The tertiary gene pool of wheat includes wild relatives like Aegilops geniculata (UUMM, 2n=4x=28) that are valuable genetic reservoirs for novel abiotic and biotic resistance genes. However, modern wheat varieties share limited genomic commonality with these gene pool members presenting barriers to recombination and genetic mapping of desirable genes. We mapped a broad-spectrum leaf rust resistance gene Lr57 located on chromosome 5Mg of Ae. geniculata using a simple but powerful methodology for high-resolution genetic mapping in tertiary gene pool members of wheat. Five gene candidates were revealed all with possible defense related functions. Strategic application of differential expression analysis, Virus-Induced Gene Silencing, and mutagenesis analysis reduced the candidate gene of interest to a singular and novel ID-NLR resistance gene containg a protein kinase, NB-Arc, and LRR domain. Using multiple strategies, validation of Lr57 candidate was completed. Gene complementation by transformation of Lr57 candidate is currently being conducted.