68
M. A. S. Abdel Monem and I. A. El Ghandour
3.3 Breeding for Heat Tolerance
It is well established that increasing tolerance to temperature by conventional breeding is an obvious approach to reduce the adverse produced eventually. Thus, the
selection of breeding lines for relatively hot regions is conducted under hot conditions [23]. Conventional breeding has also been used to intentionally develop new
heat-tolerant crop genotypes. For example, a variety of broccoli has an improved
head quality thanks to early maturation, because this trait prevents hot days later in
the season to affect the heat-sensitive flower initiation developmental stage [24].
In addition, new varieties of cowpea showed higher average grain yield when
grown under hot and long days during reproduction Ehlers and Hall [25]. And recurrent selection has also been successful for improving wheat yield using ancestor
T. tauschii as a gene donor, leading to increased rates of grain filling and larger
grains in BC1F6 plants [26]. Jha et al. [27] developed a list of quantitative trait
loci (QTLs) associated with heat tolerance in various plants, including Arabidopsis, azuki bean, barley, brassica, cowpea, maize, potato, rice, sorghum, tomato and
wheat. The authors showed several types of genetic markers linked to different traits
of interest which spanned the various aspects of a plant’s vulnerability to heat. This
included QTLs for yield traits, such as fruit set or grain filling rate, under heat.
Also, QTLs for several heat tolerance- related traits have been discovered, such as
for lower canopy temperature during vegetative and reproductive stages and higher
chlorophyll fluorescence in wheat [28–30]. Pinto and Reynolds [31] stated that, High
chlorophyll fluorescence represents heat-tolerant photosynthesis, and lower canopy
temperature reflects efficacious water uptake which has been associated with deep
rooting. A major quantitative trait loci (QTL) for high temperature seed germination
capacity in lettuce, Htg6.1, collocates with a temperature-sensitive gene encoding an
abscisic acid biosynthesis enzyme (LsNCED4) [32, 33]. In potato, nine quantitative
trait loci (QTLs) for internal heat necrosis in tubers were detected that each explain
between 4.5 and 29.4% of the phenotypic variation [34]. Many studies have focused
on the effect of high temperature on reproductive characteristics. This including
pollen germinability, pollen tube growth, grain weight, days to heading, grain filling and post-anthesis leaf senescence, fruit set and quality traits such as white-back
kernels in rice. In maize, five and six QTLs for pollen quality and tube growth have
been identified with a high heritability of 0.64 and 0.68, respectively. In response to
high-temperature stress, plants modulate the expression of a plethora of genes. These
genes and their annotation could help to identify the processes that are induced or
suppress such as those involved in adaptation and protection to heat stress [35].
3.4 Crop Simulation Models
Crop simulation models can predict several key crop characteristics over a wide range
of climatic conditions, such as the timing of flowering and physiological maturity,
M. A. S. Abdel Monem and I. A. El Ghandour
3.3 Breeding for Heat Tolerance
It is well established that increasing tolerance to temperature by conventional breeding is an obvious approach to reduce the adverse produced eventually. Thus, the
selection of breeding lines for relatively hot regions is conducted under hot conditions [23]. Conventional breeding has also been used to intentionally develop new
heat-tolerant crop genotypes. For example, a variety of broccoli has an improved
head quality thanks to early maturation, because this trait prevents hot days later in
the season to affect the heat-sensitive flower initiation developmental stage [24].
In addition, new varieties of cowpea showed higher average grain yield when
grown under hot and long days during reproduction Ehlers and Hall [25]. And recurrent selection has also been successful for improving wheat yield using ancestor
T. tauschii as a gene donor, leading to increased rates of grain filling and larger
grains in BC1F6 plants [26]. Jha et al. [27] developed a list of quantitative trait
loci (QTLs) associated with heat tolerance in various plants, including Arabidopsis, azuki bean, barley, brassica, cowpea, maize, potato, rice, sorghum, tomato and
wheat. The authors showed several types of genetic markers linked to different traits
of interest which spanned the various aspects of a plant’s vulnerability to heat. This
included QTLs for yield traits, such as fruit set or grain filling rate, under heat.
Also, QTLs for several heat tolerance- related traits have been discovered, such as
for lower canopy temperature during vegetative and reproductive stages and higher
chlorophyll fluorescence in wheat [28–30]. Pinto and Reynolds [31] stated that, High
chlorophyll fluorescence represents heat-tolerant photosynthesis, and lower canopy
temperature reflects efficacious water uptake which has been associated with deep
rooting. A major quantitative trait loci (QTL) for high temperature seed germination
capacity in lettuce, Htg6.1, collocates with a temperature-sensitive gene encoding an
abscisic acid biosynthesis enzyme (LsNCED4) [32, 33]. In potato, nine quantitative
trait loci (QTLs) for internal heat necrosis in tubers were detected that each explain
between 4.5 and 29.4% of the phenotypic variation [34]. Many studies have focused
on the effect of high temperature on reproductive characteristics. This including
pollen germinability, pollen tube growth, grain weight, days to heading, grain filling and post-anthesis leaf senescence, fruit set and quality traits such as white-back
kernels in rice. In maize, five and six QTLs for pollen quality and tube growth have
been identified with a high heritability of 0.64 and 0.68, respectively. In response to
high-temperature stress, plants modulate the expression of a plethora of genes. These
genes and their annotation could help to identify the processes that are induced or
suppress such as those involved in adaptation and protection to heat stress [35].
3.4 Crop Simulation Models
Crop simulation models can predict several key crop characteristics over a wide range
of climatic conditions, such as the timing of flowering and physiological maturity,