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The role of active compounds produced by actinomycetes in the control of Phytophthora cinnamomi

Favas, Melissa (1994) The role of active compounds produced by actinomycetes in the control of Phytophthora cinnamomi. Honours thesis, Murdoch University.


The overall aim of this project was to screen actinomycetes for the ability to produce antibiotics inhibitory to P. cinnamomi in vitro. Some of the more promising isolates were then screened in vivo in a glasshouse pot-trial. The actinomycete isolates used had been previously isolated from jarrah forest soils suppressive to P. cinnamomi, ie. areas where P. cinnamomi was present in the soil but there was little evidence of disease. They had been isolated using dry heat pretreatments ( 120°C for one hour) designed to select for less frequently isolated actinomycetes especially the genus Microbispora.

Isolates were screened against P. cinnamomi in vitro for the production of secondary metabolites inhibitory to this pathogen. Of the isolates screened 40% caused strong inhibition of P. cinnamomi , 13% caused medium inhibition and 46% caused no inhibition of P. cinnamomi. Of the 40% of isolates that caused inhibition in vitro only ±4.0% of those tested for inhibition of P. cinnamomi in the pot-trial showed a potential for inhibiting P. cinnamomi in soil.

The pot-trial was performed using actinomycete isolates that had shown different levels of inhibition in vitro. Eight actinomycetes that had produced an antibiotic inhibitory to P. cinnamomi in vitro were tested in the pot-trial, 6 showing strong inhibition and 2 medium inhibition, but only 2 of these isolates a Streptomyces, isolate 97, and a maduromycete, isolate 55A, suppressed P. cinnamomi in vivo. In addition 2 of the 4 isolates with no in vitro inhibition of P. cinnamomi showed some activity against P. cinnamomi in the pot-trial. The results emphasised the fact that the production of an antibiotic in vitro does not automatically mean that the isolate will have the ability to control the pathogen in vivo.

The actinomycete isolates 97 and 55A which had shown strong inhibition in the in vitro screening were also screened against a range of fungal plant pathogens from different taxonomic groups. The fungal pathogens included representatives from the ascomycetes, hyphomycetes, basidiomyeetes and oomycetes. Eight other species of Phytophthora were also included. Isolate 97 showed the ability to strongly inhibit all of the fungal pathogens except Pythium ultimum which was only partially inhibited. Isolate 55A did not have the ability to inhibit Pythium ultimum but did inhibit all other pathogens to different degrees. Both isolates though showed that the antibiotics they produced were active over a range of different fungal taxonomy groups.

The metabolites from Streptomyces isolate 97 which showed strong activity against a range of fungal pathogens were extracted and purified from a broth culture filtrate. The antibiotic compound did not lose its ability to inhibit P cinnamomi through the extraction or purification process. Two antibiotic compounds were extracted, YB1 and YB2, both of which were inhibitory to P cinnamomi although YB2 was the stronger of the two. Antibiotics YBI and YB2 were also inhibitory to a few bacterial plant pathogens increasing the range of pathogens that could be inhibited by isolate 97.

Due to the wide range of pathogens inhibited by Streptomyces isolate 97 and its metabolites an attempt was made to further identify the isolate to species. There was not sufficient time to determine all the data required to identify the isolate by numerical classification, which requires data from 139 unit characters but a simple outdated key was used in the attempt. The use of the older key did not result in the identification of the isolate but the isolate was characterised morphologically and with respect to carbon source utilisation.

Publication Type: Thesis (Honours)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor: Hardy, Giles and Kurtboke, I.
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