Fine Mapping of qBlsr5a, a QTL Controlling Resistance to Bacterial Leaf Streak in Rice

The quantitative trait locus (QTL) qBlsr5a on the short arm of rice (Oryza sativa L.) chromosome 5 has been proved to have the largest effect on the resistance to rice bacterial leaf streak (Xanthomonas oryzae pv. oryzicola, BLS). Using Acc8558 (highly resistant to BLS) as the donor and H359 (highly susceptible to BLS) as the recipient, a near-isogenic line (NIL) H359-BLSR5a was developed through backcross and only qBlsr5a was introgressed from the donor parent. A big F2 population (2,265 individuals) was constructed by hybridizing the NILs with H359 and 120 individuals with extreme phenotypes (lesion length < 2 cm) were selected. Eighty-five out of the 120 individuals were identified as homozygous resistant genotypes at the target QTL after examining their progeny lines (F2:3). By genotyping these homozygous individuals with SSR markers and performing linkage analysis, qBlsr5a was mapped to an interval between SSR markers RM153 and RM159, which covered a range of 2.4 cM or 290 kb.