Agriculture Reference
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to NUpE, grain N yield, N remobilisation and post-silking N uptake. They stated
that QTLs for remobilisation mainly coincided in clusters with loci for leaf senes-
cence, underlying the role of a “stay-green” phenotype in favoring N uptake
capacity, and thus grain yield and N grain yield. Similarly, in Arabidopsis a range
of variation for Harvest Index (HI) and Nitrogen Harvest Index (NHI) has been
found when 20 accessions were cultivated with a limited or ample supply of
nitrogen (Masclaux-Daubresse and Chardon 2011 ). It was observed that the range
of variation among the 20 accessions was conserved between the two nitrogen
levels. Globally HI is similar at high and low nitrogen, while NHI, which defines the
resource allocation, is twice as high at low nitrogen compared to high nitrogen,
indicating that grain NUE is higher when nitrogen fertiliser is limited.
Several studies have been conducted by investigating natural variation in crop
species, which were focused mainly on yield improvement (Shewry et al. 2013 ) and
grain composition (Li et al. 2011 ), but only a few have been done evaluating the
interaction of those traits with fluctuation of nutrient content in the environment.
This kind of study requires highly controlled conditions in order to clearly elucidate
the impact of the genotype and the environment on the variance of traits. This is
why such studies have been up until now conducted mainly in Arabidopsis ,as
shown in the review of Chardon et al. 2012 . Variation between Arabidopsis
accessions can be explored to discover ideotypes that can match with different
crop specifications: four groups, corresponding to different agronomic indicators
such as grain yield, vegetative biomass and composition of the grains at low or high
nitrogen supply, can be defined. On the basis of their physiological performance for
nitrogen uptake and remobilisation, some Arabidopsis accessions are presented as
good models for the investigation of the agronomic performances required to fit
with crops specifications. Some other examples come from the investigations of
Arabidopsis accessions grown in limiting nutrition (Reymond et al. 2006 ; North
et al. 2009 ) or complete nitrogen starvation (Richard-Molard et al. 2008 ; Ikram
et al. 2012 ). The aim of these studies was to investigate the extent of variation of
growth responses to nitrate limitation and starvation in Arabidopsis to identify
accessions showing contrasted responses and eventually different growth adaptive
strategies.
Uncovering Genes Involved in NUE Quantitative Loci by
QTL Mapping in Segregating Populations
Principles of QTL
The establishment of the genetic basis of quantitative traits is commonly referred to
as quantitative trait locus (QTL) mapping and has been hampered by their
multigenic inheritance and the often strong interaction with the environment. The
principle of QTL mapping in segregating populations is based on the genotyping of
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