Letteratura scientifica selezionata sul tema "Phytophthora cinnamomi diseases Western Australia"

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.

Phytophthora cinnamomi Rands was isolated from either dead plants or soil at 46 disease centres in Banksia woodland at national parks and reserves on the Swan Coastal Plain. Phytophthora cryptogea Pethybridge & Lafferty was also isolated from roots of dead Acacia pulchella R.Br. in one disease centre infected with P. cinnamomi. Dead plants were infected with Armillaria luteobubalina Watling & Kile in four disease centres on the Spearwood Dune System, and these centres were excluded from further analysis. Phytophthora cinnamomi diseased areas ranged from 0.01 to 30 ha in size (mean 1.6 ± s.e. 0.7 ha). The total area infested for the 46 disease centres was 71.5 ha. Impact of P. cinnamomi was high in 17% of disease centres and low in 11% of disease centres. Age of plant death was a mixture of old and recent in 85% of disease centres. Mainly old deaths occurred in only 4% of disease centres. The proportion of species dying in infested areas varied between 10-64% (mean 28 ± s.e. 2%) and was positively correlated with impact type. It was found that infestation decreased species number; on average, there were seven fewer species in infested compared to non-infested areas. Four plant species associated with moist sandy sites tended to occur more frequently in centres of high impact than by chance alone. Occurrence of P. cinnamomi was related to soil association with soils of 60% of the disease centres belonging to the Bassendean or Southern River associations of the Bassendean Dune System. Sixteen percent of disease centres occurred in the Cannington, Guildford and Serpentine River associations of the Pinjarra Plain. No disease centres of P. cinnamomi were found on soils of the Speanvood and Quindalup Dune Systems. A water table was found within 3 m of the soil surface in 48% of the centres. Disturbance was associated with all disease centres. Firebreaks were associated with 72% of disease centres. Banksia woodland remnants on the Bassendean Dune System and the Pinjarra Plain are highly vulnerable to infection by P. cinnamomi and their conservation requires control of existing infestatinns and protection from introduction af the pathogen.

The soilborne plant pathogen Phytophthora cinnamomi is listed as one of the world’s 100 worst invasive alien species by the International Union for Conservation of Nature (IUCN). The impacts on native flora and fauna habitats have been identified as a key threatening process in Australia. Identifying and mapping diseased vegetation and the rate of spread of the disease is required for management; however, this is often difficult and costly. This study investigated the ability of using a time series of orthophotos (1953–2008) in combination with Landsat satellite imagery, including trend analysis, and GIS to identify the presence of vegetation impacted by P. cinnamomi at four sites in Banksia woodlands in Western Australia. Further, the historical extent and rate of spread of P. cinnamomi was assessed at one site between 1953 and 2008. Our assessment identified that three of the four sites were affected by P. cinnamomi, results that are consistent with on-ground surveys. Investigation of disease progression at one site found a large increase in the area impacted between 1974 and 1988 and the rate of spread was highest between 1953 and 1963 (1.286 m year−1) and lowest between 1997 and 2008 (0.526 m year−1). The techniques presented provide a cost-effective tool to monitor broad-scale vegetation dynamics over time for management of this plant pathogen.

Pinus occidentalis Sw. is an endemic species of the Caribbean island of Hispaniola (Dominican Republic and Haiti). It shows an extreme ecological plasticity and grows on a wide range of soil types from 0 to 3,175 m in elevation with annual mean temperatures ranging from 6 to 25°C and annual precipitation of 800 to 2,300 mm. P. occidentalis is a major component of forests above 800 m in elevation and forms pure climax forests above 2,000 m (4). For more than 10 years, stands of P. occidentalis in the Sierra (Cordillera Central) growing on a wide range of site conditions have suffered from a serious widespread disease. Symptoms include yellowing and dwarfing of needles, a progressive defoliation and dieback of the crown, and finally, death of weakened trees often caused by attacks by secondary bark beetles. Mature stands are mainly affected, but the disease is also present in plantations and natural regeneration that is older than 10 years. Disease spread is rapid, and occurs mainly along roads and from diseased trees downslope following the path of water runoff. Initially, Leptographium serpens was isolated from necrotic roots and was thought to be the causal agent (1). However, the symptoms of the disease more closely resemble those of littleleaf disease of P. echinata and P. taeda in the southeastern United States, which is caused by the aggressive fine-root pathogen Phytophthora cinnamomi Rands (3). Moreover, spread and dynamics of the disease are similar to the diebacks of Chamaecyparis lawsoniana in Oregon and Eucalyptus spp. in western Australia, which are caused by the introduced soilborne pathogens Phytophthora lateralis and Phytophthora cinnamomi, respectively. Soil samples containing the rhizosphere and fine roots of diseased P. occidentalis trees were collected in February 2002 at five sites near Celestina and Los Montones (Dominican Republic) and transported to the Bavarian State Institute of Forestry. The pathogen was baited from the soil by floating 3- to 7-dayold leaves of Quercus robur seedlings over flooded soil and placing the leaves on selective PARPNH agar (2). Phytophthora cinnamomi was isolated from the soil of all five sites. Crossing with A1 and A2 tester strains of Phytophthora cinnamomi confirmed that all isolates belong to the A2 mating type. In cross sections of necrotic fine roots, characteristic structures of Phytophthora cinnamomi such as nonseptate hyphae and chlamydospores could be observed. Our results indicate that the disease of P. occidentalis is caused by the introduced pathogen Phytophthora cinnamomi. Because of the ecological and economical importance of P. occidentalis, the disease poses a major threat to forestry in the Dominican Republic. Future research should include the mapping of the disease, pathogenicity tests on P. occidentalis and alternative pine species, in particular P. caribaea, screening for resistance in the field, and testing of systemic fungicides such as potassium phosphonate, which is known to be effective against Phytophthora cinnamomi. References: (1) G. Dobler. Manejo y Tablas de Rendimiento de Pinus occidentalis. Plan Sierra, San José de las Matas, Dominican Republic, 1999. (2) T. Jung et al. Plant Pathol. 49:706, 2000. (3) S. W. Oak and F. H. Tainter. How to identify and control littleleaf disease. Protection Rep. R8-PR12, USDA Forest Service Southern Region, Atlanta, Georgia, 1988. (4) L. Sprich. Allg. Forst. Jagdztg. 168:67, 1997.

