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Three Clonal Lineages of Phytophthora cinnamomi in Australia Revealed by Microsatellites

First and fourth authors: School of Biological Sciences and Biotechnology, Murdoch University, Perth, W.A., 6150, Australia; second author: CSIRO Forestry and Forest Products, Perth, P.O. Box 5, Wembley, W.A., 6913, Australia; and third author: Science and Information Division, Department of Conservation and Land Management, Como, W.A., 6152, Australia

The genetic structure of populations of Phytophthora cinnamomi, a pathogen of an enormous variety of woody plants, was investigated using microsatellites. Three intensively sampled disease sites in southwest Australia were analyzed along with a large culture collection of Austra-lian isolates and some isolates from elsewhere in the world. The mutation in the four microsatellite loci analyzed revealed spatial patterns at the disease sites that correlated with the age of the infestation. Only three clonal lineages were identified in Australian populations and these same clonal lineages were present in worldwide populations, where it is suggested that a limited number of clonal lineages have spread in most regions. No evidence for sexual reproduction between these clonal lineages in Australia has been found even though the pathogen has the opportunity. Instead, mitotic recombination is frequent within the clonal lineages. The implications of this are discussed.

Additional keywords: mitotic crossing over, oomycete.