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Phylogenetic Analysis of “Candidatus Phytoplasma australiense” Reveals Distinct Populations in New Zealand

August 2006 , Volume 96 , Number  8
Pages  838 - 845

Mark T. Andersen , Richard D. Newcomb , Lia W. Liefting , and Ross E. Beever

First and second authors: HortResearch, Private Bag 92169, Auckland, New Zealand; third author: AgriGenesis Biosciences Ltd., P.O. Box 50, Auckland, New Zealand; and fourth author: Landcare Research, Private Bag 92170, Auckland, New Zealand

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Accepted for publication 10 March 2006.

The phytoplasma “Candidatus Phytoplasma australiense” has been reported from New Zealand and Australia, where it has been associated with a range of host plants, especially since the 1970s. Partial tuf gene sequences of 36 New Zealand (NZ) isolates from four different host genera revealed nine different variants, which clustered into two distinct groups without any obvious correlation with host or geographic region. Phylogenetic analysis of these sequences, together with those available from Australian isolates, revealed three distinct clades: one found solely in Australia, one found solely in NZ, and a third with representatives from both countries. These divisions are consistent with differences observed in the 16--23S rRNA internal transcribed spacer region; therefore, we conclude that they represent three distinct subgroups: tuf 1, tuf 2, and tuf 3. We estimated a time of divergence for the three clades based on a synonymous substitution rate calculated by comparing the complete tuf gene sequence from the Loofah witches'-broom phytoplasma and “Candidatus Phytoplasma australiense”. Using a calibration date of 110 million years, the estimated time to a common ancestor for all clades (6 to 9 million years ago) suggests divergence during the Miocene, well after the geological separation of NZ and Australia.

© 2006 The American Phytopathological Society