Botanical Province Of Western Australia Research Articles

Viral Diversity of Microbats within the South West Botanical Province of Western Australia.

Bats are known reservoirs of a wide variety of viruses that rarely result in overt clinical disease in the bat host. However, anthropogenic influences on the landscape and climate can change species assemblages and interactions, as well as undermine host-resilience. The cumulative result is a disturbance of bat–pathogen dynamics, which facilitate spillover events to sympatric species, and may threaten bat communities already facing synergistic stressors through ecological change. Therefore, characterisation of viral pathogens in bat communities provides important basal information to monitor and predict the emergence of diseases relevant to conservation and public health. This study used targeted molecular techniques, serological assays and next generation sequencing to characterise adenoviruses, coronaviruses and paramyxoviruses from 11 species of insectivorous bats within the South West Botanical Province of Western Australia. Phylogenetic analysis indicated complex ecological interactions including virus–host associations, cross-species infections, and multiple viral strains circulating concurrently within selected bat populations. Additionally, we describe the entire coding sequences for five alphacoronaviruses (representing four putative new species), and one novel adenovirus. Results indicate that viral burden (both prevalence and richness) is not homogeneous among species, with Chalinolobus gouldii identified as a key epidemiological element within the studied communities.

Insights into Australian Bat Lyssavirus in Insectivorous Bats of Western Australia.

Australian bat lyssavirus (ABLV) is a known causative agent of neurological disease in bats, humans and horses. It has been isolated from four species of pteropid bats and a single microbat species (Saccolaimus flaviventris). To date, ABLV surveillance has primarily been passive, with active surveillance concentrating on eastern and northern Australian bat populations. As a result, there is scant regional ABLV information for large areas of the country. To better inform the local public health risks associated with human-bat interactions, this study describes the lyssavirus prevalence in microbat communities in the South West Botanical Province of Western Australia. We used targeted real-time PCR assays to detect viral RNA shedding in 839 oral swabs representing 12 species of microbats, which were sampled over two consecutive summers spanning 2016–2018. Additionally, we tested 649 serum samples via Luminex® assay for reactivity to lyssavirus antigens. Active lyssavirus infection was not detected in any of the samples. Lyssavirus antibodies were detected in 19 individuals across six species, with a crude prevalence of 2.9% (95% CI: 1.8–4.5%) over the two years. In addition, we present the first records of lyssavirus exposure in two Nyctophilus species, and Falsistrellus mackenziei.

Host range of the stem canker pathogen Luteocirrhus shearii mainly limited to Banksia

Isolations from diseased plants and controlled inoculations indicate that the host range of the canker pathogen Luteocirrhus shearii is mainly limited to Banksia. Branches exhibiting canker symptoms were sampled from the Geraldton Sandplains, Swan Coastal Plain, Jarrah Forest, Warren and Esperance Sandplains bioregions of the South-West Botanical Province of Western Australia (n = 1,351). Luteocirrhus shearii was isolated from only Proteaceae and did not infect wound inoculated Myrtaceae. The pathogen was isolated from or formed extensive lesions in 15 Banksia species. Differences in isolation frequency and rates of lesion extension of L. shearii between Banksia spp. may indicate different modes of infection by the canker pathogen. By exerting top-down control of population dynamics of Banksia communities from lower trophic levels, L. shearii would substantially alter host species diversity and in turn ecosystem processes. Predicted climate change could influence future biotic reorganisations following L. shearii invasion. What determines the limited host range of L. shearii compared to the community of organisms on Banksia needs to be determined.

