Climate, soils, topography and susceptible plant communities, in combination with the movement of infested soil by human activity, has resulted in Phytophthora cinnamomi becoming the most destructive plant pathogen in native plant communities in the south coast region of Western Australia. Centres of disease activity occur near Albany and in the Stirling Range and Cape le Grand National Parks. Incidence generally decreases in a north-easterly direction in association with drier climatic conditions. P. cinnamomi causes death of susceptible species, in particular members of the Proteaeceae, Epacridaceae, Papilionaceae and Myrtaceae, and results in changes in community structure and species composition. Two-thirds of the Stirling Range National Park, notable for its 1,530 plant taxa and high numbers of rare and endemic species, is infested. Sixteen of these species are threatened with extinction by P. cinnamomi, eight are critically endangered. The Montane Heath and Thicket Community of the eastern Stirling Range is also critically endangered. The Fitzgerald River National Park with 1748 plant taxa is largely disease-free although a sizeable infestation occurs in the core of the Park. Appropriate management of areas with high conservation values infested by P. cinnamomi as well as the protection of those areas currently disease-free, remains an ongoing challenge.
THE DIEBACK CYCLE IN VICTORIAN FORESTS: A 30 YEAR STUDY OF THE CHANGES CAUSED BY PHYTOPHTHORA CINNAMOMI IN VICTORIAN OPEN FORESTS, MEASURED PERIODICALLY ON DEFINED QUADRATS
Changes in both vegetation and in pathogen population and distribution were monitored periodically on defined infested quadrats and on similar pathogen-free quadrats on 13 sites representing major types of forest and woodland between 1970 and 2000. The susceptible eucalypts in the overstorey of infested sites showed severe dieback, loss of crown and deaths. All trees died on some sites, others presented dead leaders with epicormic growth on lower branches. Dieback of the understorey, followed by death occurred in 50-75 % of the species in the heathy understorey, including the dominant Xanthorrhoea australis, thereby changing the community and the species composition. Species richness in infested quadrats declined, and percentage cover and percentage contribution to the community by susceptible species were almost eliminated. On steep slopes, the ground remained bare, but on other sites the susceptible flora was replaced by field resistant species of sedges and rushes, and by the partly resistant teatrees, Leptospermum spp., which formed a dense cover.
The pathogen was isolated from 100% of the root samples from infested quadrats from 1970 to 1984, but then gradually declined. In 2000, P. cinnamomi was rare on some sites and not isolated from four. Regeneration of 30 to 40 susceptible species, previously eliminated, was recorded from infested sites, and two thirds of these were growing on more than one quadrat. Copius regeneration of the previously dominant but highly susceptible X. australis occurred on four sites. Significant recovery and recruitment of the overstorey has not been observed. It is not yet clear whether the regeneration of the understorey is stable, or whether successive cycles of disease and recovery will occur.
IMPACT OF PHYTOPHTHORA CINNAMOMI ON MAMMALS IN SOUTHERN AUSTRALIA
The plant pathogen Phytophthora cinnamomi (cinnamon fungus) has a major effect on vegetation floristics and structure in sclerophyll vegetation in Australia. Effects include loss of plant species, decline in vegetation cover, increases in bare ground and the abundance of resistant plant species. These changes would be predicted to have effects on faunal communities inhabiting infected habitats. Analyses in heathlands and woodlands of south-eastern Australia have identified P. cinnamomi infection as being associated with low species richness, and low abundance of small mammals. Studies of Antechinus stuartii (Brown Antechinus) in woodlands found that there were lower capture rates in infected areas, and habitat utilisation was altered. The major contributing factor was alterations to vegetation structure, rather than food availability. In heathlands, species such as Rattus lutreolus (Swamp Rat), Rattus fuscipes (Bush Rat), Antechinus agilis (Agile Antechinus) and Sminthopsis leucopus (White-footed Dunnart) were found to be less abundant in diseased areas, or utilised them less frequently. An analysis of mammals that occur in Victoria found that for twenty-two species, five of which are rare or endangered, more than 20% of their range coincides with the reported distribution of P. cinnamomi.
