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Population and sexual genetics of Phytophthora cinnamomi in Australia using microsatellite markers

Dobrowolski, Mark Paul (1999) Population and sexual genetics of Phytophthora cinnamomi in Australia using microsatellite markers. PhD thesis, Murdoch University.

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Phytophthora cinnamomi is a plant pathogen that causes dieback disease in southern Australia. It threatens the biodiversity of many natural ecosystems due to the susceptibility of the native vegetation. If methods of control are to be successful then we must appreciate the genetic variation in the pathogen and the ways in which this variation is generated. Previously, the only genetic markers available to study P. cinnamomi were isozymes, which showed that isolates in Australia were one of three isozyme types.

In this thesis I describe the development of microsatellite DNA markers for P. cinnamomi. Five microsatellites were successfully developed into markers for the nuclear genome and protocols for their use were established. Research into microsatel1ites for the mitochondrial genome is also presented though this was unsuccessful in providing markers useful for population genetic studies.

The developed micro satellite markers were used to study inheritance in sexual progeny of four P. cinnamomi crosses. All but one of 201 progeny germinated were outcrosses. A large amount of non-Mendelian inheritance of the microsatellite alleles was observed. This could be explained by a high frequency of imperfect meiosis (e.g., nondisjunction, unequal crossing over) leading to additions and deletions in the chromosome complement of the sexually derived progeny.

A population genetic study of three intensively sampled P. cinnamomi disease fronts located in southwest Australia is also presented. A total of 647 isolates were analysed from these hierarchically sampled sites with the micro satellite markers along with 133 culture collection isolates from across Australia. This analysis revealed that P. cinnamomi in Australia consists of three clonal lineages, with no sexual reproduction evident, even though both mating types co-occur. However, within these clonal lineages I found evidence for frequent mitotic recombination (mitotic crossing over). This mechanism for producing genetic variation may explain phenotypic variation known to occur within the identified clonal lineages.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Biological Sciences and Biotechnology
Supervisor(s): O'Brien, Philip and Tommerup, Inez
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