Greenhouse experiments were carried out with six diploid, nine tetraploid and seven hexaploid wheats, including wild and primitive genotypes, to study the influence of varied zinc (Zn) supply on the severity of Zn deficiency symptoms, shoot dry matter production and shoot Zn concentrations. In addition to wild and primitive genotypes, one modern tetraploid cultivar with high sensitivity to Zn deficiency and two modern hexaploid cultivars, one highly sensitive to and one resistant to Zn deficiency, were included for comparison. Plants were grown for 44 d in a severely Zn-deficient calcareous soil, with (+Zn; 5 mg Zn kg(-1) soil) and without (-Zn) Zn fertilization. Visible Zn deficiency symptoms, including whitish-brown necrotic patches on leaf blades, appeared very rapidly and severely in all tetraploid wheat genotypes. Compared with tetraploid wheats, diploid and hexaploid wheats were less sensitive to Zn deficiency. With additional Zn, shoot dry matter production was higher in tetraploid than diploid and hexaploid wheats. However, under Zn-deficient conditions tetraploid wheats had the lowest shoot dry matter production, indicating the very high sensitivity of tetraploid wheats to Zn deficiency. Consequently, Zn efficiency expressed as the ratio of shoot dry matter produced under Zn deficiency to Zn fertilization was much lower in tetraploid wheats than in diploid and hexaploid wheats. On average, Zn efficiency ratios were 36% for tetraploid, 60% for diploid and 64% for hexaploid wheats. Differences in Zn efficiency among and within diploid, tetraploid and hexaploid wheats were positively related to the amount of Zn per shoot of the genotypes, but not to the amount of Zn per unit dry weight of shoots or seeds used in the experiments. The seeds of the accessions of tetraploid wild wheats contained up to 120 mg Zn kg(-1), but the resulting plants showed very high sensitivity to Zn deficiency. By contrast, hexaploid wheats and primitive diploid wheats with much lower Zn concentrations in seeds had higher Zn efficiencies. It is suggested that not only enhanced Zn uptake capacity but also enhanced internal Zn utilization capacity of genotypes play important roles in differential expression of Zn efficiency. The results of this study also suggest the importance of the A and D genomes as the possible source of genes determining Zn efficiency in wheat. (C) 1999 Annals of Botany Company.