The Royal Society Report - Push-Pull

or supplements are not available, both genetic and nongenetic
approaches can be used to enhance the nutritional
content of a stable crop and avoid ‘hidden hunger’ due to
shortage of micronutrients. The preferred strategy to
eliminate hidden hunger will always involve strategies to
increase the diversity of diet with increased access to fruit
and vegetables. However, in regions where the lack of
infrastructure or other factors prevents diversification of
the diet, the introduction of biofortified varieties may
provide a good short-term solution. The advantage of a
biofortification approach is that it capitalises on a regular
intake of a staple food that will be consumed over a long
period even in the absence of international development
agencies. The requirement for a one-off investment to
develop the appropriate seeds is also a consideration
(Nestel et al. 2006). The importance of nutritional content
and the dietary contribution of food crops to achieve
nutritional security, especially vitamin A, zinc and iron, is
widely recognised (Copenhagen Consensus 2008).
However, the importance of palatability to the consumer
must not be ignored. Nutritional quality can also be
enhanced by the removal of toxic components through
crop management and by genetic enhancement.
3.3.6.1 Crop management to enhance nutritional quality
There are several methods by which the nutritional content
of the harvested crop can be improved through targeted
management and particularly by the use of fertilisers
containing trace elements. These include production
systems to improve grain quality and nutritional value. There
has been an increased focus on agronomic biofortification
within the international fertiliser industry (White & Broadley
2005; Bruulsema et al. 2008). Whole crop management
systems exist to improve quality, health and nutrition, for
instance in cassava (Nassar 2006). However, the full
potential of these approaches requires further research into
the processes through which the nutrient content of crops
can be influenced by fertiliser applications.
Mild drought stresses have been shown to result in
enhanced flavour and aroma in some food crops (Santos
et al. 2007) in addition to enhanced concentration of health
related metabolites (such as ascorbic acid and other
antioxidants).
3.3.6.2 Genetic improvement of crops to enhance nutritional
quality in regions with diet deficiency
Golden rice is a transgenic line that could help to combat
vitamin A deficiency (Dawe et al. 2002). The first
generation of Golden rice varieties contained only low
levels of b-carotene and there was some scepticism as to
whether their introduction would mitigate vitamin A
deficiency and benefit poor, rice-dependent households.
However, there are now lines with much higher levels of
b-carotene (Paine et al. 2005) and good evidence from
clinical trials that it is an effective source of vitamin A
(Tang et al. 2009).
A trial of orange-fleshed sweet potato in Mozambique also
illustrates how vitamin A deficiency can be mitigated by
supplies of biofortified staple crops (see Case study 3.7).
Genetic improvement of cassava can enhance nutritional
quality (protein, carotenoids and minerals) using wild
relatives. 7 The HarvestPlus programme (see also Case study
3.7) is working to improve the nutritional quality of maize
and rice. Recently, rice plants have been engineered with
elevated iron levels in the rice kernels (Wirth et al. 2009).
Case study 3.7. Biofortification of orange-fleshed sweet potatoes for combating vitamin A deficiency
Vitamin A deficiency
Vitamin A is needed for good eyesight, and extreme deficiency leads to blindness. It is estimated that worldwide,
250,000 preschool children go blind due to vitamin A deficiency every year (Bouis 2008). One method of combating
micronutrient deficiency is through the use of supplements or fortified foods. However, this is not an option for the rural
poor, who may live too far from the nearest market and cannot afford to buy these products. An alternative method of
enhancing Vitamin A in the diet is through biofortification. This involves breeding staple crops which have high levels of
micronutrients.
How is it done
The micronutrient content of staple foods can be increased through conventional breeding where adequate germplasm
variation is available. The HarvestPlus programme is working towards producing sweet potato lines with high levels of
the vitamin A precursor b-carotene. The target level of b-carotene depends on the levels available to the consumer
following cooking and digestion, and whether the sweet potato will be the sole source of vitamin A in the diet. Studies
have shown that feeding b-carotene-rich sweet potato to school children increases their vitamin A stores in the liver
(van Jaarsveld et al. 2005). Orange-fleshed sweet potato lines with high levels of the vitamin A precursor b-carotene
have been identified.
Micronutrient-dense traits are generally stable across all environments, which makes it easier to share germplasm
internationally. Furthermore, micronutrient traits can be combined with traits for high yield.
7 ‘Decades of cassava research bear fruit.’ Available online at: http://
www.idrc.ca/en/ev-5615-201-1-DO_TOPIC.html.
36 I October 2009 I Reaping the Benefits The Royal Society