Blue mold, caused by the downy mildew pathogen Peronospora tabacina, is one of the most important foliar diseases of cultivated tobacco worldwide. Given the economic cost and possible negative environmental effects of long-term fungicide application, utilization of host resistance to blue mold is a preferred strategy. In order to map the gene of interest, a F₂ segregating population was derived from the cross between TKF2002 (susceptible to blue mold) and TKF432 (resistant to blue mold). More than 500 plants were inoculated with the blue mold pathogen. Plants with extreme phenotypes were selected for the marker test. More than 250 simple sequence repeat (SSR) markers were screened between TKF2002 and TKF4321. Seven polymorphic markers were selected to screen the F₂ population. The genetic map was constructed based on the combination frequency among markers. The blue mold resistance was localized on chromosome 7. This is the first genetic map of blue mold resistance in burley tobacco. One repulsion-phase marker PT61472 was identified to be closely linked with the blue mold resistance. Combined with the coupling-phase marker BMSCAR1, homozygous and heterozygous resistant plants can be easily distinguished. This results will highly facilitate the selection of blue mold resistance in tobacco breeding programs. (Reprinted with permission)