First Report Powdery Mildew Caused by <i>Erysiphe paeoniae</i> on <i>Paeonia suffruticosa</i> in Baoding, Hebei Province

Tree peony (Paeonia × suffruticosa ) is a widely distributed perennial ornamental plant in China. In recent years, powdery mildew on tree peony has been consistently prevalent from late summer to autumn in the campus of Hebei Agricultural University in Baoding, China. Initially, infected leaves developed white circular mildew. As the disease progressed, the entire leaf surface and stems were covered with effuse or irregular white powder (mycelium). Subsequently, small black particles (chasmothecia) were observed in September. Conidiophores were erect and conidia were single and ellipsoid to ovoid, 25.77 to 51.40×13.36 to 22.94 μm (n=50). Chasmothecia were globose and brown, around 72.01 to 185.27 μm in diameter (n=50) and contained 3-7 asci. Appendages were mycelioid, with their length ranging from 61.14 to 163.11 μm (n=100), which was about 0.85 to 2.27 times the diameter of chasmothecia. Asci were ellipsoid to ovoid, and contained 2-5 ascospores; ascospores were ellipsoid to oblong-ellipsoid, 10.57 to 18.54 × 6.76 to 11.78 μm (n=100). Based on morphological characteristics, the fungus (designated EM) was identified as Erysiphe paeoniae (La et al. 2016). For molecular confirmation, partial sequences of the internal transcribed spacer (ITS) (White et al. 1990) and the RNA polymerase Ⅱ second largest subunit (RPB2) (Bradshaw et al. 2022) of this isolate were amplified by PCR. BLASTn analysis revealed that the obtained ITS and RPB2 sequences (accession numbers: PV628181.1 and PV654332.1) shared 99.84% and 99.57% identity with those of E. paeoniae (MT309702.1 and OR045233.1) in the NCBI database. Pathogenicity was tested by gently pressing diseased leaves onto 10 healthy leaves, and non-inoculated leaves as controls, in the field at Hebei Agricultural University. After 12 days, all inoculated leaves showed symptoms with powdery mildew colonies and the PCR amplicon sequence using primers ITS1/ITS4 was identical, fulfilling Koch’s postulates. The pathogens of powdery mildew on tree peony that have been reported include E. polygoni in Yunnan Province (MHYAU 03095), E. paeoniae-suffruticosae in Gansu, Shaanxi, and Jilin Provinces (Zhang et al. 2025), and E. paeoniae in Qingdao, Shandong Province, China (Qiao et al. 2016). To our knowledge, this is the first report of powdery mildew caused by E. paeoniae on tree peony in Baoding, Hebei Province. This finding helps clarify the genetic characteristics and distribution of the pathogen in China, and lays the groundwork for the forecasting and management of this disease.