Virulence Variation and Race Identification of Puccinia coronata f. sp. avenae Causing Crown Rust on Oat

Abstract

Virulence variation and race structure of Puccinia coronata f. sp. avenae, the causal agent of crown rust on oat (Avena sativa L.), were investigated to determine pathogen diversity and implications for host resistance. Field surveys were conducted across major oat-growing regions, and urediniospores were collected from infected leaves exhibiting characteristic orange to reddish-brown pustules, chlorosis, and premature senescence. Single-pustule isolates were established and evaluated on a differential set of oat genotypes carrying known resistance genes under controlled greenhouse conditions. Results revealed significant variation in virulence among isolates, with multiple physiological races identified based on differential host reactions. Certain isolates exhibited broad virulence spectra, overcoming multiple resistance genes, while others were restricted to specific host genotypes, indicating structured pathogenic diversity within field populations. Molecular characterization using ITS rDNA and effector-associated gene markers supported genetic differentiation among virulence groups and revealed moderate population variability. Phylogenetic analysis grouped isolates into distinct clusters, suggesting ongoing evolutionary divergence driven by host selection pressure and environmental adaptation. Disease severity was strongly influenced by humidity and moderate temperature conditions, which favored spore germination and infection cycles. The presence of diverse virulence profiles highlights the dynamic nature of *P. coronata f. sp. avenae populations and their ability to overcome deployed resistance genes in oat cultivars. These findings emphasize the importance of continuous race monitoring and deployment of genetically diverse and durable resistance in oat breeding programs. Integrated disease management strategies combining host resistance, crop rotation, and timely fungicide applications are essential for sustainable control of crown rust in oat production systems.