Identification and functional validation of avirulence effectors from the wheat stem rust pathogen

Stem rust, caused by Puccinia graminis f. sp.tritici (Pgt), is among the most devastating wheat diseases worldwide.Pgt uses numerous secreted effectors to infect wheat.In response, wheat has evolved resistance (Sr) genes that recognise some of these avirulence (Avr) effectors.Here, we report functional validation of known and novel Pgt Avr genes, and their variants identified via comparative genome sequencing.Validation was performed directly in wheat carrying corresponding Sr genes using virus-mediated overexpression (VOX).We found Sr27 effectively recognises seven new AvrSr27 variants.By contrast, Sr62 recognised only two of four AvrSr62 variants.We also identified and validated AvrSr33 and AvrSr26, the latter notable as there are four genetically unlinked AvrSr26 variants that are all recognised, potentially explaining the current absence of virulence against Sr26.This analysis establishes an evolving Avr gene atlas for Pgt lineages, laying a foundation for future pathogen surveillance and resistance breeding efforts.