title: Rice Genotype Differences in Tolerance of Zinc-Deficient Soils: Evidence for the Importance of Root-Induced Changes in the Rhizosphere.
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 [Formula: see text] or Fe(2+)), or both. Traits for these and crown root number are potential breeding targets.
authors.affiliation: Crop Production and Environment Division, Japan International Research Center for Agricultural Sciences Tsukuba, Japan.
authors.forename: Asako
authors.initials: A
authors.lastname: Mori
authors.affiliation: Cranfield Soil and Agrifood Institute, School of Energy, Environment and Agrifood, Cranfield University Cranfield, UK.
authors.forename: Guy J D
authors.initials: GJ
authors.lastname: Kirk
authors.affiliation: Crop and Environmental Sciences Division, International Rice Research Institute Metro Manila, Philippines.
authors.forename: Jae-Sung
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Crop and Environmental Sciences Division, International Rice Research Institute Metro Manila, Philippines.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Morete
authors.affiliation: Crop Production and Environment Division, Japan International Research Center for Agricultural Sciences Tsukuba, Japan.
authors.forename: Amrit K
authors.initials: AK
authors.lastname: Nanda
authors.affiliation: Crop and Environmental Sciences Division, International Rice Research Institute Metro Manila, Philippines.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Johnson-Beebout
authors.affiliation: Crop Production and Environment Division, Japan International Research Center for Agricultural Sciences Tsukuba, Japan.
authors.forename: Matthias
authors.initials: M
authors.lastname: Wissuwa
keywords: crown roots; genotype; micronutrient; rhizosphere; root efficiency; root surface area