113
vent dehydration, which cause drastic reduction in transpiration rates (Taiz and
Zeiger 2004), and abscisic acid increases by as much as 50-fold in leaves, which
decreases leaf area due to lower-turgor-pressure cells, stomatal closure, the induction of senescence and ethylene production (Taiz and Zeiger 2013). A change in the
osmotic potential, relative to the plasma membrane, can be a major cause of response
to water stress at the molecular level (Bray 1993). Water stress also affects many
important biochemical processes such as osmotic adjustment, antioxidant enzyme
defense system, abscisic acid production, and lipid peroxidation (Sarto et al. 2016).
A decrease in photosynthesis and increase in leaf senescence associated with
drought stress during the grain filling period of wheat results in yield reduction
(Zhang et al. 1998). The increase in Si in the plant can increase the efficiency of
water use by some grasses (Sarto et al. 2017).
Rodrigues et al. (1998) highlighted three critical periods wherein the occurrence
of drought most affects the wheat crop: floral initiation and inflorescence development, anthesis and fertilization, and grain formation. Dias (2008) indicated that the
greatest reduction in wheat grains yield occur when plants suffer from water deficiency during 15 days before and 5 days after heading. Under severe stress, the
dehydration in mesophyll cells inhibits photosynthesis and water use efficiency
decreases as a result (Taiz and Zeiger 2004). Whereas, Kirigwi et al. (2004) indicated that the most sensitive growth stage to lack of water in wheat is the flag leaf
stage, followed by the flowering stage. A reduction in water availability in plants
leads to the reduction of cell solutes thus increasing the solute concentration. This
causes the plasma membrane to become thicker, affecting the turgidity processes of
cells, reducing the leaf area and causing stomatal closure. This results in a reduced
rate of photosynthesis, influencing the plant development (Dias 2008). Decrease in
water availability in wheat causes reduced growth by decreasing water potential,
stomatal conductance, photosynthesis, and nitrogen assimilation. During the milkgrain stage, wheat is the least sensitive to water stress (Cunha et al. 2009).
6.2.2 Effect of Deficit Irrigation
Galavi and Moghaddam (2012) stated that wheat yield, harvest index, water use
efficiency and evapotranspiration efficiency were negatively affected by deficit irrigation, compared to well-watered treatment. Malik and Ahmad (1993) indicated
that deficit irrigation was found to reduce grain yield when applied at any physiological growth stage, but the extent of damage varied from stage to stage. Irrigation
applied at the jointing and heading stages of winter wheat resulted in reasonable
grain yield and water use efficiency besides increasing root length density due to the
changes in the vertical distribution of root length density (Li et al. 2010).
Application of deficit irrigation to wheat grown in sandy soil was done and its
effects were tested by Noreldin et al. (2015), where they reduced the applied irrigation water by 25 and 20% under drip and sprinkler systems, respectively. They
found that wheat yield was reduced by 20 and 18%, respectively. Whereas,
6 Wheat Insufficiency and Deficit Irrigation
vent dehydration, which cause drastic reduction in transpiration rates (Taiz and
Zeiger 2004), and abscisic acid increases by as much as 50-fold in leaves, which
decreases leaf area due to lower-turgor-pressure cells, stomatal closure, the induction of senescence and ethylene production (Taiz and Zeiger 2013). A change in the
osmotic potential, relative to the plasma membrane, can be a major cause of response
to water stress at the molecular level (Bray 1993). Water stress also affects many
important biochemical processes such as osmotic adjustment, antioxidant enzyme
defense system, abscisic acid production, and lipid peroxidation (Sarto et al. 2016).
A decrease in photosynthesis and increase in leaf senescence associated with
drought stress during the grain filling period of wheat results in yield reduction
(Zhang et al. 1998). The increase in Si in the plant can increase the efficiency of
water use by some grasses (Sarto et al. 2017).
Rodrigues et al. (1998) highlighted three critical periods wherein the occurrence
of drought most affects the wheat crop: floral initiation and inflorescence development, anthesis and fertilization, and grain formation. Dias (2008) indicated that the
greatest reduction in wheat grains yield occur when plants suffer from water deficiency during 15 days before and 5 days after heading. Under severe stress, the
dehydration in mesophyll cells inhibits photosynthesis and water use efficiency
decreases as a result (Taiz and Zeiger 2004). Whereas, Kirigwi et al. (2004) indicated that the most sensitive growth stage to lack of water in wheat is the flag leaf
stage, followed by the flowering stage. A reduction in water availability in plants
leads to the reduction of cell solutes thus increasing the solute concentration. This
causes the plasma membrane to become thicker, affecting the turgidity processes of
cells, reducing the leaf area and causing stomatal closure. This results in a reduced
rate of photosynthesis, influencing the plant development (Dias 2008). Decrease in
water availability in wheat causes reduced growth by decreasing water potential,
stomatal conductance, photosynthesis, and nitrogen assimilation. During the milkgrain stage, wheat is the least sensitive to water stress (Cunha et al. 2009).
6.2.2 Effect of Deficit Irrigation
Galavi and Moghaddam (2012) stated that wheat yield, harvest index, water use
efficiency and evapotranspiration efficiency were negatively affected by deficit irrigation, compared to well-watered treatment. Malik and Ahmad (1993) indicated
that deficit irrigation was found to reduce grain yield when applied at any physiological growth stage, but the extent of damage varied from stage to stage. Irrigation
applied at the jointing and heading stages of winter wheat resulted in reasonable
grain yield and water use efficiency besides increasing root length density due to the
changes in the vertical distribution of root length density (Li et al. 2010).
Application of deficit irrigation to wheat grown in sandy soil was done and its
effects were tested by Noreldin et al. (2015), where they reduced the applied irrigation water by 25 and 20% under drip and sprinkler systems, respectively. They
found that wheat yield was reduced by 20 and 18%, respectively. Whereas,
6 Wheat Insufficiency and Deficit Irrigation