maximum temperature (Tmax), and Optimum temperature (Topt) at the anthesis
stage of maize and wheat are presented in Table 3.1. HT (30
C) impaired abnormal
ovary growth with reduced nucellus and short sized or no embryo sac in wheat
during meiosis (Saini et al. 1983). Overall, the effect of HS results in reduced grain
number per spike in wheat (Prasad and Djanaguiraman 2014; Dwivedi et al. 2017),
kernel number, and kernel weight in maize (Sanchez et al. 2014).
3.2.1.3 Grain and Yield
The duration of grain development experiencing 6–8
C increased in temperatures
effects the grain number, grain weight, and grain growth rate in wheat (Viswanathan
and Khanna-Chopra 2001; Dias and Lidon 2009; Yin et al. 2009; Farooq et al. 2011;
Johkan et al. 2011; Lukac et al. 2011; Ottman et al. 2012; Balla et al. 2019). In maize
reduction of fertilized structure and ear, growth rate lead to a reduction in kernel
number and ultimately affect crop yield (Cicchino et al. 2010; Khodarahmpour
2011). Furthermore, in wheat flour and bread quality including changes in protein
content (increases the ratio between gliadin and glutenin) of the flour was observed
(Wardlaw et al. 2002) which produces a weak dough (Li et al. 2013), But the
minimum effect of HS observed in protein concentration of grain (Lizana and
Calderini 2013). However, HS in the early stage of grain filling stage has a high
concentration of protein in wheat (Castro et al. 2007). HT at day and night (31/20
C)
changed the structure of the aleurone layer and cell endosperm resulting in shrinking
of grain (Dias et al. 2008). In maize impact of HT (33–40
C) seen at the flowering
stage results in higher yield reduction than at the grain filling period (Edreira and
Otegui 2012). The changes in the number and size of the grain depending upon the
growth stage encountering HS. HT !20
C during anthesis and spike initiation
promote spike development with the cost of reduction in the number of grains per
spike (Semenov 2009). HS after spike initiation reduces grain size resulting in
shriveled grains (Macas et al. 2000). In another study, Schittenhelm et al. (2020)
in wheat showed that thousand grain weight, one of the main grain yield traits,
strongly affected by terminal HS. In their studies, a 49% decrease in 1000 grain
weight was observed as it was reduced from 47 to 24 g. Thus, the cumulative effects
of all morphophysiological changes under HT stress may result in lowering grain
number per spike, grain weight per spike, harvest index, and yield (Guedira et al.
2002; Shah and Paulsen 2003; Dias and Lidon 2009; Taghizadeh and Shrifi 2010;
Refay 2011; Talukder et al. 2014).
3.2.2 Physiological Response
Heat stress tolerance is a complex phenomenon that aims to reduce the damaged
plant system. The damage may be due to cellular structure and modification to
several physiological processes viz. photosynthesis, respiration, cell membrane
fluidity, osmolytes accumulation, etc. (Wahid et al. 2007; Waqas et al. 2017).
Variation in physiological traits for thermotolerance in wheat was analyzed by
56
R. Gajghate et al.
stage of maize and wheat are presented in Table 3.1. HT (30
C) impaired abnormal
ovary growth with reduced nucellus and short sized or no embryo sac in wheat
during meiosis (Saini et al. 1983). Overall, the effect of HS results in reduced grain
number per spike in wheat (Prasad and Djanaguiraman 2014; Dwivedi et al. 2017),
kernel number, and kernel weight in maize (Sanchez et al. 2014).
3.2.1.3 Grain and Yield
The duration of grain development experiencing 6–8
C increased in temperatures
effects the grain number, grain weight, and grain growth rate in wheat (Viswanathan
and Khanna-Chopra 2001; Dias and Lidon 2009; Yin et al. 2009; Farooq et al. 2011;
Johkan et al. 2011; Lukac et al. 2011; Ottman et al. 2012; Balla et al. 2019). In maize
reduction of fertilized structure and ear, growth rate lead to a reduction in kernel
number and ultimately affect crop yield (Cicchino et al. 2010; Khodarahmpour
2011). Furthermore, in wheat flour and bread quality including changes in protein
content (increases the ratio between gliadin and glutenin) of the flour was observed
(Wardlaw et al. 2002) which produces a weak dough (Li et al. 2013), But the
minimum effect of HS observed in protein concentration of grain (Lizana and
Calderini 2013). However, HS in the early stage of grain filling stage has a high
concentration of protein in wheat (Castro et al. 2007). HT at day and night (31/20
C)
changed the structure of the aleurone layer and cell endosperm resulting in shrinking
of grain (Dias et al. 2008). In maize impact of HT (33–40
C) seen at the flowering
stage results in higher yield reduction than at the grain filling period (Edreira and
Otegui 2012). The changes in the number and size of the grain depending upon the
growth stage encountering HS. HT !20
C during anthesis and spike initiation
promote spike development with the cost of reduction in the number of grains per
spike (Semenov 2009). HS after spike initiation reduces grain size resulting in
shriveled grains (Macas et al. 2000). In another study, Schittenhelm et al. (2020)
in wheat showed that thousand grain weight, one of the main grain yield traits,
strongly affected by terminal HS. In their studies, a 49% decrease in 1000 grain
weight was observed as it was reduced from 47 to 24 g. Thus, the cumulative effects
of all morphophysiological changes under HT stress may result in lowering grain
number per spike, grain weight per spike, harvest index, and yield (Guedira et al.
2002; Shah and Paulsen 2003; Dias and Lidon 2009; Taghizadeh and Shrifi 2010;
Refay 2011; Talukder et al. 2014).
3.2.2 Physiological Response
Heat stress tolerance is a complex phenomenon that aims to reduce the damaged
plant system. The damage may be due to cellular structure and modification to
several physiological processes viz. photosynthesis, respiration, cell membrane
fluidity, osmolytes accumulation, etc. (Wahid et al. 2007; Waqas et al. 2017).
Variation in physiological traits for thermotolerance in wheat was analyzed by
56
R. Gajghate et al.