Molecular markers associated with blue mold resistance in Nicotiana langsdorffii

Some accessions of Nicotiana langsdorffii, a species of South American wild tobacco, express strong incompatibility when infected by Peronospora tabacina, the causal agent of blue mold disease in tobacco. Necrotic lesions (HR) appear 48 hours after inoculation, and pathogen growth and subsequent asexual sporulation are suppressed. Blue mold resistance in N. langsdorffii S-4-4 is determined by a single, dominant gene (Rpt2) based on genetic segregation in F sub(2) and modified backcross populations. We are currently developing AFLP and SSR markers for N. langsdorffii to identify loci linked to Rpt2. We used 46 AFLP primer pairs in bulked segregant analysis (BSA) of F sub(2) plants (segregating 3:1 for R: S) to identify 6 markers putatively linked to this gene. These and other unlinked AFLP and SSR markers will be incorporated into a linkage map of the N. langsdorffii genome. We are also using association mapping to identify AFLP markers linked in coupling to the resistance locus in a group of 13 N. langsdorffii accessions, 10 of which (77%) express similar or identical HR-mediated resistance to P. tabacina infection. We believe that N. langsdorffii is the first reported important source of genetic resistance to P. tabacina because in many accessions, the HR phenotype is expressed in seedlings and cotyledons as well as in adult plants.