Breeding of a practical rice line ‘TJTT8’ for phytoextraction of cadmium contamination in paddy fields

<p>Previously, we showed that <i>qCdp7</i>, an allele identified in the high-Cd-accumulating <i>indica</i> rice variety ‘Jarjan,’ is associated with effective phytoextraction of Cd from paddy soils. However, ‘Jarjan’ may not be practical for phytoextraction because it is susceptible to seed shattering and culm lodging, which are unfavorable traits for mechanical rice harvesting. In this study, to develop a practical rice line for phytoextraction, we introduced the <i>qCdp7</i> allele into ‘Tachisugata,’ a rice variety with a nonshattering habit and lodging resistance, to produce a new high-Cd-accumulating rice line designated ‘TJTT8.’ This line inherited high-Cd accumulation and brown pericarps from ‘Jarjan’ and a nonshattering habit and lodging resistance from ‘Tachisugata;’ all of these traits are necessary for rice intended for Cd phytoextraction in Japan. Backcross inbred lines (BILs) were produced by two backcrosses to ‘Tachisugata’ after a cross between ‘Jarjan’ and ‘Tachisugata.’ ‘TJTT8’ was selected from the BILs by means of marker-assisted selection and phenotypic evaluation. When ‘TJTT8,’ the parents, and ‘Cho-ko-koku’ which is a high-Cd-accumulating <i>indica</i> variety were cultivated in Cd-contaminated paddy fields in four locations in Japan, ‘TJTT8’ exhibited lodging resistance and shattering resistance that were higher than those of ‘Jarjan’ and ‘Cho-ko-koku’ and equivalent to those of ‘Tachisugata.’ ‘TJTT8’ accumulated Cd in the aerial parts of the plants at concentrations ranging from 6.5 to 22.7 mg m⁻²: it showed significantly higher Cd accumulation than ‘Tachisugata’ and was equivalent to ‘Jarjan’ and slightly superior to ‘Cho-ko-koku.’ Soil Cd concentration was estimated to have been reduced by 8.7–33.6% based on the amount of Cd accumulation in the aerial parts of the plants. Thus, we succeeded in using the <i>qCdp7</i> allele to produce a practical rice line for Cd phytoextraction by improving several agronomic traits for compatibility with Japanese cultivation systems.</p

Low-cadmium rice (<i>Oryza sativa</i> L.) cultivar can simultaneously reduce arsenic and cadmium concentrations in rice grains

<p>In previous research, we produced a <i>japonica</i> rice (<i>Oryza sativa</i> L.) cultivar (‘Koshihikari Kan No. 1’) with nearly undetectable levels of cadmium (Cd) in the grains. In this study, we hypothesized that growing this cultivar aerobically would simultaneously reduce arsenic (As) and Cd concentrations in the grains. We grew this cultivar and ‘Koshihikari’, its parent, in paddy fields with different soil properties under three water regimes: flooded conditions (FLD), alternate wetting and drying conditions (AWD) and water-saving conditions (WAS). FLD for several weeks before and after heading significantly increased the grain As concentration in both cultivars. AWD, with the soil re-flooded just after disappearance of the ponded water, reduced grain As concentrations by an average of 27% relative to FLD for both cultivars. WAS, with irrigation after drying of the soil surface, decreased grain As concentrations by an average of 43.1% for ‘Koshihikari Kan No. 1’ and 48.2% for ‘Koshihikari’ compared to FLD. Although AWD and WAS remarkably increased grain Cd concentrations in ‘Koshihikari’, ‘Koshihikari Kan No. 1’ had nearly undetectable levels of grain Cd in all treatments. Compared with ‘Koshihikari’ in FLD, grain yield of ‘Koshihikari Kan No. 1’ and ‘Koshihikari’ decreased by averages of 2% for AWD and 4 to 6% for WAS. In addition, WAS tended to decrease grain quality slightly for both cultivars. Although aerobic conditions such as WAS have somewhat adverse effects on grain yield and quality, growing the low-Cd cultivar aerobically is the most practical way to simultaneously reduce Cd and As contents in the rice grains.</p