globulus, another with E. nitens and another with E. obliqua). As out crossing requires physical proximity it is possible the clusters have arisen out of the host preference.

Teratosphaeria cryptica was foremost found to be homothallic. This, together with asexual reproduction often resulted in an immediate area (within 20m2) being dominated by one to three multilocus haplotypes (MLHs). In different areas however it was rare to find identical MLHs. There was one exception to this, MLH C274, which was found at multiple locations. It was almost exclusively found on E. globulus and had consistent culture morphology. It’s possible the widespread planting of E. globulus in south eastern Australia has changed the composition of the T. cryptica population with an increase in MLHs with a preference for E. globulus and suggest that this disease will continue to be a problem for plantations in south eastern Australia.

Teratosphaeria cryptica has been introduced into WA. There appears to have been at least two introductions. One of these probably occurred around the time it was first recorded in WA, the early 1990s. Although it may have been bought in with E. globulus for plantations, it could also have had different sources as many host species from south eastern Australia have been transported to WA. The evolutionary advantage of infecting endemic hosts appears to have led to a shift away from E. globulus and MLHs derived from this older introduction were rarely found in plantations. Most isolates collected from plantations were MLH C274, with the same host preference and culture morphology as found in VIC. The introduction of further MLHs, particularly those with a preference for E. globulus is of concern for plantations and quarantine procedures.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
United Nations SDGs: Goal 15: Life on Land
Supervisor(s): Burgess, Treena and Hardy, Giles
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