الفهرس 
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Abstract
This study was conducted at Zarzora Research Station, Etay El-barood, El-beheira Governorate, Egypt, during the two successive growing seasons 2017/18 and 2018/19. Seven common wheat parents (Triticum aestivum L. em Thell), ital.c., P1 (Misr-3), P2 (Shandweel-1), P3 (Sids-14), P4 (Gemmeiza-12), P5 (Sakha-95), P6 (Sakha-93) and P7 (Line-1) were chosen for this study. The main objective of the present investigation was to assess the variations amongst a half diallel cross among seven varieties and/or lines for drought tolerance characters to estimate heterosis and combining ability associated with grain yield and its components and physiological and biochemical traits under non-stress (4 times irrigated) and drought stress condition (one irrigated), in addition, to determine the best method of selection that will be used in the segregated of generations. The obtained results of this study could be summarized as follows: (A): Analysis of variance 1- Mean squares for the two irrigation treatments were found to be highly significant for all studied traits indicating as expected that the differences between the two irrigation treatments were markedly differed. 2- Mean squares due genotypes were found to be significant and highly significant for all studied traits at the two irrigation treatments as well as their combined analyses except for Chl a/b ratio and RWC under both irrigation treatments and their combined analyses, and grain yield per plant under stress irrigation. 3- Mean square due genotypes vs. irrigation treatments were also found to be highly significant and significant for all studied traits except for Chl a/b ratio, RWC, plant height, spike length, number of spikelets per spike, number of kernels per spike, 1000-kernel weight, straw yield per plant, harvest index, and filling period. 4- Mean squares due to parents were found to be significant and highly significant for all studied traits at the two irrigation treatments and their combined analyses except for total Chl, Chl a/b ratio, days to maturity, number of kernels per spike under normal irrigation, RWC under two irrigation treatments and combined data, number of spikes per plant under combined analyses, and grain yield per plant, filling period under stress irrigation. 5- In the same way, mean squares due to parents x irrigation treatments were significant and highly significant for all studied traits except for total Chl, Chl a/b ratio, RWC, days to heading, plant height, spike length, number of spikelets per spike, number of kernels per spike, 1000-kernel weight, straw yield, and filling period. 6- The crosses mean squares were found to be significant and highly significant for all traits studied at the two irrigation treatments as well as their combined analyses except for Chl a/b ratio and RWC under normal and stress irrigation and their combined analyses, and number of spikelets per spike under normal irrigation. 7- Mean squares due to crosses x irrigation treatments were found to be significant and highly significant for all studied traits except for Chl a/b ratio, RWC, plant height, number of spikes per plant, spike length, number of spikelets per spike, grain yield per plant, number of kernels per spike, straw yield, harvest index, and filling period. (B): Mean performances The mean performances for wheat parents can be summarized as follows: 1. The genotype P6 (Sakha-93) gave high values in total Chl, Chl a/b ratio, carotenoids and RWC, FLA, CAT, PPO and number of spikes per plant under both irrigation treatments and combined data. On the other side, it gave low values in days to heading and days to maturity under both irrigation treatments and combined data. 2. The genotype P1 (Misr-3) gave high values in total Chl, carotenoids, TPC, CAT and straw yield and under two irrigation treatments and combined data, and low values in MDA under two irrigation treatments and combined data. 3. The genotype P3 (Sids-14) gave high values in FLA, TPC, POX and straw yield under both irrigation treatments and combined data, but it had low values in H2O2, days to maturity and filling period under both irrigation treatments and combined data. 4. The genotype P2 (Shandweel-1) gave high values in number of spikelets per plant, number of kernels per spike, harvest index and plant height, but it gave low values in MDA under both irrigation treatments and combined data. 5. The genotype P4 (Gemmeiza-12) gave high values in Chl a/b ratio, POX, spike length, harvest index and number of spikelets per plant, but it gave low values