Can Seedling Ionomics Predict Rice Grain Ionomics?.

The study investigated the possibility of using the mineral (ionomic) composition of rice (Oryza sativa L.) seedling leaves to predict cultivars that accumulate large amounts of certain minerals in their grains. This information will be used for genetically improving the nutritional value of rice grain and for improving our understanding of mineral uptake, transport, and accumulation in rice. In 2007 and 2008, preliminary field trials were conducted on a core subset of 1640 rice accessions from the USDA National Small Grains Collection. These flooded and unflooded trials identified germplasm with varying levels of grain mineral composition. The present study investigated correlations between seedling-leaf and grain mineral contents of 16 minerals within this diverse set of germplasm to determine if seedling leaf data could be used to predict grain content. Such correlations could greatly accelerate breeding efforts aimed at developing rice cultivars with improved grain mineral composition (nutritional value). The 40 rice accessions selected for their extreme grain mineral composition were grown in an outdoor potted plant study in 2010. All 40 varieties were planted in 7-10 day intervals to provide, on a single sampling date, plants of a wide range of developmental stages. Leaf tips (5cm) for ionomic analysis were collected from the most recently fully emerged leaf per plant. For two elements, Mo and Co, several genetic lines selected for their high Mo or Co grain content were found to consistently exhibit high seedling leaf contents across several seedling stages as well, implying that for these two elements, seedling leaf tips can be used to a) select among F2s, and b) select among diverse germplasm sets. Enhanced leaf Na content seemed a better predictor of high grain K than did seedling leaf K content. For As, Ca, Cd, Fe, and Sr, genotypes selected for low grain concentrations did exhibit low seedling concentrations, but only some genotypes selected for high grain concentration of these particular elements showed high seedling leaf concentrations as well. It is possible that different genotypes have different physiological mechanisms underlying their high-grain contents, some of which may be reflected in seedling leaves, others not. Observation of F2 progeny leaf and grain mineral compositions will be used to further investigate the relationship between grain and leaf concentrations of As, Ca, Cd, Fe and Sr. For the remaining eight elements (Cu, Mg, Mn, Ni, P, Rb, S, Zn) seedling leaf content did not appear predictive of grain element content, neither in the high nor low directions. Funded by NSF DBI 070111.