First Report of Powdery Mildew Caused by <i>Blumeria graminis</i> f. sp. <i>tritici</i> on <i>Elymus nutans</i> in China

Elymus nutans (family Poaceae) plays a critical role in ecological restoration, particularly in the improvement of saline-alkali soils, and serves as an important forage crop due to its high palatability and stress tolerance. In June 2025, powdery mildew symptoms were observed on E. nutans in Harbin City, Heilongjiang Province, China (126°43' E, 45°44' N). Numerous white powdery colonies were found scattered across the adaxial surfaces of the leaves, with most coalescing into irregular patches. Approximately 40% of the surveyed plants exhibited these symptoms. Early-stage infections appeared as typical powdery masses, whereas advanced infections caused chlorosis, senescence, and necrosis of the leaves. Microscopic examination revealed conidiophores (n = 30) measuring 32.7–46.3 × 6.5–16.1 μm and consisting of foot cells and chains of mostly six conidia. The ellipsoid-shaped conidia (n = 50) measured 23.7–46.8 × 12.5–18.2 μm. Morphological analysis revealed a close resemblance to Blumeria graminis f. sp. tritici (Braun and Cook, 2012; Troch et al., 2014). Total genomic DNA was extracted from the mycelium and conidia using the method described by Zhu et al. (2020). The ribosomal DNA internal transcribed spacer (ITS) region was amplified using the primers ITS1 and ITS4 (White et al., 1990). The resulting 552 bp sequence was deposited in GenBank under the accession number PX245789. BLAST analysis showed 100% sequence identity with B. graminis f. sp. tritici isolated from Triticum aestivum in India (accession no. MT462305). Phylogenetic analysis clustered the identified fungus within the same clade as that of B. graminis f. sp. tritici. Pathogenicity tests were performed by dusting conidia from diseased leaves onto five healthy E. nutans plants, with five non-inoculated plants serving as controls. All plants were maintained separately in growth chambers at 28°C and 60% relative humidity, with a photoperiod of 16 hours of light and 8 hours of darkness. Seven to ten days after inoculation, the inoculated plants developed typical powdery mildew symptoms identical to those observed in naturally infected plants, whereas the control plants remained asymptomatic. To our knowledge, this is the first report of B. graminis f. sp. tritici causing powdery mildew on E. nutans in China. Although B. graminis has been reported as a pathogen in other crops worldwide, to our knowledge, there is no previous record of B. graminis f. sp. tritici infecting E. nutans globally prior to this study. In China, the pathogen has been documented on multiple Poaceae species—with its host range covering over 30 species—including Triticum aestivum, Hordeum vulgare (Zhuang et al., 2001), Avena sativa (Xue et al. 2017), and Poa pratensis (Zhu et al. 2021). Its identification on E. nutans highlights a newly emerging threat to this plant species in China. These findings underscore the urgent need for effective disease management strategies to mitigate further spread and potential damage, particularly in regions where E. nutans is economically or ecologically important. While B. graminis is indeed cosmopolitan on Poaceae, the first report of its tritici forma specialis infecting E. nutans fills a critical gap in the disease records of this ecologically and economically important forage crop. Given the key role of E. nutans in saline-alkali soil improvement and animal husbandry in northern China, this finding provides essential baseline data for disease monitoring and management in areas where this forage crop is extensively cultivated.