First report of Erysiphe astragali causing powdery mildew on Astragalus strictus in Tibet, China

Astragalus strictus (Fabaceae) is one of the major locoweeds commonly found in Tibet, China. In 2021 and 2022, the occurrence of powdery mildew on A. strictus leaves was investigated in Tibet with approximately 50‒70% disease incidence and 26.9‒37.5% disease severity. The typical symptoms included white powdery mildew colonies and dark chasmothecia on the host leaves. To identify the causal agent, fresh leaves covered with powdery mildew were collected and identified by morphology and molecular analyses. Phylogenetic analyses of the internal transcribed spacer (ITS) region and the 28 S (large subunit) rDNA showed that our collection was clustered with Erysiphe astragali. The morphology of our collection was appendages equatorially and flexuous, asci 4–8 per chasmothecium, ovoid to subglobose and ascospores 4 per ascus, ovoid or ellipsoid. A pathogenicity test on plants by pressing naturally infected leaves onto healthy leaves confirmed that the tested fungus was pathogenic. Therefore, E. astragali was identified as the causative agent of this disease. To our knowledge, this is the first report of E. astragali associated with powdery mildew on A. strictus in China.