5 Tolerance to Combined Stress of Drought and Salinity in Barley 109
Long et al. ( 2013 ) demonstrated that a spring barley collection of 192 genotypes
from a wide geographical range was used to identify QTLs for salt-tolerance traits
by means of an association mapping approach using a 1000 single nucleotide poly-
morphism (SNP) marker set. Linkage disequilibrium (LD) decay was found with
marker distances spanning 2–8 cM depending on the methods used to account for
population structure and genetic relatedness between genotypes. The association
panel showed large variation for traits that were highly heritable under salt stress,
including biomass production, chlorophyll content, plant height, tiller number, leaf
senescence, shoot Na+, shoot Cl−, and shoot, root Na+/K+ contents. The significant
correlations between these traits and salt tolerance (defined as the biomass pro-
duced under salt stress relative to the biomass produced under control conditions)
indicate that these traits contribute to (components of) salt tolerance. Association
mapping was performed using several methods to account for population structure
and minimize false-positive associations. This resulted in the identification of a
number of genomic regions that strongly influenced salt tolerance and ion homeo-
stasis, with a major QTL controlling salt tolerance on chromosome 6H, and a strong
QTL for ion contents on chromosome 4H (Long et al. 2013 ).
Recently, Li et al. ( 2013 ) confirmed that the distribution of meta-QTL (MQTL)
was similar to that of the initial QTL. Many of these MQTL were located on chro-
mosomes 2H (drought) and 5H (salinity). It inferred that chromosomes 2H and
5H were important for barley abiotic stress tolerance. As expected from trait cor-
relations, 22.8 % of these MQTL displayed overlapping confidence intervals (CIs).
These overlapping regions were mainly on chromosomes 1H, 2H, and 4H. The
results indicated that the tolerance to diverse abiotic stresses were associated with
each other in barley (Li et al. 2013 ).
5.9 Molecular Approaches for Improvement
of Modern Barley
The high-throughput omics analysis, including transcriptomics, proteomics, and me-
tabolomics, will improve comprehensive understanding of drought and salt stress-
induced changes in gene-protein-metabolite (Urano et al. 2010 ; Sicher et al. 2012 ).
Transcriptomics and proteomics analysis have been widely used in salt-tolerance stud-
ies (Du et al. 2008 ; Zhang et al. 2012 ). Currently, metabolomics are developed and
applied in understanding multiple physiological processes in plants, in combination
with other platforms such as transcript profiling and proteomics. Major approaches
currently used in plant metabolomics are metabolic fingerprinting, metabolite profil-
ing, and targeted analysis. Main analysis methods include gas chromatography-mass
spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), capil-
lary electrophoresis-mass spectrometry (CE-MS), Fourier transformation cyclotron
resonance-mass spectrometry (FT-ICR-MS), and nuclear magnetic resonance (NMR;
Nicholson et al. 1999 ; Shulaev et al. 2008 ). In recent years, metabolomics analysis is
being widely used to investigate abiotic stress tolerance of plants (Shulaev et al. 2008 ;