One century of Nordic barley breeding: nitrogen use efficiency, agronomic traits and genetic diversity

The current study aimed to evaluate breeding effect on nitrogen use efficiency (NUE), its components and some agronomic traits and disease resistance in barley by using extensive germplasm covering 72 landraces and 123 cultivars released since 1910. Trials were established in southern Finland with a modified strip-plot experimental design. Prior to sowing, blocks were placement fertilized with compound nitrogen : phosphorus : potassium (NPK) fertilizer (N-P-K: 20-3-8) at the rate of 35 and 70 kg N/ha and unfertilized plots were placed at the other end of the fertilization block. The germplasm collection was genotyped with 1536 single nucleotide polymorphism (SNP) markers and phenotyped during a 2-year field experiment in 2011/12. Independent of row type, a positive breeding effect was evident in NUE and for other plant N traits, except that grain N slightly decreased. Breeding has improved NUE by 0 center dot 08 kg/year (26% over the century). Nitrogen utilization and N uptake efficiencies were also improved by breeding as were straw length, lodging tolerance, grain yield and yield components, without any sign of levelling-off. Bred cultivars were more resistant to leaf-damaging diseases, especially to net blotch. The SNP data indicated no reduction in overall genetic diversity. However, genetic diversity differed along the barley chromosomes showing either reduced or increased diversity in certain regions when landraces were compared with modern varieties.