Mycosphaerella cryptica is one of the most destructive foliar pathogens of eucalypts in plantations in southern Australia. The majority of research on this pathogen has been conducted in plantations, with little focus on its distribution and impact on eucalypts in native forest. Tuart (Eucalyptus gomphocephala) is magnificent woodland tree endemic to Western Australia. With almost 75% of its original area cleared and concerns for the health of those remaining, the recruitment of tuart is highly important. The study of pathogens and pests that pose a threat to seedling survival will contribute to ensuring the regeneration of the remaining woodlands. Mycosphaerella cryptica has been recorded on E.marginata (Jarrah), E. diversicolor (Karri) and E. patens (Blackbutt) in native forests. In the present study we carried out surveys of regenerating stands of tuart between 2003 and 2005, confirming the presence of M. cryptica throughout all stands surveyed, and in some cases contributing to mortality of seedlings. These findings are somewhat surprising given M. cryptica has not previously been recorded from tuart in native forests.
In addition to these surveys, trials were established in Yalgorup N.P. in the native forest to investigate how the presence/absence of ashbeds and competition with midstorey (mainly Agonis flexuosa) affects the survival and growth of planted seedlings. These trials were assessed seasonally over a 14 month period for phytophagous insect attack and fungal pathogen damage. Initial assessments at 12 weeks confirmed the presence of M. cryptica associated with leaf lesions (also known as Crinkle Leaf). Over the subsequent 12 month period the severity of Crinkle Leaf increased across the trial and in some cases resulted in seedling mortality. In comparison to phytophagous insect damage, at the final assessment Crinkle Leaf was by for the most dominant category of damage.
Comparisons were made between the climatic conditions, seasonal growth patterns, and severity of Crinkle Leaf at the study site and in eastern Victoria where previous studies on M. cryptica have been conducted. Seasonal periods of infection by M. cryptica differed between the two sites. We propose that this is due to optimal conditions for spread and infection of the pathogen, and growth of the seedlings occurring in winter in Yalgorup N .P. compared with summer in eastern Victoria.
Knowledge gained in this study provides important information for disease management and will benefit restoration/regeneration initiatives of this threatened species of eucalypt.
Abstract Stirlingia latifolia R. Br. is a proteaceous undershrub that is widespread in open woodlands and heathlands of the south-west botanical province of Western Australia where it is subject to frequent fires, both natural and the result of fuel-reduction burns. Shoots are completely destroyed by fire but regenerate rapidly by resprouting numerous new shoots from the root crown. Flowering is strongly triggered by fire with only sparse flowering in fire-free periods. A study was undertaken to compare regrowth and flowering in populations of S. latifolia burnt in summer or autumn with populations burnt in spring as well as in unburnt population. Post-fire flowering was recorded in 92% of plants burnt in summer/autumn compared with 73% of plants burnt in spring and less than 3% in populations that had not been burnt for more than 2 years. Plants burnt in summer/autumn resprouted an average of 8.5 shoots from their root crown, of which 93% developed an inflorescence. In contrast, spring-burnt plants averaged only 5.9 shoots per plant with only 64% of these bearing an inflorescence. Ability to produce flowers was found to be related to plant age, with young individuals producing fewer or no inflorescences following spring burns in comparison with the more prolific flowering of similarly aged individuals following summer/autumn burns. Summer/autumn-burnt plants also produced significantly longer inflorescence-bearing shoots bearing a greater numbers of flower heads than those burnt in spring. Possible explanations for these results are given in the present report.
The condition of the tuart tree (Eucalyptus gomphocephala), a coastal southwestern Australian woodland species, has declined dramatically within parts of its distribution over the last decade, particularly within Yalgorup National Park. Prior to the park being gazetted in 1968, some of the woodlands were used for cattle grazing. Frequent, light, understorey burns were carried out to encourage grass fodder growth. Earlier, Aboriginal use is believed to have involved a similar regime to facilitate hunting and access. Since gazettal, the majority of the park has either been excluded from fire, or burnt infrequently by wildfire and prescribed fire. Consequently, from 1968 to the present, most fires are thought to have been more intense due to increased fuel loads. Alterations in disturbance patterns (particularly fire) elsewhere, have been linked with vegetation changes (composition and structure) and in some instances, declining tree health. For tuart woodland, it has been proposed that increased abundance and vigour of the lower storey peppermint tree (Agonis flexuosa) and a decline in the health of tuart trees are consequences of reduced fire frequency. Sample plot data from the mid – late 1970s and photographs from 1957 are contrasted with the 2003/2004 situation to describe changes in tuart woodland. Declining tuart health, changes in the health and abundance of some understorey species (for example, fewer Banksia attenuata) and a shift towards peppermint dominance are revealed. The contribution of changing fire regimes to these trends is explored. While a link between fire and changes to the woodland may be established, factors underlying the loss of tuart dominance remain to be determined. An integrated research project is in progress to examine the range of decline factors.
