A recent shift in the Puccinia striiformis f. sp. tritici population in Serbia coincides with changes in yield losses of commercial winter wheat varieties

Wheat yellow (stripe) rust, caused by the fungus <i>Puccinia striiformis</i> f.sp. <i>tritici</i> (<i>Pst</i>), is a devastating disease of wheat worldwide. The success of <i>Pst</i> is largely due to the pathogens ability to rapidly overcome host resistance, generating new races that are easily dispersed between territories through wind-borne transmission of <i>Pst</i> urediniospores. Thus, first signs of entry of new <i>Pst</i> races into a region is usually captured by changes in disease severity. To examine any alterations of winter wheat variety response to <i>Pst</i> infection in Serbia, we analyzed yield and <i>Pst</i> disease severity in field trials conducted in 2014, 2021, and 2023. We specifically focused on analyzing <i>Pst</i> disease severity at growth stages related to yield. Associations between qualitative variables (variety, year) and quantitative variables (yield in untreated plots, yield loss, and disease index (DI) of <i>Pst</i> infection) were analyzed using Principal Component Analysis with mixed data. A General Linear Model was used to investigate the most influential factors on yield, yield loss, and <i>Pst</i> infection. The results indicated that yellow rust disease severity increased over the past decade, suggesting a potential recent change in the <i>Pst</i> population in Serbia. Comparative population genetic analysis of <i>Pst</i> samples from the 2023 wheat season and those collected in Serbia in 2014 confirmed a potential change in the <i>Pst</i> population. In addition, we found that yield losses across wheat varieties varied independently of <i>Pst</i> infection levels, indicating that wheat varieties differ in their ability to overcome damage caused by high levels of <i>Pst</i> infection. Given that the level of pathogen pressure triggering susceptibility reactions is cultivar-specific, our study highlights the need for a deeper focus on the mechanisms underlying these differences. Expanding our understanding of the interactions between pathogens, plant defense responses, and the ability of cultivars to mitigate yield losses will better equip us to predict and prevent potential yield losses in commercial wheat varieties due to yellow rust in the future.