286
stomatal conductance (Sanguineti et al. 1999 ; Juenger et al. 2005 ), transpiration
efficiency (Kholova et al. 2010 ), osmotic adjustment (Diab et al. 2004 ; Saranga
et al. 2004 ; Robin et al. 2003 ), relative water content (Diab et al. 2004 ; Sanguineti
et al. 1999 ), canopy temperature (Diab et al. 2004 ; Saranga et al. 2004 ), drought
sensitivity index (Sanguineti et al. 1999 ), leaf ABA (Kholova et al. 2010 ), chloro-
phyll content (Shen et al. 2007 ), root traits (Chandra Babu et al. 2003 ; Li et al. 2005 )
and some yield-related traits (Moreau et al. 2004 ; Xu et al. 2005 ; Xiao et al. 2005 ).
Selection of germplasm with reproductive drought-tolerance has been based on
grain yield-related traits, with selection often being conducted under field condi-
tions. Several QTLs with widely varying contribution to the grain yield phenotype
under drought conditions have identified in wheat and rice (Lanceras et al. 2004 ;
Wang et al. 2005 ; Bernier et al. 2007 ; Kirigwi et al. 2007 ). A major problem with
drought tolerance selection is interference with avoidance/escape mechanisms (e.g.
early flowering), especially under field conditions, where occurrence, timing, sever-
ity and length of water stress conditions cannot be controlled (Yue et al. 2006 ;
Dolferus et al. 2011 ).
11 Conclusion
Although dryland agriculture has great importance and above 40 % of the world
agriculture is in dry areas not much attention has been given to in the past. It is
worthy to note that with the current trend of global warming and climate change dry
areas may increase and the severity of water scarcity will also increase. Most of the
varieties developed in the past for drylands are the spillovers from breeding pro-
grams for irrigated areas. More breeding programs using high- throughput tech-
nologies specifically targeting dry areas needs to be developed. Some of areas
having enough water for crop growth may have water shortage in critical crop
growth stages. Development of water efficient or drought tolerant will be a big
advantage for farmers, it will not only avoid crop failure but also increase crop
yield. For the global food security in the future, dryland agriculture is going to play
a major role. More investment and research needs to be done to insure the develop-
ment and stability of agricultural system in drylands.
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