Brown spot is a devastating rice disease. Quantitative resistance has been observed in local varieties (e.g., ‘Tadukan’), but no economically useful resistant variety has been bred. Using quantitative trait locus (QTL) analysis of recombinant inbred lines (RILs) from ‘Tadukan’ (resistant) × ‘Hinohikari’ (susceptible), we previously found three QTLs (
qBS2,
qBS9, and
qBS11) that conferred resistance in seedlings in a greenhouse. To confirm their effect, the parents and later generations of RILs were transplanted into paddy fields where brown spot severely occurred. Three new resistance QTLs (
qBSfR1,
qBSfR4, and
qBSfR11) were detected on chromosomes 1, 4, and 11, respectively. The ‘Tadukan’ alleles at
qBSfR1 and
qBSfR11 and the ‘Hinohikari’ allele at
qBSfR4 increased resistance. The major QTL
qBSfR11 coincided with
qBS11 from the previous study, whereas
qBSfR1 and
qBSfR4 were new but neither
qBS2 nor
qBS9 were detected. To verify the
qBSfR1 and
qBSfR11 ‘Tadukan’ resistance alleles, near-isogenic lines (NILs) with one or both QTLs in a susceptible background (‘Koshihikari’) were evaluated under field conditions. NILs with
qBSfR11 acquired significant field resistance; those with
qBSfR1 did not. This confirms the effectiveness of
qBSfR11. Genetic markers flanking
qBSfR11 will be powerful tools for marker-assisted selection to improve brown spot resistance.
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