الفهرس 
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Abstract
The investigation amid to study the performance and estimating stability of fifty genotypes of bread wheat; 40 promising bread wheat lines compared to their parents varieties and 6 commercial cultivars on two sowing dates under two fertilization treatments in 2018/2019 and 2019/2020 growing seasons for some agronomic and quality traits.
Two experiments were carried out during every growing season at the Experimental Farm of the Faculty of Agric., Ain Shams Univ. at Shalakan, Kalubia Governorate on two sowing dates, i.e. 14 November (recommended sowing date) and 13 December (late sowing date) under two fertilization treatments i.e. biofertilizer + 40kg N/fed., and 80kg N/fed.. The experimental design was laid out in split-plot design with three replications for each experiment. The fertilization treatments were assigned in the main-plots and genotypes were arranged in the sub-plots. The data for studied traits, days to heading and flag leaf area were recorded during the productive growth period. At harvest 10 plants randomly taken from each plot and used for recording data of the following traits, i.e. plant height, number of spikes/ plant, spike length, number of spikelets /spike, number of kernels /spike, 1000-kernel weight, grain yield/plant and grain protein content. Data were statistically analyzed for each environment and over all environments in every growing season. Also analysis of phenotypic stability was done using Eberhart and Russell (1966) model for studied traits.
The obtained results can be summarized as follows:
A. Performance of genotypes under different environments:
Mean squares due to sowing dates (D), nitrogen fertilization treatments (N) and genotypes were highly significant for grain yield and its contributors in the two seasons, indicating that these characters are influenced by factors used in this investigation. Meantime, the interaction mean squares of sowing dates and genotypes were highly significant for all studied traits except plant height and grain protein content in the two growing seasons. The interaction mean squares of nitrogen treatments and genotypes were highly significant for all studied traits in the two seasons except plant height and grain protein content in the two seasons and flag leaf area, number of spikes/plant, number of spikelets / spike and number of kernels/spike in the first season. Significance of D x N interaction for flag leaf area, number of spikes/plant, number of spikelets / spike and grain protein content in both seasons and grain yield / plant in the first season indicates that mean performance of wheat genotypes under the two N-levels are greatly differed on both sowing dates regarding these traits showing the importance of sowing dates on absorbing and assimilation of nitrogen in wheat plants. The second rank interactions of G x D x N, were also significant for all traits expect plant height and grain protein content in the two seasons as well as number of spikes/plant, number of spikelets / spike and number of kernels/spike in the first season. These results indicated that studied genotypes responded differently to the different environmental conditions suggesting the importance of the assessment of genotypes under different environments in order to identify the best genetic make up for a particular environment.
1-Days to heading: Results showed that number of days to heading in late sowing was less (earlier) than those in recommended sowing by 0.94 and 0.98% in the two seasons, respectively. Low-N level treatment caused significant reductions in number of days to heading by 0.92 and 0.94% compared with high-N, in the first and second seasons, respectively. Overall mean for days to heading ranged from 90.25 and 90.50 days for line number 25 and the cv. Giza 171 to 99.33 and 96.33 days for lines number 34 with mean values of 94.70 and 93.61 days in the first and second seasons, respectively. The earliest plants were found in lines number 25 and 30 and the cv. Giza 171 in the two seasons, the lines number 18, 19 and 37 in the first season and the lines number 10, 36 and 40 and cv. Sids 14 in the second season.
2-Flag leaf area: the late sowing date caused significant reductions by 28.02 and 28.54 % than those at the recommended sowing in the two first and second seasons, respectively. Moreover, lower level of nitrogen (biofertilizer + 40 kg N/fed) caused significant reductions by 16.81 and 17.26 % compared with high N- level (80 kg N/fed.) in the first and second seasons, respectively. Overall mean for flag leaf area ranged from 43.00 and 40.09 cm2 for line number 19 to 67.01 and 64.00 cm2 for line number 13 with mean values of 54.45 and 51.30 cm2 in the first and second seasons, respectively. The highest values for flag leaf area were found in the lines number 8 and 13 followed by lines number 3, 9 and 31 as well as the cv. Sakha 94 in the two seasons.
