Europ. J. Agronomy 25 (2006) 108–118 Unravelling environmental and genetic relationships between grain yield and nitrogen concentration for wheat Eug` ene Triboi a,∗ , Pierre Martre a , Christine Girousse a , Catherine Ravel b , Anne-Marie Triboi-Blondel a a INRA UR Agronomie, 234 Avenue du Brezet, F-63 100 Clermont-Ferrand, France b INRA-UBP UMR Am´ elioration et Sant´ e des Plantes, 234 Avenue du Brezet, F-63 100 Clermont-Ferrand, France Abstract The analysis of the evolution of crop yield reveals a change in grain composition: increases in yield have led to a decrease in the protein to starch or oil ratios. This negative relationship reflects the higher increase of C assimilation compared with N assimilation. For wheat (Triticum aestivum L.), flour protein concentration is the main quality criterion, especially for bread making. Therefore, a critical question for the future is how to manage the relationship between yield and N concentration, where the objective is to increase both the level and stability of yield and N concentration. To answer these questions, we need a better understanding of the mechanisms involved in the variations of yield and of its composition. First of all, we need to analyse genetic variability in different environments that allow the identification of genetic sources of variation that can be used for breeding or in more reductionist approaches. In this paper, we used data from controlled environment and field experiments, at canopy and plant level, and at different sink:source ratios to analyse the genetic and environmental relationship between grain productivity and composition. These experiments confirmed the strong negative relationship between grain yield and N concentration. Post-anthesis temperature and water deficit had significant effects on grain yield and protein concentration, but they did not modify the negative relationship between these variables. However, pre-anthesis water deficit decreased the sink:source ratio resulting in a lower intercept, while the slope was unchanged. Nitrogen deficiency also modified the intercept of the negative relationship, but more importantly it decreased the slope three to four-fold. Thus under limiting N conditions, grain N concentration is more sensitive to yield variation than under non-limiting N conditions. Genetic variation of single grain dry mass and of the sink:source ratios had similar effects to the environmental variation. Three major conclusions can be drawn from these results: (1) the negative relationship between grain yield and protein concentration is primarily determined at the stem level; (2) the grain itself is more limiting for starch synthesis than for protein synthesis and (3) overall any increase in yield is followed by an increase of N utilisation and use efficiency. © 2006 Elsevier B.V. All rights reserved. Keywords: Environmental effect; Genetic variability; Genotype by environment interaction; Grain yield; Grain nitrogen concentration; Sink:source ratio; Triticum 1. Introduction Over the last 50 years, the yield for various crops has increased by 0.5–2% per year (Cassman, 1999, 2001). This continuous yield increase, due to genetic and crop manage- ment progress, has been accompanied by significant changes in grain composition (e.g., Calderini et al., 1995; Simmonds, 1995; Oury et al., 2003). Regardless of the species, the increase in grain yield leads to a decrease in the protein to starch or oil ratio (Triboi and Triboi-Blondel, 2002). For example, in France, average wheat (Triticum aestivum L.) yields increased from 2.3 Mg ha -1 in 1961 to 7.6 Mg ha -1 in 2004, at a constant ∗ Corresponding author. Tel.: +33 473 624 424; fax: +33 473 624 457. E-mail address: triboi@clermont.inra.fr (E. Triboi). annual rate of 0.12 Mg ha -1 year -1 (FAOSTAT, 2005). Similar increases occurred in the United Kingdom (Austin, 1999). Con- comitantly, grain N concentration decreased by approximately 10 mg g -1 DM for a 1 Mg increase in yield (Le Buanec, 1999; Oury et al., 2003). At the local level, year-to-year variations of the climate also induce important variations of both grain yield and N concentration. Protein concentration in flour is the main quality criterion for wheat, especially for bread making. Therefore, a critical question for the future is how to manage the relationship between yield and N concentration, where the objective is to increase both the level and stability of yield and N concentration. In order to fulfil this objective, through varietal and crop management improvement, we need a better understanding of the effects and mechanisms involved in the variations of yield and yield com- position by genotype and environment, and their interactions. 1161-0301/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.eja.2006.04.004