Identification of QTLs and Validation of qCd-2 Associated with Grain Cadmium Concentrations in Rice

Cadmium (Cd) is one of heavy metals harmful to human health. As rice is the main staple food in Asia and Cd is easily contaminated in rice, the molecular regulation of Cd accumulation should be explored. In this study, a recombinant inbred population derived from Xiang 743/Katy was grown in Cd-polluted fields and used to map the quantitative trait loci (QTLs) for Cd accumulation in rice grains. We identified seven QTLs distributed on chromosomes 2, 3, 6, 7, 8 and 10. These QTLs displayed phenotypic variances of 58.50% and 40.59% in 2014 and 2015, respectively. Two QTLs, qCd-2 and qCd-7, were identified in both the two years. qCd-2 was detected on the interval of RM250–RM207 on chromosome 2, with an LOD of 2.51 and a phenotypic contribution of 13.75% in 2014, and an LOD of 3.35 and a phenotypic contribution of 14.16% in 2015. qCd-7 co-localized with the cloned qCdT7 on chromosome 7 and may represent the correct candidate. The other five QTLs were detected only in one year. To further confirm the effects of qCd-2, a residual heterozygous line designated as RHL945, with a heterozygous interval of RM263–RM207 on chromosome 2, was selected from the recombinant inbred population and used to develop an F₂ population consisting of 155 individual plants. By incorporating further simple sequence repeat markers into the segmental linkage map of the target region, qCd-2 was delimited in the interval of RM5404–RM3774, with an LOD value of 4.38 and a phenotypic contribution of 15.52%. These results reflected the genetic regulation of grain Cd in rice and paved the way for the future cloning of qCd-2.