Biology Reference
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understanding of resistance to biotic stresses
and tolerance of abiotic stresses. Genomics
approaches can enhance the precision and effi-
ciency of breeding programs through a better
prediction of phenotype from a given geno-
type - process generally referred to as genomics-
assisted breeding (GAB) (Varshney et al. 2005).
Among different GAB approaches, the
marker-assisted backcrossing (MABC) approach
has been quite successful in transferring the tar-
get genomic regions in elite cultivars (Varshney
et al. 2012). MABC for gene pyramiding cou-
pled with selection for the genetic background
of the recurrent parent and recombination at the
target region(s) could lead to faster and better
product delivery, thereby increasing productiv-
ity and improving livelihoods of the smallholder
farmers (Collard et al. 2008).
Biotic stress caused by pests and diseases con-
tinues to pose a significant risk to crop productiv-
ity in spite of years of investments in research and
development aimed at understanding host-plant
interaction and finding more effective methods
to control it (Lucas 2011). It has been estimated
that even after the deployment of pesticides and
improved cultivars in the target environment with
resistance to biotic stresses, yield losses result-
ing from pests and diseases can still reach 20-
30% (Oerke 2006). This loss may be attributed
to the constant and rapid evolution of new vir-
ulent pathogens/pests such as Ug99 for wheat
stem rust (Levine and D'Antonio 2003), as well
as to their spread to new regions in response
to climate change and the adoption of different
agricultural practices (e.g., minimum tillage).
Abiotic stresses, such as drought, salinity,
cold, submergence, mineral toxicity, and oth-
ers, also hamper growth, yield, and yield qual-
ity of crop plants. In fact, these abiotic stresses
represent the main cause of crop failure world-
wide, reducing average yields for major crops
by more than 50%. Overall, as compared to
biotic stresses, abiotic stresses pose more seri-
ous constraints to crop production, particularly
in view of rapidly deteriorating environmental
conditions. Quality traits are the other important
class of target traits that breeders select for in
order to improve crop productivity as well as
nutritional quality.
In recent years, large-scale genomic resources
have been developed and are being utilized
in breeding programs for several crop species
(Varshney et al. 2009; Tuberosa et al. 2011).
These advances in genomics research have
greatly contributed to the conversion of so-called
orphan crops to genomic resources-rich crops
(Varshney et al. 2009, 2010) and to the enhanced
precision and speed of breeding programs. In
several cases, GAB has delivered superior lines
that have been used for developing new varieties
or hybrids (Simpson et al. 2003; Sundaram et al.
2008; Ceballos et al. 2012; Singh et al. 2012).
However, introgression of QTLs has not always
been successful in crop breeding, and even less
so for the improvement of tolerance to abiotic
stresses (Collins et al. 2008). Therefore, GAB
practices have also offered some lessons to the
molecular breeding practitioners.
In view of the above, the two volumes on
Translational Genomics for Crop Breeding
com-
pile a number of manuscripts that report on suc-
cess stories either completed or still in progress,
as well as the lessons learned from GAB work on
different crops. Volume I compiles 16 chapters
that review the current status and recent advances
in the application of GAB approaches for biotic
stress resistance. Volume II is a compendium of
13 chapters on GAB for enhancing abiotic stress
tolerance and improving crop quality.
This introductory chapter of Volume I pro-
vides key highlights of GAB applications to
enhance biotic stress tolerance. Since the major-
ity (estimated to be ca. 60-70%) of our major
caloric intake is obtained directly or indirectly
from cereals, the first five chapters summa-
rize the progress on the improvement of biotic
stress tolerance in five major cereals, namely
rice, maize, wheat, barley, and sorghum. The
contribution of legumes to enhancing nutrition
in the daily diet has been largely recognized
apart from their well-known ability for nitrogen-
fixation. The next five chapters deal with GAB
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