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Abstract SUMMARY The main objectives of this study were to (1) evaluate performance and degree of drought stress tolerance of six barley genotypes and their F1’s for some agronomic and physiological traits under well watered and rainfed conditions, (2) identify the traits which can be used as selection criteria for drought stress tolerance, (3) estimate of some genetic parameters specially heterosis, combining ability and heritability as bases of improving barley under rainfed conditions at Maryout region and (4) study the interrelationships among traits under the two irrigation regimes. Six parents of barley (Hordeum vulgare L.) namely: the cv. G126 (P1), L Su12303 (P2) (are local genotypes), L 105/20 (P3), L105/27 (P4), L105/32 (P5) and L 105/36 (P6) (are introduced from ICARDA) were chosen to achieve the present study. The experiments of the present study were carried out at the Maryout Agriculture Experiment Station of Desert Research Center (North Western Coast of Egypt). In 2008/09 season, the six parents were handy crossed in all possible combinations, excluding reciprocals and seeds of the 15 F1’s were obtained. In 2009/10 season, two adjacent field trials each included the 15 F1 crosses and their respective parents (21 genotypes) were conducted in a randomized complete block design with three replications. Each experiment was devoted to one of the following two irrigation treatments; a) rainfall treatment (drought stress treatment) and b) rainfall + 2 supplemental irrigations given at sowing date and flowering stage (well watered treatment). Experimental unit consisted of one row for each genotype. Row was 3.5 m in length and rows spacing and distance between plants within row were 30cm and 10cm, respectively. Sowing date was on 20th November. Plants were thinned at one plant per hill after about three weeks from sowing date. Days to heading and maturity were recorded. Also, flag leaf area, flag leaf angle, as well as relative water content (RWC), proline content, chlorophyll a (chl.a and b) content and carotenoids content as Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 physiological traits were recorded at anthesis stage. At harvest, ten guarded plants randomly taken from each plot were used for recording data of the following traits; plant height, no. of spikes/plant, spike length, number of spikelets/spike, number of grains/spike, 100-kernel weight, grain yield/plant, straw yield/plant and harvest index. Data of all traits recorded from each experiment were subjected to the ordinary analysis of variance and combined analysis over the two irrigation regimes was done when the homogeneity test was insignificant. Significant differences between means were tested by using the least significant differences (L.S.D) test at 5% level of probability. Heterosis, combining ability and heritability were estimated for the studied traits. Estimates of combining ability effects were made by applying Griffing’s (1956) method 2 and model 1. Different groups of phenotypic correlation were estimated between the studied traits under both irrigation treatments. The obtained results can be summarized as follows: A. Analysis of variance The results revealed that irrigation regimes mean squares were highly significant for all studied traits, indicating that the genotypes performance differed under the two irrigation treatments. Also, mean squares due to genotypes were highly significant under the two irrigation treatments and their combined data, indicating the existence of sufficient genetic variability among the genotypes for the studied traits. Highly significant mean squares due to interactions of genotypes with irrigation treatments were observed for all studied traits, reflecting the fact that these genotypes were inconsistent in their responses to irrigation treatments. B. Mean performance of barley genotypes under normal irrigation and drought stress conditions 1. Results revealed that drought stress caused significant reduction in all traits with different degrees of reduction, except proline content 127 SUMMARY Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 which was increased under drought stress condition. Overall genotypes, harvest index recorded the lowest reduction (6.06%) followed by 100-kernel weight (7.74%) and spike length (8.41%), while carotenoids content recorded the highest reduction (43.32%) followed by chl. ”b” content (30.74%) and RWC (30.67%). On the other hand proline content recorded an increase percentage amounted 73.39% under drought stress conditions. 2. The cross P4xP6 for heading date, P1xP4 for maturity date, the cv. G126 for plant height, the parental line 105/32 for flag leaf area and RWC, the cross P2xP5 for flag leaf angle and spike length, P2xP6 for no. of spikes/plant and grain yield/plant, P1xP2 for no. of spikelets/spike, straw yield/plant and harvest index, P2xP4 for chl. ”a” content and carotenodis content and the parental line 105/20 for chl. ”b” content registered lowest means reduction, while the parental line 105/32 registered the highest reduction percentage under drought stress treatment. 