in filling period and FLAn under both irrigation treatments and combined data. 6. The genotype P5 (Sakha-95) gave the highest values in RWC, grain yield per plant, number of kernels per spike, 1000-kernel weight, straw yield per plant and plant height, but it had low values in days to heading under both irrigation treatments and combined data. 7. The genotype P7 (Line-1) gave high values in total Chl, 1000-kernel weight and harvest index, and low values in FLAn under both irrigation and combined data. The mean performances for wheat crosses can be summarized as follows: 1. The cross P2xP4 gave high values in CAT, PPO, grain yield, spike length, number of spikes per plant, number of kernels per spike under both irrigation and combined data, and gave low values in FLAn, plant height and H2O2 under both irrigation and combined data. 2. The cross P1xP5 gave high values in total Chl, carotenoids and CAT. 3. The cross P4xP5 gave high values in total Chl, TPC and number of spikelets per plant, and low values in H2O2 and days to maturity under both irrigation and combined data. 4. The cross P1xP3 gave high values in carotenoids, grain yield and plant height under both irrigation and combined data, and CAT under stress condition. 5. The cross P3xP6 gave high values in number in kernels per spike, and low values in MDA under both irrigation and combined data. 6. The cross P5xP6 gave high values in TPC, 1000-kernel weight under both irrigation and combined data. (C): Heterosis Mean squares due to parents x irrigation treatments were significant and highly significant for all studied traits except for total Chl, Chl a/b ratio, RWC, days to heading, plant height, spike length, number of spikelets per spike, number of kernels per spike, 1000-kernel weight, straw yield, and filling period. Mean squares due to parents x crosses x irrigation treatments were significant and highly significant for all studied traits except for Chl a/b ratio, RWC, TPC, H2O2, CAT, PPO, days to maturity, filling period, plant height, spike length, number of spikelets per spike and 1000 kernel-weight. Results indicated that: 1. The cross P4xP5 expressed positive and significant heterotic effects relative to better parent for total Chl, FLA and CAT under both irrigation treatments and combined data. 2. The cross P2xP4 expressed negative and significant heterotic effects relative to better parent for FLAn, H2O2, days to maturity and plant height under both irrigation treatments and combined data. This cross had positive and significant and highly significant heterotic effects relative to better parent for FLA, CAT and PPO under both irrigation treatments and combined data. 3. The cross P3xP6 expressed negative and significant heterotic effects relative to better parent for FLAn, MDA under two irrigation treatments and combined data, and this cross expressed positive and significant heterotic effects relative to better parent for FLA and carotenoids and 1000-kernel weight under two irrigation treatments and combined data. 4. The cross P1xP3 expressed positive and significant and highly significant heterotic effects relative to better parent for grain yield and 1000-kernel weight FLA, PPO under two irrigation treatments and combined data and days to maturity under drought stress and combined data. 5. The cross P1xP5 expressed negative and significant heterotic effects relative to better parent for H2O2, plant height, days to heading and days to maturity under two irrigation treatments and combined data, and it expressed positive and significant heterotic effects relative to better parent for FLA, CAT and number of spikelets per spike under two irrigation treatments and combined data. 6. The cross P3xP7 expressed negative and significant and highly significant heterotic effects relative to better parent for H2O2, MDA under two irrigation treatments and combined data, and this cross expressed positive and significant and highly significant heterotic effects relative to better parent for spike length and straw yield under two irrigation treatments and combined data. 7. The cross P5xP6 expressed negative and significant to better parent heterosis for plant height, days to heading and days to maturity under two irrigation treatments and combined data, and this cross expressed positive and significant and highly significant to better parent heterosis for 1000-kernel weight under two irrigation treatments and combined data. 8. The crosses P1xP2 and P5xP7 expressed negative and significant and highly significant heterotic effects relative to better parent for H2O2 under two irrigation treatments