279and sensitive screening with fully automated fluorometers. Positive correlation of
grain carbon isotope discrimination under post-anthesis drought stress with eco-
nomic yield has been established in wheat; therefore, these indices may be used as
indirect selection criteria for wheat grown under stress environments (Zhu et al.
2009 ). Siddiqi et al. ( 2009 ) screened safflower accessions for salt tolerance based
on biomass (shoot and root dry mass) and other physio-biochemical parameters i.e.,
photosynthesis, transpiration, stomatal conductance, and chlorophyll a and b at the
vegetative stage. Mohammadi et al. ( 2011 ) screened durum wheat breeding lines
using stress tolerance index (STI) for drought, heat and cold stresses. Mohammadi
et al. ( 2014 ) identified the agro-physiological traits such as canopy temperature,
SPAD reading, plant height, flag-leaf length and heading date as the most important
traits for screening drought tolerant durum wheat breeding lines.
8.5 Doubled Haploids
Doubled haploids method accelerates the breeding program in terms of develop-
ment of homozygous lines from heterozygous plants after crossing two different
parents. This procedure saves time by excluding several generations of selfing
required before obtaining pure lines. It is also attractive to breeders and genetists
because of expression of simple recessive genetic traits or mutated genes. Doubled
haploids in wheat have been produced from anther culture (Ouyang et al. 1973 ),
using wide hybridization (Schaeffer et al. 1979 ) and isolated microspore culture
(Wei, 1982 ). It is noteworthy that the doubled haploids produced by different meth-
ods are equally the same (Guzy-Wrobelska and Szarejko 2003 ), however Guzy-
Wrobelska et al. ( 2007 ) reported that doubled haploids derived by anther culture
had a high recombination frequency.
Anther culture is more cost-effective than other methods of doubled haploid pro-
duction (Guzy-Wrobelska et al. 2007 ) such as intergeneric crossing method (Pratap
et al. 2006 ). Anther culture involves the induction of embryoids into plantlets and is
known for its highly genotype specific response (Tawkaz 2011 ). Ouyang et al.
( 1973 ) reported the in vitro regeneration of plants from pollen. A certain proportion
of pollen grains in situ are embryogenic. These pollen grains when placed on an
artificial media can develop into embryos (Ouyang et al. 1973 ; Liu et al. 2002 ).
8.6 Embryo Rescue
Embryo rescue also known as embryo culture refers to subsequent collection of
techniques, which enables a weak embryo into viable plant. Embryo rescue is often
used after procedures like hybridization (especially incompatible crosses), transfor-
mation, doubled haploid production, etc.
Breeding and Genetic Enhancement of Dryland Crops