on traits correlate with higher grain yield under HS condition (Reynolds and
Langridge 2016). Direct selection can be done by the abovementioned screening
methods and selection indices (Table 3.2). However, separate evaluations on each
stage throughout the ontogeny of the plant and uncontrolled environmental factors
adversely impact the precision and repeatability of the trials (Chen et al. 1982).
Besides, for selection for indirect or associated traits few facilities like highresolution thermal imaging system to measure leaf temperature (Jones and Sirault
2014), image analysis phenotypic platform “HTpheno” (Hartmann et al. 2011) and
“Rootscope” used to measured heat shock responses in plants (Kast et al. 2013).
Soon, the new-generation phenomics platforms allow to screen huge germplasm for
HT and are very cost-effective.
For the identification of a tolerant genotype, genetic diversity is the necessities in
the breeding program (Chapman et al. 2012; Balla et al. 2019). Landraces and wild
relatives are the best sources for genetic diversity in the breeding program. To
maintain the genetic gain, it was suggested to screen and make crosses with exotic
material (Giaveno and Ferrero 2003) considered as the best method in maize to
increase heat tolerance. In wheat, the recurrent selection method has been useful to
develop heat tolerance lines (Gororo et al. 2002; Machado et al. 2010). Also, the
stable transfer of chromosomes from wild relative Leymus racemosus helps to
develop heat tolerance in the hot and arid area (Mohammed et al. 2014). Few
genus viz., Aegilops tauschii, Aegilops geniculata, A. speltoides, A. searsii,
A. longissimi, Triticum dicoccoides, and T. monococcum have been reported as
potential sources of HS tolerant germplasms in wheat (Zaharieva et al. 2001;
Pradhan et al. 2012). Few synthetic wheat also had high-temperature tolerance
ability (Trethowan and Mujeeb-Kazi 2008; Kurahashi et al. 2009) and which can
act as bridges for introgression of many alien genes into cultivated wheat pools
(Siddiqui 1976; Rajaram et al. 1977). Limited genetic variation in the existing
germplasm, long time to screen genotypes, and complexity associated with traits
are the major reason for few successes in conventional plant breeding program
(Parmar et al. 2017). To fasten the program molecular and transgenic approaches
can be used as an effective method to improve HS tolerance.
3.4.2 Molecular Breeding and Transgenic Approach
The application of QTL mapping and subsequent marker-assisted selection (MAS)
gives a better understanding of the genetic association among tolerances to environmental stress (Heffner et al. 2009). Many major or minor QTLs and linked markers
for HT are available in wheat (Pinto et al. 2010; Vijayalakshmi et al. 2010; Paliwal
et al. 2012; Mason et al. 2011; Beecher et al. 2012) and maize (Ottaviano et al. 1991;
Frova and Sari-Gorla 1994; Sanguineti et al. 1999) and can be used to develop HS
tolerant lines. All gathered information helps to facilitate targeted breeding for heat
tolerance in wheat and maize crops (Fig. 3.3). Summary of such efforts and progress
is presented and discussed in the following paragraphs.
66
R. Gajghate et al.
Langridge 2016). Direct selection can be done by the abovementioned screening
methods and selection indices (Table 3.2). However, separate evaluations on each
stage throughout the ontogeny of the plant and uncontrolled environmental factors
adversely impact the precision and repeatability of the trials (Chen et al. 1982).
Besides, for selection for indirect or associated traits few facilities like highresolution thermal imaging system to measure leaf temperature (Jones and Sirault
2014), image analysis phenotypic platform “HTpheno” (Hartmann et al. 2011) and
“Rootscope” used to measured heat shock responses in plants (Kast et al. 2013).
Soon, the new-generation phenomics platforms allow to screen huge germplasm for
HT and are very cost-effective.
For the identification of a tolerant genotype, genetic diversity is the necessities in
the breeding program (Chapman et al. 2012; Balla et al. 2019). Landraces and wild
relatives are the best sources for genetic diversity in the breeding program. To
maintain the genetic gain, it was suggested to screen and make crosses with exotic
material (Giaveno and Ferrero 2003) considered as the best method in maize to
increase heat tolerance. In wheat, the recurrent selection method has been useful to
develop heat tolerance lines (Gororo et al. 2002; Machado et al. 2010). Also, the
stable transfer of chromosomes from wild relative Leymus racemosus helps to
develop heat tolerance in the hot and arid area (Mohammed et al. 2014). Few
genus viz., Aegilops tauschii, Aegilops geniculata, A. speltoides, A. searsii,
A. longissimi, Triticum dicoccoides, and T. monococcum have been reported as
potential sources of HS tolerant germplasms in wheat (Zaharieva et al. 2001;
Pradhan et al. 2012). Few synthetic wheat also had high-temperature tolerance
ability (Trethowan and Mujeeb-Kazi 2008; Kurahashi et al. 2009) and which can
act as bridges for introgression of many alien genes into cultivated wheat pools
(Siddiqui 1976; Rajaram et al. 1977). Limited genetic variation in the existing
germplasm, long time to screen genotypes, and complexity associated with traits
are the major reason for few successes in conventional plant breeding program
(Parmar et al. 2017). To fasten the program molecular and transgenic approaches
can be used as an effective method to improve HS tolerance.
3.4.2 Molecular Breeding and Transgenic Approach
The application of QTL mapping and subsequent marker-assisted selection (MAS)
gives a better understanding of the genetic association among tolerances to environmental stress (Heffner et al. 2009). Many major or minor QTLs and linked markers
for HT are available in wheat (Pinto et al. 2010; Vijayalakshmi et al. 2010; Paliwal
et al. 2012; Mason et al. 2011; Beecher et al. 2012) and maize (Ottaviano et al. 1991;
Frova and Sari-Gorla 1994; Sanguineti et al. 1999) and can be used to develop HS
tolerant lines. All gathered information helps to facilitate targeted breeding for heat
tolerance in wheat and maize crops (Fig. 3.3). Summary of such efforts and progress
is presented and discussed in the following paragraphs.
66
R. Gajghate et al.