Summary Management interventions are needed to reverse the decline of Tuart ( Eucalyptus gomphocephala ) woodland in the Yalgorup area of south‐west Western Australia where the largest intact remaining example of this ecosystem is located. Although the cause of the decline is uncertain and several factors may be involved, management action should not be withheld because the decline process is not fully understood. We contend that the reduction in fire frequency over the last 50 years has led to an increase in understorey density, particularly of Western Australian Peppermint ( Agonis flexuosa ), resulting in greater competition for resources, which may in turn have increased the susceptibility of healthy woodland to decline. In contrast to Tuart regeneration, which is usually tied to fire, Western Australian Peppermint can establish readily in unburnt woodland. Further, once Western Australian Peppermint seedlings develop to the lignotuberous stage, they can resprout vigorously after fire. Therefore, a combination of fire and the physical removal of understorey in sites where this species has formed extensive thickets is required to: (i) provide an opportunity for regeneration of Tuart in both healthy and declining stands; (ii) improve the chances of sustained recovery of Tuart trees in declining stands; and (iii) ensure heterogeneity in the vegetation at multiple scales, a recognized strategy for conserving biodiversity and increasing ecosystem resilience. We propose that this approach may also be relevant to other tree decline syndromes in southern Australia. However, fostering community support for active intervention using thinning and fire in conservation reserves and staging the operations within an experimental framework will be important for such action to gain both the social and scientific acceptance necessary for it to be applied widely.
Fires are features of ecological communities in much of Australia; however, very little is still known about the potential impact of fire on plant diseases in the natural environment. Phytophthora cinnamomi is an introduced soil-borne plant pathogen with a wide host range, affecting a large proportion of native plant species in Australia and other regions of the world, but its interaction with fire is poorly understood. An investigation of the effects of fire on P. cinnamomi activity was undertaken in the Stirling Range National Park of south-western Australia, where fire is used as a management tool to reduce the negative impact of wildfires and more than 60% of the park is infested with, and 48% of woody plant species are known to be susceptible to, P. cinnamomi. At eight sites confirmed to be infested with P. cinnamomi, the proportion of dead and dying susceptible species was used as a proxy for P. cinnamomi activity. Subset modelling was used to determine the interactive effects of latest fire interval, average fire interval, soil water-holding capacity and pH on P. cinnamomi activity. It was found that the latest and average fire interval were the variables that best explained the variation in the percentage of dead and dying susceptible species among sites, indicating that fire in P. cinnamomi-infested communities has the potential to increase both the severity and extent of disease in native plant communities.
Phosphite is of major importance in controlling root disease caused by Phytophthora cinnamomi. It acts both directly and indirectly on the pathogen. In order to maximise the efficacy of phosphite we need to understand how the physiological status of the plant at the time of phosphite application affects control. The physiological status of plants is not constant but varies over time depending on developmental gene expression (e.g. leaf phenology, flowering/fruiting and senescence) and interactions with the environment (e.g. temperature, moisture, light, fire, nutrients and other biota). In Mediterranean environments in particular, plants experience stresses due to extremes in water availability and the incidence of wild fire is high. Furthermore, individuals and species of plants are not in synchrony due to differences in recruitment, ontogeny, longevity and rest periods. Therefore, from a management perspective when considering all of these stresses native plant communities are subjected to, it is critical to know when to apply phosphite to ensure optimal disease control.
We examined each of the key environmental stresses (water excess, water deficit, fire and flowering) independently, on the efficacy of phosphite to control disease.
Juvenile (2–4 years old) plants of a taxonomically diverse range of dicotyledonous species were examined following recruitment from seed in recently burnt habitats in S.W. Australia. Obligate seeder species (those succumbing to fire) had on average, an almost threefold greater total plant d. wt and more than a fourfold greater shoot: root d. wt ratio than comparably-aged, cohabiting, resprouter species (those capable of surviving fire). Starch was generally much more concentrated in root dry matter of resprouters than seeders, and both categories exhibited greater starch storage capacity in roots than shoots. Members of the Myrtaccae were exceptional in not showing a greater root starch reserve in resprouter than in seeder species. and in carrying as high, or higher, starch levels in shoots as in roots. Anatomical investigations on roots provided instances of zero starch storage, storage, only in rays or in cortex, in rays and in xylem parenchyma, in rays and in cortex, or in all three locations. High starch ratings of resprouter roots related mostly to higher starch grain packing density at storage sites, but in certain instances these also reflected proportionally greater areas of tissue specifically devoted to storage. Dry matter of shoots of both seeders and resprouters generally contained higher levels of N, P, K, Ca and Mg than that of roots, but there was no significant evidence of elements being more concentrated in resprouters than in seeders.
Banksia prionotes Lindley is a fire-sensitive, fast-growing tree of nutrient-impoverished deep sands of south-western Australia. Its root system is dimorphic, comprising proteoid root-bearing, lateral roots absorbing superficially concentrated nutrients during the wet winter season and a single main sinker (tap) root extending down to the water table. Shoot extension commences in early summer coincident with drying of topsoil and ceases at the end of summer upon initiation of inflorescences and resting buds. Shoot growth utilises nutrients accumulated the previous and earlier wet seasons and current photosynthate formed at the expense of ground water abstracted by the sinker root. Rooting morphologies of differently aged trees are described and yearly changes in dry matter distribution between leaves, trunk and parts of root systems are related to dry matter gain and foliage area. The seasonality of nutrient uptake by proteoid, lateral and sinker roots and nutrient translocation in shoots is assessed by xylem and phloem sap analyses. Specific hydraulic conductivities of xylem of sinker roots are considerably higher than in lateral roots and higher again than in trunk xylem. The differences involved relate to vessel lengths and diameters and proportional transectional areas devoted to conducting tissues. Seasonal changes in dependence on ground water as opposed to recent rain are estimated using deuterium : hydrogen natural abundance ratios of water extracted from xylem of lateral roots, tap root and trunk. Relationships between water stress and timing and progress of extension growth of shoots are studied using carbon isotope natural abundance ratios of new leaf dry matter and abscisic acid levels in xylem and phloem sap.
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