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Wheat stem rust incited by Puccinia graminis Pers.:Pers. = P. graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn is a major disease of wheat, with the potential to cause severe losses every year, hence making breeding for resistance important. For this project, two resistant synthetic wheat lines were studied using populations consisting of susceptible and resistant lines to determine the genetic basis of their stem rust resistance. Goodstreak has one dominant and one recessive resistance gene. Synthetics 303 and 370 each had two dominant genes present. For the Goodstreak/synthetic populations, testing F2 and F2:3 generations indicated the presence of three dominant genes and one recessive gene. To help identify individual genes, the synthetic lines were crossed to the cultivar ‘Lorikeet’ to test if the Ug99 resistance gene was Sr33, which is common in synthetic wheat lines, and the previously reported diagnostic marker Xcfd43 was used to test for the presence of Sr6 hypothesized to be in Goodstreak. The resistant synthetic lines did not contain Sr33, but Sr6 was in Goodstreak. We then postulated that the resistant lines contained one new Sr33-like Ug99 resistant gene and possibly Sr9e while Goodstreak contained Sr6 and an unknown gene. By identifying, postulating, and observing four resistance genes, these sources of resistance can be used and effectively incorporated in future cultivar improvement by wheat breeders to provide resistance to North American races of stem rust, as well as the Ug99 family of stem rust.