Differential Response of Soybean Varieties to Soil Cadmium

Of the trace elements being redistributed by our presentday society, Cd presents probably the greatest potential as a toxic agent in applications to soils. Numerous studies have indicated that various plant species accumulate differing toxic amounts of Cd, and that the toxic symptoms are exhibited differently. Studies to assess the possibility that different varieties of one plant species may exhibit a range of Cd uptake and/or susceptibility have not been conducted in a comprehensive manner. This paper presents the results of a comprehensive survey of the Cd uptake and effect by a number of the prominent soybean [Glycine max (L.) Merrill] varieties grown on several CdCI₂ or sewage sludge-amended soils in the glasshouse. In all varieties, Cd toxicity symptoms appeared as a continuum from slight effects observed as a red, red-brown, or purple coloration at the junction of the leaf blade and petiole, to severe leaf curling and extensive reddening of the leaf veins, chlorosis, and finally a brittle condition followed by abscission of the leaves. All varieties showed increased shoot Cd concentration and decreased dry weight in response to soil CdCl₂, but varietal differences in the severity of these Cd effects were observed. To quantify these differences in plant response to soil CdCI₂, indices based on the severity of visual symptoms, dry weight reduction, and shoot Cd concentration were used to rank the varieties according to Cd susceptibility. As all three rankings were significantly correlated, a composite susceptibility index based on all three criteria could be used to describe the response of each variety to Cd. Susceptibility index rankings of varieties grown on three different CdCl₂-amended soils were found to correlate with each other and with relative Cd concentrations of varieties grown on sewage sludge-amended soil. Soybean maturity groupings were not correlated with visual symptoms, dry weight reduction, or shoot Cd concentration. The data suggest that of the soybean varieties tested for Cd susceptibility on CdCl₂-amended soils that Dunfield, Harosoy, Arksoy, Dare, Flambeau, and Scioto were generally the most susceptible while Clark, Mandarin, Mukden, Jackson, and Lee were consistently ranked as less susceptible.