Modelling nitrogen stress with probe genotypes to assess genetic parameters and genetic determinism of winter wheat tolerance to nitrogen constraint Anne Laperche Æ Jacques Le Gouis Æ Eric Hanocq Æ Maryse Brancourt-Hulmel Received: 16 November 2006 / Accepted: 5 April 2007 / Published online: 22 May 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Environmental and economical con- straints in Europe will favour low nitrogen (N) input systems and wheat varieties adapted to moderate N deficiency. In this context, we studied the dynamics of genetic parameters according to N stress intensity and characterized the genetic determinants for plant tolerance to N deficiency. Thus, we combined N stress modelling with a genetic approach. Two hundred and twenty-two doubled haploid lines were experimented in the field for a range of nitrogen conditions. Those conditions were characterized by the Nitrogen Nutrition Index (NNI) of Re ´cital. Grain Yield (GY) and Kernel Number (KN) were assessed. For GY and KN, and for each line, factorial regressions using NNI of Re ´cital as environmental index were performed. In addition, we assessed the sensitivity to N stress (slopes of the regression) and the performances under low N conditions (predicted values for a NNI of 0.5). QTL detection was performed on these parameters as well as on KN and GY measured in each environment. G · N variance increased with N stress intensity whereas heritability and genetic variance decreased. 11 QTL regions were detected: 3 were N supply-specific QTL (on linkage groups 2A2, 3A and 4B) while 4 contained QTL detected under N + and under N  (2D1, 4B and 5A1). Out of these four, 2 coincided with QTL for factorial regression parameters (2D1 and 4B). Finally, 4 QTL were specific for factorial regression parameters (3B, 5A2 and 7B2). The role of genes commonly used in breeding programs (rht-B1 on 4B, and Ppd1 on 2D1) in plant adaptation to nitrogen constraint was highlighted. Future studies should focus on grain protein yield, another target for low-N breeding scheme. Keywords Factorial regression  G · N interactions  Nitrogen Use Efficiency  QTL Introduction Winter wheat is the main cultivated crop in Europe. Nowadays, environmental and economical con- straints are putting limits to high input management systems. Environmental protection measures such as reduction of ground-water pollution by nitrate leach- ing are now main objectives of the European Union (nitrate directive: 91/676/CEE). High fertilizer costs, coupled with a general decrease of market prices, are A. Laperche  J. Le Gouis  E. Hanocq  M. Brancourt-Hulmel UMR INRA/USTL 1281 SADV, Chausse ´e Brunehaut Estre ´es-Mons, BP50136, 80203 Peronne Cedex, France A. Laperche UMR EGC INRA/INA PG, 78850 Thiverval-Grignon, France A. Laperche (&) UMR INRA/Agrocampus Rennes 118 APBV, Domaine de la Motte, BP 35327, 35653 Le Rheu Cedex, France e-mail: Anne.Laperche@agrocampus-rennes.fr 123 Euphytica (2008) 161:259–271 DOI 10.1007/s10681-007-9433-3