Pathogenicity tests with Phytophthora cinnamomi were conducted on 25 perennial species from the jarrah (Eucalyptus marginata) forest of Western Australia. Most species tested had been found in a separate study to be scarce on sites affected by Phytophthora cinnamomi but frequently found in unaffected vegetation. Some species that were known to be field-tolerant of P. cinnamomi and some that were highly susceptible to infection were included in the study for comparison. Phytophthora cinnamomi was recorded from 13 of 17 species not previously known to be susceptible. Phytophthora cinnamomi was subsequently isolated from dead plants of two of these 13 species in the field. The interpretation of results from the glasshouse trials was difficult for some species because of inconsistent patterns of death and P. cinnamomi isolation in the glasshouse trials. Phytophthora cinnamomi probably causes decline in wild populations of Stylidium amoenum, based on the ease of field and glasshouse isolation of P. cinnamomi and the scarcity of this forb on dieback sites. It may also contribute to decline in populations of Boronia fastigiata, Hybanthus floribundus, Labichea punctata, Scaevola calliptera and Stylidium junceum, although further field sampling is required to confirm this.

Ten isolates of Phytophthora cinnamomi Rands from Western Australia were tested for metabolic variation using a commercial miniaturized biochemical system developed for bacteriology. The isolates included the two mating strains, and had been maintained in the laboratory for various times. The isolates were tested before and after repeated passaging on solid media. Statistical analysis of the biochemical results showed no major differences between the isolates, and for the most part they appear to be stable in cultivation. However, there were small passage effects on some of the media, particularly with glucose utilization.

The introduced soil-borne pathogen Phytophthora cinnamomi Rands infects and kills a large number of species in the jarrah (Eucalyptus marginata Donn. ex Smith) forest of Western Australia, causing great floristic and structural change. Many of the floristic changes can be explained simply by the known susceptibility of species to infection. Some common species, however, are rarely found at infested sites but are thought to be resistant to infection. It has been postulated that such species may be affected by the change in habitat caused by the death of trees, and not by P. cinnamomi directly. If this were the case, such species should cluster around surviving trees at infested sites. The occurrence of a susceptible species in the vicinity of trees surviving at infested sites has also been reported. To investigate the spatial relationship between trees and understorey species, the positions of trees and selected perennial understorey species were mapped at two sites in jarrah forest long-affected by P. cinnamomi. Random sets of plants and trees were generated and used in simulations to test whether understorey species grew closer to trees than expected. Many understorey species, both resistant and susceptible to infection by P. cinnamomi, were found to grow closer than expected to trees currently growing at the sites and closer to the trees that would have been present at the time of infestation. This suggests that not only do these trees enable some resistant species to persist at infested sites but that they also offer protection to some susceptible species against damage by P. cinnamomi. The proximity of many understorey species to trees that are likely to have appeared at the study sites since the first infestation indicates that the maintenance and enhancement of tree cover at infested sites in the jarrah forest may limit the damage caused by P. cinnamomi and assist in the protection of biodiversity.

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.

A survey of wildflower farms in the south west of Western Australia, was conducted during spring of 1997 and autumn 1998 to determine the prevalence of Phytophthora infestations. Thirty-seven randomly selected farms ranging in size from 0.5 to =30 ha were visited. The main crop plants grown included species of Banksia, Boronia, Chamelaucium, Conospermum, Eucalyptus, Protea, and Leucadendron. Eighteen sites were found to have infestations of Phytophthora. Of these, 14 sites had P. cinnamomi, and 2 sites had P. cryptogea. P. cactorum, P. citricola and P. nicotianae were each found at only single locations. One site was found to have both P. cinnamomi and P. cryptogea. Species of Phytophthora were identified morphologically, isozymically, and using species-specific PCR primers. Not every species could be identified by all 3 methods. There was no apparent association between geographical location and the occurrence of Phytophthora spp.

