New sources of resistance to oat crown rust (Puccinia coronata f. sp. avenae), the most serious disease of oat (Avena sativa L.) in the Upper Midwest U.S., are badly needed as current sources rapidly become ineffective due to pathogen virulence shifts.  Resistance to a complex rust spore bulk was identified in backcross derivatives of a cross between a diploid oat (2n = 2x = 14) A. strigosa, accession CI6954SP, and hexaploid (2n = 6x = 42) A. sativa, cv. Black Mesdag, even though the sterile F1 recovered by embryo rescue, its fertile colchicine-derived octaploid (2n = 8x = 56), and backcross 1 plants were all susceptible, thus indicating a role of a suppressor.  Nearly equal rates of male and female transmission of introgressed resistance in backcross 4 materials indicate ready male transmission of resistance.  Various crosses are being made to investigate the nature of the initial suppression observed, the number of resistance genes involved, the stability of resistance transmission, and the relationship of this resistance to previously identified resistance genes for crown rust in oat.