A rapid, seedling-based bioassay for identifying low cadmium-accumulating individuals of Durum wheat (Triticum turgidum L.)

We have developed a seedling-based bioassay that is capable of identifying low Cd-accumulating phenotypes (homozygous and heterozygous) after 96-120 h of exposure. Our experiments were conducted using Cd-109 as a tracer at subtoxic concentrations to simulate conditions that might be experienced in the field. Supply of Cd (10(-11) M) to 4-d old seedlings for 0-8 h resulted in no differences in root and leaf Cd content between the low (TL05) and high (TL04) Cd-accumulating isolines. Increasing time of exposure produced significant differences in leaf Cd accumulation between isolines, with differences becoming most pronounced after the bulk of applied cadmium (similar to 95%) was depleted from absorption solutions (greater than or equal to 72 h). Similar results were obtained with 8-d old seedlings, where differences between genotypes were more pronounced in young leaves (2nd leaf) or shoot bases. Individuals from five low and high Cd-accumulating near isogenic pairs (50 individuals/isoline) were screened using Cd concentration of shoot bases as the screening criterion. Mean scores within each isoline pair were significantly different, although overlap of individual scores was observed at intermediate foliar Cd concentrations. The 2(n)d leaf to root Cd content ratio, which reflects root to shoot translocation, provided a better parameter to distinguish low from high Cd-accumulating isolines. Plants used for this bioassay could also be rescued for subsequent experimental crosses, providing a rapid and cost-effective tool for early detection of the low Cd-accumulating phenotype.