Abstract: Bacterial leaf steak (BLS) is one of the most destructive diseases in rice. Using a recombinant inbred line population derived from a cross between a highly-resistant variety Acc8558 and a highly-susceptive variety H359, 11 QTLs controlling rice resistance to BLS were previously mapped, among which a QTL on the short arm of chromosome 5 named qBlsr5a had the largest effect. This QTL was further verified and more precisely mapped later. In this study, with Acc8558 as the donor and H359 as the recipient, an near-isogenic line H359-BLSR5a was created by backcross breeding with marker-assisted selection, in which only the QTL qBlsr5a was introgressed from the donor parent. A large F₂ population was constructed by hybridizing the near-isogenic line with H359. By selecting individuals with extreme phenotypes and examining their progeny (F_2:3) lines, individuals with the resistant homozygous genotype at the target QTL in the F₂ population were identified. By genotyping these individuals with SSR markers and performing linkage analysis, qBlsr5a was mapped to an interval between SSR markers RM153 and RM159, covering a range of 2.4 cM or 290 kb.

Key words: Rice bacterial leaf streak, QTL, Fine mapping