Is genetic engineering necessary to develop rice rich in iron? Lim Li Ching reports on successes achieved with conventional breeding.
Iron deficiency is the most common of all nutritional deficiencies. Approximately 3.7 billion people suffer from this condition, and it is most widespread in children and lactating mothers. Iron deficiency leads to anaemia; overall, 39% of pre-school children and 52% of pregnant women are anaemic, of whom more than 90% live in developing countries.
Anaemia is bad for health and development. In infants and young children, it impairs growth, cognitive development and immunity; at school age it affects school performance and reduces activity levels; at adulthood it reduces work capacity and lowers resistance to fatigue. In pregnant women, it is linked with an increased risk of maternal mortality and illness, as well as an increased risk of pre-term delivery, retarded foetal growth, low birth weight and foetal death soon after birth.
Iron tablets are a possible solution, but require a continuous supply and can cause side effects. In the long term, ensuring adequate iron intake through food is viewed as the best option. For most populations, the best sources of iron are meat products, but these are relatively expensive and little consumed by the poor.
Rice, the staple diet of millions in the developing world, is a poor source of micronutrients. Where rice is the staple, about two billion people suffer from iron-deficiency anaemia. Efforts have thus focussed on ‘biofortifying’ rice to make it nutritionally better. Genetically engineering rice to increase its iron content has been one course of action (see "Rice in Asia: Too little iron, too much arsenic", this series).
But is genetic engineering needed to develop iron-rich rice? There are already successes reported in naturally breeding and selecting rice with high iron content, which would not carry the risks associated with genetic engineering.
Plant breeders at the Philippines-based International Rice Research Institute (IRRI) have identified rice varieties that are naturally high in iron. They screened nearly 7 000 samples of rice germplasm stored in the IRRI gene bank, for high iron and zinc content. Of these, 1 138 samples were grown. They found that aromatic grains were usually higher in iron concentration and often also higher in zinc, compared to non-aromatic varieties. Data from various studies demonstrated that high iron and high zinc traits were generally expressed in all rice environments tested.
IRRI at the same time was trying to grow, by conventional breeding, new varieties that could thrive in poor soils and cold temperatures. "Quite by chance, it was discovered that one of the varieties designed to tolerate low temperatures had also inherited a richness in iron and zinc from one of its parents," explains IRRI scientist Dr. Glenn Gregorio.
This aromatic variety is a cross between a high-yielding variety and a traditional variety from India, from which IRRI identified an improved line (IR68144-3B-2-2-3) with high iron concentration. The grain has 21 parts per million (mg/kg) of iron, about double the normal content in rice, and also about 34 parts per million of zinc.
Research has shown that high zinc and iron densities are positively correlated. Zinc may enhance the body’s capacity to absorb iron. It is essential for a healthy immune system. Zinc deficiency in children is also associated with poor growth, reduced motor and cognitive development, and increased infectious diseases. It is linked to pregnancy and childbirth complications, lower birth weight and other foetal effects lasting through childhood. Moreover, high zinc density is good for seedling vigour, improving plant yields. IR68144 is also reported to have a high content of Vitamin A.
"Almost as a bonus, it had good flavour, texture, and cooking qualities. And, to please the farmers, it was also high-yielding." This bodes well, for adding new traits can sometimes have a general negative effect on yield. The rice also has good tolerance to rice tungro virus and to mineral-deficient soils. All these factors are important for maintaining crop productivity and consumer acceptance, crucial to ensure that new varieties sustain farmers’ incomes.
Does the increased iron content translate into improved iron status in the consumer? After 15 minutes of polishing, scientists found that IR68144 had approximately 80% more iron than a popular but low-iron commercial variety. Research conducted at Cornell University showed that the iron in IR68144 polished rice was absorbed by laboratory rats, and by human colon cells in culture.
"Then we fed some other high-iron varieties experimentally to a family of two parents and four children living near IRRI’s headquarters in the Philippine province of Laguna," Dr. Gregorio said. "All but the father were mildly anaemic. After the family members ate the enriched rice for two months, however, their serum ferritin levels rose dramatically, to the point where the lowest of them was double the level recommended for good health."
In 1999, a trial was carried out on 27 women in the Philippines, who ate IR68144 exclusively over six months. The volunteers - sisters at a Roman Catholic convent – had their food measured, their activity monitored and body weight noted. Once a month, their blood was tested. The sisters were selected because they represent a sex and age segment of the population at high risk of iron deficiency.
Most of the sisters, aged between 20 and 30 years old, were mildly anaemic while on their normal diet of rice purchased from the market. 74% were anaemic (haemoglobin <120 g/L) and 48% were iron-deficient (serum ferritin <12 µg/L). But, after eating IR68144, the serum ferritin (an iron storage protein) levels in their blood increased - in many instances two or three times higher. In some cases, this was sufficient to raise their iron levels from deficient to above average.