Variation in susceptibility of threatened flora to Phytophthora cinnamomi

Determination of susceptibility to Phytophthora cinnamomi affirms the exceptional broad host range of the pathogen and diversity of host–pathogen interactions in the native flora of the South-West Botanical Province of Western Australia. Positioning taxa on the P. cinnamomi resistance-susceptibility continuum prioritises taxa in relation to the threat posed by the pathogen. Variation in susceptibility of 501 Western Australian plant taxa to P. cinnamomi infection was evaluated after soil inoculation. Disease progress curves following soil inoculation were analysed with the three logistic model parameters of upper asymptote (Kmax), lag time (t½K) and intrinsic rate of increase (r). The susceptibility continuum represented by the ordination of parameters of the logistic model for % plant mortality in two dimensions was similar for threatened, priority and common taxa. Variation in parameters of the logistic model decreased with susceptibility. Although resistant taxa had low Kmax, the values for delay and rate varied. In comparison, susceptible taxa tended to have high Kmax short delay and fast rate. Most of the taxa in Fabaceae, Malvaceae, Myrtaceae and Poaceae tested were resistant to P. cinnamomi. A few taxa in Fabaceae and Myrtaceae (18 and 10 %, respectively) were susceptible to the pathogen. Casuarinaceae were mainly resistant, but showed a range of responses to P. cinnamomi. Ericaceae were mainly susceptible. Proteaceae showed a broad range of responses from resistant to susceptible. Significantly greater resistance of sprouters than seeders and the significant negative relationship between mortality and leaf phenolics, may be examples of resistance mechanisms through fortuitous side effects of ecological fitting of functional traits that evolved in response to different sets of biotic and abiotic conditions that occurred before the introduction of P. cinnamomi. Identification of resistant individuals in threatened taxa would ensure survival of taxa and conservation of genetic diversity.

Phytophthora cinnamomi visible necrotic lesion-colonisation relationships in native flora

Relationships were examined between visible necrotic lesion and colonisation following stem wound inoculated of native plant species of the South-West Botanical Province of Western Australia with Phytophthora cinnamomi. Relationships were determined over a wide range of biotic and abiotic environments of plant taxa, host susceptibility, isolate, phosphite fungicide spray, native community and glasshouse environments, seasons and soil types. Consistent significant relationships were found between necrotic lesions and colonisation over the different environments. Visible necrotic lesions were either in-phase with or greater than colonisation in 55 % of the environments analysed. ANCOVA interactions of total visible necrotic lesion with treatments were not significant for 10 out of 14 interactions, indicating homogeneity of slopes in the majority of cases. Rather than having distinct hemibiotrophic stages, P. cinnamomi switches between necrotic lesions and colonisation of symptomless tissue depending on environmental conditions. Average necrotic lesion/taxa in stems following wound inoculation was significantly positively correlated with mortality following soil inoculation. Determination of visible necrotic lesion was 10 times quicker and 30 times cheaper than colonisation, giving considerable savings for large experiments. Quantification of necrotic lesion-colonisation relationships aids determination of mechanisms of pathogen invasion and host resistance.

Variation between plant species of in-planta concentration and effectiveness of low-volume phosphite spray on Phytophthora cinnamomi lesion development

Variation between plant species of in-planta concentration and effectiveness of low-volume phosphite spray on lesion development of Phytophthora cinnamomi was determined for 14 species in two native communities of the South-West Botanical Province of Western Australia and 10 species in a glasshouse environment. There was considerable variation in stem phosphite concentrations between environments, phosphite treatment and taxa following low-volume spray. Average stem phosphite concentrations for taxa in the glasshouse environment were 8-fold greater than those in natural environments. In 48% of taxa, phosphite concentrations in stems of plants sprayed with 48 kg phosphite/ha were significantly greater than that for plants sprayed with 24 kg phosphite/ha. There was a 22 to 28-fold difference in stem tissue phosphite concentrations between taxa in the native communities and a 31 to 63-fold difference between taxa in the glasshouse environment. Phosphite was effective in 46% of the taxa based on rate of visible lesion development being significantly less in plants sprayed with 24 or 48 kg phosphite/ha than plants not sprayed. There were significant linear relationships between in-planta phosphite concentration and lesion development. Variation in phosphite effectiveness can be extended into a general hypothesis that plant species may differ in species-specific in-planta phosphite concentration thresholds that must be exceeded before effective control of P. cinnamomi can be achieved. Databases of species falling into phosphite effective or not effective groups can be used to assess variation in phosphite effectiveness between different threatened communities and assist in the development of application procedures aimed at overcoming ineffectiveness of the fungicide.

