Evolution of host-parasite relationships of Golovinomyces (Ascomycete: Erysiphaceae) inferred from nuclear rDNA sequences.

To understand the evolution of host-parasite relationships in the genus Golovinomyces (Ascomycete: Erysiphaceae), which are obligate parasitic fungi of plants, we investigated the phylogenetic relationships of the genus based on 60 internal transcribed spacer (ITS) and 41 28S rDNA sequences. Five major groups, each represented by isolates from a single tribe of the Asteraceae, were identified in the taxa analyzed in this study. Host plants of four groups were strictly restricted to the Asteraceae. The fifth group, the Lactuceae group, is a large group composed of isolates collected from the tribe Lactuceae of the Asteraceae and all other plant families, which suggests a close affinity between Golovinomyces and the Asteraceae in the early stages of their evolution. Tree topology comparisons between the asteraceous hosts and their parasites suggest that Golovinomyces diverged along with the phylogeny of host tribes Carsueae, Astereae, Heliantheae, and Lactuceae of the Asteraceae. However, a conflict of branching order between the tribe Anthemideae and their parasites suggests that host-jumping has occurred in the tribe Anthemideae. Consequently, we suggest that there are two different phases in the evolutionary history of the host-parasite relationships of Golovinomyces. One phase is divergence in accord with the phylogeny of their hosts, which occurred within the Asteraceae. The another phase is host-jumping, which occurred from the Asteraceae to other families and within the Asteraceae.