and combined data, and the two crosses expressed negative and significant heterotic effects relative to better parent for FLA and PPO under two irrigation treatments and combined data. (D): Combining ability D.1. Analysis of variance for combining ability 1. The mean squares due GCA were significant and highly significant under two irrigation treatments and their combined analysis for all studied traits, while the mean squares due to SCA were highly significant for all traits under irrigation treatments and their combined analysis except for RWC. 2. The ratio of GCA/SCA exceeded the unity were detected for total Chl in combined analysis; CAR, RWC, CAT, days to maturity, days to heading, plant height, straw yield, spike length, number of spikelets per spike, 1000-kernels weight and filling period under both irrigation treatments and their combined analysis; Chl a/b ratio, PPO, number of kernels per spike and harvest index under stress irrigation; MDA and H2O2 under normal irrigation; FLAn and POX under normal irrigation and combined analysis; FLA under normal and stress irrigation; while, in all others cases the GCA/SCA ratio were less than the unity. 3. Mean squares due to the interactions between the irrigation treatments and both GCA and SCA were significant and highly significant for GCA x irrigation treatments in all studied traits except Chl a/b ratio. For SCA x irrigation treatments were significant and highly significant except in RWC, plant height and number of spikelets per spike. The ratio of GCA x irrigation/GCA were much higher than SCA x irrigation/SCA for studied all traits except in carotenoids, total Chl, Chl a/b ratio, CAT, POX, days to heading, spike length, number of spikelets per spike, number of kernels per spike, straw yield, harvest index, filling period and 1000-kernels weight. D.2. General combining ability effects (ĝi): 1. The parental genotype P1(Misr-3) gave positive significant and highly significant desirable (ĝi) effects for total Chl, grain yield per plant and harvest index under both irrigation treatments and their combined analyses. 2. The parental genotype P2 (Shandweel-1) showed positive significant desirable (ĝi) effects for and PPO, number of spikelets per spike under both irrigation treatments and their combined analyses. Also, it scored negative significant desirable (ĝi) effects for FLAn under normal irrigation and combined analyses. 3. The parental genotype P3 (Sids-14) exhibited negative highly significant (ĝi) effects for MDA, H2O2 under both treatment irrigation and combined analyses. It scored positive highly significant GCA effects for POX, plant height and FLA under both irrigation treatments and their combined analyses. 4. The parental genotype P4 (Gemmeiza-12) showed negative highly significant desirable GCA effect for H2O2, days to maturity, plant height and filling period under both irrigation treatment and their combined analyses. Moreover, it showed positive highly significant (ĝi) effects for POX and FLA under the two irrigation treatments and the combined analyses. 5. The parental genotype P5 (Sakha-95) expressed negative significant and highly significant desirable (ĝi) effects for days to heading and days to maturity under both irrigation treatment and their combined analyses. Also, it expressed positive significant and highly significant (ĝi) effects for total Chl, CAT, POX and straw yield under two irrigation treatments and their combined analyses. 6. The parental genotype P6 (Sakha-93) showed negative significant and highly significant (ĝi) effects for, plant height (cm), days to heading under both irrigation treatments and combined data. Moreover, it showed positive significant and highly significant (ĝi) effects for carotenoids, total Chl, RWC, CAT, 1000-kernels weight and FLA under both irrigation treatments and their combined analyses. 7. The parental cultivar P7 (Line-1) showed positive highly significant (ĝi) effects for POX and 1000-kernels weight under both irrigation treatments and combined data. Also, it showed negative highly significant (ĝi) effect for FLAn under both irrigation treatments and their combined data. Generally, it could be concluded that the breeder can be used the three parents Sakha-93, Sakha-95, Gemmeiza-12 to improve yield and earliness by releasing it in crossing programs. D.3. Specific combining ability (SCA) effects 1. The cross P1xP3 showed positive significant and highly significant desirable (Ŝij) effects for PPO, grain yield per plant, harvest index, plant height and 1000-kernel weight under two irrigation treatments and combined data. 2. The