Genetic variation in nitrogen uptake and utilization efficiency in a segregating DH population of winter oilseed rape

Genetic variation in nitrogen (N) use efficiency, N uptake, and N utilization was analyzed in a doubled haploid (DH) population derived from winter oilseed rape cultivars. The aim was to analyze the relative importance of uptake and utilization efficiency and to identify parameters that allow an easy selection of N efficient genotypes. Fifty-four DH lines were tested in four to seven environments at two levels of N supply: no fertilization and 240 kg N ha^?1. N uptake efficiency is defined as the amount of N acquired by a genotype as the proportion of the N available in the soil. N utilization efficiency is measured as unit grain yield per unit of N taken up. Significant genotypic variation was observed for both uptake and utilization efficiency. At low N supply, variation in N efficiency was mainly the result of differences in uptake efficiency. Seed yield was correlated positively with N uptake and N utilization efficiencies at low N supply and with N uptake at high N supply. The correlation was positive between harvest index (HI) and N use efficiency at both N levels (r = 0.45**; r = 0.36**) and for HI and N utilization at low N supply (r = 0.46**), indicating that a shorter plant ideotype might be more N efficient. The interaction between genotypes and N supply for grain yield was highly significant, and the correlation between low N and high N was of only medium size (r = 0.60**), suggesting the possibility of selecting genotypes with specific adaptation to low N supply.