As the Eucalyptus globulus plantation industry expands and matures in southwestern
Australia (WA), the impact of disease within the plantation environment is predicted to
increase. This thesis investigated the most abundant canker-causing pathogen
associated with branch and stem cankers, Endothiella eucalypti the anamorph of
Cryphonectria eucalypti. Endothiella eucalypti was widespread, although at low
incidence, throughout the WA plantation estate and was frequently observed
sporulating on the bark of healthy hosts in the absence of disease. Regions with a long
(approximately 20 years) plantation history, such as Bunbury, had the highest incidence
of this pathogen. A high degree of variability in pathogenicity, growth rate and colony
morphology was observed between WA isolates of En. eucalypti.
In the glasshouse, a significant variation in susceptibility of seven E. globulus
provenances to En. eucalypti was observed. Although an interaction between
the E. globulus provenance and En. eucalypti isolate was recorded, some provenances
were generally more susceptible than others. In two 18-month-old plantations, the
susceptibility of three provenances to En. eucalypti was significantly influenced by
environmental conditions. Visual assessment of general tree health indicated that less
healthy trees had smaller lesions than healthy trees. It is hypothesised that the selection
of E. globulus provenances to suit site conditions in the future should decrease the risk
of serious disease, especially on marginal sites.
Endothiella eucalypti caused disease in intact stems of two-year-old E. globulus under
glasshouse conditions. This suggests that En. eucalypti may not require a wound to
infect in the field.
Vegetative compatibility groupings between WA En. eucalypti isolates indicated a
relatively high degree of genotypic diversity within the WA asexual population of
En. eucalypti, whereas inter-simple sequence repeats PCR (ISSR-PCR) analysis
indicated a lower level of genotypic diversity. Discrepancies between traditional and
molecular techniques, such as ISSR-PCR, was attributed to the more specific gene-togene
analysis afforded by molecular techniques. ISSR-PCR successfully distinguished
variability within the En. eucalypti population and with the teleomorph, isolated in
South Africa. It also separated Cryphonectria cubensis isolates from the C. eucalypti
isolates.
As copper is the micronutrient most limiting growth of E. globulus in WA, its role in
the resistance of two E. globulus provenances was examined in a glasshouse trial.
Lesion extension or defence responses of E. globulus to En. eucalypti did not differ
between Cu-adequate and Cu-deficient plants. It is suggested that constitutive levels of
host defence enzymes played a more important role in providing protection for the host
against En. eucalypti than the external supply of copper.
A reduction in the canopy volume of E. globulus within plantations due to insect
herbivory or foliar pathogens, such as Mycosphaerella spp., has been reported to
predispose the host to disease caused by non-aggressive canker-causing fungi. Under
two separate glasshouse trials, conditions of 100% defoliation and 80% defoliation
maintained over six weeks prior to inoculation, were required to significantly increase
lesion extension caused by En. eucalypti in E. globulus stems. The ability of defoliated
E. globulus to retain a degree of resistance to En. eucalypti was attributed to the rapid
replacement of foliage and up-regulation of photosynthesis in remaining leaves. The
carbohydrate reserves of the plant were depleted following defoliation and remained
depressed regardless of the length of time the trees remained defoliated.
In conclusion, the endophytic habit of En. eucalypti poses a threat to highly stressed
trees, however it does not appear to be an immediate threat to WA plantation health.
Although En. eucalypti has not yet been responsible for a major disease outbreak in
WA, the impact of this disease on plantation-grown eucalypts elsewhere in Australia
and worldwide serves as an indication of its potential to affect WA plantations.
| Identifer | oai:union.ndltd.org:ADTP/221799 |
| Date | January 2003 |
| Creators | Tania.Jackson@dec.wa.gov.au, Tania Joy Jackson |
| Publisher | Murdoch University |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.murdoch.edu.au/goto/CopyrightNotice, Copyright Tania Joy Jackson |
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