Adequate micronutrients in the daily diet are one of the prerequisites for human health. Estimates suggest that more than 900 million households worldwide suffer from micronutrient deficiency. In the developed world the nutritional content of food items is not of major concern, as individuals have access to a wide variety of foods that will meet all of their nutritional needs. In the developing world, however, this is often not the case, with people often relying on a single staple food crop for their energy intake (Christou P. and Twyman R.M., 2004). Fortification and supplementation, which are the traditional ways of balancing the diet, largely failed to nail the problem of malnutrition. An alternative approach to fortification through agricultural management and food processing is the accumulation of micronutrients directly in cereal seeds using conventional breeding or targeted genetic engineering. Two international programmes, "Harvest Plus and Grand Challenges in Global Health" using traditional and molecular techniques, are supporting the concept of biofortification.
Is Breeding For High Nutrient Content Scientifically Feasible?
Yes, the potential to increase the micronutrient density of staple foods by conventional breeding exists. Adequate genetic variation in concentrations of b-carotene, other functional carotenoids, iron, zinc, and other minerals exists among cultivars, making selection of nutritionally appropriate breeding materials possible. GM technology offers a way to alleviate some of these problems by engineering plants to express additional products that can combat malnutrition. An important example of the potential of this technology is the 'Golden Rice Project'. Vitamin A deficiency is widespread in the developing world and is estimated to account for the deaths of approximately 2 million children per year. Humans can synthesize vitamin A from its precursor β-carotene, which is commonly found in many plants but not in cereal grains. The strategy of the Golden Rice Project was to introduce the correct metabolic steps into rice endosperm to allow β-carotene synthesis. In 2000, Ye et al., engineered rice that contained moderate levels of β-carotene and since then researchers have produced the much higher yielding 'Golden Rice 2'. It is estimated that 72 g of Golden Rice 2 will provide 50% of the RDA of vitamin A for a 1-3-year-old child (Paine et al., 2005). Many different approaches have been taken to increase provitamin A content in crop plants, such as tomato, potato, brassica, maize and rice, by manipulating various genes of the carotenoid pathway (Ducreux et al., 2005; Sandmann et al., 2006 and Aluru et al., 2008). Iron deficiency is still the most important deficiency related to malnutrition. In 2002, Lucca et al., engineered rice that contained increased iron content.
Globally, nearly 200 million children younger than five years are undernourished for protein, leading to a number of health problems, including stunted growth, weakened resistance to infection and impaired intellectual development. 'Quality Protein Maize' (QPM) holds superior nutritional and biological value and is essentially interchangeable with normal maize in cultivation and kernel phenotype (Prasanna et al., 2001). The improvement of the amino acid composition of seed proteins has been a major long-term goal of plant breeding programs. In an attempt to improve the nutritional value of potato, the AmA1 gene was successfully introduced and expressed in tuber-specific and constitutive manner (Chakraborty et al., 2000)
To be successful, biofortification strategies must combine screening of germplasm for enhanced micronutrient content with breeding and genetic engineering strategies to improve the nutritional quality of cereals. Much basic research in this area is still required before future applications can be successful. Because of its social impact, and in view of public concerns about the genetic engineering of food crops, biofortification has also become an important topic in the socio-economic literature.
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