Detection of a novel Puccinia coronata f. sp. avenae genotypic lineage in Australia during the 2024 oat growing season

Crown rust, caused by Puccinia coronata f. sp. avenae ( Pca ), remains a persistent threat to oat production in Australia. To monitor recent shifts in virulence and population structure, 30 Pca isolates collected during the 2024 growing season across major Australian oat-producing regions were analysed. Phenotypic analysis of 30 isolates using 52 oat differential lines identified 27 unique races. Whole-genome sequencing of 28 of these isolates revealed that most of them belonged to previously established lineages, with L18 and L16 being dominant. Notably, L16 was again present in Western Australia after being undetected in 2023, while L18 maintained its prevalence for a third consecutive season. Beyond these dominant groups, phylogenetic analysis also identified a novel and genetically distinct lineage, designated as L19, and represented by one isolate collected in WA. Although L19 exhibited a virulence profile similar to other WA isolates, its unique genomic signature underscores the need to integrate phenotypic and genomic surveillance. These findings enhance understanding of Pca diversity and inform resistance breeding and disease management strategies in Australian oats.