الفهرس 
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Abstract
The present study was carried out at El-Mattana Agric. Res Station, Agric. Res. Center, Egypt, during the four successive seasons of 2007/2008, to 2010/2011. The objectives of this work were to (1) Study the efficiency of pedigree selection for grain yield and independent culling levels in improving grain yield after two cycles of selection under normal and late planting dates. (2) Estimate phenotypic, genotypic coefficients of variation and heritability under normal and late planting dates. (3) Study the effect of selection on the correlations among traits. (4) Estimate heat susceptibility index (HSI) and environmental sensitivity of the selected families to heat stress.
Two cycles of selection were completed under normal and late planting date on the F4 and F5-generations. The selected families under normal and late planting date were evaluated in the F5-generation under both environments.
In 2007/2008 season, 1000 F2-individual plants of the cross (Giza 168 x Anza) were grown under normal and late planting dates. Data collected on 400 random guarded plants under each of normal and late planting dates. Data were recorded on number of days to heading, plant height, number of spikes/plant, number of kernels/spike, 100-kernel weight, spike length and grain yield/plant for each individual plant.
In 2008/2009 season, the 100 F3 families as well as the F3 bulk and parents were grown at the two sowing dates. The highest 20 families in yield and 20 families which fulfilled the following independent culling levels (ICL) were selected under the two sowing dates.
In 2009/2010 season, the twenty selected families for each of grain yield and independent culling levels (ICL) under normal planting were grown under normal planting while, those selected under late planting were grown under late planting. The highest 10 families in each of grain yield and independent culling levels (ICL) were selected under the two sowing dates.
In 2010/2011 season, the F3 bulk, parents, 20 selected families for grain yield and 20 families selected on the basis of independent culling levels ICL (10 families under normal and 10 families under late planting) were grown under normal and late planting. The results could be summarized as follows:
1- Base population:
Under normal planting date, for F2 plants the average number of days to heading, plant height, number of spikes/plant, number of kernels/ spike, 100-kernel weight, spike length and grain yield/plant was 84.33 days, 113.19 cm, 12.18 spike/plant, 55.90 kernel/spike, 2.29 g, 12.34 cm and 22.39 g, respectively. Whereas, under late planting date, the average was 73.73 days, 102.56 cm, 9.83 spike/plant, 48.34 kernel/spike, 2.21 g, 11.22 cm and 19.61 g for the same traits, respectively.
1-1- Means and variance:
The analysis of variance for all studied traits revealed highly significant differences among F3 families under normal and late planting dates. The average of characters was 84.05 and 74.22 for days to heading, 106.98 and 101.48 cm for plant height, 13.13 and 10.95spikes/plant for number of spikes/plant, 69.23 and 67.97 for number of kernels/spike, 3.98 and 3.80 g for 100-kernel weight, 12.83 and 11.99 cm for spike length and 33.06 and 30.09 g/plant for grain yield/plant under normal and late planting, respectively.
1-2- Phenotypic, genotypic coefficients of variability and heritability estimates:
The results indicated that the phenotypic and genotypic coefficients of variability values were 1.87 and 1.81% for days to heading, 8.89 and 8.48% for plant height, 10.51 and 10.11% for number of spikes/plant, 11.85 and 11.57% for number of kernel/spike, 15.12 and 14.75% for 100-kernel weight, 6.65 and 6.37% for spike length and 18.66 and 18.31% for grain yield/plant under normal planting date, while those values were 2.66 and 2.60%, 10.86 and 10.29%, 10.44 and 10.03%, 9.27 and 8.91%, 16.35 and 16.25%, 6.97 and 6.70% and 17.54 and 17.08% for the above mentioned traits under late planting date, respectively. These results indicate the presence of sufficient variability for grain yield and some correlated traits among the F3 families.
