Watkins landraces contain novel sources of Puccinia striiformis f. sp. tritici (Pst) resistance effective against Yr15-breaking Pst isolates

In early 2025, Puccinia striiformis f. sp. tritici (Pst) isolates were detected in the UK that were able to overcome resistance conferred by the widely deployed yellow rust resistance gene, Yr15. As Yr15 is highly prevalent in modern European wheat varieties, this placed approximately half of the UK wheat market share vulnerable to infection. Subsequently, it was shown that these emergent Pst isolates were derived from Pst isolates belonging to the ‘Warrior’ Pstrace groups that dominate in Europe. Here, we set out to determine if thirty-three A.E. Watkins heritage wheat landraces previously shown to harbour resistance to ‘Warrior’ Pst race group isolates, could also confer resistance to Yr15-breaking Pst isolates. One Yr15-breaking Pst isolate found in the UK in 2025 was used to conduct infection assays with the 33 Watkins landraces, alongside 11 additional Watkins landraces known to be susceptible to ‘Warrior’ Pst isolates. We found that 32 of the 33 Watkins landraces displayed resistant phenotypes when inoculated with the emergent Yr15-breaking Pstisolate. These 32 wheat landraces now represent a rich and valuable resource for identifying potentially novel sources of Pst resistance that could be mobilized to diversify modern wheat resistance breeding and reduce the future risk of similar widespread single-gene breakdowns.