Introgressing the allelic variation of a major locus in reducing the grain cadmium accumulation in indica rice hybrids

Cadmium (Cd) is a toxic element that can accumulate in rice grains, presenting a threat to human health. Indica rice hybrid is dominant in southern China, and this genetic background is linked to high-level Cd accumulation in grains. Thus, lowering grain Cd levels in indica hybrids is a priority in the breeding programs. Previously, a locus on chromosome 7 was found to be associated with grain Cd variation in 617 rice hybrids and exhibited apparent indica-japonica differentiation. In this present study, a backcross population was generated to investigate the genetic control of this locus, as qCd7, on grain Cd performance in rice. Quantitative trait locus (QTL) analysis revealed qCd7 as an incomplete dominant factor that has a major effect on grain Cd variation; the NPB' allele can reduce grain Cd content. Using a 3x13 NCII design population, we evaluated qCd7's potential to decrease grain Cd content in indica hybrid combinations, and phenotypic comparisons indicated that introgression of qCd7-NPB effectively reduced grain Cd accumulation. Combining ability analysis revealed that parental lines carrying qCd7-NPB consistently displayed negative general combination ability (GCA) effects on grain Cd accumulation, which could be used to predict stable combiners in breeding programs. These results suggest that introgression of qCd7-NPB has great potential to decrease grain Cd content in indica hybrid breeding, which suggested that identifying allelic variation derived from indica-japonica genetic differences could facilitate genetic improvement in low grain Cd indica hybrid breeding programs.