Investigation of fungi pathogenic towards seedlings of Parkinsonia aculeata – their potential for use as mycoherbicides

Ruey Toh (2009). Investigation of fungi pathogenic towards seedlings of Parkinsonia aculeata – their potential for use as mycoherbicides MPhil Thesis, School of Land, Crop and Food Sciences, The University of Queensland.

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Author Ruey Toh
Thesis Title Investigation of fungi pathogenic towards seedlings of Parkinsonia aculeata – their potential for use as mycoherbicides
School, Centre or Institute School of Land, Crop and Food Sciences
Institution The University of Queensland
Publication date 2009-06
Thesis type MPhil Thesis
Supervisor Dr Victor Galea
Dr Rieks van Klinken
Total pages 130
Total colour pages 21
Total black and white pages 109
Subjects 07 Agricultural and Veterinary Sciences
Abstract/Summary Parkinsonia aculeata L. (Fabaceae) is an exotic shrub that threatens most of the Australian rangelands and is listed as one of Australis' 20 Weeds of National Significance. To date some control strategies have been studied and applied such as mechanisms, flaming, herbicides, grazing, and exotic and native insects. These can be expensive, are not always effective, and can cause other, environmental problems. However, a phenomenon popularly referred to as “parkinsonia dieback” has been observed for decades which affects otherwise healthy plants and can cause high levels of mortality. Fungal isolates have been extracted from affected trees across northern Australia and stored in an isolate bank to help identify causative organisms. This thesis aimed to investigate the potential of the fungal isolates as biocontrol agents on parkinsonia seedlings. Three main subjects have been studied in this thesis, determining the effect of temperature and timing of inoculation on the pathogenicity of selected isolates, isolate screening using a combination of laboratory and greenhouse studies to identify the most pathogenic isolates, and examining and contrasting the infection process of the most lethal isolates. The effect of temperature (15 to 40°C) and timing of inoculation (pre- and post- emergent seedling stage) were examined on the four most common species (Fusarium sp., Phoma sp., Lasiodiplodia theobromae (Pat.) Griffon & Maubl., and Neoscytalidium dimidiatum (Penz.) Crous & Slippers) in the isolate bank. A temperature of 30°C was shown to be ideal for conducting experimentation as it was optimal for both seedling growth and isolate activity. The two most aggressive pathogenic species Lasiodiplodia theobromae and Neoscytalidium dimidiatum caused significantly higher seedling mortality when inoculated at the pre-emergent stage. However, mainly Lasiodiplodia theobromae caused pre-emergent death, and Neoscytalidium dimidiatum caused post-emergent death. In the isolate screening study, 84 isolates were selected from the isolate bank of 200 isolates to best represent the available taxa and the six biogeographic and climatic regions across which samples were available. A standard laboratory assay using parkinsonia seedlings was developed and used to screen for their pathogenicity. The laboratory study identified five lethal isolates (four species: Lasiodiplodia theobromae, Neoscytalidium dimidiatum, Macrophomina phaseolina (Tassi) Goid., and Botryosphaeria sp.) all of which belong to the family Botryosphaeriaceae. Seedling mortality from the five most lethal pathogens was much lower in the glasshouse trials, although Lasiodiplodia theobromae was consistently the most lethal species. The infection process was examined for three of the lethal species Lasiodiplodia theobromae, Neoscytalidium dimidiatum, and Macrophomina phaseolina using the time series histological microscopic method. All three species showed similar histologies starting with the collapse of the epidermis and parenchyma with infections reaching the pith within four days. Lasiodiplodia theobromae, which was the most aggressive species in laboratory and glasshouse trials, was the only species detected in the intra- and intercellular spaces of the pith. This thesis suggests that Lasiodiplodia theobromae shows the most potential out of the 200 isolates collected from dieback-affected parkinsonia to be developed into a biocontrol agent against parkinsonia seed bank. Features include rapid infection, and a gradual and steady cell collapse until seedling death within four days of inoculation.
Keyword Parkinsonia
seed bank
biocontrol agent
Lasiodiplodia theobromae
Additional Notes *Colour page numbers: 24, 25, 38-40, 42, 46, 47, 51, 60, 67, 70, 71, 73, 81, 96, 99-103. *Landscape page numbers: 54, 60, 61, 78, 83, 98, 125-130.

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Created: Wed, 11 Nov 2009, 13:15:18 EST by Ms Ruey Toh on behalf of Library - Information Access Service