الفهرس 
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Abstract
The field experiments were carried out in four seasons during the period from 2015 to 2018 at the experimental farm of the faculty of agriculture, Menoufia University, in Shebin El-Kom, Egypt. The local cultivar Gemmeiza (yellow) and Tep#5 (white) were used as a base population to practice one cycle of S1 recurrent selection for drought tolerance. The main objectives of this study are to study the effect of water stress on different maize traits and identify the effectiveness of S1 recurrent selection for improving drought tolerance in the two maize genotypes.
In 2015 summer season, S1 recurrent selection procedure was provided (Tep#5 and Gemmeiza yellow), where 200 S0 plants from each population were selfed to produce S1 progenies. At harvest, one hundred ears with enough seeds were selected and each was divided into two parts, the first part was assigned for evaluation traits. The second part was kept as remnant S1 seeds for developing the second cycle for each population.
In 2016 summer season, kernels of 100 S1 lines that selected from each two populations were separately sown at Shebin El-Kom farm for evaluation under two water regimes, i.e normal irrigation (NI) and drought stress conditions (DS) (just prior and during flowering stage; with a water-stress period of 24 days). Each trial was provided in Randomized Complete Block Design with three replications. All data were recorded for grain yield and its components. Based on grain yield per plot, the best 10% (10 S1’s) of each group were selected under each environment, so two groups of selected S1’s were obtained for each population (10 S1’s under NI and 10 S1’s under DS).
In 2017 summer season, the highest 10% of S1 progenies (10 S1
progenies of first Population (Tep#5) and 10 % S1 progenies of second Population (GMY) under normal and drought stress conditions were defined and their seeds were prepared from the remnant seeds (the second seed parts) for randomly mated by bulking pollen from the S1 plants and using it to make crosses by hand in all possible combinations. kernels harvested, four blends of seeds were obtained (Tep#5-NI, Tep#5-DS, GMY-NI and GMY-DS).
In 2018 summer season, for each population the original cycle (C0) and the improved cycle (C1) were evaluated under normal irrigation (NI) and drought stress (DS) in a Randomized Complete Block Design experiments with four replications. All data were recorded for Physio-chemical constituents, yield components and kernels quality.
The results could be summarized as follows:
Experiment I: Evaluate of 100 S1 progenies of the white population (Tep#5) for drought tolerance.
1- Analysis of variance showed significant differences among the genotypes (S1 progenies) for all studied traits under both normal and drought stress conditions.
2- Means of grain yield/plot of the 100 S1 progenies were 1.72 kg and (ranging from 1.45 to 2.61 kg/plot) under normal irrigation and 0.69 kg (0.35 to 1.18 kg/plot) under drought stress conditions. A significant average reduction of 59.88% in grain yield/plot of the 100 S1’s due to drought stress was accompanied by a reduction in ear length (17.54%), number of kernels/row (19.66%), 100-kernels weight (7.62%), ear diameter (0.75%) and number of rows/ear (0.08%). On the other hand, drought stress caused significant increases in the means of ASI (88.49 %), days to 50 % silking (5.91%) and days to 50 % anthesis (3.16%).
3- Mean grain yield/plot of the selected 10 S1 progenies was 2.35 kg (ranging
from 2.05 to 2.61 kg/plot) under normal irrigation and 1.08 kg (from 1.01 to 1.18 kg/plot) under drought stress conditions. The superiority of the selected 10 S1’s over the 100 S1’s in grain yield was higher under drought stress than under normal conditions. Reductions due to drought stress were lower for the selected 10 S1’s than those of the 100 S1’s for grain yield/plot and number of kernels/row traits.
4- Magnitude of δ2p and δ2g were considerably smaller under normal irrigation than under drought stress conditions for number of kernels/row, 100-kernels weight and ear length traits. On the other hand, the magnitude of δ2p and δ2g was larger under normal irrigation than under drought stress conditions for remaining traits. This indicates that selection for number of kernels/row, 100-kernels weight and ear length traits is predicted to be more efficient under drought stress than under normal irrigation and vise versa for the remaining studied traits.
5- Broad-sense heritability (h2b) for grain yield/plot showed a general tendency to increase with imposing drought stress from 79.54% under the normal to 93.17% under drought stress environments. Moreover, for all studied yield components, including number of rows/ear, number of kernels/row and 100-kernels weight the magnitude of h2b was larger under drought stress than normal conditions.