Temporal and spatial soil inoculum dynamics followingPhytophthora cinnamomiinvasion ofBanksiawoodland andEucalyptus marginataforest biomes of south-western Australia

Soil baiting was used to monitor temporal and spatial soil inoculum dynamics of Phytophthora cinnamomi in disease centres in four Banksia woodland biomes of the Swan Coastal Plain bioregion and an Eucalyptus marginata forest biome of the Jarrah Forest bioregion of the South-West Botanical Province of Western Australia. Patterns of inoculum occurrence in P. cinnamomi disease centres in Banksia woodland biomes were similar to those in E. marginata forest biomes. Significantly lower frequency of isolation was from near-surface (top 0.03 m) soil and greater occurrence of viable inoculum from soil at depth (∼1 m below the soil surface) and from near-surface soil around the collar of dead Banksia. Seasonal fluctuations in soil inoculum were not as distinct or consistent as that shown for rainfall and temperature and soil water content. Viable inoculum was most frequently isolated from near-surface soil in spring. In all Banksia woodland biomes isolation of inoculum from soil at depth was lowest in summer and greatest in autumn to spring. In all but one biome, isolation of inoculum from soil around dead Banksia was lowest in summer. Inoculum of P. cinnamomi was isolated from groundwater 3-5 m below the soil surface for Banksia woodland biomes in winter and spring 1987 and the winters of 1988 and 1989. Spatial patterns of viable inoculum from soil at depth were aggregated in 42% of quadrats analysed and 34% of quadrats sampled. The pattern of inoculum occurrence found in P. cinnamomi disease centres was influenced by creation of dynamic spatiotemporal niche refuges favourable to the pathogen through ecosystem engineering by host and pathogen.

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.

Hemispherical digital photographs offer advantages over conventional methods for quantifying pathogen-mediated changes caused by infestation ofPhytophthora cinnamomi

Estimates of canopy closure using hemispherical digital images, canopy cover using a point-intercept method, ground cover, number of plant species and total plant species cover were used to quantify the impact of Phytophthora cinnamomi in disease centres in Banksia shrubland, Banksia woodland and Eucalyptus marginata forest biomes of the South-West Botanical Province of Western Australia. Estimates of the time required to capture and analyse data and correlations were used to contrast the five methods. For canopy closure or cover, hemispherical digital images were on average, seven times faster to capture and analyse than the point-intercept method. For both canopy closure and ground cover, mean values from three point samples were not significantly different to mean values from transects across the disease front. Differences in canopy closure and ground cover between biomes and disease obtained from point sampling showed the same trends as transects. Canopy closure differed significantly between biome, being greatest for E. marginata forest, least for Banksia shrubland and intermediate for Banksia woodland. Ground cover was greatest for Banksia shrubland, least for E. marginata forest and intermediate for Banksia woodland. For all biomes there was significantly less canopy closure in diseased than adjoining healthy areas. There was no significant difference in ground cover between diseased and adjoining healthy areas of Banksia shrubland, but significantly less ground cover in diseased than adjoining healthy areas in the Banksia woodland and E. marginata forest. Canopy closure and ground cover are likely measuring different aspects of the impact of P. cinnamomi and, therefore, both should be measured when determining pathogen-mediated changes. Advantages of using hemispherical digital images over the other methods for determining temporal and spatial changes associated with P. cinnamomi infestation are discussed.

Assessment of threatened flora susceptibility toPhytophthora cinnamomiby analysis of disease progress curves in shadehouse and natural environments

