Additive, dominant parental effects control the inheritance of grain cadmium accumulation in hybrid rice

Rice, a staple crop for more than half of the world's population, takes up and accumulates more cadmium (Cd) than do other cereal crops (Chaney et al. in Z Naturforsch C 60(3-4):190-198, 2005). Rice is the leading source of dietary Cd for people who consume rice as their main food resource. A low grain Cd (GCd) concentration is a highly desirable trait for food safety. Low GCd is a top priority target in hybrid rice breeding, which dominates the rice-growing areas with high Cd bioavailability in southern China and South Asia. Thus, the genetic controls of grain Cd accumulation need to be dissected to facilitate the breeding of low grain Cd cultivars. In this study, the genetics of GCd accumulation in hybrids was analyzed in 24 hybrids using a 3 x 8 incomplete diallel mating design in two Cd-polluted fields. Estimates for narrow heritability and combining ability, including both general combining ability (GCA) and specific combining ability, revealed the importance of additive gene effects from both parental lines in determining grain Cd concentration in hybrid rice, suggesting that hybrids do not necessarily show high GCd in the case of effective additive effects from the parents. In addition, wefound that the average values for GCA effects and the mid-parent values for Cd in node I after heading could be used as effective predictors for selecting parental lines for breeding low-Cd hybrids. Of 11 parental lines, 108A, Yifeng26A, Yifeng98A, AnfengA, 11C2292, and 11C2265 were found to be the better cytoplasmic male sterile and/or restorer lines for breeding low GCd hybrids. Of the 24 hybrid combinations, considering yield performance, six of the crosses in our study were identified as hybrids that had low grain Cd levels without losing their yield advantages.