Australian grasstrees are a long-lived group of arborescent, monocotyledonous plants that persist in fire-prone landscapes. Renowned for their capacity to survive fire, and flower soon after, these species have long attracted the attention of biologists. A southwestern Australian species, Xanthorrhoea preissii, has been the subject of several recent studies, including use and verification of the "leafbase banding technique" that prompted my study. This technique, which is used to determine the age and fire history of grasstrees, correlates alternating brown- and cream-coloured, transverse bands along the stem of grasstrees with seasonal growth, and intermittent black bands with the burning of the plant. Combined, this information provides a chronology for the fire events. Fundamental to this interpretation is the assumption that grasstrees grow continually, and this growth varies annually in accordance with changes between the two contrasting seasons of its mediterranean climate. I studied X. preissii in two habitats (jarrah forest and banksia woodland) adjacent to the Perth metropolitan area, in southwestern Australia, focussing on leaf growth and phenology in relation to four factors important to the species lifecycle; climate, fire, reproduction and herbivory. Leaf production monitored for grasstrees in both habitats revealed continuous growth, oscillating between maximum rates (2.5-3.2 leaves/d) from late-spring (November) to autumn (April/May), to a minimum rate of as low as 0.5 leaf/d during winter. In additional support of the "leafbase banding technique", annual leaf production was not different from the number of leafbases comprising one cream and one brown band. / Synchronised with leaf production, grasstree water potentials cycled annually, with predawn readings commonly measured as 0 MPa during winter-spring and were as low as -1.26 MPa during summer, but they never exceeded the turgor loss point (-1.85 to -2.18 MPa). The fast summer growth was characterised by a fluctuating pattern of leaf production, particularly in banksia woodland, where grasstrees reliably responded to >18 mm of rainfall. Twenty-four hours after 59 mm of simulated rainfall, grasstrees in banksia woodland showed a significant increase in water potential and increased leaf production by 7.5 times. Reflecting this result, rainfall was the best climatic variable for predicting banksia woodland grasstree leaf production rate during summer, whereas leaf production of jarrah forest grasstrees was most closely correlated with daylength. Substrate differences between the two habitats can explain this variation in leaf growth patterns. While water appears to have played an important role in the evolution of this species, growth phenology suggests that X. preissii may have retained a mesotherm growth rhythm from the subtropical early Tertiary Period. To distinguish fire-stimulated growth from the underlying growth patterns imposed by season, leaf production and starch reserves of X. preissii were compared between plants from unburnt sites and those burnt in spring and autumn. Immediately following fire, X. preissii responded with accelerated leaf production, regardless of season. Rapid leaf accumulation during the initial flush of growth was partly at the expense of starch reserves in the stem. Although this initial flush was relatively short-lived (12-32 weeks), the effect of fire on leaf production was sustained for much longer (up to 19 months). / Mean maximum leaf production rate was higher for spring-burnt grasstrees (up to 6.1 leaves/d) than those burnt in autumn (up to 4.5 leaves/d), due to optimum growing conditions in late spring/early summer. Similarly, the timing of autumn burns in relation to declining temperatures with the approach of winter appeared to dictate how rapidly grasstrees resprouted. These consequences of fire season may have implications for the reproductive success of X. preissii, reflected in the greater mean spike mass of spring-burnt grasstrees (1.19 kg) than those burnt in autumn (0.78 kg). Leaf and spike growth, starch reserves and the effect of restricting light to reproductive plants on spike elongation were assessed. The emergence of the spike from within the plant's apex triggers a reduction in leaf production of up to 4.6 times that of a vegetative grasstree that is sustained until seed release 4.5-5 months later. Jarrah forest grasstrees experienced the largest trade-off in leaf production (7% lower leaf production than grasstrees in banksia woodland), and produced the shortest mature inflorescences (50% of banksia woodland grasstree inflorescences), suggesting a constraint imposed by resource availability in this habitat. During the period from inflorescence elongation to seed release starch reserves were depleted. / Experimentation in the banksia woodland revealed that, although the developing spike is itself photosynthetic, it is the daily production of photosynthates by the surrounding foliage that contributes most significantly to its growth. When light was prevented from reaching the leaves the starch stored within the stem was not a sufficient substitute, evidenced by a significant reduction in spike biomass of 41%. A fire simulation experiment with a factorial design was used to assess three factors considered important for postfire grasstree leaf growth in banksia woodland: water, ash and shade. While results identified that ash and reduced shade significantly affect leaf growth, their effects were small compared with the stimulation derived solely from leaf removal by fire, simulated in this experiment by clipping. Clipping, also used to simulate herbivory, was imposed on a series of grasstrees at different frequencies. X. preissii demonstrated a strong capacity to recover in both jarrah forest and banksia woodland, even after clipping every month for 16 months. Starch reserves were depleted as the result of clipping, providing a cause of the eventual deterioration of grasstree 'health' associated with chronic herbivory. The similarity of growth responses to leaf removal independent of the mechanism (eg. fire or herbivory), provided reason to question the interpretation that grasstrees are essentially adapted to fire, rather than the alternative, that they are adapted to herbivory.

