Identification and characterization of pathogens causing oat anthracnose in China

Oat anthracnose is a destructive global disease that severely compromises grain yield and forage quality. To determine its distribution, severity, and principal etiology in China, field surveys were conducted across major oat-producing regions. Anthracnose was endemic across all surveyed regions, reaching peak severity in central Inner Mongolia, northern Shanxi, and northwestern Hebei (maximum disease index of 68.31). Early infection manifested as small, circular, yellow-to-brown foliar lesions surrounded by water-soaked halos. These spots expanded into fusiform or irregular dark brown lesions featuring central black acervuli. Similar symptoms occurred on stems, glumes, sheaths, and leaf-sheath junctions. A total of 162 pathogenic isolates were obtained from 16 oat survey sites. Pathogenicity testing of 50 representative isolates confirmed their ability to infect oat leaves, reproducing field symptoms and yielding falcate conidia within necrotic tissues. Interestingly, while only falcate conidia developed in vivo, isolates produced both falcate and oval conidia on potato sucrose agar. Multi-locus phylogenetic analysis (four gene loci) combined with morphological evaluations resolved all 31 representative isolates as Colletotrichum cereale. These findings establish that C. cereale is the dominant pathogen driving oat anthracnose in China. Furthermore, this study provides the first documentation of conidial dimorphism in C. cereale alongside its symptomatic manifestation on oat glumes and stems.