Technical Abstract: Sunflower rust Puccinia helianthi is a serious disease that has been increasingly prevalent in much of the North America sunflower producing region. To effectively control this disease, three independent but complementary projects were initiated in the Sunflower Research Unit. One was evaluation of USDA-released sunflower breeding lines for resistance to rust race 336, the predominant race in North America, and to race 777, the most virulent race currently known. A total of 104 entries were tested for their reaction to races 336 and 777. Only 13 were resistant to both races, whereas another six were resistant only to race 336. The interspecific germplasm line, Rf ANN-1742, was resistant to both races and was identified as a new rust resistance source. The second project was to transfer identified rust resistance genes (R2, R4, R5) into confection sunflower by means of marker-assisted backcrossing. Two USDA recently released confection inbred lines, CONFSCL B1 and CONFSCL R5, were selected as recurrent parents. Three oil sunflower inbred lines, MC29 (R2 gene), HA-R3 (R4), and HA-R2 (R5), were selected as resistance gene donors. An approach of marker-assisted background selection (MABS)-based gene introgression will be employed to speed up selection for the recurrent parent genome. The third project was molecular mapping of rust resistance gene R4. A total of 544 SSR primers were used to screen two parents, HA 89 as a susceptible parent and HA-R3 as a resistant parent. Ninety-four F2:3 families (twenty plants for each family) were evaluated their reaction to rust race 336. The rust resistance gene R4 was mapped to linkage group13 and flanked with the markers ZVG61 and ORS581 at the genetic distances of 1.6 and 0.8 cM, respectively, providing DNA markers for selection of the R4 gene in the breeding program.