Nitrogen Use Efficiency : From Field Trial to Gene Discovery

In a context of increasing world demand for cereal production, the European agriculture has to deal with nitrogen fertilization cost and environmental concerns. So, breeding for nitrogen use efficiency is becoming a priority for breeders. As phenotyping for such trait is time and money consuming, genetic progress will also depend on the development and use of diagnostic molecular markers linked to chromosomal regions of interest. Considering this, a panel of 225 European wheat elite varieties registered between 1985 and 2010 was experimented in eight trials as a combination of four environments and two nitrogen levels. Genetic progress was assessed on genotypic additive value revealing genetic progresses on grain yield, remobilization and global nitrogen use efficiency. Difference in genetic progress between low and high nitrogen trials was significant only on nitrogen use efficiency attesting an improvement in yield stability. Indirect selection efficiency and application of this these results to breeding are discussed. This panel was then used in a multi-environment genome-wide association study (MET-GWAS) using more than 23 000 mapped SNP and 30 traits. The use of this panel to identify quantitative trait loci (QTL) is discussed regarding its small linkage disequilibrium. Then, the utilization of combined approaches of MET-GWAS, epistasis, synteny and genomics to localize candidate genes in QTL through the use of the IWGSC chromosome survey is illustrated.