An Introgressed Nicotiana rustica Genomic Region Confers Resistance to Phytophthora nicotianae in Cultivated Tobacco

ABSTRACT Black shank, caused by the pathogen Phytophthora nicotianae, is an important disease affecting tobacco (Nicotiana tabacum L.) production in many parts of the world. Host resistance offers an efficient means of reducing economic loss due to this pathogen. Previous observations suggested that a genomic region introgressed from Nicotiana rustica L. may affect resistance to black shank. The effect of this genomic region, designated as Wz, on resistance to multiple races of P. nicotianae had not previously been investigated in a systematic way, however. We used growth chamber and field experiments to evaluate resistance of a doubled haploid (DH) mapping population segregating for the Wz region. We also genotyped the population with amplified fragment length polymorphism (AFLP) markers found to be polymorphic between the parental lines. In addition, we determined resistance and marker genotypes for individuals of a larger BC1F1 population segregating for Wz. A set of 29 AFLP markers determined to be of N. rustica origin were found to cosegregate with each other and were associated with resistance to both race 0 and race 1 of P. nicotianae in the DH population. A selected subset of these markers was also found to cosegregate with resistance in the BC1F1 population. Consistent with other introgressed alien genomic regions in N. tabacum, no recombination was observed between these selected markers. The N. rustica‐derived genetic variation and associated DNA markers will be of value for breeding for black shank resistance in tobacco.