3. Rainfed conditions significantly decreased (earliered) time to heading and maturity of various barley genotypes. The average reduction in heading date was relatively higher (17.27%) than that of maturity date (14.97%). The cross P1xP6 and the cv. G126 were the earliest genotypes in heading date under the two irrigation regimes, respectively, while the cross P1xP4 under both irrigation regimes as well as the parental line 105/20 and the crosses; P2xP3, P3xP4 and P3xP5 under rainfed treatment were the earliest in maturity date. 4. Reduction percentages in vegetative growth traits revealed that flag leaf area was more sensitive to drought stress compared with flag leaf angle and plant height. The cross P3xP6 under the two irrigation regimes as well as the cv. G126 and the two crosses; P4xP6 and P5xP6 under rainfed treatment were the tallest among all genotypes. Meantime, the cross P5xP6 under the two irrigation treatments had the highest flag leaf area. For flag leaf angle, the parental line 105\20 and the crosses P1xP4 and P3xP6 under the two irrigation regimes as wel Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 as the cross P2xP4 under normal irrigation and the crosses; P1xP5, P3xP4, P4xP6 and P5xP6 under drought stress gave the highest values for this trait. 5. Results revealed that reduction was relatively high in no. of grains/spike, which averaged 19.24% relative to the control treatment followed by grain yield/plant (15.68%), no. of spikes/plant (15.68%), no. of spikelets/spike (10.92%), spike length (8.41%) and100-kernel weight (7.74%), demonstrating that no. of grains/spike caused the greatest reduction in grain yield/plant under water stress treatment and was more sensitive to water deficit than other yield components. The cross P5xP6 had high grain yield/plant under well watered and stressed treatments, therefore this cross can be used in barley breeding programs for improving tolerance to drought stress. For no. of spikes\plant the crosses; P2xP5, P3xP5 and P3xP6 under normal irrigation and P5xP6 under the two irrigation treatments had the highest means for this trait, while the parental line 105/32 and the crosses; P5xP6 and P2xP3 under the two irrigation treatments gave the highest values for spike length. The cross P5xP6 under normal irrigation and P3xP5 under drought stress recorded the highest means for no. of spikelets/spike, while the cross P3xP6 followed by P5xP6 under the two irrigation treatments recorded the highest means for no. of grains/spike. For 100-kernel weight, the two crosses; P3xP6 and P5xP6 under normal irrigation as well as the parental line 105/27 and the two crosses; P1xP5 and P2xP5 under rainfed conditions had the highest mean values for this trait. 6. The results indicated that low soil moisture stress significantly decreased straw yield by 10.53% compared to well watered treatment. The cross P1xP2 recorded the lowest reduction (1.98%). The cross P1xP6 under both irrigation treatments as well as the cross P3xP5 and P5xP6 under rainfed treatment gave the highest mean values for this trait. 129 SUMMARY Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 7. Results showed that harvest index significantly affected by drought stress which reduced by 6.06% than under well watered treatment. The parental line L105/36 under normal irrigation treatment as well as the cross P4xP6 under drought stress treatment had the highest mean values of 0.40 and 0.37, respectively. 8. Results revealed that the physiological traits are greatly affected by drought stress, where the relative water content, chlorophyll ”a” and ”b” content and carotenoids content were significantly reduced by drought stress, while proline content was significantly increased (73.39%) when plants subjected to drought stress. Meantime, carotenoids content was adversely affected (43.32% reduction) followed by chlorophyll ”b” content (30.74%), relative water content (30.67%) and chlorophyll ”a” content (26.90%) by drought stress. The cross P5xP6 had the highest values for RWC under the two irrigation regimes. For chl. ”a” content and carotenoids content, the cv. G126 under normal irrigation and the cross P5xP6 under rainfed treatment recorded the highest means for the two traits, while the same cross under normal irrigation and the cross P2xP3 under rainfed treatment gave the highest means for chl. ”b” content. For proline content, the parental line 105\32 under normal irrigation and the cross P1xP4 under rainfed treatment gave the highest values for this trait. 9. As general conclusion from the above results of reduction percentages, the traits studied can be classified into three categories as follows: 1- Drought tolerant traits included 100-kernel weight, spike length, harvest index, straw yield/plant, no. of spikelets/spike, plant height and maturity date which recorded reduction percentages less than 15%, suggesting that these traits could be used as selection criteria for screening drought resistant genotypes in barley breeding programs, 2- Moderately tolerant traits included no. of spikes/plant, grain yield/plant, heading date, no. of grains/spike, flag leaf angle, chlorophyll ”a” content, and flag leaf area which recorded reduction percentages more than 15% up to 30% and 3- Drought susceptible Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 traits included relative water content, chlorophyll ”b” content and carotenoids content, which recorded reduction percentages more than 30%. It is worthy to note that the breeder should be taken into consideration increase positive percentages in proline content occurred under drought stress, which related to tolerance grain yield under such conditions. C- Drought