Phylogeny and evolution of the powdery mildew fungi (Erysiphales, Ascomycota) inferred from nuclear ribosomal DNA sequences

Abstract

Powdery mildew fungi (Erysiphales, Ascomycota) are obligate biotrophs that infect a wide range of angiosperms. Phylogenetic analyses based on the nucleotide sequences of the nuclear ribosomal DNA revealed that the powdery mildew fungi are divided into five major lineages. The respective lineage was well defined by the morphology of conidial stage, but not of ascomata. In this fungal group, tree-parasitic taxa are generally ancestral, and multiple events of host expansion from trees to herbs have occurred within the respective lineage. Accompanying the host expansion to herbs, simplification of appendage morphology has occurred multiple times. The simple, mycelioid appendages are thus a result of convergence. The host expansion route was investigated in detail in the tribe Cystotheceae. Two sections of the genus Sphaerotheca were derived from the genus Podosphaera separately. The section Magnicellulatae was derived from a Podosphaera species parasitic to Prunus (Rosaceae), acquired parasitism to the Scrophulariaceae, and then expanded host range into the Asteraceae. After genetic radiation on the Asteraceae, they further expanded their host ranges into other plant families. According to the molecular clock (1.26%/100 million years, myr) reported by Berbee and Taylor, splitting of the Erysiphales and the Myxotrichaceae and first divergence within the Erysiphales was calculated to have occurred 100 and 76 myr ago, respectively.