Effect of breeding on nitrogen use efficiency associated traits in oilseed rape.

Oilseed rape is one of the most important dicotyledonous field crops in the world, where it plays a key role in productive cereal crop rotations. On the other hand, its production requires high nitrogen fertilization and its nitrogen footprint exceeds that of most other globally important crops. Hence, increased NUE in this crop is of high priority for sustainable agriculture. We report a comprehensive study of macro-physiological characteristics associated with breeding progress, conducted under contrasting nitrogen fertilization levels in a large panel of elite oilseed rape varieties representing breeding progress over the past 20 years. The results indicate that increased plant biomass at flowering, along with in primary yield components, have increased NUE in modern varieties. N uptake efficiency has improved through breeding, particularly at high N. Despite low heritability, the number of seeds per silique associates positively with increased yield in modern varieties. Seed weight remains unaffected by breeding progress, however recent selection for high seed oil content appears to have promoted a negative correlation (r=-0.38 at high and r=-0.49 at low N) between seed weight and seed oil concentration. Overall our results reveal valuable breeding targets to improve NUE in oilseed rape.