QTL mapping of nitrogen use efficiency traits at the seedling and maturity stages under different nitrogen conditions in barley (Hordeum vulgare L.)

Nitrogen (N) is an essential element for plant growth and development. The identification and utilization of N use efficiency (NUE) loci are essential for breeding high NUE cultivars. In this study, 15 NUE traits were measured in a recombinant inbred line population containing 121 lines derived from the cross between a cultivated barley (Baudin) and a wild barley (CN4027). The hydroponic culture was conducted with normal N and low N treatments in one-time frame, and field trials were conducted with N sufficiency and N deficiency treatments in two growing seasons. Twenty-two quantitative trait loci (QTLs) and four clusters were detected. Of them, the five stable QTLs Qgna.sau-3H for grain N concentration, Qtna.sau-3H for total N accumulation per plant, Qnhi.sau-3H for N harvest index, Qnutegy.sau-3H for N utilization efficiency for grain yield and Qanutedm.sau-3H.1 for N utilization efficiency for aboveground dry matter were co-located on chromosome 3H flanked by the markers bpb6282426 and bpb4786261. These two novel QTL clusters simultaneously controlled NUE traits at the seedling and maturity stages. Some genes related to NUE traits in intervals of the major QTLs were predicted. The significant relationships between NUE traits and agronomic and physiological traits were detected and discussed. In conclusion, this study uncovers the most promising genomic regions for the marker-assisted selection of NUE traits to improve NUE in barley.