This study examined the ability of foliar applications of the fungicide phosphite to contain colonisation of Phytophthora cinnamomi in a range of plant species growing in natural plant communities in the northern sandplain and jarrah (Eucalyptus marginata) forest of south-western Australia. Wound inoculation of plant stems with P. cinnamomi was used to determine the efficacy of phosphite over time after application. Colonisation by P. cinnamomi was reduced for 5–24 months after phosphite was applied, depending on the concentration of phosphite used, plant species treated and the time of phosphite application. Plant species within and between plant communities varied considerably in their ability to take up and retain phosphite in inoculated stems and in the in planta concentrations of phosphite required to contain P. cinnamomi. As spray application rates of phosphite increased from 5 to 20 g L–1, stem tissue concentrations increased, as did the ability of a plant species to contain P. cinnamomi. However, at application rates of phosphite above 5 g L–1 phytotoxicity symptoms were obvious in most species, with some plants being killed. So, despite 10 and 20 g L–1 of phosphite being more effective and persistent in controlling P. cinnamomi, these rates are not recommended for application to the plant species studied. The results of this study indicate that foliar application of phosphite has considerable potential in reducing the impact of P. cinnamomi in native plant communities in the short-term. However, in order to maintain adequate control, phosphite should be sprayed every 6–12 months, depending on the species and/or plant community.

The south-west of Western Australia has a Mediterranean climate and flora endemic to this area, including the keystone species, jarrah (Eucalyptus marginata), have adapted to the droughted summer conditions. The introduction of an exotic soil borne pathogen, Phytophthora cinnamomi, has challenged the survival of this and many other species. The expectation might be that plants stressed by drought are more susceptible to disease and this study examined the development of disease caused by P. cinnamomi in E. marginata and the significance of water status to that development. Seedlings of E. marginata, clonal plants resistant to P. cinnamomi and clonal plants susceptible to P. cinnamomi, were subjected to different watering regimes in a number of field and glasshouse experiments. To determine the level of drought stress that could be imposed on container-grown E. marginata seedlings without killing them, a preliminary experiment progressively lowered the moisture levels of the substrate in their containers, until the plants reached wilting point, at which time moisture was restored to a predetermined droughted level and the process repeated. With each subsequent droughting the wilting point was lower until it was found that the seedlings could survive when only 5% of the moisture lost from container capacity to wilting point was restored. No deaths had occurred after seedlings had been maintained at this low level for 14 days (Chapter 2). Based on these findings, the level of droughting maintained in all experiments conducted under controlled glasshouse conditions was 10% restoration. After testing the appropriateness of underbark inoculation, and a zoospore inoculation method for which no wounding was necessary, a new, non-invasive stem inoculation technique was developed. Stems were moistened in a pre-treatment, then agar plugs colonized with P. cinnamomi mycelium were held against the stem with wads of wet cotton wool and bound in place with tape. This technique resulted in a high proportion of infection in E. marginata (Chapter 4) without the need for underbark inoculation or the use of zoospores (Chapter 3). It was successfully used in a large field trial in a rehabilitated bauxite mine site with 2-year-old E. marginata clonal plants, resistant to P. cinnamomi (Chapter 5). Inoculation was in late spring after the winter and spring rainfall. This timing was to allow comparison of disease development in stressed plants under normal droughted summer conditions compared with itsdevelopment in non-stressed, irrigated plants. However, two months after inoculation, the area was deluged with unseasonal and abnormally heavy summer rainfall, negating any difference in the treatments and causing an outbreak of P. cinnamomi in the soil from an adjacent infested site. This resulted in the infection and death of some noninoculated control clones. Monitoring of the site continued for twelve months and the advance of P. cinnamomi at the site was mapped. To test the effect of drought on the expression of P. cinnamomi under more controlled conditions, a series of glasshouse experiments was set up that simulated two possible summer conditions; drought or drought followed by abnormally high summer rainfall. These experiments utilised E. marginata seedlings and clonal plants, some resistant and some susceptible to P. cinnamomi. Plants were inoculated with P. cinnamomi prior to or after droughting. Results were compared to those of control plants that had not experienced water deficit. In both seedlings and clonal plants, the greatest extent of colonization was found in plants which had experienced no water deficit. These results indicated that drought stress played a role in inhibiting the in planta development of P. cinnamomi in all genotypes (Chapter 8). This finding was consistent for both clones, susceptible and resistant to P. cinnamomi. Most recoveries were made from non-stressed clonal plants, resistant to P. cinnamomi (Chapter 6) and more colonization was found in non-stressed clonal plants, susceptible to P. cinnamomi (Chapter 7), than was recorded for droughted plants. The results of the field trial showed that P. cinnamomi was not recovered from some inoculated stems, which had obvious lesions, when segments were plated onto selective agar. This led to an intensive in vitro investigation into improved methods of recovery. Dark brown exudates from some segments of inoculated stems stained the surrounding agar onto which they were plated, suggesting the presence of phenolic compounds. Recovery of the pathogen from stems increased by about 10% when segments were first soaked in distilled water to leach out the phenolic compounds, then replated onto agar. Other recovery methods were also tested, including (1) baiting with Pimelea ferruginea leaves floated on the surface of water or soil filtrate, in which the infected stem segments were immersed and (2) the application of different light and temperature regimes. It was clearly shown that exudates from infected stems of field grown E. marginata inhibited the outgrowth of P. cinnamomi onto the agar. To counter the possible toxic effect that oxidized phenolics had on the growth of the P. cinnamomi, an antioxidant was added to the agar. P. cinnamomi was grown on media whichincorporated exudates from infected stems and different concentrations of ascorbic acid, with and without adjusted pH levels. There was a pronounced pH effect, with less growth on media with lower pH and no significant increase in growth of the mycelium with increased ascorbic acid concentration on pH adjusted agar (Chapter 9). The inhibitory effect of the exudates from the stem segments led to an investigation of the possibility that, if seedlings to be planted in the rehabilitation process could be pre-treated with phenolic compounds to render them more resistant, they may have an advantage when establishing in areas where there was a potential threat of P. cinnamomi. E. marginata seeds were germinated and the seedlings grown hydroponically in a constant temperature growth room. Different concentrations of synthetic catechol, a phenolic compound naturally occurring in E. marginata, were added to the nutrient solution. Roots remained immersed in the catechol solutions for three days, before being inoculated at the root tip with zoospores of P. cinnamomi. Roots in higher concentrations of catechol were less colonized than those in lower concentrations, indicating an increased resistance to the pathogen (Chapter 10). Further work is required to determine if seedlings treated before being planted in areas threatened by an outbreak of P. cinnamomi have a greater capacity for survival, and for how long the protection persists. The improved recovery of P. cinnamomi from infected plants is important for accurate assessment of the spread of the disease in an area and for the subsequent implementation of management strategies of containment and control. An outbreak of P. cinnamomi can impact on the revegetation of rehabilitated mine sites and the aetiology of the pathogen in mine sites needs to be more fully understood. The interaction of plant defences with the invasive pathogen has been examined in a range of environments in the field, the glasshouse, in a hydroponics system and in vitro. The results indicate that summer droughting increases the resistance of E. marginata to P. cinnamomi. However, more work is required to understand the mechanisms involved. The study also indicates that clones of E. marginata, selected as resistant to P. cinnamomi, are not resistant under all conditions and that environmental interactions should be further investigated. Lastly, for effective management strategies to be implemented it is critical that the pathogen can be confidently isolated from plants. It was shown that exudates from infected hosts inhibit the recovery of P. cinnamomi. Recovery methods that can overcome these inhibitory compounds are required. The findings invite further research into the complexity of host-pathogen relationships.

