Virulence Dynamics of Puccinia coronata f. sp. avenae in 2023: Insights from the USDA's Oat Crown Rust Survey.

Abstract

The USDA's annual oat crown rust survey provides critical insights into the pathogen's regional and temporal virulence patterns. In the 2023 survey, 238 single pustule Puccinia coronata f. sp. avenae (Pca) isolates from nine states were screened against 40 differential lines. Pathogen race diversity was high with 94.7% of races represented by a single isolate, similar to previous surveys. The two most common races were represented by 5 and 8 isolates and were exclusive to the Southern region of the United States which lacks the pathogen's alternate host. Mean number of virulences per Pca isolate was 24.6 with Northern region isolates having significantly more virulences than Southern Region isolates. Pc94 is rapidly breaking down in the North, with 84% of Northern isolates virulent having increased from ~5% before 2021. Virulence to Pc96 is also steadily increasing to about 50% in both regions. Virulence to twelve resistance genes is consistently greater than 90% signaling complete breakdown of resistance. There were a few regional virulence patterns in the data: For Pc14 and Pc40, virulence is more common in Southern isolates, with 86 and 88% of Southern isolates virulent as compared to about 20% in Northern isolates. Virulence frequencies have decreased to ~60% of Southern isolates while remaining greater than ~90% in the north to Pc45, Pc48, Pc52, Pc68, and Pc91. Moving forward, the differential line set is being revised to reduce redundancy and increase relevance with newer genes, with the long-term goal of developing a complete set of near isogenic lines.