Revision of powdery mildews (Ascomycota, Erysiphaceae) on Rosa in China: unexpected taxonomic complexity with phytopathological implications

Powdery mildew is a persistent disease affecting the cultivation of Rosa, a genus of substantial horticultural and economic value worldwide. Despite more than a century of study, the true diversity of powdery mildews infecting roses has remained unclear, largely due to the long-standing and overly broad application of the name Podosphaera pannosa. To reassess this system, we conducted an extensive investigation of powdery mildew specimens infecting Rosa.

A total of 112 collections were examined, including recently gathered material from 23 provinces, historical types, representative specimens from the Herbarium Mycologicum Academiae Sinicae (HMAS), China, and a neotype specimen from Germany. Morphological observations combined with phylogenetic analyses (ITS, 28 S, and IGS rDNA) resolved several long-standing taxonomic problems and revealed unexpected diversity within the rose powdery mildew complex.

Molecular data from Erysiphe rosae provide the first phylogenetic evidence supporting the synonymy of Medusosphaera with Erysiphe. Sphaerotheca rosae, previously treated as a synonym of P. pannosa, is reinstated as a distinct species as Podosphaera rosae comb. nov., and a previously unrecognized lineage is described as Podosphaera rosae-xanthinae sp. nov. In addition, earlier varieties of E. simulans are shown to lack diagnostic morphological or genetic characters and are no longer supported.

Taken together, these results demonstrate that powdery mildews on Rosa represent a complex of five species across two genera, structured by host phylogeny. Clear patterns of host preference and distribution indicate a history of co-evolution and ecological differentiation driven by host availability. This study fundamentally revises our understanding of rose powdery mildews, revealing a level of taxonomic and evolutionary complexity much greater than previously recognized and highlighting Rosa as a key host lineage in the diversification of the Erysiphaceae.