Parkinsonia dieback: investigations into its cause, ecology and potential for biological control

Diplock, Naomi Dove (2016). Parkinsonia dieback: investigations into its cause, ecology and potential for biological control PhD Thesis, School of Agriculture and Food Sciences, The University of Queensland. doi:10.14264/uql.2016.148

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Author Diplock, Naomi Dove
Thesis Title Parkinsonia dieback: investigations into its cause, ecology and potential for biological control
School, Centre or Institute School of Agriculture and Food Sciences
Institution The University of Queensland
DOI 10.14264/uql.2016.148
Publication date 2016-03-24
Thesis type PhD Thesis
Supervisor Victor Galea
Ken Goulter
Total pages 181
Total colour pages 40
Total black and white pages 141
Language eng
Subjects 0607 Plant Biology
0703 Crop and Pasture Production
Formatted abstract
Parkinsonia aculeata, a Weed of National Significance (WoNS) has been observed displaying unexplained mortality within populations across northern Australia since the 1950s. This disorder is commonly referred to as parkinsonia dieback and causes substantial plant death in some areas. In some observed cases, plants suffering from dieback show symptoms starting from the tip of the branch which begins to die back, with phyllodes and pinnae drying up and remaining attached to the plant. A distinct dark, necrotic region on the stem appears to move down the plant as the disease develops. Vascular staining is often evident when the vascular tissue of stems are exposed. It was hypothesised that this disorder is caused by a fungal pathogen or pathogen complex, offering potential for biological control of parkinsonia.

Stem samples from dieback affected plants were collected through the use of surveys, totalling 77 samples from across 5 defined climatic areas in Australia. This resulted in 159 fungal isolates representing 41 different species from 13 defined families. Eight species were represented from the Botryosphaeriaceae family and as a group of fungi were present in all of the five climatic regions sampled.

A selection of these fungal organisms were used to develop techniques to bring about successful infection of parkinsonia plants, and to determine their capability to cause disease symptoms under field conditions. Five individual field trials were established across northern Australia assessing the use of various wounding methods, inoculation formulation types and fungal species including Phoma sp., P. macrostoma, Fusarium chlamydosporum var. fuscum, F. equiseti, Lasiodiplodia pseudotheobromae, Neoscytalidium novaehollandiae and Macrophomina phaseolina. The development of inoculum formulation indicated that dry solid inoculum grown on French White millet (Panicum miliaceum) seed was the most suitable for the harsh field conditions experienced. Interactions between wounding method and plant health ratings varied across experiments, as did lesion length and interaction with inoculum treatments. This may indicate unmeasured stresses and environmental factors played a role in plant predisposition to pathogen infection and disease expression. On one site, large numbers of trial plant deaths was observed. Transects established through these inoculated plants and non-inoculated plants indicated a direct correlation between distance to nearest inoculated plant and plant health 21 months after inoculation.

Dieback movement in a naturally occurring area was studied over a period of seven years. Plant health in two 50m transects was assessed to monitor the movement of parkinsonia dieback and to establish a general base line understanding of the time taken for an adult parkinsonia tree to be killed by dieback. Individual plant health generally declined over consecutive years, with 98% of plants dying over the study period and no new seedling recruitment observed.

These studies confirmed that a range of fungi, particularly those from the Botryosphaeriaceae family are associated with parkinsonia dieback. Field inoculation trials proved some of these species are capable of causing large lesions on adult plants, and in some instances are able to cause plant mortality when formulated using a dry, solid medium. Transect studies assessing the movement of naturally occurring dieback through a stand of parkinsonia plants provide the first long term study of this phenomenon and its effect on plant health over time. This provides a significant contribution to our understanding of parkinsonia dieback and offers potential for the formulation of biocontrol agents following further investigations.
Keyword Parkinsonia
Parkinsonia aculeata
Biological control
Invasive weed

Document type: Thesis
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Created: Wed, 23 Mar 2016, 22:42:37 EST by Naomi Dove Diplock on behalf of Learning and Research Services (UQ Library)