Investigating the genetics of polygenic soil-borne disease resistance in tobacco
Bacterial wilt and black shank, caused by Ralstonia solanacearum and Phytophthora nicotianae, respectively, are the most important diseases affecting tobacco production in the United States. An increased understanding of the genetics controlling resistance to these soil-borne diseases, as well as identification of DNA markers associated with genomic regions controlling this resistance, could aid in the development of improved varieties. Flue-cured tobacco cultivar ‘K346’ exhibits high levels of resistance to both diseases. In an effort to understand the genetics of soil-borne resistance in this cultivar, we developed a recombinant inbred line (RIL) mapping population consisting of 186 lines derived from a cross between K346 and disease-susceptible tobacco accession ‘TI1068’. The population was genotyped with more than 300 microsatellite markers and evaluated for two years for field resistance to both black shank and bacterial wilt. Several genomic regions of K346 origin were found to affect resistance to both pathogens, a finding that may at least partially explain previously observed correlations between resistance to black shank and bacterial wilt among current cultivars and within breeding populations. Quantitative trait loci (QTLs) discovered to affect disease resistance in K346 were compared to those previously identified for ‘Florida 301’ and ‘Beinhart 1000’.