Developing of a simple method for screening soybean seedling cadmium accumulation to select soybean genotypes with low seed cadmium

Significant inter-cultivar differences of soybean seed cadmium (Cd) concentrations arise from the inter-cultivar differences in root Cd accumulation ability. The Cd concentration in the shoots of plants at the vegetative stage is already controlled by the roots Cd concentration in the same way that it determines seed Cd concentration. Based on these results we conjectured that there is no need to wait until the full maturity stage because the inter-cultivar difference in seed Cd concentration can be predicted from the Cd concentration in the shoots of seedlings. To test this theory, we cultivated 150 cultivars/lines to the harvest stage in a field not contaminated with Cd and measured seed Cd concentration. We also planted seeds in pots filled with contaminated soil, cultivated them for 3 weeks, and measured the Cd concentration of the seedling obtained at the 5th-node (V5) stage when the 4th trifoliolate leaf had expanded. The 150 cultivars/lines were roughly divided into 2 groups based on the relationship between these 2 Cd concentrations. One group was cultivars in which seedlings and seeds both had low Cd concentrations (low Cd accumulation group, n = 129), and the other group was the opposite (high Cd accumulation group, n = 21). Further, when we predicted seed Cd concentration using the ratio of Cd and Zn concentrations in seedlings, we were able to clearly divide the 2 groups with no overlap. Measuring Cd/Zn in seedlings therefore makes it possible to select cultivars with low Cd accumulation tendency readily, without waiting to harvest the seeds. Additionally, by investigating genealogies we found that varieties in the high-Cd accumulation group were descended from certain cultivars such as Harosoy.