Unwounded and wounded periderm tissue of 1-year old stems of Eucalyptus marginata were infected and lesioned after 5 days’exposure to either mycelium or motile zoospores of Phytophthora cinnamomi. Lesions produced by P. cinnamomi were longer in wounded than in unwounded stems. The inclusion of non-sterile mine site soil with inocula in the unwounded treatments did not affect the rate or extent to which P. cinnamomi colonized E. marginata stem tissue. The ability of P. cinnamomi zoospores to infect unwounded suberized woody tissue of E. marginata, has important implications for mine site rehabilitation in P. cinnamomi infested areas. This is the first study to demonstrate clearly that zoospores of P. cinnamomi can infect and invade unwounded suberized tissue.

The ability of Phytophthora cinnamomi to infect through unwounded and wounded periderm tissue of Eucalyptus marginata

Colonization and survival of Phytophthora cinnamomi in roots was tested in 3 months old, axenically grown seedlings of Eucalyptus maculata (field resistant) and E. sieberi (susceptible). The roots were inoculated, then one week later were excised and buried in three non-sterile, conducive soils; a lateritic gravel, an infertile duplex soil, a loamy sand as well as in a fertile, suppressive krasnozem. Pathogen viability, percentage root colonization and chlamydospore numbers were examined at matric potentials of −1/3, −5 and −10 bar after periods of 10, 100 and 200 days at 21°C.



At 10 days, survival was 100% in the form of mycelium and the only significant difference was between the two Eucalyptus species. At 100 days survival was solely due to chlamydospores, but the pathogen was viable in all inoculated roots and at each matric potential. At 200 days soils had dried to less than −10 bars and the pathogen failed to survive. No significant differences were found between the two pathogen isolates but significant differences were obtained between the susceptible and field resistant Eucalyptus species.



Pathogen viability, percentage root colonization and chlamydospore number were highly correlated with soil types and matric potential. These components declined with decreasing soil matric potential. The Krasnozem was only suppressive at relatively high soil matric potentials (−1/3 bar). At lower values (−5, −10 bar) survival of the pathogen, chlamydospore numbers and percentage colonization of the roots in the Krasnozem were comparable with that of the 3 conducive soils tested.



Chlamydospores were present, but in low numbers in roots buried in the suppressive soil at −1/3 bar.

Survival of Phytophthora cinnamomi in Buried Eucalyptus Roots

An epidemic of severe root rot of Pinus radiata seedlings caused by Phytophthora cinnamomi in the 1970's at Benalla Nursery, 220 km north-east of Melbourne, was followed by a rapid disappearance of the disease in 1981. This phenomenon coincided with the application of simazine and propazine for weed control between 1971 and 1980 and glyphosate and chlorthal dimethyl after 1980. In laboratory and greenhouse tests, chlorthal dimethyl and glyphosate significantly (P

Phytophthora cinnamomi: Effects of herbicides on radial growth, sporangial production, inoculum potential and root disease in Pinus radiata

Phytophthora cinnamomi (Cinnamon fungus) is a pathogenic soil fungus which infects plant communities along the south-eastern coast of Australia, and the south-western corner of Western Australia. The symptoms of this disease include chlorosis, death of branches (ie. ‘dieback’), retarded growth and the eventual death of infected plants. This leads to devastating effects upon plant communities by altering both the structural and floristic characteristics of these communities. Small mammal species are dependent on specific features of their habitat such as vegetation structure and floristics. This thesis investigated alterations to the habitat of the insectivorous marsupial mouse, Antechinus stuartii, due to the presence of P. cinnamomi. The study was undertaken in an area of an open forest in the Brisbane Ranges, Victoria. Significant changes were found in both the floristic composition and structure of the vegetation at study sites infected with P, cinnamomi, compared to uninfected sites. The habitat utilization by A. stuartii of uninfected and infected vegetation was investigated using live trapping and radio-telemetric techniques. Capture rates were higher at sites uninfected by P. cinnamomi, and both male and females selected areas free from infection. Home range areas of males were significantly larger than those of females as assessed by telemetry. Both sexes spent a high proportion of time in areas dominated by Xanthorrhoea australis (Austral grass tree). There were significant relationships between the abundance of A. stuartii and the denseness of vegetation above 1 metre in height, and in particular, the proportion of cover afforded by X. australis. There were no significant differences in the cover of Eucalyptus spp. between uninfected and infected sites, but there were significantly more nest hollows in infected areas. The abundance of invertebrates was examined using pitfall traps. There were no significant differences in the abundance of the larger invertebrate taxa at infected and uninfected sites, but higher abundances of some micro-invertebrate groups in infected areas were recorded. The most likely factors considered to be influential in the habitat selection of A. stuartii were vegetation structure, and the presence of X. australis. To assess whether these factors were important the leaves of X. australis were removed with a brushcutter, to mimic the early effects of infection with P. cinnamomi. Animals did not respond to the alteration of vegetation structure in the short term (3-4 days). Longer-term experiments are required to assess the habitat utilization of A. stuartii at different periods following habitat manipulation. The implications of the presence of P. cinnamomi on the conservation of fauna are discussed. The destructive nature of the pathogen, and the slow rate of recovery from the disease, means that P. cinnamomi can be considered a threatening process to plant communities and the fauna that reside within that habitat. Future management of this disease within natural areas must therefore be cognisant of the potential of P. cinnamomi to significantly affect faunal as well as vegetative communities.

