Molecular data do not support a southern hemisphere base of Nothofagus powdery mildews

Three powdery mildew species present on Nothofagus (viz. Erysiphe magellanica, E. nothofagi and E. patagoniaca) are endemic to South America and have unique ascomatal appendages that are not found in powdery mildews of the northern hemisphere. We determined the nucleotide sequences of the rDNA internal transcribed spacer regions and D1/D2 domains of the 28S rDNA of these three powdery mildew species to reveal their phylogenetic relationships with powdery mildews of the northern hemisphere. Although the molecular phylogenetic analyses indicated that the three Nothofagus powdery mildews are closely related to each other they did not group into one clade in either the ITS or 28S trees. Kishino-Hasegawa, Shimodaira-Hasegawa and Templeton tests could not significantly reject the constrained trees that were constructed based on the assumption that the Nothofagus powdery mildews would form a single clade. Based on this result and the evidence that all Nothofagus powdery mildews are endemic to South America and have similar morphological characteristics, it is likely that these three species diverged from a single ancestor present on Nothofagus. Calibration of evolutionary events with molecular clocks suggested that the Nothofagus powdery mildews split from the northern hemisphere relatives 22-16 million y ago (Ma) in the middle Miocene, and divergence among the Nothofagus powdery mildews occurred 17-13 Ma. These results do not support a southern hemisphere base of the Nothofagus powdery mildews.