Cereal Biofortification: Challenges and Strategies
Authors: VANITA PANDEY, SEWA RAM, SNEH NARWAL, RINKI & PRIYANKA CHANDRA


The micronutrient deficiencies, particularly arising from zinc and iron, have been reported to cause serious health problems for more than two billion people worldwide. Iron deficiency anemia is by far the most widespread micronutrient deficiency, and it results in impaired physical growth, mental development, and learning capacity ( WHO, 2012). Numerous health problems link zinc deficiency to retarded growth, skeletal abnormalities, delayed wound healing, increased abortion risk, and diarrhea. The situation is even more adverse in developing countries where more than half of the children and pregnant women are suffering from iron and zinc deficiencies (Carter et al. 2010). This condition is largely attributed to the high consumption of cereal based foods, like rice, wheat and maize in these countries as the edible parts (endosperms) of modern cereal cultivars are inherently poor in iron and zinc minerals (Bouis et al., 2011). Iron and zinc concentration in whole grain of wheat are in the range of 29 to 73 mg/kg and 7 to 85 mg/kg, respectively. However, more than 75% of these nutrients are located in the seedy parts other than endosperm is lost during milling, ensuing in mineral deficient end products. Several strategies can be employed to alleviate the prevailing micronutrient deficiency, like:

• Supplementation

Nutrients directly delivered by means of syrups or pills

• Dietary diversification

Production, processing, marketing and consumption of a wide variety of foods.

• Fortification

Utilize widely accessible, commonly consumed foods to deliver one or more micronutrients.

• Biofortification

Biofortification is the process of increasing the bioavailable concentration of essential elements in the edible portions of crops leading to the enhancement of nutritional content of the crops and cultivars (White and Broadley 2005). In cereals biofortification can be realized by:

• Increasing the overall mineral content in seed grains.
• Increasing the levels of nutrients and compounds that promote bioavailability of essential minerals.
• Reducing the level of antinutrients in the food staples which reduce the bioavailability of dietary essential minerals.

Importance of biofortification in cereals

Wheat and rice are the major food crops of the world, contributing most to the edible dry matter production and up to 90% of the daily energy intake in several developing and developed countries (Wang et al., 2011). Therefore, the composition and nutritional quality of the cereal grains have a significant impact on human health and the enhancement of their nutritional profile which can significantly alleviate malnutrition for the economically weaker section of the society ( Welch and Graham, 2004). Biofortification in cereals can be successfully achieved through genetic or agronomic interventions.

• Genetic biofortification

Many studies have shown that there is a wide variation in grain Fe and Zinc concentrations in wild relatives of modern wheat and the concentrations found can significantly exceed those found in modern elite cultivars. This natural variation can be utilized to biofortify wheat for Fe and Zinc minerals. Targeted breeding for these biofortified varieties is initiated by exploiting this available genetic diversity in the wild relatives of cultivated wheat and the synthetic hexaploid progenitors. The proof-of-concept results from the performance of competitive biofortified wheat lines have showed good adaptation in target environments without compromising essential core agronomic traits (Cakmak et al., 2000). Moreover, improving crop varieties by either conventional breeding or transgenic methods has the advantage that once the initial research and development is completed, the benefits from these nutritionally-enhanced crops will be sustainable with little further investment.

Another aspect of genetic biofortification involves reduction of inhibitors of mineral absorption or availability like phytic acid ( Bouis, 2003). This involves increased expression of its degradation genes like phytase or silencing of the genes involved in phytic acid biosynthesis and transport. Both the strategies are under consideration and significant research is being done.

Genetic biofortification is more cost effective than food fortification, supplementation or dietary diversification in the long run, because it requires only one period of (breeding) investments.

• Agronomic Biofortification

Agronomic biofortification is achieved through micronutrient fertilizer application to the soil and/or foliar application directly to the leaves of the crop. The most effective agronomic practices for the iron enrichment of crops are through litter fertilization or foliar application of mineral iron. Foliar application of iron has led to increased concentration in both wheat and rice grains (Zhang et al. 2010). Further, evidence suggests that nitrogen nutritional status of plants can have a positive impact on root uptake and the deposition of micronutrients in seed (Distelfeld et al. 2007). Extensive research has been completed on the role of zinc fertilizers in increasing the zinc density of grain, suggesting that where fertilizers are available, making full use of zinc fertilizers can provide an immediate and effective option to increase grain zinc concentration, and productivity in particular, under soil conditions with severe zinc deficiency (Zhang et al. 2010).

Agronomic biofortification is often considered as a short-term solution to increase micronutrient availability and is mainly used to complement genetic biofortification (breeding). Agronomic biofortification through fertilizer approaches could complement the existing breeding approach; for instance, foliar application of zinc fertilizer can increase grain zinc above the breeding target set by nutritionists.

Conclusion

Biofortification of cereals is the most promising intervention to overcome iron and zinc malnutrition due to its cost-effectiveness. Bioavailability of iron and zinc from cereal grains can be increased by genetic interventions by modulating accumulation of either anti-nutrient agents or prebiotics. Enhanced accumulation of iron and zinc in cereal grains can be achieved by fertilization or genetically manipulating iron and/or zinc homeostasis-related genes. Future research should involve analyzing the accumulation of iron and zinc in the edible parts of cereal grains rather than whole grains. It is also advised that the impact of genetic modifications on the agronomic performance of crops, including grain yield, drought tolerance, insect resistance, disease resistance, and so on should also be assessed. In addition, the focus should be on studies involving field crop trials and human beings as experimental subjects to analyze the effectiveness of agronomic or genetic biofortification.

References:


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About Author / Additional Info:
VANITA PANDEY and RINKI are Scientist, SEWA RAM and SNEH NARWAL are Principal Scientist at ICAR-IIWBR, Karnal; and PRIYANKA CHANDRA is Scientist at ICAR-CSSRI, Karnal.