In a survey of rehabilitated bauxite mines m south-west Western Australia, Phytophthora cinnamomi was isolated from the collar, but not from the root system of dead and dying Eucalyptus marginata Garrah) seedlings. Surface water ponding occurs in rehabilitated mines from autumn through to spring, and infected collars were commonly associated with ponding. This suggested that P. cinnamomi infects seedlings directly through periderm at the collar. The objective of this project was to ascertain whether infection by P. cinnamomi through periderm was possible, to study the disease in seedlings infected in this manner, and the methods by which P. cinnamomi circumvented the periderm to infect the seedlings. An inoculum receptacle was designed to simulate water ponding around the main stem of jarrah seedlings, and into which zoospores could be introduced. Under controlled glasshouse conditions in December (early summer) it was demonstrated that zoospores can infect through the stems of non-wounded and wounded jarrah seedlings. This was confirmed in a rehabilitated bauxite mine in May/June (late autumn/early winter), when ponding is most prevalent and sustained. In the field trial, P. cinnamomi was isolated from stems of non-wounded and wounded seedlings 3 weeks after inoculation. However, lesions did not develop in the non-wounded seedlings, or in most of the wounded seedlings. Another field trial examined the long-term prognosis for jarrah seedlings infected by zoospores at the collar. Within 3-6 months of either winter or spring inoculations, 7% ofthe seedlings died. In a further 6% of seedlings, the inoculated shoot died but the seedling survived through coppice growth from the lignotuber. As time from inoculation increased the reisolation of the pathogen from surviving seedlings decreased. Seedlings were severely water stressed during the summer with pre-dawn xylem pressure potentials as low as -1.5 MPa. In two post-summer harvests an intensive baiting and wetting regime was required to reisolate the pathogen from inoculated seedlings. Histological studies were undertaken to investigate: the origin and nature of jarrah periderm; the effects of pending on jarrah tissue; and the methods by which P. cinnamomi invades jarrah through periderm. The production of periderm was described from its origin in the peri cycle of the roots in 4-week old jarrah seedlings, through to rhytidome production in lignotuberous seedlings and 3- to 4-year old saplings. The first periderm in jarrah stems occurred internal to the primary phloem tissue, but it eventually migrated to a more superficial position in the stem. The first periderm consisted of phellogen, phelloderm, and a single type of phellem which was thin-walled and suberised. Between sequent periderms a second type of phellem formed, the cells of which were thick-walled and lignified. The formation of spongy rhytidome occurred when secondary phloem tissue underwent gross expansion after isolation between layers of periderm. Jarrah stems took up water in the region of inundation, and there was an increase in the frequency, but not size, of intercellular spaces after 5 weeks of localised ponding. There was also an increase in size of non-tanniferous parenchyma cells, but no overall increase in stem diameter. There was a measurable quantity of soluble carbohydrates in the pond liquid after 1 week, which had significantly increased after 5 weeks. Zoospores of P. cinnamomi were attracted primarily to sites of axillary shoot emergence in jarrah stems. Rapid and extensive infection and colonisation occurred through the new tissue of the emerging axilla1y shoots. Zoospores also bound randomly to other parts of the stem and were occasionally observed to attempt intercellular penetration of thin-walled suberised phellem, but extensive infection and colonisation was not observed as a result of such interactions. Zoospores were not preferentially attracted to either stem or leaf stomata, although penetration was occasionally observed through stem stomata. Zoospores were not attracted to lenticels and there was no evidence of infection through lenticels. The results of the project are discussed in the light of a 'disease tetrahedron', where mining and rehabilitation have resulted in a highly altered environment in which the host and pathogen operate. Conditions peculiar to rehabilitated sites are discussed in terms of their ability to exacerbate or reduce disease severity.

