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Abstract

In order to evaluate the range of stem canker fungi in natural eucalypt forest and
plantations in Tasmania, a systematic survey was conducted. A total of 210 samples
representing 30 fungal species were collected. The three species most frequently
encountered were Endothia gyrosa, Cytospora eucalypticola and Valsa ceratosperma.
Ten of the fungal species detailed in this survey were newly published and five were
reported for the first time in Australia.
Pathogenicity studies were conducted with 11 fungal species collected from the
survey. Three species (E. gyrosa, Phoma sp. and Seiridium eucalypti) could cause
significant cankers on both E. nitens and E. globulus. Influences by host species,
provenance, age, vigour and bark type on canker development are discussed.
The incidence of canker is higher in rough-barked E. nitens compared to smooth-barked
trees. Longitudinal cracking in rough bark provides natural infection courts.
However, once infected artificially, smooth-barked E. nitens is more susceptible than
rough-barked. This susceptibility is attributed to the anatomical structure of smooth
bark facilitating post-infection penetration.
A high incidence of severe E. gyrosa cankers was observed in 1993 at Tewkesbury
(northwestem Tasmania) within a vigorously growing plantation of mixed (smooth or
rough barked) provenances of 16 yr old E. nitens. This observation initiated an in-depth
investigation of E. gyrosa.
Stem inoculations with isolates of E. gyrosa originating from different locations
across Australia showed that all can infect E. nitens and E. globulus. However,
isolates from Tasmania, Victoria and Western Australia were generally more
aggressive than those from the Australian Capital Territory and New South Wales.
Endothia gyrosa isolates from Australia and overseas were compared. Four main
types of colony morphology were recognised among 133 isolates based on the colour
and density of the vegetative mycelium.
Vegetative incompatibility was detected using a pH amended medium. Sixteen
isolates from different origins in Australia, South Africa, North America and Europe
were grouped into 9 vegetative compatibility groups with this method.
There was correspondence between the grouping of these sixteen isolates as
determined by colony morphology and vegetative compatibility and those revealed by
DNA polymorphisms in RFLP and RAPD analyses. Overseas and Australian isolates
appear closely related. Within Australia isolates from as geographically distant
locations as Western Australia and Victoria were grouped together. The significance
of observed levels of intraspecific variation in E. gyrosa is discussed.
The potential threat of canker fungi, especially E. gyrosa, to the plantation forestry is
reviewed.

Item Type:	Thesis - PhD
Authors/Creators:	Yuan, Zi Qing
Keywords:	Eucalyptus
Copyright Holders:	The Author
Copyright Information:	Copyright 1998 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1998. Includes bibliographical references
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