Location: Plant, Soil and Nutrition ResearchTitle: The usefulness of iron bioavailability as a target for breeding maize (Zea mays L.) with enhanced nutritional value Author
Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2011
Publication Date: 6/21/2011
Citation: Pixley, K., Glahn, R.P., Palacious-Rojas, N. 2011. The usefulness of iron bioavailability as a target for breeding maize (Zea mays L.) with enhanced nutritional value. Field Crops Research. 123(2)153:160. Interpretive Summary: Since only a small fraction of iron from plant sources is available and absorbed in humans, this study was to test iron concentrations and bioavailability for corn grown in different locations to see if corn can be selected for increased iron bioavailability in breeding programs. A number of factors – genetic, environmental, and enhancers and inhibitors – were studied to see the effects on iron bioavailability. Iron bioavailability estimates and iron concentrations in grain demonstrate that these traits are genetically independent from each other and have the potential to be used to select in a breeding program. However large variance due to location effects tends to limit the usefulness of this trait in breeding. The Caco-2 cell model estimates of Fe bioavailability were generally affected by location effects. Whereas genetic variance was significant for Fe concentration, this was not the case for parameters measuring Fe bioavailability, which differed among hybrids of two of the three trials. Parental lines can be screened and selected for iron bioavailability with the expectation that the superior lines will transmit this quality to their hybrids. The Caco-2 cell model is highly attractive for use in breeding programs in that it integrates the effects of a meal, or food matrix, into estimates of Fe bioavailability. Fe concentration and bioavailability were distinct and largely unrelated traits, but it is disappointing that environmental effects were similar, and heritability was lesser for most Fe bioavailability estimates relative to Fe concentration. Although use of the Caco-2 cell model is promising, the complex nature of the assay and moderate heritability of corn make it most suitable as an intermediate selection tool, and then efficacy trials with animal and human models are needed as a follow up to validate the results in vivo.
Technical Abstract: Iron deficiency is the most widespread nutritional problem, affecting as many as half of the world’s population. Only a small fraction (2-15%) of iron from plant sources is typically bioavailable, that is, available for absorption and nutritionally useful for humans. This study evaluated iron concentration and bioavailability for three diverse sets of 12, 14 and 16 maize hybrids grown in two- or three-location trials to assess the feasibility of selecting for iron bioavailability in breeding programs. Bioavailability of iron, assessed using the in vitro digestion/Caco-2 cell model, varied significantly among hybrids in two of the three trials. Location effects were much larger than location by genotype interaction effects, additive but not non-additive gene action was significant, and heritability estimates were mostly between 0.55 and 0.65 for iron bioavailability estimators. Weak negative correlation of Fe bioavailability with zinc concentration in grain, and weak positive correlation with provitamin A concentrations were indicative of inhibitor and enhancer effects on iron bioavailability, respectively. Although use of the Caco-2 cell model is promising, particularly because it integrates the whole meal, or food matrix effect on iron bioavailability, the complex nature of the assay and moderate heritability of bioavailability estimators make it most suitable as an intermediate selection tool, following high throughput selection for molecular markers of iron bioavailability, currently in development by other researchers, and preceding validation and efficacy trials with animal and human models.