Phytophthora cinnamomi Rands is a common and devastating pathogen of cultivated proteas worldwide. Webb (1997) described a Sudden Death plant disease of proteas in Western Australia (WA) protea plantations. Proteas that suffer the syndrome display symptoms such as stunted growth, wilting, chlorosis and often death. In the current study, a number of protea plantations in the southwest of WA were visited to quantify the extent that P. cinnamomi was attributing to deaths of cultivated proteas. The survey indicated that P. cinnamomi is the major cause of Sudden Death in proteas. A range of other fungi (Fusarium, Botryosphaeria, Pestalotiopsis, Alternaria) and pests (nematodes, mealy bug, scale insects) were also identified to be contributing to protea death and decline in WA plantations. In many cases the factors contributing to protea disease appeared complex, with a range of physical factors or nutritional imbalances commonly associated with these pathogens and pests. As P. cinnamomi was the major cause of death of cultivated proteas the remainder of the experiments described in this dissertation investigated its control in horticultural plantings. Biofumigation has the potential to become an important technique in an overall integrated management approach to P. cinnamomi. In this thesis, biofumigation refers to the suppression of pathogens and pests by the incorporation of Brassica plants into the soil. Two biofumigants (Brassica juncea (L.) Czern., B. napus L.) were screened for their effect on the in vitro growth of five common Phytophthora species (P. cinnamomi, P. cactorum (Lebert & Colin) Schroeter., P. citricola Sawada, P. cryptogea Pethyb. & Laff. and P. megasperma Drechsler). Growth was determined by the measuring dry weight and radial growth of vegetative hyphae. B. juncea was found to be superior in its suppressive effect compared to B. napus. There was also significant variation in the sensitivity of the Phytophthora species to the suppressive effects of the biofumigants. P. cinnamomi was the most sensitive of the five species investigated. Where the rates of the biofumigant were sufficient to suppress growth of Phytophthora, the suppressive effect was mostly fungicidal. To determine how B. juncea and B. napus affect the infective ability and survival of P. cinnamomi, their effects on sporangia and chlamydospores production in soil was investigated in vitro. P. cinnamomi colonised Miracloth discs were added to soil amended with the two Brassica species, before being removed every two days over an eight day period for the determination of sporangia production, chlamydospore production and infective ability. Only the soils amended with B. juncea significantly reduced sporangia production in P. cinnamomi. Both Brassica species increased the percentage of aborted or immature sporangia and reduced the infective ability of the pathogen. Neither Brassica species had any effect on zoospore release or chlamydospore production in P. cinnamomi. Soil cores and soil leachate were collected from biofumigant-amended field soils to determine the inoculum potential and infective ability of the pathogen under glasshouse conditions. Amending the soil with both Brassica species had an immediate suppressive effect on the inoculum potential and infective ability of the P. cinnamomi. However, after this initial suppression there was a gradual increase in the recovery of the pathogen over the monitoring period of four weeks. To determine if the suppression would result in decreased disease incidence in a susceptible host, Lupinus angustifolius L. seeds were planted in the biofumigant amended soil. B. juncea amended soils reduced the disease incidence of P. cinnamomi by 25%. B. napus had no effect on disease incidence in L. angustifolius. Although the current study had demonstrated that biofumigants could suppress the growth, sporulation and infection of P. cinnamomi, it was unclear if this would equate to a reduction in disease incidence when applied in the field. A field trial was conducted on a protea plantation in the southwest of Western Australia that compared biofumigation with B. juncea to chemical fumigation (metham sodium) and soil solarisation. The three soil treatments were used in an integrated management approach to control P. cinnamomi that included the use of a hardwood compost, mulch and water sterilisation. All treatments were monitored during their application to ensure the treatments were conducted successfully. The three soil treatments significantly reduced the recovery of the pathogen and the infective ability of the pathogen to a soil depth of 20 cm. Metham sodium was the most suppressive soil treatment and soil solarisation was the least suppressive treatment. Only the metham sodium treatment resulted in a significant reduction in the incidence of root rot in Leucadendron salignum P.J. Bergius x laureolum (Lam.) Fourc (c.v. Safari Sunset) over the monitoring period of three years. Another field trial was conducted on the same protea plantation to compare the effectiveness of B. juncea and B. napus, without the use of other control strategies, to reduce the incidence of P. cinnamomi infection of Leucadendron Safari Sunset. The concentration of isothiocyanates was monitored for seven days after the incorporation of the biofumigants. Although both Brassica species reduced the recovery and infective ability of the pathogen, neither biofumigant reduced the incidence of root rot in Leucadendron Safari Sunset. In conclusion, P. cinnamomi is the most common and devastating pathogen in WA protea plantations. The current study demonstrated that P. cinnamomi is sensitive to the suppressive nature of biofumigants. Biofumigants can suppress the in vitro growth, sporulation, infective ability of P. cinnamomi and reduce the incidence of the disease caused by the pathogen in the glasshouse. Of the two Brassica species investigated, B. juncea was superior in its ability to control P. cinnamomi compared to B. napus. When applied in the field, biofumigation using B. juncea was found to be more suppressive that soil solarisation, but not as effective as metham sodium.

