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

Abstract

Oat stem rust, caused by Puccinia graminis f. sp. avenae Erikss and Henning (Pga), is a disease of considerable relevance on a global scale, recognized for its destructive capacity under favorable environmental conditions. The characterization of the Pga population provides valuable insights into 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 Pga populations collected in different sites in Argentina between 2021–2023 and compares it with a population sampled in 2005. We identified 22 different races among the 70 isolates collected during the period, showing a high level of diversity in the 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 reported that current populations are more virulent and complex, and the predominant “race 11” demonstrated virulence against all 11 differential oat lines used in this study, emphasizing its potential threat to oat cultivation in Argentina. 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 Pga phenotypes with virulence to these resistance genes. Additionally, our results demonstrated that the frequency of virulence of Pga isolates increased on most of the resistance genes compared to the 2005 population, and there are no 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 evolution of Pga populations and their interaction with Pga genes.