Identification of QTLs for brown spot resistance in rice

Rice brown spot (BS), caused by Bipolaris oryzae, is the third most prevalent rice disease in Japan and causes yield losses. In this study, quantitative trait loci (QTLs) associated with BS resistance were identified from the indica cultivars 'Tupa 121-3', 'Naba', and 'IR58'. Two QTLs, qBSR6-kt (from 'Tupa 121-3') and qBSR11-kn (from 'Naba'), were detected through QTL analysis of two F₂ populations derived from crosses between the BS-susceptible japonica cultivar 'Koshihikari' and two resistant lines selected from chromosome segment substitution lines with chromosome segments from 'Tupa 121-3' and 'Naba' in the 'Koshihikari' genetic background. Another three QTLs from 'IR58' (qBSR2-im, qBSR11-im, and qBSR12-im) were detected by QTL analysis of recombinant inbred lines derived from a cross between 'IR58' and the BS-susceptible japonica cultivar 'Mienoyume'. Among these detected QTLs, qBSR6-kt, qBSR11-kn, and qBSR11-im were confirmed to confer effective BS resistance in japonica rice cultivars. The two QTLs qBSR11-kn and qBSR11-im were located near the previously reported BS resistance QTL bsr1 on chromosome 11. BS resistance QTL qBSR6-kt (on chromosome 6) was identified as a novel QTL that confers effective resistance to BS and may be valuable for pyramiding with bsr1 or other BS resistance QTLs.