Diversity of seed cesium accumulation in soybean mini-core collections

Abstract

Radiocesium is an extremely harmful radionuclide because of its long half-life; it is important to reduce its transfer from contaminated soil into crops. Here we surveyed genetic variation for seed cesium (Cs) concentration in soybean mini-core collections representing large genetic diversity. The collections grown over 3 years in rotational paddy fields exhibited varying seed Cs concentrations with significant year-to-year correlations, although the phenotypic stability of Cs concentration was lower than that of the congeners potassium (K) and rubidium (Rb). Although Cs is supposedly accumulated in plants via the K transport system, there was no apparent relationship between Cs and K concentrations, whereas a clear positive correlation was observed between Cs and Rb concentrations. Cs and K concentrations in seed showed slightly positive and negative correlations, respectively, with days to flowering. We selected several high or low Cs accumulator candidates on the basis of the 3 years of seed concentration data. These two groups showed significantly different seed Cs concentrations in another field. The differences could not be explained by flowering time alone. These results suggest that genetic variation for seed Cs concentration is present in soybean germplasm and would be useful for breeding low Cs-accumulating varieties.

Keywords: Glycine max; cesium; core collection; genetic diversity; potassium; rubidium.

Fig. 1

Frequency distributions of days to flowering (A) and seed weight (B) in the mini-core collections grown in the Yawara field in 2013. Black and white bars represent JMC and WMC, respectively. JMC, Japanese Soybean Core Collection; WMC, World Soybean Core Collection.

Fig. 2

Frequency distributions of seed Cs concentration in the mini-core collections grown in the Yawara field in 2011 (A), 2012 (B), and 2013 (C). Black and white bars represent JMC and WMC, respectively. JMC, Japanese Soybean Core Collection; WMC, World Soybean Core Collection.

Fig. 3

Year-to-year correlation for seed concentration (mg/kg DW) of Cs (A) and K (B) in the mini-core collections grown in the Yawara field. Closed and open circles indicate JMC and WMC, respectively. Cs, cesium; JMC, Japanese Soybean Core Collection; K, potassium; WMC, World Soybean Core Collection.

Fig. 4

Correlations between the concentrations of Cs and other two alkali metals (mg/kg DW) in seeds of mini-core collections grown in the Yawara field; Cs-K (A) and Cs-Rb (B). Upper, middle and lower panels represent populations grown in 2011, 2012, and 2013, respectively. Closed and open circles indicate the JMC and WMC, respectively. Cs, cesium; JMC, Japanese Soybean Core Collection; K, potassium; Rb, rubidium; WMC, World Soybean Core Collection.

Fig. 5

Box-plot of seed Cs concentration in two experimental fields, Yawara (A) and Tsukuba (B). Filled box (left) and open box (right) indicate the two accession groups categorized as low or high Cs accumulator candidates, respectively, which were selected based on the Cs concentrations in the Yawara field. Boxes represent quartiles 25–75%, and horizontal line within the box represents the median of the distribution (quartile 50%). Bars indicate quartiles 1–25% (above) and 75–100% (below). ** indicates a significant difference between low and high Cs-accumulating groups at the 1% level using Welch’s t-test. Cs, cesium.