African Journal of Biotechnology Vol. 10(55), pp. 11340-11344, 21 September, 2011
Available online at http://www.academicjournals.org/AJB
ISSN 1684–5315 © 2011 Academic Journals
Review
Potentials of molecular based breeding to enhance
drought tolerance in wheat (Triticum aestivum L.)
Mueen Alam Khan1*, Muhammad Iqbal1, Moazzam Jameel1, Wajad Nazeer2, Sara Shakir1,
Muhammad Tabish Aslam1 and Bushra Iqbal1
1
College of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur, Pakistan.
2
Cotton Research Station, Multan, Pakistan.
Accepted 22 July, 2011
The ability of plant to sustain itself in limited water conditions is crucial in the world of agriculture. To
breed for drought tolerance in wheat, it is essential to clearly understand drought tolerant mechanisms.
Conventional breeding is time consuming and labor intensive being inefficient with low heritability
traits like drought tolerance. Recent progress made in the field of genomics enabling us to access
genes linked with drought tolerance has enhanced our understanding of this complex phenomenon.
The purpose of this review paper was to briefly overview the accomplishments in molecular breeding
for drought tolerance in wheat. Thus, by knowing the genetics of drought tolerance and identifying
quantitative trait loci (QTLs) linked with DNA markers will help wheat breeders to develop high yielding
drought tolerant cultivars.
Key words: Triticum aestivum L, drought tolerance, QTLs, marker assisted selection (MAS).
INTRODUCTON
Wheat (Triticum aestivum L) is a cereal of choice in most
countries of the world. Constant efforts are therefore
needed to boost its production to keep the pace with ever
increasing population. But unfortunately, these efforts are
seriously being hampered by a number of abiotic
stresses among which is drought (Boyer, 1982).
According to Pfeiffer et al. (2005), 50% of wheat
production area is affected due to drought worldwide.
Drought leads to abnormal germination and poor crop
stand (Harris et al., 2002; Kaya et al., 2006). Furthermore, drought prevailing at various critical growth stages
like flowering and grain filling greatly reduce crop yield
and due to that reason, its importance have been realized
at the global level. Thus, developing drought resistant
cultivars has been the objective of plant breeders and
plant biotechnologists.
Considerable efforts have been made in the past to
develop drought tolerant cultivars of wheat through
conventional breeding. But with little success due to
quantitative (polygenic) nature of drought tolerance which
*Corresponding author. E-mail: mueen_1981@yahoo.com Tel:
+92-62-9255531.
is more influenced by external environmental conditions
than by the genetic component (El-Jaafari, 1999;
Krishnamurthy et al., 1996; Ingrams and Bartels, 1996;
Zhang, 2004).
The recent progress in the field of genomics is
astonishing providing breeders new tools for crop genetic
improvement with reference to drought tolerance
(Cattivelli et al., 2008) This review paper therefore
analyses how genomic based approaches can contribute
to the accelerating release of drought tolerant wheat
cultivars.
DROUGHT TOLERANT MECHANISMS
Drought tolerance is the ability of plant to sustain itself in
limited water supply (Ashley, 1993). As aforementioned,
drought tolerance is a complex polygenic trait, therefore a
number of factors come in to play making the plant to
sustain drought. Drought affects the plant at the cellular,
tissue and organ levels (Beck et al., 2007) and drought
tolerant plants tackle the injurious effects of drought by
initiating various defense mechanisms which should be
understood in order to breed for drought tolerant cultivars
Khan et al.
(Chaves and Oliveira, 2004; Zhou et al., 2007). Drought
tolerant mechanisms can be morphological, physiological
or molecular (Bohnert et al., 1995; Farooq et al, 2009).
Morphological mechanisms include; drought escape
which is the ability of plant to complete its life cycle
before the onset of drought season (Mitra, 2001), drought
avoidance which is the plant’s ability to retain the water
by increasing the uptake of water and reducing its loss
through reduced transpiration which is made possible by
long and thick root network as well as leaf and stomatal
characteristics (Blum, 1988; Turner et al., 2001; Izanloo
et al., 2008; Agbicodo et al., 2009).
Among the physiological mechanisms, osmotic
adjustment (OA) is perhaps the most crucial factor which
allows the cell to decrease osmotic potential and maintain
the turgor and the plant is able to sustain itself in
decreased water supply (Blum, 2005; Farooq et al., 2009;
Taiz and Zeiger, 2006).
The role of abscisic acid (ABA) a stress hormone
cannot be overlooked. Under water deficit environment,
ABA induces the closure of stomata and thus reducing
water transpiration (Turner et al. 2001). Glucousness (a
waxy covering over the cuticle) is also considered to be a
reliable parameter leading to increase in water use of
efficiency in wheat plant thus providing a mechanism of
drought tolerance (Richards et al; 1986).
The molecular mechanisms involve activation of a
cascade of genes which ultimately make the plant desiccation tolerant (Agarwal et al., 2006; Umezawa et al.,
2006)
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MAPPING QTLS THROUGH MARKER ASSISTED
SELECTION (MAS) IN WHEAT
Marker assisted selection (MAS) refers to selection
based on DNA markers linked to QTLs. The DNA
markers are very powerful. Once these are identified,
their mapping on the chromosome in relation to QTLs is
carried out. Thus, presence of QTLs for drought tolerance
can then be tracked by careful monitoring of these DNA
markers (Thoday, 1961; Everson and Schaller, 1955).
