Characterizing the Response of Puccinia striiformis f.sp. tritici to Periods of Heat Stress Common in Kansas and the Great Plains Region of North America

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici, is considered a disease of cool environments, and it has been observed that high temperatures can suppress disease development. However, recent field observations in Kansas suggest that the pathogen may be recovering from heat stress more quickly than expected. Previous research indicates that some strains of this pathogen were adapted to warm temperature regimes, but did not consider how the pathogen responds to periods of heat stress that are common in the Great Plains region of North America. Therefore, the objectives of this study were to characterize the response of contemporary isolates of P. striiformis f. sp. tritici to periods of heat stress, and to look for evidence of temperature adaptations within the pathogen population. These experiments evaluated nine isolates of the pathogen including eight isolates collected in Kansas between 2010-2021 and a historical-reference isolate. Treatments compared the latent period, and colonization rate of isolates given a cool temperature regime (12-20 C), and as they recovered from 7 days of heat stress (22-35 C). Results documented that contemporary isolates of the pathogen had similar latent periods and colonization rates as the historical reference under the cool temperature regime. Following exposure to 7 days of heat stress, the contemporary isolates had shorter latent periods and higher colonization rates than the historical isolate. There was also variability in how the contemporary isolates recovered from heat stress with some isolates collected during 2019-2021 recovering sooner than those collected just 5-10 years ago.