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The ecology of insect pests and fungal pathogens of drought stressed eucalypt plantations in southern Queensland

Whyte, Gilbert (2012) The ecology of insect pests and fungal pathogens of drought stressed eucalypt plantations in southern Queensland. PhD thesis, Murdoch University.

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The eucalypt plantation industry is rapidly expanding to supply an increasing demand for wood both in Australia and other parts of the world. Despite rapid industry development, most eucalypt plantations are restricted to four coastal areas. These include the southwest corner of Western Australia, eastern New South Wales, the ‘Green Triangle’ (western Victoria and eastern South Australia) and Tasmania. Eucalypt plantations are traditionally grown in these areas because they have favourable climatic conditions which allow high productivity. Eucalyptus globulus is a fast growing eucalypt species and is currently the most widely planted species in Australia (55.3% of all eucalypt plantations).

More recently, plantations have been grown in other parts of Australia which are less suited to E. globulus. The eucalypt plantation industry in southern Queensland is in its infancy and has received less attention from researchers compared with Australia’s main plantation centres. Species selection has been a major focus and E. dunnii is quickly emerging as one of the most widely planted species. Most of the biological research of Eucalyptus dunnii has been carried out in plantations in Brazil and South Africa where the species is an important source of pulp for paper production. The suitability of E. dunnii in Australian plantations is still being explored and little is currently known about its susceptibility to pests, pathogens or climatic extremes.

This is the first comprehensive study of E. dunnii plantations in southern Queensland. Unlike most research in plantations which examines the impacts of insect pests and fungal pathogens as separate areas of research, this study focuses on both groups simultaneously. Understanding the ecology of pests and pathogens is an important aspect of plantation management and is essential to the development of the plantation industry in southern Queensland.

A large diversity of pests and pathogens were identified from E. dunnii plantations during the study. Impacts by insects were generally more severe than pathogens although most pests and pathogens were found to cause low levels of damage. Severe impacts were caused by chrysomelid beetles such as Paropsisterna cloelia which was the most destructive chrysomelid species. Differences in the abundances of chrysomelid damage were observed in different aged plantations and between plantations occurring in different regions of southern Queensland.

Several genera of pathogenic fungi were identified and the most abundant species belonged to the genera Mycosphaerella and Teratosphaeria. The most damaging of these species was Mycosphaerella heimii, which was previously unknown in Australia. Canker pathogens such as Holocryphia eucalypti, Neofusicoccum ribis and Cytospora eucalypticola were also common in younger plantations (aged 1-2 years). H. eucalypti was identified as the causal pathogen of ‘sudden death syndrome’ and was the only pathogen observed to be capable of killing its host.

Three new species of foliar fungal pathogens were identified belonging to the genus, Teratosphaeria. These species were associated with drought stressed hosts and are likely to represent a small fraction of a potentially larger assemblage of undescribed species awaiting discovery in southern Queensland.

It was expected that the subtropical climate in southern Queensland would be conducive to a large diversity of pests and pathogens. Despite these expectations, widespread drought in eastern Australia (2003-2007) created atypical conditions within the region which had adverse effects on many species. Drought effects may have benefited some insects, such as those which feed on new foliage produced by stressed trees; however, most foliar pathogens appeared to be adversely affected. Some canker

pathogens appeared to exploit stressed trees and thirteen weak opportunistic pathogens were identified from stem cankers and necrotic stem tissues. Some saprophytic fungi may have benefited from greater availability of dead tissue due to a higher incidence of wilting and premature leaf loss.

Although drought effects may have overshadowed the effects of pests and pathogens, the resulting conditions provided valuable insight into the ecology of drought stress in plantations. A conceptual model called the ‘Recovery-Decline Seesaw’ has been developed to illustrate the complex interactions of drought stressed trees and their associated pests and pathogens. The study also contributes valuable information which aims to facilitate development of the southern Queensland plantation industry.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): Burgess, Treena and Hardy, Giles
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