Genomic selection using maize ex-plant variety protection germplasm for the prediction of nitrogen-use traits

Maize (Zea mays L) yield increases associated with better usage of N fertilizer, (i.e., increased N use efficiency [NUE]), will require innovative breeding efforts. Genomic selection (GS) for N-use traits (e.g., uptake or utilization efficiency) may speed up the breeding cycle of programs targeting NUE in maize. We evaluated the GS accuracy of 12 N-use traits for training populations (TPs) varying in composition (TC) and size, predicted yield performance under different N fertilizer rates, and investigated the usefulness of GS for NUE in maize breeding programs. A total of 552 maize hybrids were planted under low (0 kg N ha ⁻¹ ) and high N fertilizer (252 kg N ha ⁻¹ ) conditions across 10 environments. Training composition scenarios included T0 (hybrids in which none of the parents were included in the random subset of inbreds), T1 (hybrids in which one of their parents were included in the random subset of inbreds), and T2 (hybrids in which both of their parents were included in the random subset of inbreds). Training population sizes ranged from 10 to 40 or 30 to 90 hybrids, depending on the N-use trait. Across different TC, TP sizes, and N-use traits, GS accuracy ranged from −0.12 to 0.78 and was greatest with larger TP sizes when both parents of untested hybrids appeared in the training and validation sets (T2 hybrids). Moreover, GS accuracy in response to different TC and TP sizes was dependent on the N-use trait. Successful breeding for N stress tolerance or improved yield response to N fertilizer level will require selection of specific N-use traits.