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

Abstract

Previously, we showed that qCdp7, an allele identified in the high-Cd-accumulating indica 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 qCdp7 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 markerassisted selection and phenotypic evaluation. When 'TJTT8,' the parents, and 'Cho-ko-koku' which is a high-Cd-accumulating indica 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 qCdp7 allele to produce a practical rice line for Cd phytoextraction by improving several agronomic traits for compatibility with Japanese cultivation systems.

The Road to Practical Application of Cadmium Phytoremediation Using Rice

“…‘TJTT8’ was developed from BILs derived from ‘Jarjan’ and ‘Tachisugata’ [ 38 ]. ‘Tachisugata’ is a japonica - indica hybrid variety used as a livestock feed.…”

“…The grains of ‘TJTT8’ are dark brown color and can easily be distinguished from the grains of general japonica varieties like ‘MJ3’ ( Table 1 ). ‘TJTT8’ was selected using the qCdp7 allele and showed the same level of Cd extraction as ‘Jarjan’ at several locations of Cd-contaminated paddy fields in Japan [ 38 ]. However, the heading date and maturing date of ‘MJ3’, ‘MA22’, and ‘TJTT8’ were too late in northern parts of Japan.…”

Breeding and characterization of the high cadmium-accumulating rice line ‘Akita 119’

“…However, high Cd-accumulating rice cultivars such as 'Cho-ko-koku', 'Jarjan', and 'Anjana Dhan' are difficult to cultivate because they tend to shatter and are easily lodged. Abe et al (2013Abe et al ( , 2017 produced the rice line 'MJ3', 'MA22', and 'TJTT8' for Cd phytoremediation. 'MJ3' and 'MA22' were obtained by a gamma ray mutation of 'Jarjan' and 'Anjana Dhan', respectively.…”

“…'TJTT8' was obtained by backcrosses of 'Tachisugata', a rice variety used as a livestock feed after it is crossed with 'Jarjan'. 'MJ3' and 'TJTT8' accumulate high levels of Cd, with both varieties having a non-shattering habit and lodging resistance (Abe et al 2013(Abe et al , 2017. However, the heading and maturing day of 'MJ3' are too late for it to be grown in Akita Prefecture, and it is difficult to obtain 'TJTT8' seeds due to sterility.…”

“… Abe et al (2013 , 2017 ) produced the rice line ‘MJ3’, ‘MA22’, and ‘TJTT8’ for Cd phytoremediation. ‘MJ3’ and ‘MA22’ were obtained by a gamma ray mutation of ‘Jarjan’ and ‘Anjana Dhan’, respectively.…”