Disease progress curves were evaluated for the assessment of the susceptibility of the flora of the South-West Botanical Province of Western Australia threatened by Phytophthora cinnamomi infection. Disease progress was analysed with the logistic model because this model describes numerous observed disease progress curves. In addition, the three logistic model parameters, upper asymptote (Kmax), lag time (t1/2K) and intrinsic rate of increase (r), have rational physical interpretations. Because the logistic model parameters for percentage of plants with collar lesions were significantly related to parameters for percentage mortality, only the logistic model parameters for percentage mortality were used in subsequent analysis. Susceptible hosts had the greatest Kmax, shortest t1/2K and fastest r. These parameters change to lowest Kmax, longest t1/2K and slowest r for resistant plant taxa. There was a greater change of Kmax with t1/2K than with r. The Kmax and r parameters did not differ significantly between isolates of the pathogen. Variation in mortality curve parameters between years was greater for Banksia grandis than for the more susceptible B. brownii. There was no significant linear relationship between mortality curve parameters for B. brownii and temperature variables. For B. grandis there were four significant linear relationships between a mortality curve parameter and a temperature variable. Potting mix soil favoured greatest disease progress with the shortest t1/2K and fastest r. Susceptibility to P. cinnamomi determined in a shadehouse environment following soil inoculation was significantly positively correlated with susceptibility recorded in disease centres in natural environments.

Effect of season of burn on shoot recovery and post‐fire flowering performance in the resprouter Stirlingia latifolia R. Br. (Proteaceae)

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.

Quantification of the susceptibility of the native flora of the South-West Botanical Province, Western Australia, to Phytophthora cinnamomi

This study compares, for the first time, variation in estimates of susceptibility of native flora to Phytophthora cinnamomi Rands among four databases and proposes an estimate of the proportion of the flora of the South-West Botanical Province of Western Australia that is susceptible to the pathogen. Estimates of the susceptibility of south-western native flora to P. cinnamomi infection were obtained from databases for Banksia woodland of the Swan Coastal Plain, jarrah (Eucalyptus marginata Donn. ex Smith) forest, the Stirling Range National Park and Rare and Threatened Flora of Western Australia. For the woodland, forest and national park databases, hosts were naturally infected in uncontrolled diverse natural environments. In contrast, threatened flora were artificially inoculated in a shadehouse environment. Considerable variation occurred within taxonomic units, making occurrence within family and genus poor predictors of species susceptibility. Identification of intra-specific resistance suggests that P. cinnamomi could be having a strong selection pressure on some threatened flora at infested sites and the populations could shift to more resistant types. Similar estimates of the proportion of species susceptible to P. cinnamomi among the databases from the wide range of environments suggests that a realistic estimate of species susceptibility to P. cinnamomi infection in the south-western region has been obtained. The mean of 40% susceptible and 14% highly susceptible equates to 2284 and 800 species of the 5710 described plant species in the South-West Botanical Province susceptible and highly susceptible to P. cinnamomi, respectively. Such estimates are important for determining the cost of disease to conservation values and for prioritising disease importance and research priorities. P. cinnamomi in south-western Australia is an unparalleled example of an introduced pathogen with a wide host range causing immense irreversible damage to unique, diverse but mainly susceptible plant communities.

Comparative population structure and reproductive biology of the critically endangered shrub Grevillea althoferorum and two closely related more common congeners

Grevillea althoferorum is a critically endangered, sprouting shrub known from two disjunct populations within the South-West Botanical Province of Western Australia. This study compares the conservation biology of G. althoferorum and two closely related but more common congeners, the non-sprouter G. rudis and the sprouter G. synapheae subsp. pachyphylla in order to determine whether there are differences in reproductive and ecological attributes that might explain why G. althoferorum is rare. In contrast to the more common species, neither population of G. althoferorum exhibited evidence of seedling recruitment. However, the northern population was confirmed to be clonal and was actively recruiting from root suckers. Both populations of G. althoferorum were found to have reduced amounts of viable pollen on stigmas in comparison with the other species. The fruit set at the southern population of G. althoferorum was considerably lower than that found for the common species, with only 0.15% of flowers setting fruit and no fruit was produced in the northern population. In addition no evidence of a soil seed bank was found for either population of G. althoferorum, but G. rudis and G. synapheae subsp. pachyphylla both had soil stored seed which germinated following treatment with aqueous smoke solution. Sexual recruitment at both populations of G. althoferorum was absent, and reproduction appears to be predominantly clonal in the northern population. Management strategies for G. althoferorum should therefore focus on the protection of adult plants from accidental destruction.