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Abstract

Micronutrient deficiency in soils is a fast emerging phenomenon and a challenging abiotic stress in world agriculture. Most important micronutrients that the developing and developed world is concerned from point of view of sustaining grain productivity and malnutrition in human beings are iron and zinc. Biofortification of staple food crops with micronutrients by either breeding for higher uptake efficiency or fertilization can be an effective strategy to address widespread dietary deficiency in human populations. Cereal species greatly differ in their micronutrient efficiency (MiE), defined in this paper as the ability of a plant to grow and yield well under micronutrient deficiency. MiE generally has been attributed to the efficiency of acquisition of nutrients under conditions of their low soil availability rather than to its utilisation or (re)-translocation within a plant. A higher zinc and iron acquisition efficiency of genotypes could be attributed to either or all of the following; an efficient ionic metal uptake system, better root architecture i.e., long and fine roots with architecture favouring exploitation of micronutrients from larger soil volume, higher synthesis and release of metal mobilising phytosiderophore by the roots and uptake of Fe- and Zn-phytosiderophore complex. Seed Zn content has also been suggested to affect the respective MiE. Root morphology and characteristics and interaction between micronutrients and other ionic radicals have been implicated as determinants of MiE. This review attempts to examine critically the scanty and scattered reports available on status of micronutrient deficiency with special reference to Zn, globally; morphological, biochemical and physiological basis of regulation of MiE in cereals and approaches to improve MiE in terms of grain productivity and grain Fe and Zn vis-à-vis its bioavailability under conditions of poor micronutrient availability.