Phytophthora cinnamomi is an introduced soilborne phytopathogen to Western Australia (WA) and impacts on 2000 of the approximately 9000 plant species indigenous in the southwest of WA. Amongst these is Eucalyptus marginata (jarrah), the dominant and economically important hardwood timber species of the jarrah forest. This thesis aimed to investigate the morphological, pathogenic and genotypic variation in two local WA populations of P. cinnamomi isolates. The populations were selected from areas where jarrah clonal lines selected for resistance to P. cinnamomi may be used in the rehabilitation of infested jarrah forest and rehabilitated bauxite minesites in the southwest of WA. Resistance against a range of isolates using different inoculation methods. Seventy-three isolates of P. cinnamomi were collected from diseased jarrah and Corymbia calophylla (marri) trees from two populations located 70 km apart and these were examined for phenotypic and genotypic variation. Microsatellite DNA analysis showed that all isolates were of the same clonal lineage. In P. cinnamomi for the first time I show that there is a broad and continuous variation in the morphology and pathology between two populations of one clonal lineage, and that all phenotypes varied independently from one another. No relationship was found between morphological and pathogenic characters. The ability of isolates in both populations to cause deaths ranged from killing all plants within 59 days to plants being symptomless 182 days after inoculation. Single and multiple paragynous antheridia formed along with amphigynous ones in mating studies with all WA isolates and a sample of worldwide isolates. Developmental studies and cytological examination showed fertilisation tubes developed asynchronously or synchronously from both antheridial types and indicated that either antheridial type contributed a nucleus for fertilisation of the oosphere. This is the first report of paragynous antheridial associations in P. cinnamomi. Antheridial variation is a characteristic that needs to be adjusted in the taxonomic Phytophthora identification keys. In underbark and zoospore stem inoculations of three 1.5-year-old jarrah clonal lines (two ranked as resistant (RR) and one as susceptible (SS) to P. cinnamomi in the original selection trials) at 15, 20, 25 and 30°C, it was found that the method of inoculation did not produce comparable results, particularly at 25 and 30°C. At these temperatures, all three clonal lines had 100% mortality when inoculated underbark, but when inoculated with zoospores, one RR line had 60% survival and the SS and remaining RR line had 100% mortality. Generally, the level of resistance of all clonal lines declined with increasing temperature. Lesion development was measured at 20, 25 and 30°C for 4 days in detached branches of an RR and SS clonal line inoculated underbark with four different P. cinnamomi isolates. Detached branches were found to be a potential screen for jarrah resistance to P. cinnamomi and to allow the identification of susceptible and resistant clonal lines at 30°C. Lesion and colonisation development of P. cinnamomi isolates were assessed in situ (late autumn) of seed-grown and clonal lines of 3.5 to 4.5 year-old jarrah trees growing in a rehabilitated minesite jarrah forest in underbark inoculation of lateral branches (1995) or simultaneously in lateral branches and lateral roots (1996). Trees were underbark inoculated in lateral branches and lateral roots. Colonisation was more consistent as a measure of resistance than lesion length over the two trials because it accounted for the recovery of P. cinnamomi from macroscopically symptomless tissue beyond lesions, which on some occasions, was up to 6 cm. In the two trials, one RR clonal line consistently had small lesion and colonisation lengths in branches and roots. In contrast, the remaining two RR clonal lines had similar lesion and colonisation lengths to the SS clonal line and may, therefore, not be suitable for use in the rehabilitation of P. cinnamomi infested areas. The relative rankings of the jarrah clonal lines by colonisation lengths were similar between branch and root inoculations. Branch inoculations are a valid option for testing resistance and susceptibility of young jarrah trees to P. cinnamomi. The pathogen was recovered on Phytophthora selective agar 3–6 months after inoculation from 50% of samples with lesions and 30% of symptomless samples in a series of growth cabinet, glasshouse and field experiments. However, up to 11% of samples with and without lesions and from which P. cinnamomi was not initially isolated contained viable pathogen after leaching the plant material in water over 9 days. This indicates that the pathogen could be present as dormant structures, such as chlamydospores, where dormancy needs to be broken for germination to occur, or fungistatic compounds in the tissue need to be removed to allow the pathogen to grow, or both. These results have important implications for disease diagnosis and management, disease-free certification and quarantine clearance. No clonal line of jarrah was found to be 100% resistant using different inoculation methods, environmental conditions and when challenged by individuals from a large range of P. cinnamomi isolates. Even the most promising RR line had individual replicates that were unable to contain lesions or died with time. This suggests that further screening work may be required using more isolates varying in their capacity to cause disease and a broader range of environmental conditions. Jarrah clonal lines that survive such rigorous screening could then be expected to survive planting out in a range of environments in the jarrah forest and rehabilitated bauxite minesites.

