Albert A. Schneiter

Screening for low grain cadmium phenotypes in sunflower, durum wheat and flax

Cadmium (Cd) level in nonoilseed sunflower (Helianthus annuus L.), flax (Linum usitatissimum L.), and durum wheat (Triticum turgidum L. var. durum) grown on uncontaminated, alkaline soils has exceeded limits established in Northern Europe. Separate field experiments were conducted to investigate variability of grain Cd levels among sunflower, durum wheat and flax germplasm, and to seek an efficient screening method for future breeding. There were large variations in leaf Cd concentration among 200 sunflower lines. These lines performed more consistently for Cd uptake at the R5 stage than at the V8 stage across 4 locations with markedly differing soils. Cd concentration in V8 leaves was not related to Cd in grain. The positive correlation between R5 leaf Cd and kernel Cd level was obtained from nonoilseed hybrid (Sigco 954) (R2; = 0.74**), and 200 lines (R2 = 0.44**) tested over 4 locations in 2 field trials, respectively. This indicates that an efficient and low cost screening method can be developed for genotype selection, but plants must be grown to the R5 stage. A preliminary evaluation of 30 durum wheat and 74 flax lines indicated large variations in grain Cd level of durum wheat and flax. Grain Cd concentration ranged from 0.11 to 0.34 mg Cd kg-1 DW for durum wheat, and 0.14 to 1.37 mg Cd kg-1 DW for flax, respectively. This variability indicates that breeding for low grain Cd in durum wheat and flax should be feasible.

Effect of soil chloride level on cadmium concentration in sunflower kernels

Understanding soil factors related to cadmium (Cd) uptake and accumulation in plants is important for development of agronomic technologies, and breeding strategy to produce low Cd crops. The objective of the study was to examine the effect of soluble salts (chloride and sulfate) and other soil factors on the Cd concentration in sunflower (Helianthus annuus L.) kernels. Commercial nonoilseed hybrid kernels and soils were sampled from 22 farmers production fields in North Dakota and Minnesota. The sites sampled included saline and nonsaline variants from 7 soil series. Soils were sampled at four depths. Relationships between kernel Cd level and soil physical and chemical characteristics were examined. The soil pH covered a narrow range (7.3–8.1) at these sampled sites. Regression analysis showed that there was no correlation between kernel Cd and soil pH at any depth. The kernel Cd level was highly correlated with DTPA-extractable Cd in all 4 depths, and with clay content in sub-soils. Soil chloride and sulfate concentrations varied among soil series and within soil series. The absence of a statistically significant effect of soil sulfate level on kernel Cd concentration, indicated that soil sulfate levels did not affect Cd uptake by sunflower plants. However, soil chloride levels in sub-soil were correlated with kernel Cd. The most important soil factor was DTPA-extractable Cd. When chloride was included in the multiple regression equations, R square (R2) values improved significantly. These results demonstrate that soil chloride concentration is another important factor related to Cd uptake in sunflower plants.

Effect of field limestone applications on cadmium content of sunflower (Helianthus annuus L.) leaves and kernels

Nonoilseed sunflower (Helianthus annuus L.) is naturally higher in cadmium (Cd) than many other grain crops. Because raising soil pH usually depresses Cd uptake by most species, a study was designed to determine if application of agricultural limestone to neutralize soil acidity would decrease Cd uptake by sunflower plants grown on different soils in the production area of North Dakota. The field experiments were conducted at 3 locations in 1991 and 2 locations in 1992. At each site, limestone was applied to bring soil pH to 6.5–7.0, or an additional 45 Mg ha-1 more limestone was applied, and these two treatments were compared to no-lime control. Commercial nonoilseed hybrid 954 was planted in these experiments. The rapid short-term lime-soil reaction occurred in first 12 weeks following limestone application. Mean kernel Cd concentration for each treatment varied from 0.35 to 1.45 mg kg-1 DW in the first year of the experiments, and from 0.37 to 1.23 mg kg-1 DW in the experiments of 1992 across all locations. Large variations in kernel Cd levels between locations were obtained. There were no significant differences among control and limestone treatments for kernel Cd, seedling leaf Cd and diagnostic leaf Cd within each location, respectively. In regression analysis, we found that kernel Cd level correlated with diagnostic leaf Cd concentration in each treatment, but poor correlations were obtained among other variables. These results indicated that limestone application did not reduce Cd uptake and transfer to kernels of sunflower, in contrast with most species studied.