First report of leaf spot caused by <i>Heterophoma verbasci‐densiflori</i> on <i>Avena sativa</i> in China

Oat (Avena sativa) is an important annual grain and forage crop which plays role in animal husbandry, agricultural restructuring ecological construction China (Chen et al., 2022). In July 2020, leaf spots were observed on oat during stem elongation near the town of Ertai, Zhangbei county, Hebei province, China. The disease severity was estimated at around 25% over area c. 1-1.5 ha. At onset, symptoms appeared as dark brown to black, oval or irregular small dots, surrounded by light yellow halos. As expanded merged with each other, lesions reached up 9 mm length (Figure 1). A large number scattered black fruiting structures (pycnidia) within these progressed under humid conditions. spread rapidly, causing leaves wither. With dryer conditions, colour centre lesion became lighter expansion slowed down. Diseased tissue from five different plants, fields, cut into pieces (5 × 5 mm), surface-sterilised a 75% ethanol solution for 30 seconds 1% NaClO two minutes, rinsed three times sterilised distilled water, air dried plated onto potato dextrose agar (PDA). Colonies PDA 60–65 diameter after seven days, regular margins, covered floccose aerial mycelium, pale grey; reverse buff 2). Conidiomata pycnidial, solitary, spherical broad ellipsoid, glabrous some hyphal outgrows, 120–260 110–200 μm (mean 180 155 μm; n = 50) size. Ostioles mainly 1–2, (uncommon), slightly papillate non-papillate. Conidia ellipsoidal ovoid allantoid, thin-walled, smooth, hyaline, aseptate, 1.9-2.7 2.5-5.3 2.2 3.8 μm, size 3). internal transcribed spacer (ITS) region rDNA, RNA polymerase II second largest subunit (RPB2) gene beta-tubulin (TUB) genes amplified primers described previously (Hou 2020) sequenced. Sequences representative strain Y-1-Y-6 deposited GenBank (Accession Nos. MZ182321 ITS, MZ394576 RPB2 MZ199222 TUB). BLAST analysis showed 99–100% identity several reference sequences isolate CBS 127.93 reported Netherlands 2020). On basis morphological molecular characteristics, identified Heterophoma verbasci-densiflori. To confirm pathogenicity Y-1-Y-6, plants (cv. Baiyan 7) grown greenhouse 18–25°C weeks. Ten inoculated spore suspension (1 106 spores/ml). control, another ten treated sterile water instead suspension. All maintained wet humidity chamber 25°C 48 hours later transferred greenhouse. days inoculation, 4) but not control plants. Subsequently, H. verbasci-densiflori re-isolated infected based characteristics above, fulfilling Koch's postulates. has wide host range (Aveskamp 2010) our knowledge, this first report