The Potential for Increasing the Iron and Zinc Density of Maize through Plant-breeding

The Centro Internacional de Mejoramiento de Maiz y Trigo ( CIMMYT) maize-breeding programme has been focusing on identifying white-grained maize germplasm that has the potential to increase kernel iron and zinc concentrations, especially in sub-Saharan Africa. In addition, research at Cornell University has focused on traits such as multiple aleurone layer, which can increase kernel iron and zinc concentrations, and low phytic acid concentration, which holds promise for improving the bioavailability of iron and zinc. More than 1,400 improved maize genotypes and 400 landraces were grown and evaluated to assess grain iron and zinc concentrations. These materials represented all white-grained landraces that belonged to the core collection of CIM-MYT's germplasm bank, all white- and yellow-grained CIMMYT maize germplasm pools and populations, all white-grained materials that are currently in the active breeding programme of CIMMYT-Zimbabwe, and 57 white-grained maize cultivars currently grown in southern Africa. After a very thorough evaluation of the genetic variability of iron and zinc potentially available in white-grained tropical maize germplasm, promising genetic variability was found in both improved maize germplasm and landraces. One difficulty that maize breeders encounter is that grain iron and zinc concentrations are often correlated negatively with grain yield, which may result from the increased carbohydrate content of high-yielding materials, so that a given amount of iron and zinc is diluted. The multiple aleurone trait may be a fast track to overcome this effect. This trait is being introgressed into various materials in both the United States and southern Africa.