The oomycete pathogen Phytophthora cinnamomi is causing massive devastation of
natural forests in the southwestern corner of Western Australia. It is estimated that
2284 of the 5710 described native plant species in the southwest corner of Western
Australia are susceptible to P. cinnamomi, of which 800 are regarded as being highly
susceptible. One option for management of the disease is biological control using a
bacterium or fungus or both to antagonize the pathogen. Bacterial and or fungal
endophytes are a good source of biocontrol agents that can be used to protect plants
against disease. Many endophytes increase the resistance of the host plant to biotic
and abiotic stresses. They increase resistance to disease in a variety of ways: by
inducing the defence systems of the host, by the production of antibiotics to inhibit
pathogenic microorganisms, by production of enzymes to degrade the cell wall of the
pathogen, by competing for space and nutrients. For a biocontrol agent to be
successful, it must be culturable, have the ability to colonise a variety of plant hosts in
different environmental conditions and within different tissue types, and inhibit
different plant pathogens. Most importantly however, it must not be recognized in the
host tissues as a pathogen itself. The aim of this project was to look for a potential
biological control agent that will protect plants against P. cinnamomi. This study
focused on culturable endophytic bacteria within different Australian native plant
species, located in P. cinnamomi infested and non-infested areas. A total of two
hundred and fifty two isolates were recovered from root, stem and leaf samples from a
range of plant species at three sites from healthy and adjacent infested areas. These
isolates were grouped into forty eight morphotypes based on colony morphology.
The morphotype distributions differed significantly across sites and sampling areas
that were infested or not-infested with P. cinnamomi. To determine the potential of
iii
5
these endophytes as biocontrol agents, isolates were tested in vitro using a plate
confrontation assay and in planta with Lupinus angustifolius seedlings against P.
cinnamomi. A number of isolates inhibited the growth of P. cinnamomi in vitro,
suggesting they produced secondary metabolites such as antibiotics. Also, six
endophyte morphotypes significantly decreased lesion lengths caused by P.
cinnamomi in L. angustifolius seedlings, suggesting their ability to reduce infection in
plants against the pathogen. This shows their potential effectiveness as biocontrol
agents; however, further research needs to be undertaken on their viability and
persistence over time within different host plants, and their ability to confer resistance
under different environmental conditions