Fine mapping and candidate gene analysis of Bwr-6 conferring bacterial wilt resistance in tomato

Bacterial wilt is a devastating soil-borne disease that severely affects tomato production worldwide. Previously, two quantitative trait loci (QTLs), Bwr-6 and Bwr-12 , conferring resistance to bacterial wilt were identified in Solanum lycopersicum ‘Hawaii 7996′. However, the large size of these QTL intervals has limited candidate gene identification. In this study, F 2 –F 5 populations derived from a cross between the resistant cultivar Hawaii 7996 and the susceptible cultivar E6203 were used to fine-map Bwr-6 . A total of 44 PCR-based markers dissecting the Bwr-6 region were developed and applied. Seventeen homozygous recombinant lines carrying different Hawaii 7996-derived segments at Bwr-6 with the homozygous resistance at Bwr-12 were selected, enabling the Bwr-6 interval to be narrowed to a 108.5 kb region containing 13 candidate genes. Among these candidate genes, the sugar transporter gene SlSTP11 showed induced expression following infection with strain SL882 in resistant cultivars. Furthermore, virus-induced gene silencing of SlSTP11 in the resistant cultivars resulted in increased susceptibility to bacterial wilt, suggesting a functional role of SlSTP11 in resistance. Together, these results show SlSTP11 as a candidate gene underlying the Bwr-6 locus. This study provides valuable insights into the genetic basis of bacterial wilt resistance and offers practical implications for breeding resistant varieties.