Evaluating and Contrasting Regionally Adapted Soft Red Winter Wheat Lines for Nitrogen Use Efficiency.

The application of nitrogen fertilizers in soft red winter wheat (SRWW) boosts grain yields and quality but presents a significant expense to growers and poses environmental concerns associated with soil nitrogen losses. In addition to improved management practices, developing cultivars expressing high nitrogen use efficiency (NUE) can promote greater nitrogen uptake in addition to producing higher grain yields per unit of applied nitrogen. This study evaluated the effect of five nitrogen rates by timing combinations on grain yield, grain protein content, tissue nitrogen yield, trait stability, and morpho-physiological traits in panel of six “high” and six “low” NUE SRWW lines across 11 environments in Virginia and Ohio. Three SRWW lines (KY06C-1003-139-8-3, OH08-161-78, and VA08MAS-369) were validated for consistent production of high grain yields per unit of nitrogen applied and were able to maintain adequate grain protein content. Furthermore, the pre-defined “high” NUE group of SRWW lines had significantly greater protein content under similar grain yields across nitrogen treatment rates. Correlations between high-throughput phenotypic traits and NUE were also examined as a means of accelerating the selection process in regional SRWW breeding programs. Canopy temperature depression was correlated, particularly under nitrogen-stressed conditions, with nitrogen utilization efficiency across testing environments while under moderate nitrogen stress conditions normalized difference vegetation index (NDVI) was strongly correlated with yield stability. The results of this study further indicate the potential for selecting SRWW lines that consistently express high NUE for introduction into breeding programs. High-throughput phenotyping technologies, such as infrared thermometers to measure canopy temperature and CropCircle to measure NDVI, may be implemented as a means efficiently assessing nitrogen stress in a given SRWW line.