3-Plant height: Results illustrated that the late sowing date caused significant reductions in plant height by 9.80 and 9.47% than those at the recommended sowing in the two seasons, respectively. Low nitrogen level (biofertilizer + 40 kg N/fed) caused significant reductions by 7.53 and 8.01 % compared with high N- level (80 kg N/fed.) in the first and second seasons, respectively. Mean values across environments for plant height ranged from 88.00 and 86.88 cm for lines number 26 and 23 to 131.63 and 130.86 cm for lines number 22 and 25 with mean values of 101.15 and 99.35 cm in the first and second seasons, respectively. The tallest plants were found in the lines number 16, 22 and 25 followed by line 24 in the two seasons.
4-Number of spikes/plant: Results revealed that the late sowing date caused significant reductions in number of spikes/plant by 27.01 and 24.92% than those at the recommended sowing in the two growing seasons, respectively. lower level of nitrogen (biofertilizer + 40 kg N/fed) caused significant reductions by 10.57 and 11.34% compared with high N- level (80 kg N/fed.) in the first and second seasons, respectively. Overall mean values for number of spikes/plant of fifty wheat genotypes ranged from 10.18 and 9.72 spikes for the check variety Giza 168 to 15.63 and 13.36 spikes for line number 6 with mean values of 13.03 and 11.48 spikes /plant in the first and second seasons, respectively. The highest spikes number per plant were found in line number 6 followed by lines numbers 2, 11, 13, 24, 31, 38 and 39 and the cv. Misr 2 in the two seasons, the lines number 7, 8, 12, 19, 27, 32 and 40 in the first season, the cv. Sids 1 in the second season.
5-Spike length: The late sowing date caused significant reductions by 17.63 and 21.35 % than those at the recommended sowing in the two seasons. Moreover, plants receiving lower nitrogen (biofertilizer + 40 kg N/fed.) showed reductions of 9.56 and 11.63 % in the first and second seasons, respectively, when compared with plants receiving high-N levels (80 kg N/fed.). The overall means for spike length of 50 wheat genotypes ranged from 9.78 and 9.42 cm for the lines number 22 and 30 to 11.97 and 10.94 cm for check variety Gemmeiza 12 and line number 1 with mean values of 10.91 and10.17 cm in the first and second seasons, respectively. The tallest spikes were noticed in lines number 1, 3, 5, 8, 9, 10, 12 and 21 as well as the two check varieties Gemmeiza 12 and Giza 171 in both seasons, lines number 2, 4 and 15 in the first season, lines number 11, 19, 26 and 34 in the second season.
6-Number of spikelets/spike: Results illustrate that the late sowing date caused significant reductions in number of spikelets/ spike by 10.59 and 11.06% than those at the recommended sowing in the two seasons, respectively. Low-N level (biofertilizer + 40kg N/fed) caused significant reductions in this trait by 7.44 and 6.86 % compared with high-N in the first and second seasons, respectively. Means of number of spikelets/ spike ranged from 19.53 and 18.42 spikelets for lines number 37 and 38 to 22.57 and 20.73 spikelets for the lines number 5 and15 with mean values of 21.02 and 19.47 spikelets in the first and second seasons, respectively. The highest number of spikelets/ spike were noticed in lines number 3, 5 9, 10 and 15 in the two seasons, the lines number 2, 4, 7, 8, and 26 and the cv. Misr 2 in the first season and the line number 19 in the second season.
7-Number of kernels /spike: Results illustrate that the late sowing date caused significant reductions in number of kernels /spike by 23.92 and 24.34% than those at the recommended sowing in the first and second seasons, respectively. Low-N level treatment caused significant reductions in number of kernels /spike by 10.65 and 10.69% compared with high-N, in the first and second seasons, respectively. Mean values across environments for number of kernels / spike ranged from 57.29 and 54.58 kernels for line number 15 to 69.70 and 71.58 kernels for lines number 10 and 38 with mean values of 64.40 and 62.22 kernels in the first and second seasons, respectively. The highest numbers of kernels /spike were found in the lines number 5, 9, 10, 28 and 38 in the two seasons, the line number 8 in the first season and the line number 40 in the second season.