cross P4xP5 showed negative significant and highly significant desirable (Ŝij) effects for H2O2 under two irrigation treatments and combined data and this cross showed positive significant and highly significant desirable (Ŝij) effects for data total Chl, FLA, TPC, CAT and number of spikelets per plant under two irrigation treatments and combined data. 3. The cross P2xP4 showed negative significant and highly significant desirable (Ŝij) effects for H2O2, FLAn and plant height under two irrigation treatments and combined data, and this cross showed positive significant and highly significant desirable (Ŝij) effects for CAT and PPO under two irrigation treatments and combined data. 4. The cross P4xP6 showed positive significant and highly significant desirable (Ŝij) effects for total Chl and CAT under two irrigation treatments and combined data. 5. The cross P2xP7 showed positive significant and highly significant desirable (Ŝij) effects for total Chl, FLA, CAT, POX and straw yield per plant under both irrigation treatments and combined data. 6. The cross P5xP7 showed negative significant and highly significant desirable (Ŝij) effects for H2O2 under two irrigation treatments and combined data, and it showed positive significant and highly significant desirable (Ŝij) effects for FLA and PPO under two irrigation treatments and combined data. 7. The cross P1xP7 showed negative significant and highly significant desirable (Ŝij) effects for FLAn under two irrigation treatments and combined data, this cross showed positive significant and highly significant desirable (Ŝij) effects for CAT and POX under two irrigation treatments and combined data. 8. The cross P1xP6 showed negative significant and highly significant desirable (Ŝij) effects for H2O2 under two irrigation treatments and combined data, and this cross showed positive significant and highly significant desirable (Ŝij) effects for PPO under two irrigation treatments and combined data. 9. The cross P1xP5 showed positive significant and highly significant desirable (Ŝij) effects for FLA, CAT and POX under both irrigation and combined data. 10. The cross P6xP7 exhibited positive highly significant desirable (Ŝij) effects for grain yield per plant, harvest index and 1000- kernel weight under two irrigation treatments and combined data. 11. The cross P5xP6 exhibited positive highly significant desirable (Ŝij) effects for 1000-kernels weight and negative for plant height under two irrigation treatments and combined data. (E): Drought tolerance/sensitivity indices and correlation coefficient According to all tested drought tolerance indices, the most drought tolerant parents were P1 (Misr-3) and P3 (Sids-14), while the most drought sensitive one was P2 (Shandaweel-1). Moreover, the most drought tolerant crosses were P1xP3 and P2xP4, while the most susceptible crosses to drought stress were P2xP3 and P3xP4. The correlation coefficient among grain yield under non-stress (Yn) and nine drought tolerance indices was significantly positive for MP, GMP, STI, TOL and HM. While, YSI and SSI had a significantly negative correlation with Yn. On the other side, the correlation coefficient among grain yield under stress conditions (Ys) and nine drought tolerance indices was significant for all drought tolerance indices except (TOL). Additionally, grain yield per plant had highly significant correlation at 0.01 with harvest index, and significant correlation at 0.05 with number of grains per spike and flag leaf area under normal irrigation. Under drought stress, grain yield per plant had highly significant correlation at 0.01with MDA, and significant correlation at 0.05 with number of spikes per plant, TPC and POX. (F): The hierarchical cluster analysis According to the hierarchical cluster analysis, the wheat genotypes could be classified into six groups based on grain yield and stress tolerance indices as follows: group 1: Six genotypes (P2xP5, P3xP7, P4xP5, P2xP6, P3xP4 and P2xP3) attained low grain yield and were sensitive to drought stress. group 2: Three genotypes (P4, P2 and P1xP4) attained high grain yield and were sensitive to drought stress. group 3: Eight genotypes (P1xP2, P4xP7, P3xP6, P3xP5, P5xP6, P1xP6, P6 and P1xP7) attained moderate grain yield and were moderate drought tolerant. group 4: Three genotypes (P6xP7, P5 and P7) attained high grain yield and were moderate drought tolerant. group 5: Seven genotypes (P2xP4, P1, P1xP5, P5xP7, P3, P4xP6 and P2xP7) attained moderate grain yield and were high drought tolerant. group 6: One genotype (P1xP3) attained high grain yield and was drought tolerant.