Breeding Wheat for Zinc Efficiency Improvement in Semi-arid Climate - A Review

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Wheat (Triticum aestivum L.) is one of the most important cereal crops of the world. Zinc deficiency is one of the most common deficiencies in soils worldwide. Several plant metabolic processes and biological functions are impaired under Zn deficient conditions. The most visible symptoms of zinc deficiency are a reduction in shoot growth, decrease in leaf size, chlorophyll degeneration and the emergence of whitish-brown necrotic patches on leaves. The genotypes that show the highest percent response to added Zn and are unable to grow well without Zn are defined as being susceptible to Zn deficiency and vice versa. Zinc efficiency is the ability of a plant to grow and produce grain when Zinc availability is low. Breeding cereals with enhanced zinc efficiency can decrease fertilizer dependency, improve seed-ling vigor, increase resistance to abiotic and biotic stress and enhance yield and nutritional value of wheat. A survey of the literature, as well as own experiences, show that there is enough genetic variation in wheat and alien species, particularly rye, for suitable zinc-efficient alleles. Genetic control is fairly simple, making breeding for this trait feasible. Since selection for Zinc efficiency in a breeding program is limited by the high spatial variability of zinc in field sites, better field screening techniques and selection criteria are needed to allow screening of early-generation segregating materials. Zn specific diagnostic methods like reflectance analysis and molecular markers (proteins /DNA markers) could complement the screening of wheat genotypes for zinc efficiency. Breeding wheat for enhanced zinc efficiency and higher grain yield would require concentrating the quantitative trait loci governing these traits in a few agronomic backgrounds through recombination breeding. This literature review paper delves into genetic variability, screening methods, plant breeding options and methodologies and other related issues for improving zinc efficiency in wheat.