Genetic variation in traits for nitrogen use efficiency in wheat.

Crop nutrient and especially nitrogen use efficiency (NUE) is both an economically and an environmentally highly desirable trait. It has been estimated that only a third of nitrogen inputs to cereal crop worldwide are recovered in grain for consumption, resulting in a huge waste of resource with major negative impacts on the environment. Most measures of NUE in wheat and other cereals are based on field assessments of crop yields at given N inputs, performance responses to added N fertilizer, or by quantifying N fertilizer recovery rates. However, NUE is a complex trait comprising two key major components, N uptake and N utilization efficiency, both also complex traits in themselves, each involving many physiological processes and biochemical pathways. A deeper understanding of the processes involved in NUE has been a target of the UK Wheat Genetic Improvement Network project (http://www.wgin.org.uk/). This has enabled the breakdown of characteristics contributing to NUE and an assessment of the variation present in those characteristics, predominantly in modern cultivars; a total of 13 years of data have been obtained to date. Significant but limited variation suggests a requirement for broader germplasm screening such as older varieties, landraces, and wild relatives.