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.

Phytophthora cinnamomi is a soil-borne plant pathogen that causes dieback, a disease that devastates many native vegetation ecosystems in Australia, particularly in south-west Western Australia. Feral pigs have long been implicated as vectors in the spread of this introduced plant pathogen due to their contact with infested soil and foraging habits. This study aimed to investigate the potential for feral pigs to disseminate P. cinnamomi and to determine their role in the spread of dieback. Feral pigs trapped in three sampling areas within the northern jarrah (Eucalyptus marginata) forest of south-west Western Australia were sampled for the presence of P. cinnamomi. Faecal (n=208) and soil samples (n= 140) were collected from trapped pigs. In addition, 374 faecal and 36 soil samples were also collected from sites frequented by feral pigs. Phytophthora cinnamomi was not recovered from any of the faecal or soil samples. However saprophytic pathogens such as Mucor and Fusarium spp. were detected in the faeces and Pythium spp. was also detected in the soil samples, suggesting that feral pigs can act as vectors for the spread of soil-borne pathogens. Stomach contents from 100 feral pigs trapped across the three sampling areas were analysed to investigate the proportion of P. cinnamomi susceptible plant matter present in the feral pig diet. A high frequency of plant material (85%) was found in the pig stomachs, of which 25.8% consisted of subterranean plant structures such as roots and tubers. Underground fruiting bodies of ectomycorrhizal fungi belonging to the genus Rhizopogon were also a significant food item. There was no statistically significant preference detected for food items by pigs between the three sampling areas, regardless of sex and/or month of capture. However, older and larger pigs consumed significantly more bark (p= 0.0002). To further investigate the potential for P. cinnamomi to survive passage through the pig digestive tract a feeding trial was undertaken. Phytophthora cinnamomi inoculated millet (Panicum miliaceum) seeds, pine (Pinus radiata) plugs, and Banksia leptophylla roots were fed to pigs and subsequently recovered after passage. The viability of P. cinnamomi inoculated plant materials post digestion ranged from 25.5% to 98.3%. Detection for P. cinnamomi presence in the materials via qPCR confirmed a decrease in P. cinnamomi DNA with increasing time to passage. These investigations demonstrated that plant material infected with P. cinnamomi can remain viable following passage through the pig digestive tract suggesting that the plant material may provide protection for P. cinnamomi against the adverse conditions of the pig digestive tract. Subsequently, plant infection trials using infected pine plugs passaged through the pig digestive tract highlighted that material passaged 7 days after initial consumption was capable of infecting healthy susceptible plants. This provides evidence that feral pigs have the ability to act as a vector for P. cinnamomi through the ingestion of infected plant materials. A species-specific fluorescent in situ hybridization (FISH) assay was developed to enable the examination of P. cinnamomi within plant tissues. The probe was found to be specific for P. cinnamomi when tested against other Phytophthora, Pythium and enteric bacteria species. Using the FISH assay, the location of P. cinnamomi structures were detected within a variety of plant materials such as millet seeds, pine sections and root samples. Phytophthora cinnamomi structures such as hyphae and chlamydospores were found in the epidermal layer of millet seeds and within the axial rays of pine that were recovered after passage from the feeding trial. This aided understanding of how viable P. cinnamomi were able to survive passage within these plant materials. In addition, the FISH assay was also successfully applied to both laboratory-cultured and naturally infected plant roots enabling detection of the pathogen in the intracellular and intercellular spaces of roots. The assay has proven to be a useful tool in the detection of P. cinnamomi structures within plant tissues. In conclusion, this study provides evidence that, whilst the potential consequences of pig-vectored dispersal of P. cinnamomi are high, the likelihood of feral pigs dispersing the pathogen through transport of infested soil is low. Investigations of their diet composition and the passage of viable P. cinnamomi has established the additional threat that feral pigs could spread ingested P. cinnamomi within organic substrates. This study has also highlighted the fact that there is still much to be learned about the interaction between the feral pig and the plant pathogen. Further research is therefore required to ensure that appropriate management decisions for both species can be made.