Heritability estimates in broad sense were 94.06 and 95.67% for days to heading, 90.93 and 89.89% for plant height, 92.59 and 92.42% for number of spikes/plant, 95.23 and 92.41% for number of kernels/spike, 95.12 and 98.75% for 100-kernel weight, 91.67 and 92.28% for spike length and 96.27 and 94.86% for grain yield/plant under normal and late planting dates, respectively.
1-3 - Phenotypic and genotypic correlation coefficients:
Results indicated negative and low phenotypic and genotypic correlations between heading date and each of no. of spikes/plant, no. of kernels/spike, 100-kernel weight, spike length and grain yield/plant under normal planting and late planting dates while, phenotypic and genotypic correlations between grain yield/plant and all studied traits were positive for all studied traits except days to heading under normal and late planting dates.
2- Selection for grain yield/plant:
2-1- Phenotypic, genotypic coefficients of variability and heritability:
The analysis of variance revealed highly significant differences families selection criterion, grain yield and the other correlated traits among genotypes in the F4 and F5-generation under normal and late planting dates. The pcv and gcv% for grain yield/plant were 4.19 and 3.79% under normal planting date, and 5.52 and 4.78% under late planting date, respectively. The pcv and gcv% were low for days to heading and plant height under both dates and were high for 100-kernel weight and grain yield/plant under normal planting date. The gcv% was slightly less than the pcv% under both dates, and decreased from the base population C0 (F3) to C2 (F5). Broad sense heritability estimates for grain yield/plant after two cycles of selection were 81.76% under normal planting date, and 75.04% under late planting date. However, the realized heritability was 49.47 and 70.98% under normal planting date and 44.90 and 53.92% under late planting date, after C0, C1 and C2, respectively.
2-2-Means and direct observed gain for grain yield/plant:
Mean grain yield/plant of the normal planting of families evaluated under normal planting group was 38.80 g/plant, and was 35.03 g/plant for the late group. While, the average grain yield of the late planting date under normal planting group was 31.00 g/plant and was 30.60 g/plant for the late group. The average direct gain of the normal group and evaluated under normal planting date significantly (P<0.01) out yielded the bulk sample by 13.08%, and the better parent by 25.04%, and the late planting group was significant and out yielded the bulk sample by 3.36% and the better parent by 15.04%. Under late planting date evaluation, the normal planting group of families showed significant direct observed gain in grain yield/plant of 6.73% and 16.05%, from the bulk sample and the better parent, respectively. The late planting group showed significant observed gain of 7.78 and 22.10 from the bulk sample and the better parent, respectively.
2-3- The correlated response to selection for grain yield/plant:
The observed direct gain and correlated response from the bulk sample and the better parent under normal group, and evaluated under normal planting date. Direct selection for grain yield increased days to heading and 100-kernel weight by an average 1.29 and 2.29% but decreased plant height, no. of spikes/plant, no. of kernels/spike and spike length by an average -5.08, -3.98, -4.54 and -0.51%, respectively from the bulk sample. Meanwhile increased no. of spike/plant, no. of kernels/spike and 100-kernel weight by an average 6.67, 0.96 and 8.78%, respectively from the better parent after two cycles of selection.
Under late group, and evaluated under normal planting the observed direct gain selection for grain yield decreased days to heading, plant height and spike length by an average -1.98, -1.27 and -2.40%, respectively from the bulk sample. Meanwhile, increased no. of spikes/ plant, no. of kernels/spike, 100-kernel weight and spike length by an average 3.71, 7.61, 8.62 and 6.21%, respectively from the better parent.
The observed direct gain and correlated response from the bulk sample and the better parent under normal group, and evaluated under late planting date. Direct selection for grain yield decreased days to heading, plant height, no. of spikes/plant, no. of kernels/spike and spike length by an average -2.09, -3.28, -2.68, -1.35 and -1.08%, respectively from the bulk sample. Meanwhile, increased 100-kernel weight by an average 1.46%. While, selection for grain yield increased plant height, no. of spikes/plant, no. of kernels/spike, 100-kernel weight and spike length by an average 3.17, 9.09, 2.62, 21.01 and 17.46%, respectively from the better parent.
