First report of rust on Leymus secalinus and Leymus chinensis caused by Puccinia coronati-hordei in Shanxi Province, China

Leymus secalinus and Leymus chinensis (family Poaceae) are perennial herbaceous plants. They are important ecological restoration grass species in northern China, and they also serve as high-quality forage. In July 2024, a foliar rust was observed throughout the cultivated grasslands of L. secalinus and L. chinensis in Shuozhou City, Youyu County, Shanxi Province, China, resulting in lesions covering averages of 19% and 87% of the total leaf tissue, respectively. Yellow uredinia and dark brown telia were observed primarily on the abaxial surface of the leaves. Urediniospores were ovate to broadly ellipsoid, measured 22–33 × 15–27 μm, and had 1–2 scattered germ pores. Their walls were dark brown and 1.0–2.0 μm thick. Teliospores were two-celled and measured 35–121 × 8–19 μm, with a short, light-brown stalk at the base. The apical cells of the teliospores had appendages varying in both number and length. The morphology of teliospores matched the description of Puccinia coronati-hordei (Synonym, Puccinia coronata var. hordei) reported previously (Jin et al., 1971). Urediniospores of this strain from L. chinensis, termed LcRust002, were collected through monospore isolation using a fine brush, and genomic DNA was extracted using a DNA extraction kit. PCR amplification of the internal transcribed spacer (ITS) region ITS4/ITS5 (White et al. 1990) and the partial 28S rDNA region with primers NL1/NL4 (Boekhout et al. 1995) was performed. A 676-bp and 557-bp PCR product was sequenced and a BLAST analysis showed 94% and 99% similarity to Puccinia coronati-hordei in the GenBank database, respectively (KU500626, MW404939). The sequences were deposited under GenBank accession numbers PQ797104 and PQ797120. Koch's postulates were performed with spray inoculations of urediniospores (LcRust002) suspended in water (1 × 106 spores/ml) onto the leaves of three healthy L. secalinus and L. chinensis plants. As a control, three additional plants of each species were sprayed with sterile water. The same process of inoculation was carried out on barley (Hordeum vulgare) and oat (Avena sativa) to verify the host specificity testing. All plants were then covered with plastic bags and transferred to a growth chamber with 12-h day/night cycles at 20/18°C. All inoculated L. secalinus, L. chinensis, and barley plants developed typical symptoms of rust with orange uredinia after 12 days, while no symptoms were observed on any of the control plants. Although oat plants developed some necrotic spots, uredinia were not observed in the leaves of inoculated oat. Puccinia coronati-hordei has previously been reported in the United States and Hungary, infecting hosts from the genera Elymus, Leymus and Hordeum. In China, Puccinia coronati-hordei was only reported on barley (Tian et al., 2021). To our knowledge, this is the first report of Puccinia coronati-hordei causing leaf rust on L. secalinus and L. chinensis in China. Given the high susceptibility of L. chinensis observed in the field, it is necessary to develop effective management strategies for this rust disease in China.