Three key findings from the field pathogenomics study of wheat yellow rust: 1) Gene sequencing of 40 rust samples from UK fields in 2013 found four distinct populations that correlated with location. 2) A small number of genes were specifically differentially expressed between the populations, some of which may encode candidate effector proteins. 3) The pathogen's transcriptome could be matched to wheat varieties, allowing rapid identification of the host variety from RNAseq data alone.