Virulence Dynamics of the Barley Leaf Rust Pathogen () in the United States from 1989 to 2020.

Barley leaf rust, caused by , is an important disease of barley worldwide. The pathogen can develop new races that overcome resistance genes, emphasizing the need for monitoring its virulence. This study characterized 519 isolates collected in the United States from the 1989 to 2000 and 2010 to 2020 survey periods on 15 (Reaction to ) genes. We analyzed linearized infection type data to detect virulence patterns across the United States and in five geographical regions: Pacific/West (PW), Southwest (SW), Midwest (MW), Northeast (NE), and Southeast (SE). Over 32 years, we observed high mean infection scores for , , and ; intermediate scores for , , , , and ; and low scores for , , , , , , and . Virulence for , , , , , , and significantly differed between the two survey periods. From 1989 to 2020, regional patterns of virulence were found for , , , and , while regionalities of virulence for , , were only observed in the 2010 to 2020 survey period. Virulence associations were also detected in the population. Notably, isolates that were virulent to and were more likely to be avirulent to and , and vice versa. In decreasing order of effectiveness, , , , , , , and were the most effective genes in the United States from 1989 to 2020. Pyramiding with other widely effective and adult plant resistance genes may provide long-lasting resistance against .