8-1000-kernel weight: The late sowing date caused significant reductions by 19.85 and 19.90% than those at the recommended one in the first and second seasons, respectively. Low-N level caused significant reductions in 1000-kernel weight by 11.38 and 11.39% compared with high-N in the first and second seasons, respectively. Means of 1000-kernel weight across environments ranged from 30.69 and 30.04g for lines number 19 and 1 to 45.42 and 43.89 g for line number 9 with mean values of 37.53 and 35.84g in the first and second seasons, respectively. The highest 1000-kernel weight were noticed in the lines number 9 and 28 followed by lines number 10, 31 and 38 in the two seasons.
9-Grain yield/plant: Reductions of grain yield / plant reached 31.88 and 33.75% on late sowing date compared to the recommended one in the two seasons, respectively. Low-N level caused significant reductions in grain yield/plant by 14.40 and 13.54% compared with high-N, in the first and second seasons, respectively. Means of grain yield/plant on overall mean across environments ranged from 14.71 and 13.68 g for line number 1 to 22.43 and 20.86 g for the line number 9 with mean value of 19.07 and 17.36 g in the first and second seasons, respectively. The highest grain yield/plant were noticed in lines number 3, 9 and 31 in the two seasons, the lines number 8, 26, 28 and 33 in the first season and the lines number 10, 36 and 38 in the second season.
10- Grain protein content: The best 20 yielding lines as well as the check cultivar Misr 2 and Bohouth 6 were used to determine grain protein content in the two seasons. Reductions of grain protein content reached 6.10 and 4.09 % than those at the recommended sowing in the two seasons, respectively. lower level of nitrogen (biofertilizer + 40 kg N/fed) caused significant reductions by 5.42 and 4.61 % compared with high N- level (80 kg N/fed.) in the first and second seasons, respectively. Mean values across environments for grain protein content ranged from 12.69 and 12.68% for lines number 31 and 36 to 14.13 and 13.73% for lines number 27 and 9 with mean values of 13.36 and 13.18% in the first and second seasons, respectively. The highest grain protein content was found in the lines number 9, 10, 13 and 27 as well as the two cvs. Misr 2 and Bohouth 6 in the two seasons.
B. Concerning phenotypic stability:
Genotype x environment interaction (Linear) was significant, therefore it could be proceeded in the stability analysis (Eberhart and Russell 1966). Six promising lines out of 50 wheat genotypes (9, 10, 11, 27, 29, and 30) were stable because of their respective bi and S2di values, which did not differ significantly from a unit and zero, respectively, hence, these lines exhibited general adaptability across different environments. The genotypes 12, 26, 28, 31, 33, 34, Sakha 94, and Cham 8 gave high mean values compared with the grand mean, and performed better in favorable environments (bi > 1), whereas line 14 gave a high mean value and performed better in unfavorable environments (bi < 1).
We can conclude that lines 9, 10, 11, 27, 29, and 30 performed well for the stability of grain yield and its contributed characters, thus such lines are considered to be promising and could be used in breeding programs for wheat improvement.
Conclusions
Yield and yield contributes increased by planting wheat genotypes at the recommended sowing date in mid-November under optimum nitrogen levels (80 kg N/fed.). Conversely, planting under delayed sowing dates and low nitrogen conditions led to a drastic reduction in grain yield/plant and its contributes. This study revealed that the lines number 9, 10, 11, 26, 27, 28, 29, 30, 31 and 33 gave high mean value in grain yield and its contributions and exhibited general adaptability across different environments; thus, such lines are considered to be promising genotypes and could be used in breeding programs for wheat improvement.