Phytophthora cinnamomi invasion, a major threatening process to conservation of flora diversity in the South-west Botanical Province of Western Australia

The invasive soilborne plant pathogen Phytophthora cinnamomi Rands is a major threatening process in the South-west Botanical Province of Western Australia, an internationally recognised biodiversity hotspot. Comparatively recent introduction of P. cinnamomi into native plant communities of the South-west Botanical Province of Western Australia since the early 1900s has caused great irreversible damage and altered successional change to a wide range of unique, diverse and mainly susceptible plant communities. The cost of P. cinnamomi infestation to community values is illustrated by examination of direct (mortality curves, changes in vegetation cover) and indirect impacts on biodiversity and ecosystem dynamics, the proportion of Threatened Ecological Communities infested, Declared Rare Flora either directly or indirectly threatened by infestation and estimates of the proportion of the native flora of the South-west Botanical Province susceptible to the pathogen. While direct impacts of P. cinnamomi have been poorly documented in the South-west Botanical Province, even less attention has been given to indirect impact where destruction of the habitat by the pathogen affects taxa not directly affected by infection. Current poor understanding and quantification of indirect impacts of P. cinnamomi through habitat destruction results in an underestimation of the true impact of the pathogen on the flora of the South-west Botanical Province. Considerable variation of susceptibility to P. cinnamomi among and within families of threatened flora and responses of taxa within the genus Lambertia show how classification within family and genus are poor predictors of species susceptibility. Within apparently susceptible plant species, individuals are resistant to P. cinnamomi infection. Intra-specific variation in susceptibility can be utilised in the long-term management of threatened flora populations and needs to be a high research priority. Current control strategies for conservation of flora threatened by P. cinnamomi integrate hygiene and ex situ conservation with disease control using fungicide. Application of the fungicide phosphite has proven effective in slowing progress of P. cinnamomi in infested, threatened communities. However, variation in plant species responses to phosphite application is a major factor influencing effective control of P. cinnamomi in native communities. A greater understanding of the mechanisms of action of phosphite in plant species showing different responses to the fungicide may provide options for prescription modification to increase phosphite effectiveness in a range of plant species. The range of responses to P. cinnamomi infection and phosphite application described for Lambertia taxa suggests that the genus would make an ideal model system to elucidate the mechanisms of resistance to P. cinnamomi and the effectiveness of phosphite against the pathogen.

[1]  P. Gioia,et al.  The Southwest Australian Floristic Region: Evolution and Conservation of a Global Hot Spot of Biodiversity , 2004 .

[2]  J. A. Harris,et al.  Variations in mortality in families of Eucalyptus regnans caused by Phytophthora cinnamomi, up to 5 years after planting [fungus] , 1985 .

[3]  J. Cho.  Variability in susceptibility of some Banksia species to Phytophthora cinnamomi and their distribution in Australia , 1983 .

[4]  B. Shearer,et al.  Corrigendum - Susceptibility of Plant Species in Banksia Woodlands on the Swan Coastal Plain, Western Australia, to Infection by Phytophthora cinnamomi , 1996 .

[5]  D. Sheil,et al.  Assessing forest canopies and understorey illumination: canopy closure, canopy cover and other measures , 1999 .

[6]  D. Richardson,et al.  Novel ecosystems: theoretical and management aspects of the new ecological world order , 2006 .

[7]  D. Guest,et al.  The risk of extinction resulting from disease caused by Phytophthora cinnamomi to endangered, vulnerable or rare plant species endemic to the Grampians, Western Victoria , 2004 .

[8]  J. McGrath,et al.  Site and Seasonal Effects on Susceptibility of Eucalyptus marginata to Phytophthora cinnamomi , 1989 .

[9]  B. Grant,et al.  THE COMPLEX ACTION OF PHOSPHONATES AS ANTIFUNGAL AGENTS , 1991 .

[10]  M. Dudzinski,et al.  Pathogenic Variability in Australian Isolates of Phytophthora cinnamomi , 1993 .

[11]  D. Coates,et al.  The translocation of two critically endangered Acacia species , 2002 .

[12]  G. Hardy,et al.  The potential of five Western Australian native Acacia species for biological control of Phytophthora cinnamomi , 2004 .

[13]  P. Vitousek,et al.  INTRODUCED SPECIES: A SIGNIFICANT COMPONENT OF HUMAN-CAUSED GLOBAL CHANGE , 1997 .

[14]  R. Hobbs,et al.  Vegetation of Phytophthora cinnamomi-infested and adjoining uninfested sites in the northern jarrah (Eucalyptus marginata) forest of Western Australia , 2002 .

[15]  Daniel Simberloff,et al.  Introduced species policy, management, and future research needs , 2005 .

[16]  M. Stukely,et al.  Genetic variation in resistance of Pinus radiata to Phytophthora cinnamomi , 1984 .

[17]  Neville Nicholls,et al.  Shifts in the synoptic systems influencing southwest Western Australia , 2006 .

[18]  B. Shearer,et al.  Sporulation of Septoria Species on Wheat and Barley in Minnesota , 1980 .

