Fine mapping of QTLs for resistance to Phytophthora nicotianae in flue-cured tobacco using a high-density genetic map

Tobacco (Nicotiana tabacum L.) is an important agronomic crop and model system for studies of plant-pathogen interactions. Black shank, caused by Phytophthora nicotianae, is an important disease affecting tobacco production worldwide. In this study, a mapping population of 177 F7:8-9 recombinant inbred lines was generated from a cross between the highly resistant cultivar ‘Yunyan 85’ and a susceptible line ‘Dabaijin 599’. A high-density genetic linkage map containing 7734 single-nucleotide polymorphic markers based on restriction site-associated DNA tag sequencing technology was used to finely map quantitative trait loci (QTL) for resistance to P. nicotianae. A total of 10 QTLs were detected as being associated with resistance to P. nicotianae across multiple environments, and two major QTL qBS7 and qBS14 were repeatedly identified under all five environments. They explained 16.48-62.20% and 3.94-11.29% of the phenotypic variance with high LOD score, respectively. One hundred thirty-eight candidate genes were identified for two major QTLs qBS7 and qBS14, and annotation analysis showing that several predicted genes encoded proteins associated with plant defense response to pathogens. This high-density single-nucleotide polymorphic genetic linkage map of flue-cured tobacco based on restriction site-associated DNA sequencing was useful in the QTL finely mapping of resistance to P. nicotianae. This study increases our understanding of the genetics of resistance to P. nicotianae and aids in marker-assisted selection.