Various DNA markers like restriction fragment length
polymorphism (RFLP), amplified fragment length
polymorphism (AFLP), and simple sequence repeat
(SSR) have been used to tag QTLs for drought stress in
wheat (Quarrie et al., 2005). Application of microsettalite
markers in wheat for tagging QTLs for disease
resistance, grain protein contents, and yield have also
been documented by a number of scientists (Fahima et
al., 1998; Huang et al., 2000; Del Blanco et al., 2003;
Huang et al., 2003; Prasad et al., 2003).
Kirigwi et al. (2007) used simple sequence repeat
(SST)/expressed sequence tag (EST) marker for
mapping QTL on chromosome 4A for grain yield and
yield components in wheat. The markers associated with
the QTL were XBE637912, Xwmc89, and Xwmc420.
Thus, the DNA markers closely linked with QTLs
conferring drought tolerance would greatly enhance the
selection efficiency (Cattivelli et al., 2008).
CANDIDATE GENES AND FUNCTIONAL GENOMICS
MAPPING QTLS FOR DROUGHT TOLERANCE IN
WHEAT
As aforementioned, conventional breeding strategies like
selection and hybridization have met with little success in
breeding for drought tolerance in wheat. The genomic
based approaches provide excellent opportunities to
search and map quantitative trait loci (QTLs) for drought
tolerance. This is due to our increased understanding of
gene structure and function at the cellular and molecular
level (Gosal et al., 2009). Various QTLs for drought
tolerance in wheat are summarized in Table 1.
Earlier, Quarrie et al. (2005) conducted mapping of
QTLs for drought tolerance in hexaploid wheat which
were located on chromosomes 1A, 1B, 2A, 2B, 2D, 3D,
5A, 5B, 7A, and 7B.
Double haploid populations serve as a permanent
source of mapping QTLs. Dashti et al. (2007) used 96
doubled haploid lines of wheat to analyze QTLs for
drought tolerance. They found drought tolerant indices for
QTL effects ranged from 13 to 36%. Recombinant inbred
lines developed from crossing drought resistant and
drought susceptible lines were used to produce mapping
populations for QTL analysis regulating yield under
drought (Tuberosa et al., 2002).
A candidate gene is one which is associated with the
function and development of any trait. There has been a
growing interest to map and sequence the candidate
genes with known or proposed function determining
QTLs associated with drought tolerance (Byrne and
McMullen, 1996; Gutterson and Zhang, 2004; Nguyen et
al., 2004).
The technologies of microarrays and DNA chips are
being successfully employed to quickly monitor or predict
the expression of millions of genes and search the
genomes of target crops (Schena et al., 1996; Lemieux et
al., 1998). The technology of microarray becomes more
useful when coupled with EST analysis (Sreenivasulu et
al., 2007). EST markers are available for rice and efforts
for developing EST markers for wheat are in progress
(Goff, 1999). In short a dedicated effort is what is
required to isolate and develop EST markers for drought
tolerance to be able to get full potential of microarray
technology.
TRANSGENIC DROUGHT TOLERANT WHEAT
In recent years, introducing drought tolerant genes from
different sources into drought susceptible plants has
11342
Afr. J. Biotechnol.
Table 1. Summary of QTLs associated with drought tolerance in wheata
QTL
Mapping
DHL*
RIL*
Number of
QTL
1
1
Yield interaction with water
supply and hot conditions
DHL
1
Kuchel et al. (2007)
Durum x Wild emmer
Various morphophysiological traits
RIL
many
Peleg et al. (2009)
Seri M82 x Babax
Various productivity and
physiological traits
RIL
many
McIntyre et al. 2010;
Suzuky Pinto et al., 2010.
Cross
Trait
Chinese Spring x Ciano 67
Songlen x Cobdor 4/3Ag14
ABA concentration
Osmoregulation under
drought
Trident x Molineux
Reference
Quarrie et al. (1994)
Morgan and Tan (1996)
a
*DHL= doubled haploid; RIL= recombinant inbred lines; Similar studies reported in the text were not included in this table.
Table 2. List of recently produced transgenic wheat with drought tolerant genes.
Gene
DREB1A
HVA1
mtlD
P5CS
TaLTP1
Mechanism of tolerance
Regulatory control
Protective proteins
Mannitol as osmoprotectant
Osmoprotectant
Lipid transfer protein
become one of the promising avenues for plant genetic
engineers. A transgenic approach involves the structural
modification in traits by transferring genes from one
species to another (Ashraf, 2010). A number of genes
conferring drought tolerance from different sources have
been incorporated in wheat making it transgenic (Table
2).
Most of these transgenic lines have been tested in the
laboratory. Their full scale utilization in the field would
provide important information for continued exploitation of
transgenic work. Nonetheless it is expected that transgenic approach will have an increased role in the future
as far as the mapping and engineering of QTLs for
drought tolerance is concerned (Cattivelli et al., 2008;
Ashraf, 2010).
CONCLUSION
Drought is a major cause of yield losses of wheat in the
world. Applications of conventional selection based
breeding are limited due to complex nature of drought
stress and drought tolerance. The molecular based tools
would ultimately help us to identify potential candidate
genes and valuable QTLs for drought tolerance and their
effective utility in marker assisted breeding (Tuberosa
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