Mapping of Quantitative Trait Loci for the Occurrence of White-Back Kernels Associated with High Temperatures During the Ripening Period of Rice (Oryza sativa L.)

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To identify the chromosomal regions controlling the occurrence of undesirable white-back kernels (WBK) in rice under growth conditions at high temperatures, we performed a quantitative trait locus (QTL) analysis in F_6 recombinant inbred lines (RILs). We constructed a linkage map using 106 simple sequence repeat (SSR) markers from 107 RILs derived from a cross between the japonica cultivar 'Chiyonishiki', which shows a high incidence of WBK at high temperatures, and the japonica cultivar 'Koshijiwase', which is tolerant to high temperatures and displays a low incidence of WBK. Each RIL was exposed to high temperatures in a greenhouse during the ripening period (from heading to maturity). The number of heat-damaged kernels was counted to obtain the rates of WBK in each RIL. Four putative QTLs for the occurrence of WBK-qWK1-1, qWK1-2, qWK2 and qWK8-were detected near the SSR markers RM8068 and RM5501 on chromosome 1, RM5916 on chromosome 2, and RM2680 on chromosome 8, respectively. The Koshijiwase alleles at the qWK1-2, qWK2 and qWK8 loci decreased the incidence of WBK and showed additive effects. qWK1-2 explained 15.0% of the total phenotypic variance, while qWK1-1, 8.8%, qWK2, 9.3%, and qWK8, 9.2%.