Root morphology of wheat genotypes differing in zinc efficiency

The root morphology (root length, diameter) of the three wheat genotypes (Triticum aestivum L. cvs Excalibur and Gatcher, and T. turgidum conv. durum (Desf.) McKay cv Durati) grown in zinc (Zn)-deficient, sandy soil under controlled conditions has been measured by a root scanner coupled to a computer. Wheat plants were supplied with 0, 0.025, 0.05, 0.1, 0.2, or 0.4 mg Zn/kg soil. Excalibur has previously been identified as the Zn-efficient genotype which can take up more Zn and has higher yield in soils with low plant-available Zn. Durati is Zn-inefficient and Gatcher an intermediate genotype with respect to Zn efficiency. Root and shoot dry matter significantly increased at 0.1 mg Zn/kg soil compared to the 0 Zn level. Zinc content in shoots was lower in Durati than in Excalibur and Gatcher at sufficient supply of Zn. Zinc applications had no significant effect on root morphology at two weeks after sowing. At that time, however, the Zn-efficient genotype Excalibur developed a longer and thinner roots (greater proportion of fine roots with diameter ≤0.2 mm) than the less efficient Gatcher and Zn-inefficient Durati. Hence, growing longer and thinner roots and having a greater proportion of thinner roots in the total root biomass early in the growth period may be the two characters associated with the Zn-efficient genotypes.