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Infection of Paulownia by Alternaria and influence of abiotic and biotic factors

Barron, Harley (2003) Infection of Paulownia by Alternaria and influence of abiotic and biotic factors. Honours thesis, Murdoch University.

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Paulownia is a newly developed industry in Western Australia. Relying on high levels of fertiliser and irrigation to attain maximum growth, Paulownia often has nitrogen levels of 4.5 to 5 %. Alternaria, a pathogen with the potential to defoliate trees, has been isolated from blighted leaves of Paulownia for the first time in the literature. It was hypothesised that luxury fertiliser treatments may predispose Paulownia fortunei to disease.

To test for the influence of luxury fertiliser regimes on Alternaria blight of Paulownia fortunei, clonal trees were grown in a glasshouse and fertilised using a nil, low, medium and high fertiliser regime. Plants were measured
for height, stem diameter, gas exchange, chlorophyll, soluble protein and inorganic nutrient concentrations in the leaves.

It was found that rising fertiliser supply resulted in all measures increasing, then plateauing at the two highest fertiliser rates. The only exceptions to this trend were leaf sodium and stem boron and potassium concentrations which dropped with increasing fertiliser. Photosynthesis
and leaf nitrate were the only measures which were significantly higher in the highest fertiliser treatment. Thus, concluding that additional N, up to 46%, is of limited benefit to plant growth and function.

Three inoculation treatments were conducted, leaf disc, excised leaf and in-situ. Each infection trial only produced lesions where leaves were wounded prior to infection. Fertiliser treatments had no effect on disease
development in the leaf disc and excised leaf inoculation treatments. However, the in-situ inoculation trial had significantly (p < 0.01) larger lesions in the nil fertiliser treatment than all other fertiliser treatments.
Unfortunately, there was no significant difference between the inoculated and control leaves within the nil fertiliser treatment.

A systemic fungicidal influence on Paulownia by VAM was also examined. Seedlings inoculated with VAM were measured by the same methods as the nutrition trial with the exception of gas exchange. The presence of VAM increased plant height, root weight and approximately half of the
nutrients analysed. Fertiliser treatment significantly increased the majority of plant biomass and function measurements. However, the inorganic nutrient analysis of the leaves revealed that the soil sterilisation process
resulted in more nutrients becoming available to the plants.

The infection of the VAM trial with Alternaria resulted in no lesions on the leaves and stems.

There is no evidence to suggest that the luxurious fertiliser applied to field grown Paulownia predisposes them to infection by Alternaria. However, there is evidence that this pathogen may be opportunistic as only wounded leaves produced lesions during all nutrient infection trials. The impact of VAM on Paulownia growth is limited and needs further research.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
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, Dell, Bernard and Malajczuk, Nicholas
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