Cereal Breeding For Zinc Deficiency and Its Importance to Alleviate Drought Stress

Drought stress limits zinc absorption by cereal plant because of reduction of root growth and development as well as declining zinc movement in soil. On the other hand, tolerance to drought needs enough available zinc for plant to well regulate expression of genes that are responsible for cell protection against drought stress. Moreover, zinc deficient plants unable to detoxify reactive oxygen species (ROS) under drought stress conditions. Hence, zinc deficiency along with drought lessen grain yield and its nutritional quality, which cause hidden hunger in billions people worldwide. Although, zinc fertilizers can solve the problem, but it is not a sustainable solution in drylands because of soil surface dryness, zinc fixation in clay soils, and fertilizer unavailability. Along with zinc fertilizers, cultivation of zinc efficient varieties will be a complementary and viable solution in drylands. Hence, breeding zinc efficient cereals is a sustainable and necessary method to improve grain yield and nutritional quality of people food in 2025. Zinc deficiency in crops is the most widespread micronutrient deficiency, with about 50% of the cereal-growing area worldwide containing low levels of plant-available Zn. Zinc deficiency in soils reduces yield and nutritional quality of cereal (e.g. wheat) and afflicts 1 billion people especially in many developing countries like Iran. Sustainable solutions can only be developed through agricultural system approaches such as plant breeding. Micronutrient enrichment traits are available within wheat genomes that could allow for substantial increases in Fe, Zn and without negatively impacting protein and yield. There is considerable genotypic variation both within and between cereals for micronutrient efficiency. A number of studies have demonstrated differential Zn efficiency in barley, suggesting that genotypic variation could be exploited in breeding programs to produce genotypes with higher Zn efficiency. Various mechanisms may explain Zn efficiency in crops, including increased Zn uptake, increased Zn availability in the rhizosphere due to release of root exudates, and more efficient internal Zn use. In wheat and barley, Zn-uptake capacity of roots is one of the mechanisms of Zn efficiency. Drought stress and zinc (Zn) deficiency are serious abiotic stress factors limiting crop production in drylands of Iran, but the interaction between Zn deficiency and drought stress has not been studied extensively. Zinc nutritional status of plants may affect the drought sensitivity of plants in different ways. Zinc-deficient plants use water less efficiently and are less able to respond to increasing soil water deficits by osmotic adjustment than plants that are supplied with adequate levels of Zn. Moreover, drought stress kills plants by inducing production of reactive oxygen species (ROS). An adequate Zn nutrition can be involved in detoxification of ROS, and it is also important for reducing the production of free radicals. Therefore, likely that drought stress-related yield loss is additionally accentuated when plants would simultaneously suffer from Zn-deficiency stress. On the other hand, the review of literature indicates that application of Zn fertilizers has a potential to increase availability of Zn to plants, which will result in enhanced drought tolerance.