One of the major aims of the research presented in this thesis was to assist managers of native vegetation communities in southeastern Australia in understanding the dynamics of P. cinnamomi with an important ecological species, Xanthorrhoea australis. It trialed the use of phosphite in large-scale field applications to establish the usefulness of this management option for the first time on Victorian flora. This thesis describes the process of disease development within mature X. Australia plants. For the first time it was shown that within X. australis plants, secondary disease symptoms are related to the percentage of stem that has been infested by the disease. It was evident that after initial invasion the pathogen moves via root xylem and throughout the plant within vascular to the stem, especially within the desmium. The research shows that the pathogen could not be isolated consistently even though it was considered to be responsible for disease symptoms. Trials of a control fungicide (Foli-R-fos 200) shows that protection occurs in many susceptible plants when 2 and 6g a.i./L phosphite is applied. Phytotoxicity occurred in native plants at Anglesea and within controlled environment trials when using ≥ 6g a.i./L. It will be shown that 2g a.i./L phosphite controls disease in sprayed plots within heathlands at Anglesea and a recently burnt coastal woodland community at Wilson’s Promontory. The proportion of healthy X. australis plants treated with phosphite was significantly higher than the proportion in control plots without phosphite. The research shows that phosphite was recovered from leaves of three species treated with Foli-R-fos 200 in the field. For the first time it has been shown that seed germination was reduced in two species when high concentrations of phosphite were applied. The first documentation of the effect that phosphite has on soil properties showed that nitrogen and oxidised organic carbon were the only parameters to alter significantly. This thesis provides answers to some important questions, answers that can now be used by managers in formulating better policies and actions at an operational level. There has been a dire need in Victoria to address many issues regarding P. cinnamomi and this thesis provides relevant and informative approaches to disease control, and a better understanding of the disease progress.

Diseases in natural ecosystems are often assumed to be less severe than those observed in domestic cropping systems due to the extensive biodiversity exhibited in wild vegetation communities. In Australia, it is this natural biodiversity that is now under threat from Phytophthora cinnamomi. The soilborne Oomycete causes severe decline of native vegetation communities in south-western Victoria, Australia, disrupting the ecological balance of native forest and heathland communities. While the effect of disease caused by P. cinnamomi on native vegetation communities in Victoria has been extensively investigated, little work has focused on the Anglesea healthlands in south-western Victoria. Nothing is known about the population structure of P. cinnamomi at Anglesea. This project was divided into two main components to investigate fundamental issues affecting the management of P. cinnamomi in the Anglesea heathlands. The first component examined the phenotypic characteristics of P. cinnamomi isolates sampled from the population at Anglesea, and compared these with isolates from other regions in Victoria, and also from Western Australia. The second component of the project investigated the effect of the fungicide phosphonate on the host response following infection by P. cinnamomi. Following soil sampling in the Anglesea heathlands, a collection of P, cinnamomi isolates was established. Morphological and physiological traits of each isolate were examined. All isolates were found to be of the A2 mating type. Variation was demonstrated among isolates in the following characteristics: radial growth rate on various nutrient media, sporangial production, and sporangial dimensions. Oogonial dimensions did not differ significantly between isolates. Morphological and physiological variation was rarely dependant on isolate origin. To examine the genetic diversity among isolates and to determine whether phenotypic variation observed was genetically based, Random Amplified Polymorphic DNA (RAPD) analyses were conducted. No significant variation was observed among isolates based on an analysis of molecular variance (AMQVA). The results are discussed in relation to population biology, and the effect of genetic variation on population structure and population dynamics. X australis, an arborescent monocotyledon indigenous to Australia, is highly susceptible to infection by P. cinnamomi. It forms an important component of the heathland vegetation community, providing habitat for native flora and fauna, A cell suspension culture system was developed to investigate the effect of the fungicide phosphonate on the host-pathogen interaction between X. australis and P. cinnamomi. This allowed the interaction between the host and the pathogen to be examined at a cellular level. Subsequently, histological studies using X. australis seedlings were undertaken to support the cellular study. Observations in the cell culture system correlated well with those in the plant. The anatomical structure of X australis roots was examined to assist in the interpretation of results of histopathological studies. The infection of single cells and roots of X. australis, and the effect of phosphonate on the interaction are described. Phosphonate application prior to inoculation with P. cinnamomi reduced the infection of cells in culture and of cells in planta. In particular, phosphonate was found to stimulate the production of phenolic material in roots of X australis seedlings and in cells in suspension cultures. In phosphonate-treated roots of X australis seedlings, the deposition of electron dense material, possibly lignin or cellulose, was observed following infection with P. cinnamomi. It is proposed that this is a significant consequence of the stimulation of plant defence pathways by the fungicide. Results of the study are discussed in terms of the implications of the findings on management of the Anglesea heathlands in Victoria, taking into account variation in pathogen morphology, pathogenicity and genotype. The mode of action of phosphonate in the plant is discussed in relation to plant physiology and biochemistry.