THE IMPACT OF PHYTOPHTHORA CINNAMOMI ON THE FLORA AND VEGETATION OF NEW SOUTH WALES: A RE-APPRAISAL
Although Phytophthora cinnamomi is widely regarded as having a significant impact on native vegetation in many parts of southern Australia, the pathogen has been considered benign and possibly endemic in New South Wales. The evidence for the different behaviour in NSW has included that 1) P. cinnamomi is extremely widespread and easy to detect in soils, 2) generally susceptible genera such as Banksia are unaffected when it is present (suggesting a long host/pathogen interaction), 3) multiple plant deaths associated with P. cinnamomi are extremely rare and 4) P. cinnamomi has been recovered in remote areas (suggesting that it is endemic). Recent surveys of National Parks in eastern NSW have found that although P. cinnamomi is widespread it cannot be detected in some areas despite extensive soil sampling. Although most Banksia spp. seem to be relatively resistant to symptoms of infection, other taxa (especially some Xanthorrhoea spp.) are very susceptible. The loss of Xanthorrhoea cover may adversely affect threatened animals such as the Smoky Mouse and Southern Brown Bandicoot, which use the plants for cover and nesting. Glasshouse susceptibility trials have shown that a number of rare taxa are very susceptible to infection. The NSW floral emblem, Telopea speciosissima, is also susceptible. P. cinnamomi may be widespread in NSW, however it is doubtful that it is endemic and is certainly not always benign.
HOW SUSCEPTIBLE IS THE FLORA OF SOUTH-WESTERN AUSTRALIA TO PHYTOPHTHORA CINNAMONI?
Despite the high impact of Phytophthora cinnamomi infection on the flora of south-western Australia, the susceptibility of the component plant species to infection is poorly understood. From an assessment of the impact of P. cinnamomi in the plant communities of the Stirling range National Park, Wills (3) concluded that the proportion of the plant species susceptible to the pathogen was 36-43%. Susceptibility databases from Eucalyptus marginata forest (1), Banksia woodland (2) and threatened and rare flora (Shearer, Crane and Cochrane unpublished) will be used to analyse and compare estimates of the susceptibility of south-western flora to P. cinnamomi.
1. Shearer B.L., Dillon M. (1995) Susceetibility of plant species in Eucalyptus marginata forest to infection by Phytophthora cinnamomi. Australian Journal of Botany 43, 113-134.
The fungicide phosphite has been used in recent years to protect native plant species and communities threatened by Phytophthora cinnamomi. Native plant species may vary considerably in their uptake of phosphite and in their sensitivity to phosphite as expressed by phytotoxicity. In planta phosphite concentrations of nine species five weeks after low volume phosphite application at 36, 72 and 144 kg ha-1 showed a significant correlation with phytotoxicity symptoms. In planta phosphite concentrations varied significantly between species and application rates. Growth abnormalities and chlorosis after low-volume phosphite application at rates ranging from 24 to 144 kg ha-1 were observed from five months post-spray in 32 and 36 of the 207 species assessed, respectively.
Shoot growth, root and shoot dry weight and root length in Corymbia calophylla and Banksia brownii were not significantly reduced by low-volume phosphite application at rates of 24, 48 and 96 kg ha-1 in a glasshouse study. Percentage vesicular-arbuscular (VAM) and ectomycorrhizal colonisation and total VAM and ectomycorrhizal root lengths were not significantly different in treated and control plants of C. calophylla four months after phosphite application. Low volume phosphite application at 24 kg ha-1 appears to be an appropriate rate for native vegetation in terms of effects on root development. Selection of appropriate aerial phosphite application rates for native plant communities must ensure a balance between achieving adequate phosphite concentrations for disease control while minimising phytotoxicity symptoms in the range of species present.
