Agriculture Reference
In-Depth Information
ute either directly in the human diet or indirectly as animal feed in the
next century [200]. Thus, considering both the economical and environ-
mental challenge represented by reducing both the cost and application
of N fertilizers, all major maize seed breeding companies such as Mon-
santo, DuPont-Pioneer and Syngenta are investing in genomic research
for improving NUE. Moreover, improvement in yield for most crops over
the last 50 years has been estimated to be 40%, due to improvements in
cultural practices and 60% due to genetic gains, thus indicating that breed-
ing for improved NUE is still possible [206]. However, to our knowledge,
improving NUE either through genetic engineering or marker assisted
breeding is still at the stage of proof of concept. Therefore, very little in-
formation is currently released from both the private and public sector in
consideration of the potential economic value of crop NUE improvement.
However, both on the genetic and physiological side, the identifi ca-
tion of key steps involved in the control of NUE from gene expression to
metabolic activity remains incomplete. It is likely because the regulatory
mechanisms involved in the control of the two components of NUE (N
uptake and utilization effi ciencies) are species-specifi c [6]. Moreover, they
are subjected to changes or adaptation in a constantly changing soil and
aerial environment during plant growth and development that require the
taking into account the various genotypic/environment interactions [207].
NUE is controlled by a complex array of physiological, developmental
and environmental interactions that are organ and tissue-specifi c and which
are specifi c to the genotype of a given species. It is therefore essential that
a much more extensive survey of a wide range of genotypes covering the
genetic diversity of a crop should be performed. This can be achieved using
the various available “omics” techniques, combined with agronomic and
physiological approaches in order to identify both common and specifi c ele-
ments controlling NUE and plant productivity of plants grown in the fi eld
under organic or mineral N fertilizer conditions [208].
Over the last two decades, the construction of cereals that can fi x atmo-
spheric N has always been a challenge for plant scientists, in order to re-
duce the need for mineral N fertilization. Although, the signaling pathway
for recognition of N-fi xing bacteria is present in cereals, complex genetic
modifi cation will be necessary to allow bacterial colonization and nodule
organogenesis [209].
