Differences in zinc efficiency among and within diploid, tetraploid and hexaploid wheats

Greenhouse experiments were carried out with six diploid, nine tetraploid a nd 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 addit ion to wild and primitive genotypes, one modern tetraploid cultivar with hi gh sensitivity to Zn deficiency and two modern hexaploid cultivars, one hig hly sensitive to and one resistant to Zn deficiency, were included for comp arison. Plants were grown for 44 d in a severely Zn-deficient calcareous so il, with (+Zn; 5 mg Zn kg(-1) soil) and without (-Zn) Zn fertilization. Vis ible Zn deficiency symptoms, including whitish-brown necrotic patches on le af blades, appeared very rapidly and severely in all tetraploid wheat genot ypes. Compared with tetraploid wheats, diploid and hexaploid wheats were le ss sensitive to Zn deficiency. With additional Zn, shoot dry matter product ion was higher in tetraploid than diploid and hexaploid wheats. However, un der Zn-deficient conditions tetraploid wheats had the lowest shoot dry matt er 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 hexa ploid wheats. Differences in Zn efficiency among and within diploid, tetrap loid and hexaploid wheats were positively related to the amount of Zn per s hoot of the genotypes, but not to the amount of Zn per unit dry weight of s hoots or seeds used in the experiments. The seeds of the accessions of tetr aploid wild wheats contained up to 120 mg Zn kg(-1), but the resulting plan ts showed very high sensitivity to Zn deficiency. By contrast, hexaploid wh eats and primitive diploid wheats with much lower Zn concentrations in seed s had higher Zn efficiencies. It is suggested that not only enhanced Zn upt ake capacity but also enhanced internal Zn utilization capacity of genotype s play important roles in differential expression of Zn efficiency. The res ults of this study also suggest the importance of the A and D genomes as th e possible source of genes determining Zn efficiency in wheat. (C) 1999 Ann als of Botany Company.