[19]  B. Dell,et al.  The long-term ability of phosphite to control Phytophthora cinnamomi in two native plant communities of Western Australia , 2001 .

[20]  T. Wardlaw,et al.  Susceptibility of Selected Tasmanian Rare Plants to Phytophthora cinnamomi , 1995 .

[21]  D. Mabberley,et al.  Ferdinand Bauer’s field drawings of endemic Western Australian plants made at King George Sound and Lucky Bay, December 1801 – January 1802. I , 2000 .

[22]  M. Stukely,et al.  Genetically based resistance of Eucalyptus marginata to Phytophthora cinnamomi , 1994 .

[23]  J. Zadoks,et al.  Epidemiology and plant disease management , 1979 .

[24]  B. Shearer,et al.  Three Clonal Lineages of Phytophthora cinnamomi in Australia Revealed by Microsatellites. , 2003, Phytopathology.

[25]  F. Podger.  Comparative Pathogenicity of Fourteen Australian Isolates of Phytophthora cinnamomi Determined on Transplants of Tasmanian Temperate Heathland , 1989 .

[26]  B. Shearer,et al.  Resistance of Eucalyptus spp. to Invasion by Phytophthora cinnamomi , 1985 .

[27]  D. Coates.  Defining conservation units in a rich and fragmented flora: implications for the management of genetic resources and evolutionary processes in south-west Australian plants , 2000 .

[28]  R. Mittermeier,et al.  Biodiversity hotspots for conservation priorities , 2000, Nature.

[29]  P. Taylor,et al.  The invasion of native forest by Phytophthora cinnamomi. I. Brisbane Ranges, Victoria. , 1971 .

[30]  J. J. Havel.  Site vegetation mapping in the northern Jarrah forest (Darling Range). 2. location and mapping of site vegetation types , 1975 .

[31]  G. Newell.  Characterization of vegetation in an Australian open forest community affected by cinnamon fungus (shape Phytophthora cinnamomi): implications for faunal habitat quality , 1998, Plant Ecology.

[32]  B. L. Shearer,et al.  Effective concentration of phosphite in controlling Phytophthora cinnamomi following stem injection of Banksia species and Eucalyptus marginata , 2006 .

[33]  B. Shearer,et al.  Susceptibility of Plant Species in Eucalyptus marginata Forest to Infection by Phytophthora cinnamomi , 1995 .

[34]  J. McGuire,et al.  Efficacy of two new systemic fungicides and ethazole for control of Phytophthora root rot of rhododendron, and spread of Phytophthora cinnamomi in propagation benches. , 1980 .

[35]  R. Hobbs,et al.  Distribution of understorey species in forest affected by Phytophthora cinnamomi in south-western Western Australia , 2005 .

[36]  E. Davison,et al.  PHYTOPHTHORA SPP. IN INDIGENOUS FORESTS IN AUSTRALIA , 1989 .

[37]  G. Weste,et al.  Vegetation changes associated with invasion by Phytophthora cinnamomi on monitored sites in the Grampians, Western Australia , 1986 .

[38]  D. Cooke,et al.  The Invasion of Native Forest by Phytophthora cinnamomi. II. Post-Infection Vegetation Patterns, Regeneration, Decline in Inoculum and Attempted Control , 1973 .

[39]  B. Shearer,et al.  Invasion of Bassendean Dune Banksia Woodland by Phytophthora cinnamomi , 1994 .

[40]  G. Weste.  Vegetation Changes Associated With Invasion by Phytophthora cinnamomi of Defined Plots in the Brisbane Ranges, Victoria, 1975-1985 , 1986 .

[41]  B. Shearer,et al.  Impact and Disease Centre Characteristics of Phytophthora cinnamomi Infestations of Banksia Woodlands on the Swan Coastal Plain, Western Australia , 1996 .

[42]  K. Dixon,et al.  Variability in the Resistance of Banksia L.f. Species to Phytophthora cinnamomi Rands , 1985 .

[43]  R. Wills.  The ecological impact of Phytophthora cinnamomi in the stirling range national park, Western Australia , 1993 .

[44]  G. Weste,et al.  Regeneration of Susceptible Native Species Following a Decline of Phytophthora cinnamomi over a Period of 20 Years on Defined Plots in the Grampians, Western Victoria , 1997 .

[45]  Doeh.  Environment Protection and Biodiversity Conservation Act 1999 , 2005 .

[46]  B. Shearer,et al.  Variation in seasonal population fluctuations of Phytophthora cinnamomi within and between infected Eucalyptus marginata sites of southwestern Australia , 1987 .

[47]  C. Crane,et al.  Quantification of the susceptibility of the native flora of the South-West Botanical Province, Western Australia, to Phytophthora cinnamomi , 2004 .

[48]  B. Shearer,et al.  Diseases of Banksia woodlands on the Bassendean and Spearwood dune systems , 1989 .

[49]  P. Somerford,et al.  Effects of isolate and time of inoculation on invasion of secondary phloem of Eucalyptus spp. and Banksia grandis by Phytophthora spp. , 1988 .