Virulence characterization of Puccinia graminis f. sp. avenae in Argentina

Abstract Oat stem rust in oats, caused by Puccinia graminis f. sp. avenae Erikss and Henning (Pg), is a disease of great relevance on a global scale, recognized for its destructive capacity under favourable environmental conditions. The characterization of the Pg population provides valuable insights into population size, diversity, and complexity, and allows the identification of race specific genes potentially useful for breeding. This study documents for the first time the structure and complexity of Pg populations in Argentina and their evolution over a period of 17 years, based on 70 isolates collected in different sites during 2005, 2021, 2022 and 2023. We identified 22 different races among the 70 single-uredinial isolates collected during the period, showing a greater diversity in population. Moreover, most of the races identified in 2021, and all the races identified in 2022 and 2023, were different from those found in 2005. We found that current populations are more virulent and complex, and the predominant race demonstrated virulence against all 11 reference oat lines utilized in this study, emphasizing its potential threat to oat cultivation in the region. The change in population dynamics detected here suggests that the use of a few genes as a basis for resistance to stem rust in the Argentinian germplasm has resulted in the continuous selection of Pg phenotypes with virulence to these resistance genes. Additionally, our results demonstrated that the frequency of virulence of Pg isolates increase on most of the resistance genes compared to the 2005 population, and there are not genes potentially useful for breeding under Argentinian conditions. These findings underscore the pressing need to expand our search for new resistance genes and deepen our understanding of the genetic mechanisms governing resistance to stem rust in oats. Moreover, our research highlights the dynamic nature of plant-pathogen interactions, emphasizing the continual evolution of Pg populations and their interaction with oat Pg genes.