Harvestplus Strategies for Zinc Molecular Marker Development in Wheat and Rice.

To enhance the breeding of Zn-dense wheat and rice, HarvestPlus has initiated a program to develop molecular markers that include both forward and reverse genetic approaches. This task is not easy, given the trait is multigenic. While ttotal grain Zn has good heritability, there is still an environmental effect present which needs to always be considered when running field trials. For wheat, lattice designs are being employed to reduce variability in the field. A new Association Mapping (AM) panel consisting of 90,000 SNP markers was specifically developed for wheat, that introduced genomic regions from wild relatives into the panel through the development of synthetics crossed back into more modern varieties. The panel consists of 330 genotypes with similar maturity, plant habit, seed weight and yield. These plant traits are important to consider as they can greatly impact on final grain Zn and can lead to false-positives when identifying marker candidates. For rice, the strategy has been to use AM on a PRAY Indica panel consisting of 700,000 SNPs. The panels have been grown at multiple sites throughout the world and results indicate multiple QTL for Zn, with bioinformatics currently underway to identify candidate genes. On top of this work, a reverse genetic approach is testing Zn-candidate genes identified in rice endosperm, to see what role they have in creating sink strength for Zn. Expression analysis of candidates during the reproductive phase in a large number of rice lines that differ in Zn is currently underway at IRRI. There is also a program to find candidate genes for total absorbable Zn, which is a theoretical calculation of Zn absorption in the human gut. TAZ is being calculated in whole wheat grain and also in milled rice which requires a major analytical effort for measurement of not only Zn but also Ca, total protein and phytate in thousands of samples. Ionomic pipelines have also been specifically set up to analyse the many samples from HarvestPlus, by both ICP-MS and XRF technology. An increased capability in high quality analysis is at the forefront of any successful marker development program.