الفهرس 
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Abstract
The present work aims to study the efficiency of pedigree selection for grain yield and earliness in two segregating populations of bread wheat (Triticum aestivum L.).
The experiments were carried out during the three successive seasons, i.e., 2008/2009, 2009/2010 and 2010/2011, at Fac. Agric. Edu. Farm, Minia University, Egypt. Randomized complete block design of three replications was used in all experiments.
The two populations were originated from of the cross between:-
(1) Population I (Giza 164 x Sids 4)
(2) Population II (Giza 168 x Sids 4)
Two cycles of pedigree selection to improve earliness and yield were completed using the above two populations of bread wheat (T. aestivum L.) in F3, F4 and F5 generations. Single trait for days to heading, grain yield/plant; and days to heading restricted by yield were applied.
Results could be summarized to four main topics:
1- Description of the base populations.
2- Evaluation of the first cycle of pedigree selection; F4-generation, season 2009/2010.
3- Evaluation of the second cycle of pedigree selection; F5-generation, season 2010/2011.
4- Effect of selection on correlation among traits.
1- Description of the base populations.
1- Days to heading in the F3-generation of pop I ranged from 57.0 to 89.0 with an overall mean of 78.18 days, and from 57.0 to 96.0 with an overall mean
of 72.02 days for pop II indicating wide range of variability in both populations, and selection for earliness could be feasible.
2- Comparing the population mean with the parental means indicating over-dominance towards lateness. However, in pop II, days to heading showed nearly no-dominance.
3- The coefficient of variability in grain yield/plant was very high and accounted for 40.71% with a range of 3.84 to 84.26 g/plant. Indicating feasibility of selection for grain yield in the F3-generation of pop I. The variability in pop II was larger than that in pop I, in which cv % reached 62.48%. Grain yield/plant in pop II ranged from 2.15 to 82.87 g.
4- Estimates of broad sense heritability in the F3 generation were high in pop I for days to heading (89.66%), biological yield (62.59%), spike length (66.76%), grain yield (75.80%) and harvest index (83.05%), intermediate for plant height (44.07%) and low for number of spikes/plant (25.64%) and 100-grain weight (24.28%).
5- Estimates of heritability in pop II were in line with those in pop I except for days to heading in which it was (67.49%) lower than that in Pop I (89.66%).
6- Days to heading showed positive and significant (p<0.01) correlation with plant height in both populations, and with harvest index in pop I, and negative significant (p<0.01) with spike length (-0.28) and 100-grain weight (-0.50) in pop I. Otherwise, days to heading showed positive significant correlation with 100-grain weight and very low insignificant correlation with harvest index in pop II. Furthermore, days to heading showed low insignificant and negative correlations with number of spikes/plant, biological yield/plant and grain yield/plant in pop I, and significant correlations (p<0.01) with the same traits in pop II, indicating different gene associations in the two populations, and selection for earliness may result in decrease in plant height and increase in 100-grain weight in pop I, and decrease in plant height, number of spikes/plant, biological yield/plant, grain yield/plant and 100-grain weight in pop II.
7- The correlation coefficients between grain yield/plant and each of plant height, spike length, number of spikes/plant, biological yield/plant, harvest index and 100-grain weight were positive significant (p<0.01) in pop I. Therefore, selection for high grain yield/plant could increase these traits in pop I, and in pop II except for spike length.
2- Evaluation of the first cycle pedigree selection; F4-generation; season 2009/2010.
2-1. Pedigree selection for days to heading.
1- Significant differences (p<0.01) among the selected families for the selection criterion; days to heading were obtained in the two populations. Furthermore, mean squares of the other correlated traits were significant (p<0.01) in both populations.
2- Mean days to heading of the selected families in pop I ranged from 63.67 to 83.33 with an average of 67.02 days. Non of the selected families was earlier than the earlier parent Sids 4 (62.0 days), but, the average of the selected families was significantly earlier than the unselected bulk sample by 6.31 days. The average of the earliest ten families was earlier than the unselected bulk sample by 11.36%.
3- Results of the selection for days to heading in pop II indicated that days to heading varied from 61.33 to 79.00 with an average of 68.68 days. Average days to heading of the selected families, lies midway between the two parents, and significant (p<0.01) earlier than the bulk sample. Selection for heading date significantly decreased plant height, and increased significantly grain yield/plant and number of grains/main spike.
4- The remained phenotypic (6.77%) and genotypic (6.6%) coefficients of variability in pop I for days to heading after one cycle of pedigree selection were moderate, but still sufficient for further cycles of selection, but it was lower than that in the F3-generation (10.88%). The Phenotypic variability in pop II behaved the same as Pop I.
5- Broad sense heritability were very high for days to heading in pop I (95.00%) , pop II (97.65%) and the other traits in the two populations except for the harvest index (60.10%) in pop II.
2.2. Pedigree selection for grain yield/plant.
1- Mean squares of the selected families was significant (p<0.01) for the criterion of selection; grain yield/plant and other traits in two populations except 100 grain weight in pop I. This indicates the presence of genetic variability among the selected families in the F4-generation after one cycle of selection.
2- Mean grain yield/plant as a selection criterion after one cycle of selection ranged from 14.66 to 21.18 with an average of 17.65 g. in pop I, and from 14.56 to 27.23 with an average of 16.92 g. in pop II.
3- Mean grain yield/plant of the selected families in pop I (17.65 g.) differed significantly (p<0.01) from the unselected bulk sample, but not from either of the two parents. But, ten families significant outyielded the better parent.
4- Concerning to pop II, average grain yield/plant of the 20 selected families significant outyielded the unselected bulk sample by 22.88%, but it did not outyielded the better parent Giza 168. Two families; No. 228 and No.167 outyielded the better parent Giza 168.
5- One cycle of pedigree selection for grain yield/plant decreased rapidly the pcv% from 40.71 in the F3 to 23.19% in the F4 in pop I, and from 62.48 in the F3 to 17.13% in the F4-generation in pop II. The pcv% of the other correlated traits was decreased also by selection for grain yield.
2.3. Pedigree selection for days to heading restricted by grain yield/plant.
1- Mean squares of the studied traits of the selected families for days to heading restricted by grain yield/plant were significant (p<0.01) in the two populations except for harvest index in pop I which was significant (p<0.05).
2- Mean days to heading of the selected families ranged from 71.67 to 76.00 with an average of 73.85 days in pop I, and from 67.00 to 80.00 with an average of 74.70 days in pop II. Likewise, means of the selected families for grain yield/plant ranged from 10.67 to 23.06 with overall mean of 16.65 g. in pop I, and from 12.41 to 18.58 with overall mean of 14.36 g. in pop II.
3- Seven families in pop I were significantly earlier than the unselected bulk sample and the latest parent Giza 164, and four of them significant out yielded the bulk sample in grain yield/plant. Furthermore, selection for days to heading restricted by grain yield/plant showed significant increase in plant height, spike length and biological yield/plant.
4- Concerning pop II, the overall mean of days to heading (74.70 days) was significant earlier than the bulk sample (77.33 days) but not earlier than the earlier parent Sids 4.
5- The pcv and gcv % decreased rapidly after one cycle of pedigree selection for earliness restricted by grain yield in the two