6- Data indicated a strong positive genetic correlation (rg) under drought stress between grain yield/plot and number of kernels/row (rg = 0.47), and ear length (rg = 0.45), ear diameter (rg = 0.41), 100-kernels weight (rg = 0.40) and number of row/ear (rg = 0.27). While, indicated a negative correlation (desirable) between grain yield/plot and days to 50% silking (rg = -0.67), anthesis-silking interval (rg = -0.62) and days to 50% anthesis (rg = -0.53) under drought stress. Under normal condition, grain yield/plot had a
positive strong genetic association with ear length (rg = 0.94), number of kernels/row (rg = 0.82), number of rows/ear (rg = 0.81), 100-kernels weight (rg = 0.69) and ear diameter (rg = 0.66). While, indicated a negative genetic associations between grain yield/plot and anthesis-silking interval (rg = -0.35), days to 50% silking (rg = -0.28) and days to 50% anthesis (rg = -0.20) under normal conditions.
Experiment II: Evaluation of the effectiveness of S1 recurrent selection of the two cycles for Tep#5 population under normal and drought conditions.
1- Analysis of variance revealed non-significant differences between Tep#5 and Tep#5-WW populations under normal conditions for all studied traits, except for relative water content, phenoloxidase activity, ear length, ear diameter, number of ears plant and number of rows/ear. Under drought stress revealed significant differences between Tep#5 and Tep#5-DS populations for all studied traits, except for ear length, ear diameter and number of rows/ear.
2- Mean grain yield of Tep#5 and Tep#5-NI was 2.81 and 3.16 ton/fad respectively under normal condition. While, Tep#5 and Tep#5-DS obtained grain yield about 1.81 and 2.09 ton/fad, respectively under drought stress. The two improved populations showed significant superiority in grain yield/fad over origin population under normal and drought stress conditions. Reduction in grain yield/fad due to drought stress in Tep#5-DS (33.86%) population was lower than the corresponding reduction of Tep#5 population (35.59%), indicating superiority of improved population over the original population (Tep#5) in drought tolerance.
3- One cycle of S1 recurrent selection under water-stress as a selection
environment caused a significant actual improvement of grain yield of the newly developed population (Tep#5-DS) over its original population (Tep#5) of 15.47% under water stress condition. The improved population Tep#5-NI developed by using normal irrigation as a selection environment showed significant actual improvements in grain yield under normal irrigation (12.46%) environment. Both water stressed and non-stressed selection environments were efficient in improving grain yield under target environments.
4- Grain yield ton/fad at normal condition was positively and significantly correlated coefficient with chlorophyll, relative water content, plant height, ear height, number of ears/plant, number of kernels/row, 100-kernels weight, kernels weight /ear, crude protein in kernels and protein yield. However, under drought stress grain yield ton/fad had a positive strong and significantly correlated coefficient with chlorophyll, relative water content, osmotic pressure, peroxidase activity, phenoloxidase activity, proline content, plant height, number of ears/plant, number of kernels/row, 100-kernels weight, kernels weight /ear and protein yield.
Experiment III: evaluate of 100 S1 progenies of the yellow population (GMY) for drought tolerance.
1- Analysis of variance showed significant differences among the genotypes (S1 progenies) for all studied traits under both normal and drought stress conditions.
2- Means of grain yield/plot of the 100 S1 progenies were 1.76 kg and (ranging from 1.39 to 2.62 kg/plot) under normal irrigation and 0.67 kg (0.10 to 1.90 kg/plot) under drought stress conditions. A significant average reduction of 61.93% in grain yield/plot/ of the 100 S1’s due to drought stress was accompanied by a reduction in number of kernels/row (24.07%), ear length
(19.33%), ear diameter (12.31%), 100-kernels weight (10.96%), and number of rows/ear (1.83%). On the other hand, drought stress caused significant increases in the means of ASI (21.28%), days to 50 % silking (1.11%) and days to 50 % anthesis (0.60%).
