Genetic Improvement of Nitrogen Use Efficiency in Oilseed Rape

Abstract

Oilseed rape ( Brassica napus L.) is the third most important oil crop worldwide after perennial oil palm and soybean. Increasing demand for high-quality rapeseed oil for human nutrition and biofuel, coupled with a high-value protein used as an animal feed, has resulted in significant production increases during the past four decades. In major cultivating areas throughout Canada, Northern Europe, China, and Australia, oilseed rape as the dominant dicotyledonous crop has assumed an integral role in cereal crop rotations, imparting an essential role in soil rejuvenation and in management of monocotyledonous cereal diseases and pests. As for all non-legume crops, nitrogen (N) is a most limiting macronutrient in oilseed rape production systems and has to be fertilized in high quantities for sufficient productivity. However, with its relatively high acquisition of nitrogen during vegetative growth stages, but a comparatively low nitrogen seed yield, oilseed rape cultivation releases noteworthy amounts of nitrogen after harvest. Thus, the crop is often associated with an N-balance surplus. This unused nitrogen can potentially cause environmental damage in other ecosystems, as NOx emissions or nitrate leaching. Furthermore, energy-dependent mineral fertilizer production by the Haber-Bosch process raises carbon dioxide emissions and lowers the greenhouse gas balance of crops dependent on high nitrogen inputs. In light of the fact that oilseed rape is the primary feedstock for European biodiesel production, legislation in the European Union demands reductions in greenhouse gas generation resulting from oilseed rape. As an overall consequence, increased nitrogen use efficiency (NUE) is a promising strategy to address these constraints and achieve more sustainable vegetable oil production in temperate agricultural regions. In this chapter, we traverse the recent history of winter-type oilseed rape breeding in the context of NUE, tracing a path from discovery of genetic diversity and interrelationships between relevant traits, toward further strategies for NUE improvement. We begin with a characterization of breeding progress over the past decades, including use of the potential advantages of hybrid varieties, and outline environmental and management interaction. Furthermore, we review current knowledge about relevant plant traits, including root traits, whose exploitation can potentially lead to enhanced nitrogen acquisition and nitrogen utilization efficiency. Particular attention is paid to genetic variation within available gene pools and its relevance in future breeding programs. Finally, we introduce contemporary techniques as suitable selection methods for crop scientists and (pre)breeders to accelerate breeding progress.