Significant genetic diversity loss following pathogen driven population extinction in the rare endemic Banksia brownii (Proteaceae)

•We investigated genetic consequences of disease driven extirpation in an endemic plant.•Over 37% of total genetic diversity has been lost due to disease.•Substantial genetic structure indicates geographically separate conservation units.•These findings have been important in developing reintroductions to disease free sites for each conservation unit.

Rapid range-wide extinction of whole populations due to introduced disease would be expected to lead to significant loss of genetic diversity, with impacts being greater for a species that is geographically restricted and with disjunct populations. We investigated the genetic consequences of extirpation in the rare endemic woody shrub, Banksia brownii, following the introduction of the pathogen Phytophthora cinnamomi. B. brownii shows a pattern of disease driven population extinction typical of significant numbers of threatened plant species within south-western Australia. Based on microsatellite genotyping of material from extinct (ex situ seed collections) and extant populations we estimated that 38.2% (gene diversity) and 36.7% (allelic richness) of total genetic diversity, based on contributions of within population variation and differentiation, have been lost from Banksia brownii due to P. cinnamomi. Furthermore, a loss of genetic diversity was reflected in the loss of 16 out of 55 and 6 out of 33 private alleles respectively from two geographically disjunct genetically distinct population groups. We found significant genetic structure within B. brownii with three geographically disjunct population assemblages that should be regarded as separate units for conservation. These findings have been important in developing reintroductions to disease free sites for each conservation unit.