INTROGRESSION OF EFFICIENT AERIAL ROOT NITROGEN-FIXATION FROM TROPICAL MAIZE LANDRACES INTO SELECTED ELITE MATERIALS

Our primary goal is to improve the sustainability of agricultural systems in the United States (US), specifically in the production of food, feed, and biofuels. Our primary objective is to reduce the reliance on synthetic nitrogen fertilizers in maize cultivation nationwide. To achieve this, we intend to incorporate the aerial root nitrogen fixation trait, found in select tropical landraces, into elite materials already well-adapted to the Midwest region of the US. Our efforts are aimed at creating a sustainable and efficient agricultural system.Objective 1: Determine the nitrogen-fixing ability of parent lines and establish a correlation with "proxy traits". Measuring the amount of nitrogen from biological nitrogen fixation in plants can mostly be done in the field using 15N dilution or 15N natural abundance techniques. However, these methods are costly and time-consuming, making them impractical for genetic mapping and breeding and more suitable for validation. To facilitate high-throughput phenotyping, we have developed a hypothesis based on our preliminary data that suggests a correlation between the levels of biological nitrogen fixation on maize aerial roots and the diameter of these roots. Additionally, the number of nodes with aerial roots seems to correlate with the duration of nitrogen acquisition from the air. Once we have confirmed these correlations, we can use these easily measurable parameters to speed up our breeding efforts.Objective 2: Identify genetic markers associated with traits related to nitrogen fixation. Our team is developing genetic mapping populations segregating for aerial root nitrogen-fixation-related traits. To achieve this, we will make various crosses between inbred lines adapted to the US Midwest and three tropical landrace parents, generating recombinant inbred lines and doubled haploid populations. Our team will evaluate traits such as aerial root diameter, number of nodes with aerial roots, number of aerial roots per node, flowering time, stalk diameter, ear and plant height, and ear morphology. Combining these genetic and phenotypic data will support the genetic mapping of nitrogen fixation-related traits.Objective 3: Evaluate the nitrogen benefits and potential yield trade-offs across multiple environments. By comparing physiological indices, such as photosynthetic efficiency, and the yield of segregating populations for characteristics previously correlated with biological nitrogen fixation in soils with restricted fertilization, we will determine the potential savings in nitrogen using this trait in elite materials. We will gain insights into better management of agricultural systems to reap the benefits of this trait. However, we must also consider the development of more aerial roots and the resulting increase in mucilage production, which incurs significant energy costs and may affect the yield performance of these materials. Therefore, we will investigate any potential drawbacks or "penalties" and assess how this trait introgression could impact their yield potential.