Abstract
Zinc (Zn) deficiency is a major constraint to rice production and Zn is also often deficient in humans with rice-based diets. Efforts to breed more Zn-efficient rice are constrained by poor understanding of the mechanisms of tolerance to deficiency. Here we assess the contributions of root growth and root Zn uptake efficiency, and we seek to explain the results in terms of specific mechanisms. We made a field experiment in a highly Zn-deficient rice soil in the Philippines with deficiency-tolerant and -sensitive genotypes, and measured growth, Zn uptake and root development. We also measured the effect of planting density. Tolerant genotypes produced more crown roots per plant and had greater uptake rates per unit root surface area; the latter was at least as important as root number to overall tolerance. Tolerant and sensitive genotypes took up more Zn per plant at greater planting densities. The greater uptake per unit root surface area, and the planting density effect can only be explained by root-induced changes in the rhizosphere, either solubilizing Zn, or neutralizing a toxin that impedes Zn uptake (possibly or Fe2+), or both. Traits for these and crown root number are potential breeding targets.
Highlights
Decreased crop growth and yield under low soil zinc (Zn) availability is a widespread problem in rice because of the particular chemistry of submerged paddy soils (Dobermann and Fairhurst, 2000)
The objectives of this study were to establish whether superior Zn uptake in Zn-deficient soil by tolerant rice genotypes is causally related to genotypic differences in crown root development or Zn uptake efficiency
That Zn was the growth-limiting factor was confirmed by the sharp decline of shoot Zn concentrations below the critical threshold level of 15 μg Zn g−1 (Dobermann and Fairhurst, 2000) from 14 days after transplanting (DAT) onwards, whereas Zn concentrations remained above 20 μg Zn g−1 in the +Zn treatment (Table 1)
Summary
Decreased crop growth and yield under low soil zinc (Zn) availability is a widespread problem in rice because of the particular chemistry of submerged paddy soils (Dobermann and Fairhurst, 2000). Reducing conditions in submerged soils tend to make Zn insoluble and unavailable to plants, even though total amounts are generally many orders of magnitude greater than crop requirements. Deficiency in the crop causes deficiency in human populations with rice-based diets, and human Zn deficiency is one of the most widespread and serious health problems in developing countries (WHO, 2002; Gibson, 2006; Hess et al, 2009; Graham et al, 2012). Dietary and crop Zn deficiency are inevitably linked in areas with Zn-deficient soils, as in large parts of south and south-east Asia where rice is the staple (Maclean et al, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
