106 I. M. Ahmed et al.
starch granules, especially B-type granules, which were located adjacent to crushed
cell layer (CCL), while many A-type starch granules in this region were either pit-
ted or showed surface erosion. The appearance of pitting can be associated with
degradation of the proteinaceous layer, exposing the starch granule to severe stress.
However, XZ5 and XZ16 showed more protein deposited on the surface of starch
granules under drought stress (Ahmed et al. 2013c).
5.8 Identification of QTLs Controlling Drought
and Salinity Tolerance in Barley
Quantitative trait locus (QTL) mapping is a powerful approach for locating genomic
regions controlling complex traits (Gyenis et al. 2007 ). By linking phenotypic and
genotypic data, QTL mapping enables the identification of the action, interaction,
numbers and chromosomal locations of loci affecting particular traits (Miles and
Wayne 2008 ). Large numbers of barley mapping populations have been developed
to map genes and QTLs controlling agronomic and quality traits (Table 5.1) and
have been reviewed by Fox et al. ( 2003 ). Several barley populations have been
developed to map the QTLs for drought tolerance in both controlled environments
and Mediterranean field trials. These included Tadmor x (ER/Apm) RIL population
(Teulat et al. 1998 ), Derkado x B83-12 DH population (Forster et al. 2004 ), Apex
x ISR101-23 (Pillen et al. 2003 ), and Barke x Hor11508 populations (Talame et al.
2004 ).
Kalladan et al. ( 2013 ) used advanced backcross quantitative trait locus (AB-
QTL) analysis of a BC 3 -doubled haploid population developed between the culti-
vated parent Brenda ( H. vulgare ssp. vulgare) and the wild accession HS584 ( H.
vulgare ssp. spontaneum) to study the contribution of wild barley in improving
various agronomic and seed quality traits under postanthesis drought. QTL analysis
indicated that wild barley contributed favorably to most of the traits studied under
both control and drought conditions. A total of seven hotspot QTL regions with
colocalizing QTL for various traits harbored more than 80 % of the stable QTL de-
tected in their study. For yield and 1000-grain weight and their respective drought-
tolerance indices, most of the QTLs were derived from Brenda. On the other hand,
for traits like seed length and seed nitrogen content, all the QTLs were contributed
by HS584, the parent with higher trait value.
Many QTL studies carried out using wild barley as a donor parent for various
traits indicated that it is a potential source for trait improvement (Nevo 1992 ; Volis
et al. 2000 ; Pillen et al. 2004 ; Li et al. 2005 , 2006 ; Rostoks et al. 2005 ; Schmalen-
bach et al. 2009 ; Schnaithmann and Pillen 2013 ). In addition, H. vulgare ssp.
spontaneum was also found to possess positive alleles for abiotic stresses such as
drought and salt (Talame et al. 2004 ; Suprunova et al. 2007 ; Ceccarelli et al. 2007 ;
Lakew et al. 2011 , 2013 ). Major hindrances to the utilization of wild species in crop
improvement using conventional breeding are the quantitative nature of most of the
agronomic traits and the linkage drag of undesirable genes present in wild species