Abstract
Cadmium (Cd) is a toxic element, and rice is known to be a leading source of dietary Cd for people who consume rice as their main caloric resource. Hybrid rice has dominated rice production in southern China and has been adopted worldwide. The characteristics of high yield heterosis of rice hybrids makes the public think intuitively that the hybrid rice accumulates more Cd in grain than do inbred cultivars. A detailed understanding of the genetic basis of grain Cd accumulation in hybrids and developing Cd-safe rice are one of the top priorities for hybrid rice breeders at present. In this study, we investigated genetic diversity and grain Cd levels in 617 elite rice hybrids collected from the middle and lower Yangtze River Valley in China and 68 inbred cultivars from around the world. We found that there are large variations in grain Cd accumulation in both the hybrids and their inbred counterparts. However, we found grain Cd levels in the rice hybrids to be similar to the levels in indica rice inbreds, suggesting that the hybrids do not accumulate more Cd than do the inbred rice cultivars. Further analysis revealed that the high heritability of Cd accumulation in the grain and the single indica population structure increases the risk of Cd over-accumulation in hybrid rice. The genetic effects of Cd-related QTLs, which have been identified in related Cd-QTL mapping studies, were also determined in the hybrid rice population. Four QTLs were identified as being associated with the variation in grain Cd levels; three of these loci exhibited obvious indica-japonica differentiations. Our study will provide a better understanding of grain Cd accumulations in hybrid rice, and pave the way toward effective breeding for high-yielding, low grain-Cd hybrids in the future.
Highlights
Cadmium (Cd) is a highly toxic heavy metal that has accumulated in agricultural paddy soils and threatens human health via the soil-to-crop pathway (Chaney, 1980; Satarug et al, 2010)
A cultivar grown in field II accumulated more Cd in the grain than it did in field I (R2 = 0.72, P = 4.0E-88), indicating that the grain Cd concentrations were greatly affected by the soil Cd levels (Figure 1C)
The heritability of grain Cd levels was detected as 50.8%, which predicted a stable heritability for grain Cd accumulation in hybrid rice
Summary
Cadmium (Cd) is a highly toxic heavy metal that has accumulated in agricultural paddy soils and threatens human health via the soil-to-crop pathway (Chaney, 1980; Satarug et al, 2010). To mitigate Cd contamination in rice grain without compromising rice production, Chinese scientists have developed an integrated control measure known as “VIP” to reduce the Cd levels in grain; low Cd varieties (V), reasonable irrigation (I), and increasing the field pH (P) (Wang et al, 2016). Of these three components, development of low Cd varieties is preferred because it is the most cost effective
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