This study investigated how the presence of the plant pathogen Phytophthora cinnamomi in vegetation assemblages impacts on habitat utilisation by the honey possum (Tarsipes rostratus). The study took place in coastal heathlands at Cape Riche, Western Australia, between January 2007 and November 2007. Honey possums were radio tracked through an area affected with P. cinnamomi as well as healthy areas to determine the extent to which habitat utilisation is impacted on. This will then allow for a more robust prediction of how further spread of P. cinnamomi is likely to impact on honey possums in the future. The presence of P. cinnamomi was confirmed by plating samples of dying plants. The areas of P. cinnamomi at the study site are extensive but patchy with ‘islands’ of healthy vegetation assemblages still remaining. A comparison of microclimate at the study site showed that unaffected areas had a larger range of temperatures than affected areas which may be due to differences in wind which is restricted (having a buffering effect) due to dense vegetation in unaffected sites. In affected areas, a greater proportion of the time was recorded where temperature was below 5C compared with unaffected areas. This could potentially impact on honey possums, which go into torpor during cool weather, and at temperatures below 5C, have a higher metabolic rate to maintain their body temperature. This means they need to forage for more nectar and pollen during cooler weather in affected areas where foodplants are less abundant. The number of honey possums captured was correlated to season (2=13.1, p<0.0005) with the largest number of honey possums captured during the summer field trip when more plants were flowering. Honey possum preferred foodplants were identified from pollen collected from captured honey possums. A total of 20 different pollen species were identified from samples, nine of which were identified as important honey possum preferred foodplants as they were found in more significant amounts. Based on pollen, Banksia plumosa subsp. plumosa was identified as the preferred foodplant at the Cape Riche study site followed by Adenanthos cuneatus. Both are common throughout the study area and flower all year. Banksia plumosa subsp. plumosa is susceptible to P. cinnamomi and was only found in unaffected areas whereas Adenanthos cuneatus was found to less susceptible and was prevalent throughout P. cinnamomi affected areas. Honey possums fed on a diverse range of plant species (determined by pollen) during all seasons, except autumn when B. plumosa subsp. plumosa was the most prevalent pollen species collected from honey possums. A total of 18 honey possums (body mass 5.9 – 16g) were radio tracked for up to 9 days using radio transmitters weighing 0.36g and 0.9g (Holohil Systems Ltd, Canada). Radio tracked honey possums demonstrated a particular preference for Banksia plumosa subsp. plumosa which they utilised for food, shelter and as a daytime refuge. Comparison of vegetation structure indicated that sites selected by radio tracked honey possums had significantly denser vegetation between 40-140 cm in height compared with randomly selected sites. Significant differences were identified between Phytophthora cinnamomi affected and unaffected locations with vegetation at affected locations being sparser and shorter than that at unaffected sites. This study clearly showed that honey possums are influenced by the presence of P. cinnamomi affected vegetation at Cape Riche. The presence of P. cinnamomi at the study area results in large areas which are generally lacking in susceptible Proteaceous species such as Banksia and food resources tend to be sparse through these areas. Honey possums are capable of moving relatively large distances with estimated distances ranging from 4m to 1400m over a period of 30 minutes to 9 days. In areas affected with P. cinnamomi some honey possums fed on less susceptible plant species. Other honey possums moved long distances to healthy unaffected areas with higher densities of preferred foodplants. Further spread of P. cinnamomi is likely to have a serious impact on honey possums as healthy areas become affected and food resources become too limited to sustain honey possum populations.

Soil ecosystem is a living and dynamic environment, habitat of thousands of microbial species, animal organisms and plant roots, integrated all of them in the food webs, and performing vital functions like organic matter decomposition and nutrient cycling; soil is also where plant roots productivity represent the main and first trophic level (producers), the beginning of the soil food web and of thousands of biological interactions. Agroecosystems are modified ecosystems by man in which plant, animal and microorganisms biodiversity has been altered, and sometimes decreased to a minimum number of species. Plant diseases, including root diseases caused by soil-borne plant pathogens are important threats to crop yield and they causes relevant economic losses. Soil-borne plant pathogens and the diseases they produce can cause huge losses and even social and environmental changes, for instance the Irish famine caused by Phytophthora infestans (1845–1853), or the harmful ecological alterations in the jarrah forests of Western Australia affected by Phytophthora cinnamomi in the last 100 years. How can a root pathogen species increase its populations densities at epidemic levels? In wild ecosystems usually we expect the soil biodiversity (microbiome, nematodes, mycorrhiza, protozoa, worms, etc.) through the trophic webs and different interactions between soil species, are going to regulate each other and the pathogens populations, avoiding disease outbreaks. In agroecosystems where plant diseases and epidemics are frequent and destructive, soil-borne plant pathogens has been managed applying different strategies: chemical, cultural, biological agents and others; however so far, there is not enough knowledge about how important is soil biodiversity, mainly microbiome diversity and soil food webs structure and function in the management of root pathogens, in root and plant health, in healthy food production, and maybe more relevant in the conservation of soil as a natural resource and derived from it, the ecosystem services important for life in our planet.