susceptibility index (S) Results indicated that S mean values ranged from 0.50 for the cross P2xP6 to 1.73 for the parental line 105/36 with an average of 1.00. The crosses; P1xP3, P1xP4, P2xP6, P3xP4, P3xP5, P4xP5, P4xP6 and P5xP6 showed stress susceptibility index (S) values less than unity ranging from 0.5 to 0.79, indicating that these genotypes are the most drought tolerant for grain yield/plant. D. Estimates of genetic parameters D.1. Heterosis Results revealed that values of heterosis greatly varied under the two irrigation regimes and heterotic effects were more pronounced under soil moisture stress than under well watered conditions for most studied traits. The crosses showing the best heterobeltiosis under well watered and/or rainfed conditions could be recommended to improve the respective traits. Overall crosses, values of heterosis over mid-parents ranged from -19.43% for carotenoids content to 23.04% for relative water content under well watered treatment, whereas values ranged from - 27.12% for chlorophyll ”a” content to 25.46% for carotenoids content under rainfed conditions. For better-parent heterosis, values ranged from - 27.10% for carotenoids content to 8.44% for RWC under well watered treatment, whereas values ranged from -31.59% for chlorophyll ”a” content to 14.33% for days to maturity and grain yield/plant under rainfed conditions. The cross P5xP6 gave the maximum mid-parents heterosis value of 317.28% for chlorophyll ”b” content under well watered Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 conditions, whereas the cross P3xP5 gave the maximum value of 98.36% for carotenoids content under rainfed conditions. For better-parent heterosis, the cross P5xP6 recorded the highest value of 284.09% under well watered conditions, whereas the cross P2xP4 recorded the highest value of 94.52% for carotenoids content under rainfed conditions. The obtained results also indicated that the five F1 hybrids; P2xP4, P3xP4, P3xP5, P3xP6 and P5xP6, expressed higher mid and better parent heterosis under rainfed condition than under well watered condition for grain yield/plant, therefore if the hybrids development is feasible in barley these hybrids are considered more desirable to be grown under water shortage conditions for increasing grain yield per unit area and selection could be exercised in segregating generations for developing drought tolerant genotypes. D.2. Combining ability D.2.1. Combining ability analysis The results revealed that mean squares associated with general(GCA) and specific (SCA) were found to be highly significant for all the studied traits under both irrigation regimes and combined analysis, indicating that both additive and non-additive genetic effects were involved in the inheritance of these traits. The ratios of k2GCA/k2SCA were less than unity under the two irrigation treatments and combined data, suggesting that the studied traits were mainly controlled by the nonadditive gene effects. The interactions of GCA and SCA with irrigation treatments were also highly significant for all the studied traits, revealing that variance magnitudes of different types of gene action were fluctuated from one environment to another. Such results indicate that the irrigation treatments are considered as an effective factor for declaring GCA and SCA variances. Thus, the breeder should utilize the appropriate breeding method under each environment for developing desired barley genotypes. Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 D.2.2. Evaluation of the six parents for desired GCA effects were as followes: - The cv. G126: for earliness in heading and straw yield\plant under the two irrigation treatments, earliness in maturity, flag leaf area, chl. ”a” and ”b” contents and carotenoids content under normal irrigation and for proline content under drought stress. - LSu12303: for carotenoids content under the two irrigation regimes, hrvest index under well watered treatment, earliness in heading, RWC and chl. ”a” and ”b” contents under drought stress - L150/20: for improving earliness in maturity and RWC under the two irrigation regimes, plant height under normal irrigation and chl. ”a” and ”b” contents under drought stress. - L150/27: for improving 100-kernel weight under the two irrigation treatments, flag leaf area under well watered treatment, earliness in heading, harvest index, proline content and chl. ”a” content under drought stress treatment. - L150/32: for flag leaf area, no. of spikes/plant, spike length, no. of spikelets/spike, grain yield/plant, straw yield/plant, RWC and carotenoids content under the two irrigation levels, no. of grains/spike, proline content and chl. ”a” content under normal irrigation and 100- kernel weight under drought stress. - L150/36: for improving the traits of plant height, flag leaf area, no. of spikes/plant, spike length, no. of grains/spike, 100-kernel weight, grain yield/plant, harvest index and RWC under the two irrigation levels, earliness in heading, chl. b content and carotenoids content under normal irrigation and no. of spikelets/spike under drought stress. D.2.3. Some crosses exhibited desirable SCA effects and included at least one parent as good general combiner as follows - P1xP2: for maturity date, flag leaf area and spike length under the two irrigation treatments, proline content under normal irrigation, no. of Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 spikelets/spike, straw