Submitted to: Proceedings of the Second Workshop on Risk Assessment and Management of Environmental Cadmium
Publication Type: Proceedings
Publication Acceptance Date: 11/15/2003
Publication Date: 12/1/2003
Citation: Grant, C.A., Clarke, J.M., Duguid, S., Chaney, R.L. 2003. Use of genetic variability in reducing cadmium uptake by plants. Proceedings of the SCOPE Workshop on Risk Assessment and Management of Environmental Cadmium (Ghent, Belgium, September 3-5, 2003) UNEP-SCOPE, Paris.
Interpretive Summary: All crops accumulate some cadmium from soils, but some crops accumulate soil cadmium more effectively that others, and some soils are geochemically enriched in cadmium or contaminated with cadmium. Excessive lifetime cadmium consumption can cause renal tubular dysfunction in susceptible individuals, especially subsistence rice consumers. One method to minimize the possibility that consumers will ingest excessive cadmium in foods is to breed crop cultivars which accumulate lower levels of cadmium in the edible plant tissue (e.g., grain). Major or staple foods are of greater importance if breeding for low cadmium is needed, but minor foods which accumulate higher levels of cadmium than most other crops may also need crop breeding work to lower crop Cd. The present paper summarizes the literature on research and development activities to breed lower cadmium cultivars of rice, durum wheat, soybean, flax and confectionery sunflower. In each case, diverse genetic types were grown at one location and analyzed to find parent genotypes with lower cadmium accumulation. Then inheritance studies were conducted to learn how best to incorporate the low cadmium trait into modern adapted cultivars. In the case of durum wheat, a single dominant gene gave about 60% lower grain cadmium than most adapted cultivars in 1994. This gene was incorporated in all breeding lines of durum wheat in Canada and the first low cadmium cultivars were recently released. Lower grain cadmium was observed on all test fields in the development research. In the case of sunflower kernels, 200 diverse genotypes were evaluated and low Cd types identified. The low Cd trait was incorporated into inbred and restorer lines so that low Cd hybrids could be produced. The first lower cadmium sunflower hybrid was released in 2003. For other crops, research has shown significant cultivar differences in cadmium accumulation into the edible crop tissue in each crop evaluated. However, only flax has been examined for diversity of parent materials to develop lower Cd types. Although breeding lower cadmium cultivars is possible, it is more difficult and expensive than most recognize. Cultivars are continuingly improved over time, and the lower cadmium trait would have to be monitored or it could be lost. Other important breeding goals usually control investment in plant cultivar improvement, including yield, disease resistance, quality, and nutrient content. Because the low cadmium trait must be characterized by analysis of plant tissues, it is relatively more expensive than many other breeding goals. Biotechnology methods to assay the Cd trait in seedlings have been developed, and analysis of seedlings can also allow one to discard undesired progenies in the breeding process. Further, because crop iron and zinc play a significant role in the bioavailability of crop cadmium, one method to reduce risks from soil cadmium is to breed rice with higher levels of iron and zinc in polished grain.
Technical Abstract: Trace element content of food has a large impact on human health. Deficiencies of essential nutrients such as Fe, Zn and Se are widespread, while excess accumulations of potentially toxic trace elements such as Cd may also occur. This is of particular concern in staple crops such as cereals, which make up a large proportion of the diet. Natural variation occurs in the uptake and distribution of essential and nonessential trace elements in crop species and in cultivars within species. Therefore, plant breeding can be an important tool to improve crop quality, both by increasing crop concentrations of desirable trace elements and reducing the concentration of potentially harmful trace elements such as Cd. Selection programs for low Cd content of various crops have been established and low-Cd durum wheat cultivars and sunflower hybrids have been developed. In durum wheat (Triticum turgidum L. var durum), low Cd concentration is controlled by as single dominant gene. The trait is highly heritable, and incorporation of the low-Cd allele reduces average grain Cd to levels below proposed international limits. The allele for low Cd concentration does not appear to affect major economic traits or the concentrations of other ions, and should not cause problems when incorporated into durum cultivars. Maintaining a specific trait, such as low Cd, in newly developed lines requires continued selection and investment in an on-going breeding effort. Production of low-Cd crops cultivars can be used as a short-term tool to reduce the risk of movement of Cd into the human diet. However, accumulation of phytoavailable Cd in soils may still be a concern for the long-term sustainability of crop production and quality.