Is thermal aptitude a pivotal driver in the establishment of recent Puccinia striiformis f. sp. tritici lineages in Europe?

In the context of global warming, it is crucial to focus on the effects of temperature on the emergence of new lineages of endemic pathogen species, such as Puccinia striiformis f. sp. tritici ( Pst ) the causal agent of yellow rust on wheat. We characterized the thermal aptitude of representative isolates from the most recent common European Pst races. We assessed two key aggressiveness components—infection efficiency (IE) and latency period (LP)—under warm and cold thermal regimes, comparing 10 Pst isolates collected from 2010 to 2020 with three “old” reference isolates. The significant differences observed suggest that this species has the potential to adapt to temperature changes, but that such adaptation probably did not drive the establishment of neither the previously dominant races ‘Warrior’ and ‘Warrior(-)’, nor the following most recent races. These races display “generalist” behavior with respect to temperature, with ‘Warrior(-)’ showing no more aggressiveness than the races replaced since the 1990s. The differences in competitive success between emerging Pst lineages are probably due to the deployment of resistance genes in wheat and the advantages of new forms of virulence emerging independently of thermal adaptability. However, variations in thermal adaptability for both aggressiveness components suggested an impact of geographic origin within the ‘Warrior’ and ‘Warrior(-)’ races, as previously reported for the “old” reference isolates. Furthermore, the independence of thermal adaptability established for IE and LP implies that the effects of temperature may depend on the stage of the epidemic (early or late), potentially modifying seasonal dynamics.