yield\plant, chl ”a” content and carotenoids content under drought stress. - P1xP3: for flag leaf area and spike length under the two irrigation treatments, straw yield\plant and RWC under normal irrigation, 100- kernel weight and proline content under drought stress. - P1xP3: for maturity date and flag leaf area under normal irrigation, RWC, proline content and carotenoids content under drought stress treatment. - P1xP5: for 100-kernel weight and carotenoids content under the two irrigation regimes, harvest index and RWC under normal irrigation and chl. ”b’ content under drought stress. - P1xP6: for heading date, spike length and straw yield\plant under the two irrigation treatments, heading date and plant height under normal irrigation, 100-kernel weight and RWC under drought stress. - P2xP3: for flag leaf area, spike length, chl. ”b” content and carotenoids content under the two irrigation treatments, heading date under normal irrigation, RWC, proline and chl. ”a” contents. - P2xP4: for no. of spikes/plant, no. of spikelets/spike, no. of grains/spike, grain yield\plant, straw yield/plant, RWC, chl. ”a” content and carotenoids content under the two irrigation treatment, maturity date and flag leaf angle under normal irrigation and proline content under drought stress. - P2xP5: for maturity date, no. of spikelets/spike and straw yield\plant under the two irrigation regimes, no. of spikes/plant, no. of grains\spike, grain yield/plant and RWC under normal irrigation and 100-kernel weight under drought stress treatment. - P2xP6: for spike length under the two irrigation regimes, heading and maturity dates and chl. ”a” and crotenoids contents under normal irrigation treatment, no. of spikes\plant, no. of spikelets/spike and 100- kernel weight under drought stress. 134 SUMMARY Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 - P3xP4: for no. of spikes\plant under the two irrigation treatments, 100- kernel weight under normal irrigation and grain yield/plant under drought stress. - P3xP5: for no. of spikes/plant, spike length, no. of spikelets/spike, no. of grains/spike, grain yield/plant, straw yield\plant and chl.”a” and carotenoids contents under the two irrigation treatments, plant height, flag leaf area and RWC under normal irrigation and heading date under drought stress. - P3xP6: for plant height, no. of spikes\plant, no. of spikelets/spike, no. of grains/spike, 100-kernel weight, grain yield\plant, RWC and proline content under the two irrigation treatments, maturity date and harvest index under normal irrigation, flag leaf area, straw yield/plant and chl. ”a” and ”b” contents under drought stress. - P4xP5: for heading date under the two irrigation regimes, spike length under normal irrigation treatment, flag leaf area, RWC and proline content under drought stress treatment. - P4xP6: for RWC under the two irrigation treatments, heading and maturity date, proline and carotenoids contents under normal irrigation, plant height, no. of spikes\plant, no. of spikelets/spike and no. of grains\spike under drought stress conditions. - P5xP6: for plant height, flag leaf area, no. of spikes/plant, spike length, no. of spikelets/spike, no. of grains/spike, grain yield/plant, straw yield\plant, RWC, prolin content, chl. ”a” and ”b” contents and carotenoids content under the two irrigation treatments as well as 100- kernel weight under well watered treatment. D.3. Hertability Results showed that high to moderate or low broad sense heritability estimates were obtained which ranged from 62.85% for flag leaf angle to 99.83% for chlorophyll ”b” content under well watered conditions and from 38.68% for flag leaf angle to 99.86% for spike length under rainfed conditions. However, the wide range between heritability 135 SUMMARY Soad S. Abou El-Fotoh, M.Sc. Thesis, 2015 values attributable to irrigation treatments, reveal that heritability percentages are altered ’in some extent’ from normal irrigation to drought stress conditions Moreover, heritability estimates under drought stress were higher than those under normal irrigation conditions for heading and maturity dates, plant height, flag leaf angle, 100-kernel weight, straw yield, harvest index, chl. ”b” content and carotenoids content , while the opposite was true for the other traits, indicating that selection for improving these traits would be effective under rainfed than under well watered conditions. E- Correlation studies Significant and positive phenotypic correlation coefficients were found between grain yield/plant and each of no. of spikes/plant, no. of spikelets/spike, no. of grains/spike and RWC under the two irrigation treatments, indicating that selection for one or more of these traits may be amenable for grain yield/plant improvement under any of the two irrigation treatments. Also, results of correlation between every trait under normal irrigation treatment and drought stress treatment revealed the presence of positive and significant correlation for all the studied traits except, proline and chl. ”b” contents which correlation was not significant. Meantime the correlation between mean performance of genotypes for different studied traits under normal irrigation treatment and reduction percentages under drought stress treatment was positive and significant for the traits of maturity date, flag leaf angle, 100-kernel weight, straw yield/plant, harvest index and proline and chl. ”b” contents. |