Under late group, and evaluated under late planting the observed direct gain selection for grain yield increased plant height, no. of spikes/ plant, no. of kernels/spike and 100-kernel weight by an average 1.00, 0.28, 2.17 and 1.89% from the bulk sample, respectively. Meanwhile, selection for grain yield increased no. of spikes/plant, no. of kernels/ spike, 100-kernel weight and spike length by an average 10.65, 6.79, 7.89 and 7.87% from the better parent, respectively.
2-4- Heat susceptibility index, sensitivity to environment and correlation coefficients for grain yield/plant:
The results of the selected families for the two cycles under normal planting date, and evaluated under both environments indicate that, five families no. 4, 36, 70, 75 and 81 showed heat susceptibility index (HSI) values less than one. Likewise, under late planting date, and evaluation under both environments indicated that the six families no. 3, 4, 17, 29, 66 and 72 gave (HSI) values less than one. These families could be considered less susceptible to heat. Selection for grain yield at normal planting date evaluated under both dates, increased sensitivity of the selected families, while selection at late planting date, decreased the sensitivity.
Under normal planting date (normal group), and evaluated under two sowing dates. A highly significant and positive correlation was established between the mean grain yield/plant under normal and the heat susceptibility index (r = 0.88**). On the other hand, a negative correlations between days to heading and grain yield under late planting date and heat susceptibility index (r = -0.66*) and (r = – 0.71*), respectively.
Under heat stress (late group), and evaluated under two sowing dates. A highly significant and positive correlation was established between the mean grain yield/plant under normal and the heat susceptibility index (r = 0.75**). Likewise, a negative and insignificant correlations between days to heading under normal, days to heading under stress , grain yield under stress and heat susceptibility index (r = - 0.03), (r = – 0.11) and (r = – 0.08), respectively.
2-5- Effect of heat stress on grain yield and correlated traits:
The reduction in grain yield and related traits as affected by heat stress in F3, F4 and F5 generations. The reduction in grain yield/plant, no. of spikes/plant, no. of kernels/spike, 100-kernel weight and spike length was (8.98, 18.46 and 16.53%), (16.60, 21.45 and 16.40%), (1.82, 9.18 and 1.17%), (4.52, 6.21 and 5.82%) and (6.78, 10.36 and 8.19%) in F3, F4 and F5 generations, respectively, as compared with the normal planting date.
2-6- Phenotypic and genotypic correlations for grain yield/plant:
After two cycles of selection for grain yield/plant under normal planting date, the phenotypic and genotypic correlations were negative between grain yield/plant and each of days to heading (-0.232 and -0.203), plant height (-0.104 and -0.040), no. of spikes/plant (-0.414 and -0.579) and no. of kernels/spike (-0.388 and -0.675). Meanwhile, it had positive value of correlation coefficient with 100-kernel weight (0.464 and 0.862) and spike length (0.022 and 0.052), respectively.
After two cycles of selection, for grain yield/plant under late planting date, the phenotypic and genotypic correlation between grain yield/plant and each of, days to heading, no. of spikes/plant, 100-kernel weight and spike length were positive and reached (0.048 and 0.100), (0.594 and 0.804), (0.427 and 0.518) and (0.012 and 0.014), respectively. However, the correlations of grain yield/plant with the other traits were negative with plant height (-0.117 and -0.181) and no. of kernels/spike (-0.023 and -0.072). In general, genotypic correlation was higher than phenotypic ones for most pairs of traits, reflecting the relatively large error variance and covariance.
