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, 28S, 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 .