India has achieved self-sufficiency in food production and the country possesses surplus stock at present, but availability of food is not enough; access to nutritious food for the millions of struggling, especially children, adolescent girls, pregnant and lactating women and labour classes is as important.
Nutritional security remains a big challenge but it can be tackled with committed scientific efforts and policy support, in terms of development of crop varieties rich in nutrients, especially micronutrients, and an efficient distribution mechanism.
Micronutrient malnutrition, which is often referred to as “hidden hunger”, has been and continues to be a major global health issue. It not only retards growth but also reduces productivity, human resource efficiency and mental ability. It also causes blindness in children, lower resistance to disease in both children and adults, and increased risks for both mothers and infants during childbirth. According to the estimates of World Health Organization (WHO), more than 2 billion people in the world today may be affected by micronutrient malnutrition.
Global mortality of children due to iron, zinc and vitamin A deficiency is alarming and, paradoxically, the most affected populations exist in rural areas where food is produced. The medical supplementation and fortification programmes under health department schemes may be expensive and not sustainable, so biofortification of staple food is a logical approach for addressing vitamin and micronutrient deficiencies.
Earlier, scientists emphasised on development of crop varieties for yield potential and resistance to biotic and abiotic stresses, but now micronutrient concentration in the edible parts of crops has also become an important criterion while developing new genotypes. Leading global economists have identified investing in crop biofortification as a cost-effective measure. The problem of hidden hunger is mostly concentrated in the under-developed and developing countries where dietary intake comprises very high amounts of staple foods, mainly rice, maize and wheat, but also a few micronutrient-rich foods such as fruits, vegetables, and animal products. Bio-fortification of these cereals, therefore, can help provide much needed vitamins and minerals without a change in eating habits.
The greatest potential, however, lies in bio-fortification of rice, which is the staple food for more than half the world’s population and for billions of poor in the developing world. In the past few decades, rice has occupied a prominent position as a strategic crop for food security and economic development in many nations of the world. In India it is the staple food of about 65% of the population and reaches the most vulnerable and poorer sections across the country. A small increase in its nutritive value would be highly significant due to high daily consumption of rice. This makes rice an ideal staple crop to bio-fortify.
There are two approaches to the bio-fortification of rice: the breeding approach, i.e., exploring possibility of gene transfer for improving micronutrient density in grains; and agronomical bio-fortification, which is maintaining soil environment for adequate supply of mineral nutrients. Both these approaches have resulted in a new paradigm for improved nutrition. Improving mineral nutrition through biotechnology may be a more sustainable strategy to combat deficiencies in human populations but the view that breeding approach is the only convenient and sustainable bio-fortification approach is wrong in our opinion, because if the soils are starved and critically deficient in micronutrients, the benefits of these varieties cannot be harvested.
Moreover, commercial cultivation of genetically biofortified crops will create more pressure on soil micronutrient pool. This will be more important in those soils which are already hungry. Biofortification should therefore be considered as an integrated approach in which both genetic and management components must remain equally important for sustainability.
The ability and efficiency of a crop or a crop variety to uptake, translocate, assimilate and accumulate micronutrients in certain body parts is a genetically controlled physiological activity. Scientists are searching for genotypes which naturally possess the desired concentration of micronutrients and further can be used to breed new varieties with higher yield potential and micronutrient density.
In view of widespread micronutrient deficiency, particularly with respect to iron and zinc, bio-fortification of rice has become an issue of global significance. Some institutes and private companies have already made breakthroughs in this regard. Harvest Plus, for instance, is involved in a research project on increasing the density of iron and zinc in the edible portion of staple food crops including rice. Indian Council of Agriculture Research (ICAR) has so far released 17 varieties belonging to 8 crops which are rich in nutrients including 6 rice varieties (DRR Dhan 45, DRR Dhan 48, DRR Dhan 49, Zinco Rice MS, CR Dhan 311 and CR Dhan 315). These rice varieties are rich in Zn and its content in polished grain of these varieties ranges from 20.1 ppm to 27.4 pmm compared to 12 to 16 ppm found in popular varieties. The advantage of these varieties is that they are also high yielding for the recommended ecologies. There are other varieties which may contain a bit higher Zn content but yield may be an issue.
Like Zinc, Iron (Fe) is an essential micronutrient that is deficient in a huge chunk of the population. It is needed to produce haemoglobin and prevents anaemia, a deadly Fe-deficiency disease. It is also important for brain, lungs and nervous system. Its deficiency results in diminished work performance, impaired body temperature regulation and intellectual performance, detrimental behavioural changes and decreased resistance to infection. Women are particularly at risk of Fe deficiency owing to elevated requirements of Fe for child-bearing. In rice, most of the Fe is accumulated in the aleurone layer of the grain. During the milling process the removal of the outer layers of the rice seed therefore considerably reduces the level of Fe in the grains. Varieties with high level of Fe in the endosperm hold the key to improving Fe intake.
