Historical grain yield genetic gains in Norwegian spring wheat under contrasting fertilization regimes

Spring wheat is currently dominating wheat production in Norway. The introduction of combine harvesting in the 1950s spurred breeding efforts to improve lodging and preharvest sprouting resistance, and to integrate good breadmaking quality in the locally adapted germplasm. Release of landmark cultivars Runar and Reno in the 1970s revitalized the country's production and marked the onset of modern wheat cultivation in Norway. Since that time, new cultivars have been developed but little is known about the genetic basis of the achieved yield gains. We collected 21 representative cultivars released since 1972 in Norway and tested them in a multiyear field trial including two fertilization rates: 75 and 150 kg ha(-1) N. We assessed grain yield, plant height, heading, maturity, length of grain filling period, grain protein content, protein yield, aboveground biomass, harvest index, grain weight, test weight, grains per spike, grains per square meter, and spikes per square meter and their response to fertilization. We document an annual increase in grain yield of 17.8 kg ha(-1) (0.34%), at both rates of N fertilization. None of the traits exhibited significant genotype x management interaction. Wheat breeding has led to the development of higher-yielding cultivars with higher protein yield that mature later, have a prolonged grain-filling period, and produce more grains per spike and grains per unit area.