PHOSPHITE CONTROLS PHYTOPHTHORA CINNAMOMI AT ANGLESEA AND WILSON'S PROMONTORY NATIONAL PARK, VICTORIA
The use of phosphite at concentrations of 2 and 4g a.i./L proved to be successful in controlling the spread of Phytophthora cinnamomi within different vegetation communities at Anglesea (Alcoa lease area) and Tidal River (Wilson?s Promontory National Park). At nine sites, phosphite was sprayed to runoff with a SoloÒ 422 motorised backpack sprayer with 2L/25m2 quadrat. Using aerial and ground photography, quadrats were monitored over a two-year period to determine changes in species abundance due to the pathogen. There was a significant difference (p<0.05) between the proportions of healthy Xanthorrhoea australis in phosphite sprayed quadrats (2 and 4g a.i./L with 0.5% surfactant) compared to those sprayed with a control (water and 0.5% surfactant, water only). Vegetation in quadrats where P. cinnamomi was present was protected by phosphite for 2 years (4g a.i./L) and 12 months (2g a.i./L). However, vegetation in quadrats where the pathogen was present died where phosphite was not sprayed. Phosphite provided protection for X. australis, Isopogon ceratophyllus and Monotoca scoparia (3 species highly susceptible to P. cinnamomi). From the results of this research we recommend the use of phosphite in susceptible vegetation communities with 4g a.i./L phosphite to assist with already existing management strategies for the protection of Victorian heathlands and forests from P. cinnamomi.
Operational phosphite applications in autumn 1997 were monitored at the Bell Track in the Fitzgerald River National Park and on Bluff Knoll in the critically endangered Eastern Stirling Range Montane community. The Montane community, which is extensively infested by Phytophtora cinnamomi, is notable for 11 Threatened plant taxa, four of which are critically endangered. Aerial phosphite application at 24 kg a.i. ha-1 resulted in significantly higher percentage survival of Phytophthora-susceptible species in sprayed compared with non-sprayed quadrats on a dieback front at the Bell Track for up to two years post-spray. Similar observations were made at Bluff Knoll after phosphite application to uniformly infested vegetation. Sphenotoma sp. Stirling Range sampled from Bluff Knoll had considerably higher phosphite concentrations at two weeks and five months post-spray than Lambertia inermis sampled from the Bell Track. Phytotoxicity symptoms in terms of foliar necrosis and defoliation post-spray were generally mild although selected species showed greater sensitivity. Growth abnormalities were observed in a small percentage of species assessed at the Bell Track site. Concerns regarding potential phytotoxic effects of phosphite on plant health must be balanced by the threat posed to the survival of critically endangered species and plant communities by Phytophthora cinnamomi.
Research into the trunk injection of phosphite, a buffered solution of phosphorous acid (H3PO3), to protect native plants against Phytophthora cinnamomi disease was first carried out in Western Australia in the late 1980's. Initial aerial application trails took place near Albany in autumn 1993 at one fifth of the present standard application rate because of concerns about possible phytotoxicity. The current standard rate for aerially applied phosphite is 24 kg/ha-1 of 400g/kg-1 formulation together with a surfactant or wetting agent at 0.3% (v/v). Symptoms of phytotoxicity at these rates are minor. Generally, the chemical is applied as two treatments in autumn, about one month apart. The first broadscale aerial application of phosphite took place in 1997, since then about 640 ha of native vegetation at more than 50 sites has been treated, mostly to protect endangered flora. Several sites near Albany received their third application this year. Spraying is normally done in autumn to take advantage of calm, clear weather in the Stirling Ranges where most aerial application takes place. Recent research has indicated, for some species at least, that autumn application may lead to greater foliar uptake of phosphite. Monitoring indicates that aerial phosphite treatments will need to take place at least every two years and in some cases, where only a few wild plants are left, annual applications may be needed. The area of most urgent research need is the interaction between phosphite, wildfire and regeneration of rare flora to determine optimum application rates and frequency.
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