3- Selection by independent culling levels method (ICL):
3.1-Phenotypic, genotypic coefficients of variability and heritability:
The analysis of variances for the selection criterion and the other correlated traits were highly significant differences among genotypes in the F4 and F5-generation under normal and late planting dates. The pcv and gcv% were slightly higher under normal planting date than under late planting date. The gcv% for the selection criteria in the F5-generation was 5.49, 3.46 and 3.61% under normal planting date, and 4.10, 9.18 and 4.37% under late planting date, for number of spikes/plant, 100-kernel weight and spike length, respectively. Under normal date, the pcv% of number of spikes/plant decreased from 10.51% in the base population to 5.78%, and from 15.12 to 3.84% for 100-kernel weight and from 6.65 to 3.90% for spike length after two cycles of selection. The same trend of decreased in variability pcv% and gcv% was observed under late planting date. After the two cycles of selection, broad sense heritability estimates were and reached 90.14, 81.22 and 85.71% under normal planting date, and 75.00, 78.97 and 85.71% under late planting date, for number of spikes/plant, 100-kernel weight and spike length, respectively.
3-2-Means and direct observed gain by ICL method:
Average no. of spikes/plant, 100-kernel weight and spike length in the normal planting group, and evaluated under normal planting date as 12.40 spikes/plant, 4.06 gm/plant and 12.60 cm and was 11.03 spikes/ plant, 4.00 gm/plant and 11.53 cm for the same above traits in the late group, respectively. After the second cycles in the F5-generation, in the normal planting group, and evaluated under normal planting date showed the observed direct gain of 0.57, 3.97 and 2.19%, while under late planting group was 0.90, 22.21 and 4.85% from the bulk sample, for no. of spikes/plant, 100-kernel weight and spike length. Meanwhile, the observes gain showed highly significant for the above mentioned traits from the better parent under normal and late planting group when evaluated under normal planting date.
While, under normal group and evaluated under late planting the average was 11.87 spikes/plant, 3.92 g/plant and 11.60 cm and was 10.40 spikes/plant, 3.88 g/plant and 11.10 cm for the same above traits in the late planting group, respectively. The observed gain from the bulk sample was 1.69, 6.18 and 2.38% for the normal group, and 7.55, 11.12 and 4.04% in the late planting group, for the same respective traits. Meanwhile, the observes gain showed highly significant for the above mentioned traits from the better parent under normal and late planting group when evaluated under late planting date.
3-3- Heat susceptibility index and sensitivity environmental for ICL:
The results of the selected families for two cycles under normal or late planting date, and evaluated under both environments indicate that families’ no.(35 and 37) and families no. (50, 60 and 73) for no. of spikes/plant showed heat susceptibility index (HSI) values less than one, respectively. Likewise, 100-kernel weight the selected families after the second cycles under normal or late planting dates, and evaluated under both environments showed that families no. (8, 14, 23, 33, 35, 37 and 40) and families no (60, 80 and 81) showed heat susceptibility index (HSI) values less than one, respectively. Heat susceptibility index for spike length under normal or late planting date, and evaluated under both environments indicate that families’ no. (23 and 35) and families no. (57, 60, 73 and 81) showed (HSI) values less than one, respectively. These families could be considered less susceptible to heat.
Two cycles of pedigree selection for no. of spikes/plant, 100-kernel weight and spike length indicated that selection at normal date (synergistic selection) increased the sensitivity. Likewise, selection at late planting (antagonistic selection) decreased the sensitivity. The relative merits of selection under late to selection under normal planting in changing the mean of number of spikes/plant indicated that antagonistic selection was better than synergetic selection.
3-4- Phenotypic and genotypic correlations for (ICL):
Phenotypic and genotypic correlations under normal planting date were negative between no. of spikes/plant and each of 100-kernel weight (-0.349 and -0.399) and spike length (-0.196 and -0.198), respectively. Meanwhile, it had positive value of correlation coefficient with no. of kernels/spike (0.452 and 0.536) and grain yield/plant (0.665 and 0.791), respectively. While, under late planting date phenotypic and genotypic correlations were positive between no. of spikes/plant and each of no. of kernels/spike (0.488 and 0.627), 100-kernel weight (0.370 and 0.420), spike length (0.175 and 0.189) and