3- Mean grain yield/plot of the selected 10 S1 progenies was 2.39 kg (ranging from 2.21 to 2.62 kg/plot) under normal irrigation and 1.46 kg (from 1.21 to 1.90 kg/plot) under drought stress conditions. The superiority of the selected 10 S1’s over the 100 S1’s in grain yield was higher under drought stress than under normal conditions. Reductions due to drought stress were lower for the selected 10 S1’s than those of the 100 S1’s for grain yield/plot and number of kernels/row traits.
4- Magnitude of δ2p and δ2g were considerably smaller under normal irrigation than under drought stress conditions for anthesis-silking interval, ear length, ear diameter, number of rows/ear, number of kernels/row, 100-kernels weight and grain yield/plot traits. On the other hand, the magnitude of δ2p and δ2g was larger under normal irrigation than under drought stress conditions for remaining traits. This indicates that selection for anthesis-silking interval, ear length, ear diameter, number of rows/ear, number of kernels/row, 100-kernels weight and grain yield/plot traits is predicted to be more efficient under drought stress than under normal irrigation and vise versa for the remaining studied traits.
5- Broad-sense heritability (h2b) for grain yield/plot showed a general tendency to increase with imposing drought stress from 70% under the normal to 97% under drought stress environments. Moreover, for all studied yield components, including number of rows/ear, number of kernels/row and 100-kernels weight. Moreover, Data indicate that the magnitude of heritability (h2b) for days to 50% anthesis, days to 50% silking, anthesis-
silking interval, ear length and ear diameter.
6- Data indicated a positive genetic correlation (rg) under drought a significant positive genetic correlation between grain yield/plot and kernels/row (rg = 0.48), ear diameter (rg = 0.43) and ear length (rg = 0.22). In addition, Results showed a significant negative correlation between grain yield/plot and days to 50% silking (rg = -0.35) and days to 50% anthesis (rg = -0.27) under drought stress conditions.
Under normal condition, grain yield/plot had a significant positive genetic association with ear length (rg = 0.74), number of kernels/row (rg = 0.56), number of rows/ear (rg = 0.45), 100-kernels weight (rg = 0.43) and ear diameter (rg = 0.30). On the other hand, a significant negative genetic associations was observed between grain yield/plot and anthesis-silking interval only (rg = -0.27) under normal conditions.
7- Experiment IV: evaluatation of the effectiveness of S1 recurrent selection of the two cycles for Gemmeiza yellow population under normal and drought conditions.
1- Analysis of variance revealed significant differences between GMY and GMY-NI populations under normal conditions for all studied traits, except for chlorophyll, transpiration rate, phenoloxidase activity, proline content, ear diameter and number of rows/ear. Under drought stress, revealed significant differences between GMY and GMY-DS populations for all studied traits, except for ear height, ear length, ear diameter, number of rows/ear and crude protein in kernels.
2- Mean grain yield of GMY and GMY-NI was 2.87 and 3.13 ton/fad respectively under normal condition. While, GMY and GMY-DS obtained grain yield about 1.80 and 2.03 ton/fad, respectively under drought stress. The two improved populations showed significant superiority in grain
yield/fad over origin population under normal and drought stress conditions. Reductions in grain yield/fad due to drought stress in GMY-DS (35.41%) population were lower than the corresponding reduction of GMY population (37.28%), indicating superiority of improved population over the original population (GMY) in drought tolerance.
3- One cycle of S1 recurrent selection using water-stress as a selection environment caused a significant actual improvement of grain yield of the newely developed population (GMY-DS) over its original population (GMY) of 12.78% under water stress condition. The improved population GMY-NI developed by using normal irrigation as a selection environment showed significant actual improvements in grain yield under normal irrigation (9.06%) environment. Both water stressed and non-stressed selection environments were efficient in improving grain yield under target environments.
4- Grain yield ton per fad at normal condition was positively and significantly correlated coefficient with relative water content, osmotic pressure, peroxidase activity, plant height, ear height, number of ears/plant, number of kernels/row, 100-kernels weight, kernels weight /ear, crude protein in kernel and protein yield. Under drought stress, grain yield ton/fad had a positive strong and significantly correlated coefficient with chlorophyll, relative water content, osmotic pressure, peroxidase activity, Phenoloxidase activity, proline content, ear length, number of ears/plant, number of kernels/row, 100-kernels weight, crude protein in kernels and protein yield.