Towards sustainable spring wheat cultivation: enhancing nitrogen use efficiency through strategic breeding

Nitrogen (N) is essential for plant growth; however, the frequent use of N-based fertilizers to maintain high crop yields is associated with several environmental risks. Sustainable agriculture requires crops that maintain high yields with less fertilizer. Spring wheat, a promising staple crop in Nordic regions, was used as a model to evaluate the breeding potential for N use efficiency traits, which are not typically targeted in crop breeding programs. The overall objective of this thesis was to explore the application of N use efficiency traits in spring wheat breeding programs for high latitude environments. The aims were to (i) explore the relationships between breeding target and non-target traits across various varieties grown in Central Sweden over a two year period; (ii) assess the genetic and environmental influences on early-vigor root traits; (iii) develop a methodology to rapidly assess N use efficiency traits; and (iv) identify genomic regions and candidate lines with desirable trait combinations in a population of 183 recombinant inbred lines (RILs). Stable associations were found between certain N use efficiency traits and breeding targets, as wheats bred for high yield were characterized by high N utilization efficiency. High N uptake efficiency was not linked to any breeding target. Early-vigor root traits were strongly influenced by both variety and environmental conditions, but unassociated with breeding target. A simple methodology for phenotyping N use efficiency traits in large populations was developed based on allometry, and promising candidate lines with favorable trait combinations were identified, along with 186 genomic regions associated with N use efficiency. The results demonstrate the potential of incorporating N use efficiency traits as breeding targets for crops, thereby supporting a more sustainable agriculture