Nitrogen remobilization during grain filling in wheat: genotypic and environmental effects

In wheat (Triticum aestivum L.), nitrogen remobilization from the vegetative organs of the crop to the grains has been shown to depend on environmental factors and genotype. We performed, for a set of 10 winter wheat genotypes, field experiments at six sites over a 2-yr period. By measuring nitrogen uptake at flowering (NUF from 32-284 kg ha(-1)), the amount of remobilized nitrogen (REMN from 24-228 kg ha(-1)) and nitrogen remobilization efficiency (NRE from 0.44-0.92) we were able to determine the effect of genotype and environment on the relationship between REMN and NUF. Environment and genotype had significant effects on nitrogen remobilization and nitrogen remobilization efficiency, which mainly depended on treatment (nitrogen and fungicide) and site. For environments without limiting factor during the grain-filling period, we found that REMN was not dependent on the genotype and could be estimated by a single two-parameter linear relationship (REMN = 4.13 + NUF x 0.76, r2 = 0.97). We analyzed the effect of drought stress before and after flowering, high temperature during these periods, nitrogen availability and disease pressure on REMN by comparing observed and estimated REMN. The effect of the environment on the relationship between nitrogen uptake at flowering and nitrogen remobilization depended on nitrogen uptake during grain-filling period and disease pressure and was also affected by genotype. Disease-resistant genotypes seemed to be able to keep remobilization efficiency stable in conditions of strong disease pressure, whereas nitrogen remobilization efficiency decreased strongly in susceptible genotypes under the same conditions.