Both plants and animals use ferritin (organic form) as the form of Fe storage during developmental stage. The ferritin protein stores Fe in a non-toxic form and releases it when needed for metabolic functions, as Fe stored in ferritin rice is bioavailable. Initially in some experiments with rice, ferritin gene expression driven by a constitutive promoter led to an increase in Fe content of the vegetative parts of rice but not in the seeds. However, the initiative by IRRI in collaboration with Department of Plant Science, University of Adelaide, Australia opened new vistas in rice biofortification. During the investigations it was found that traditional varieties Jalmagan and Zuchen, for instance, contained almost double the Fe content in comparison to widely grown high yielding varieties IR-36 and IR-64. Crossing high yielding varieties with these traditional varieties have yielded progenies with elevated Fe content and higher grain yields.
Introduction of soya gene (ferritin) into japonica rice (kita-ake) through genetic engineering has resulted in transgenic rice with Fe content twice as much. Researchers using the targeted expression of two transgenes, nicotianamine synthase and ferritin, reported an increase in Fe content of rice endosperm by more than six-fold, perhaps the highest reported in genetically engineered rice. ICAR again has accomplished the target of Fe fortification in crops like wheat millets and pulses. Five wheat varieties have been released which are rich in Fe, Zn and protein. The Fe content in these varieties ranges from 39.5 ppm to 43 ppm compared to 28 to 32 ppm in popular varieties.
In addition to this, varieties of millet crops developed by ICAR have Fe content ranging from 39 to 131.8 ppm which is much higher than normal. Similarly, vitamin A is considered vital for growth and repair of body tissues, healthy eyes, good night vision and strong immune system. Vitamin A deficiency is widespread particularly in women and children. Some Asian and African countries are particularly considered as black spots with respect to vitamin A deficiency. Since rice is staple food for million in these countries, genotypes with high vitamin A content will prove of immense significance. Rice grain does not contain β carotene, the precursor of vitamin A. Efforts have been made to develop the biosynthetic pathway to produce β carotene into rice endosperm to yield rice with higher vitamin A level. Such rice varieties are known as “golden rice”. The idea was basically conceived during a Rockfeller Foundation-sponsored meeting held at IRRI in 1984, which eventually led to the development of Golden Rice through a research programme implemented by a team of scientists led by Ingo Potrykus in Switzerland. In this project, daffodil and bacterium (Ervinia uredovora) genes were transferred in a rice variety Taipei 309. Lower yield potential of this variety however hindered its acceptability. Research is in progress to introduce beta carotene into improved genotypes using Taipei 309 as donor.
Syngenta has also developed some rice varieties known as Syngenta Golden Rice (SGR1 & SGR2) and donated it to Humanitarian Golden Rice Project. SGR1 trials in USA yielded grain expressing 4-8 µg carotenoid per gram of rice endosperm, besides no abnormal taste. Adoptability of these varieties for commercial cultivation will largely depend on performance under field conditions and acceptability of yellow endosperm.
Breeding approach is a long-term task and needs exhaustive efforts, requiring a number of crossing and back-crossing activities over many years, and its success depends on the stability of the targeted micronutrient trait under various environmental conditions. Low organic matter in soil and indiscriminate use of chemical fertilisers over the years have created poor availability of micronutrients in soil. There are cases with soils possessing enough level of micronutrients but the adverse soil properties reduce the nutrient forms available to plants. Correction of soil reaction and nutrient imbalance plus addition of adequate quantities of organic manures and micronutrient will therefore be essential to tapping the potential of biofortified crops. Studies show that crops are quite responsive to soil amendments, organic manures, crop residues incorporation and micronutrient application. Thus, need-based agronomical interventions are equally important for increasing the nutritive value of rice and other food crops.
After almost achieving the biological limits in rice yields per unit area, MRCFC-SKUAST Kashmir contemplates research on specialty rice for traits other than yield. Biofortification will be one of these targets for future. Local landraces of rice (Red rice) popularly known as Zag/ Lal chawal, being rich in Zn and Fe content, make them suitable candidates for research on biofortification. This will help in conserving heritage rice through its cultivation at farmers’ fields and being sold as branded functional food from Kashmir Valley.
Dr T. Mubarak is Chief Scientist Agronomy (MRCFC) SKUAST-Kashmir; Dr N.R. Sofi is Associate Director Research (MRCFC) SKUAST-Kashmir; and Dr Sarfaraz A Wani is Director Research, SKUAST-Kashmir. Email: [email protected]