http://dro.deakin.edu.au/eserv/DU:30023349/newell-effectofphytophthora-1994.pdf

Effect of Phytophthora cinnamomi on the habitat utilization of Antechinus stuartii in a Victorian forest

When propazine was used continuously for S years as a pre-emergent herbicide in a large Pinus radiata nursery at Benalla. where the soils were not believed to be conductive to Phytophthora cinnamomi root rot. disease appeared after ca 2 years and rapidly increased in intensity despite attempts to control it with fungicides. The disease and the fungus virtually disappeared, within one season, when chlorthal dimethyl replaced propazine. An explanation for these observations was sought by examining the effects of propazine and chlorthal dimethyl on soil, rhizosphere and rhizoplane bacteria. Actinomycetes and fungi and the effect of the herbicides on the resistance per se . of P. radiala seedlings to Ph. cinnamomi. These tests were carried out in a laboratory, phytotron and greenhouse. The nursery disease symptoms were reproduced in the phytotron when Ph. cinnamomi —free soils were inoculated and treated with both herbicides. Chlorthal dimethyl was found to strongly inhibit root disease and soil inoculum potentials of Ph. cinnamomi in 5 month-old seedlings while propazine had the opposite effect. When the stems of hcrbicidal-trcatcd seedlings growing in Ph. cinnamomi —free soils were inoculated with Ph. cinnamomi, there was evidence that propazine increased disease sensitivity considerably while the effect of chlorthal dimethyl was not consistent. Examination of the effects that both herbicides had, in phytotron tests, on soil, rhizosphcrc and rhizoplane microflora showed that chlorthal dimethyl reduced numbers of Gram-positive and -negative and spore forming bacteria ca 90% while propazine increased their numbers. In the rhizosphcrc and rhizoplane the inhibitory ctfcct of chlorthal dimethyl and the stimulatory influence of propazinc on bacteria was very variable which suggests that the root cxudatcs had a greater influence on microbial numbers than that of the herbicides. Examination of the effects various bacterial types on sporangial formation of Ph. cinnamomi showed that the spore-forming bacteria associated with propazine soil drenches strongly stimulated sporangial production. The evidence suggest that the disease outbreak at the Benalla nursery may have been due to an increase in numbers of soil bacteria that stimulated production of Ph. cinnamomi inoculum and a reduction in disease resistance. The disease reduction following applications of chlorthal dimethyl may have been due directly to fungitoxicity to Ph. cinnamomi and failure to stimulate soil microflora that may have increased inoculum levels. Its influence on disease resistance of P. radiala was possibly negligible.

Effects of propazine and chlorthal dimethyl on Phytophthora cinnamomi root disease of Pinus radiata seedlings and associated soil microflora

When Eucalyptus sieberi was grown in either a steamed or unsteamed krasnozem that suppressed Phytophthora cinnamomi root rot and repotted when either 6 or 12 weeks old in a larger container of inoculated sandy loam, seedling survival was significantly greater in the unsteamed treatments By varying the treatments in the inner core soil and outer inoculum jacket, substituting a biologically inert coarse sand in place of the krasnozem in the core, and using eucalypt species of varying disease tolerance while maintaining very strict hygiene conditions throughout these experiments, it was possible to either demonstrate or deduce that: (a) the seedlings were killed when infection spread into the major roots, root collar and lower stem; (b) the microflora in the unsteamed krasnozem appeared to slow down the decay process within the root, possibly when the fungus was attempting to establish itself within the root; (c) the phenotypic resistance of a seedling to root disease depended, inter alia, on its genetic resistance and on the microflora in the surrounding soil; (d) once the fungus was established in the suberized tissues the microflora in the external environment had no influence on disease

Development of Phytophthora cinnamomi Infection in Roots of Eucalypt Species Growing in a Soil That Suppresses Phytophthora Root Disease

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Development of Phytophthora cinnamomi Infection in Roots of Eucalypt Species Growing in a Soil That Suppresses Phytophthora Root Disease