Biofortification Strategies in Theory and Practice.

Biofortification of staple crops offers a cost-effective, sustainable and effective strategy to combat chronic malnutrition among populations that fail to afford or access balanced, nutritious diets.  The breeding strategy of choice to biofortify each crop with each target nutrient is determined in the same ways as for any other trait; genetic variation must be identified or created, effective and high throughput selection schemes must be developed and implemented, and pleiotropic effects must be monitored and managed.  Recent examples of successful biofortification strategies include selection among existing cultivars for high beta-carotene sweet potato, marker-assisted selection for favorable alleles of genes encoding enzymes along the carotenoid biosynthetic pathway in maize, exploitation of variation for zinc concentration in wild species of wheat, and genetic modification to produce beta-carotene-rich ‘golden’ rice.  Exciting opportunities for biofortification exist in breeding for traits conferring enhanced nutritional value to the increased quantities of nutrients bred into grain, for example, breeding for decreased levels of anti-nutrients such as phytate may enhance the bioavailability of iron, selection for increased amounts of promoters of bioavailability may enhance minerals bioavailability, and increased content of beta-carotene may enhance the availability of iron and zinc.  Genotypic differences for bioavailability of nutrients exist and may offer opportunities for selection gains even when the causal factors are poorly understood.  Similarly, genotypic differences exist for retention – or losses – of nutrients during drying, storage and especially during processing or cooking, again offering opportunities for breeders of biofortified crops.  The wealth of possible strategies, many as yet untried and un-validated, make breeding of biofortified crops as exciting and challenging as it is potentially valuable in combating malnutrition that affects close to one-third of the world’s population.