Agriculture Reference
In-Depth Information
nomics and synteny approaches similar to those of Quraishi et al. [186]
can complete such analyses by linking the genetic maps of maize, rice,
barley and wheat harboring N related QTLs, thus allowing the reinforce-
ment of the weight of selected putative candidate genes.
Ultimately, following the functional validation of candidate genes us-
ing all the available approaches offered by mutagenesis, genetic modifi -
cation and association genetics, marker-assisted selection (MAS) can be
then undertaken (Figure 3). However, there are still a number of technical
and scientifi c challenges that remain to be resolved before MAS can be
routinely used in breeding for complex traits such as NUE. This is mainly
due to the number of interactions that govern the expression of such traits
both at the genetic and environmental levels [199], whether we are dealing
with conventional or organic farming growth conditions.
15.7 CONCLUSION AND PERSPECTIVES
A large number of studies have been carried out over the last two de-
cades to identify by means of agronomic, physiological and genetic stud-
ies, the rate limiting steps of NUE both in model and crop species, as a
function of environmental conditions. For abiotic stress improvement in
crops, NUE has become the second priority after drought both in the pri-
vate and in the public sector. To decipher the genetic and physiological
basis of NUE, many tools are available for most crops and for cereals in
particular. They include mutant collections, wide genetic diversity, recom-
binant inbred lines (RILs) or Doubled Haploid Line populations (DHLs),
straightforward transformation protocols and physiological, biochemical
and genomic data for systems biology development [6,200]. In addition,
the commercial crop research effort is paralleled by research in the public
sector, notably with the release of the genome sequences for rice [201] and
maize [202] and the current development of sequencing projects for wheat
[203], barley [204] and a number of other crops.
Cereal grains such as rice, wheat and maize provide 60% of the world's
nutrition, the rest being represented by barley, coarse grains of legumes
along with root crops. These crops account for the majority of end prod-
ucts used for human diets [205] and it is likely that they will still contrib-
