Species-specific primers for rapid identification of Erysiphe paeoniae, the powdery mildew pathogen in Paeonia lactiflora in Beijing: morphological characteristics, phylogenetic analysis, and host range expansion

Powdery mildew poses a substantial threat to Chinese herbaceous peony (Paeonia lactiflora) cultivation, yet efficient identification methods for the pathogen are currently lacking, hampering early disease control. This study successfully identified Erysiphe paeoniae as the causative agent of powdery mildew in P. lactiflora in Beijing, leveraging morphological characteristics and rDNA ITS region sequencing. Furthermore, a high specificity and sensitivity specific PCR detection primers targeting E. paeoniae were developed based on ITS region sequences. Notably, these primers effectively circumvent contamination by host plant or other fungal DNA, enabling the detection of E. paeoniae DNA at concentrations as low as 1 x 10(-15) ng/mu L. This technological advancement provides a valuable tool for the early and rapid detection of E. paeoniae. Moreover, host range of E. paeoniae strain in our study was tested by inoculation combined with specific primers we developed. The isolated strain BJ20210618 can infect four species of Paeonia plants, including P. lactiflora, P. anomala, P. obovata, and P. veitchii. Among them, P. veitchii is a new host of E. paeoniae, reported for the first time in this study. Strikingly, this strain exhibited no infectivity towards Chinese tree peony (P. suffruticosa), diverging from prior reports suggesting E. paeoniae infects Chinese tree peony. We speculate that there may be different physiological races in E. paeoniae. We aligned the E. paeoniae strain BJ20210618 isolated from P. lactiflora in Beijing, China, E. paeoniae strain YN20220506 isolated from P. suffruticosa in Yunnan, China, along with the ITS sequences of 15 E. paeoniae strains and 13 closely related powdery mildews available on NCBI, and constructed a phylogenetic tree. Phylogenetic analysis of ITS sequences further supports these observations, distinguishing E. paeoniae from both P. lactiflora and P. suffruticosa into discrete clusters, highlighting the presence of distinct strains of E. paeoniae with different host specificities. This study not only enhances our understanding of the pathogen's behavior and specificity but also provides invaluable tools and insights for effective disease management strategies.