A much larger and carefully structured clinical trial, involving 300 sisters from eight convents around Manila concluded in September 2003. In one of the largest human feeding trials of a staple food, each sister was randomly assigned to receive either regular (low-iron) rice or the high-iron variety. The sisters and the research team were not told what they were receiving during the trial. The food was cooked in a common kitchen and consumed in a common dining room, so the distribution and consumption of different rice varieties could be carefully monitored.
The sisters’ iron status, as shown by haemoglobin and other biochemical indicators, was measured before the trial began, halfway (4.5 months) and at the conclusion (9 months). Women remaining - or newly - iron-deficient at the end of the trial were given iron supplements to ensure this deficiency was corrected. The trial also examined the interplay of minerals and nutrients within the body to look at their interactions, and observed the sisters’ cognitive functions and capacity to concentrate.
Preliminary analysis of the data indicates positive results. There was modest improvement in blood iron levels, showing that iron in rice endosperm is absorbed by the body. Among the women who were iron-deficient but not yet anaemic at the start of the trial, total body iron reserves improved significantly. The women who consumed high-iron rice took in about 20% more iron per day than those who ate regular rice, and increased their body iron by 10%, while the women consuming control rice actually lost 6% of their body iron. The greatest increases in body iron were seen in the women who consumed the most iron from biofortified rice. The results of the study are being published.
The next step would be to conduct trials on the effect and use of high-iron rice in a community setting and on the effect on children’s iron status. A study is planned in Bangladesh in 2004–2005. If successful, IR68144 seeds will be given to agricultural research organizations in various countries for adaptability testing and to begin crossbreeding for pest and disease resistance as well as hardiness for local conditions.
IR68144 or its offspring could then be released to farmers in developing countries, for free, in two or three years. Meanwhile, IRRI’s search continues, among the 26 000 samples of rice varieties it holds in trust for humankind. Dr. Gregorio is sure that a new variety could be bred with even higher iron content. IR68144 could be the first of several traditional rice varieties found to be nutritionally richer than previously thought.
Already, recent reports indicate that Thailand’s Department of Agriculture has identified two rice strains - selected from 45 strains of Thai rice - that can accumulate iron. Korkhor 23 has an iron content of 36.67 parts per million (ppm) when unpolished, reduced to 22.5ppm when polished. Unpolished Khao Hom Phitsanulok 1 rice has an iron content of 25ppm, compared with 22.5ppm in it polished state. Rice grown in different areas have different rates of iron accumulation. Research continues to find better iron-accumulating strains, and to determine the best growing and milling techniques to preserve iron in the rice. However, Dr. Laddawal Kannanut of the Rice Research Institute was quoted as saying that genetic engineering would be used to improve the strains’ ability to accumulate iron.
This is unnecessary, for as the IRRI research shows, conventional breeding can successfully develop high-iron rice that is both high yielding and disease resistant. Conventional breeding works because iron occurs naturally in rice grains and the high variability in the grain iron content allows selection of high-iron parents for crossbreeding. Moreover, farmers will grow the iron-dense rice because its high-yielding characteristic makes it profitable to do so. And, trace minerals such as iron are undetected by the human eye and thus do not affect consumer’s preference.
In future, it won’t be just rice that is targeted for biofortification. Significant funding has been committed to develop biofortified crops. The IR68144 research is now part of a larger initiative by the Consultative Group on International Agricultural Research (CGIAR) and its research centres worldwide, coordinated by the International Food Policy Research Institute (IPFRI). In October 2003, the Gates Foundation committed $25 million to this initiative, HarvestPlus, which aims to develop crops with enhanced nutrient status: not just with iron but also with vitamin A and zinc and in other key staple crops important to the poor (wheat, maize, beans, cassava, and sweet potato).
The danger is that the efforts will focus on genetic engineering, at the expense of safer alternatives. For example, IRRI claims that for vitamin A enhancement, genetic engineering is needed, as vitamin A does not occur naturally in rice grains. In 1999, Swiss scientists successfully expressed vitamin A in transgenic rice grains – the so-called ‘Golden Rice’. IRRI is now incorporating the vitamin A genes into high yielding varieties.
Biofortifying food crops, even by means of conventional breeding, must not replace other interventions such as diversifying diets, conventional fortification and supplementation. Efforts to enhance the iron content of rice must also be mindful of the interaction between iron and arsenic, a particular problem for the arsenic-contaminated paddy fields of Asia (see "Rice in Asia: Too little iron, too much arsenic", this series). In addition, in areas where iron intake is high, iron overload can become a real problem.
The need for biofortification today is largely due to the mistakes of the past. For example Green Revolution methods have mined the soil of nutrients and monocultures have resulted in the loss of diverse traditional varieties. Alternative food sources rich in iron should be promoted, as should diverse cropping and sustainable agriculture. This could prove to be a much more sustainable strategy in addressing iron deficiency.
Article first published 14/09/04
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