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  • 1
    Electronic Resource
    Electronic Resource
    Heterosis and mixing effects in barley under drought stress (2005)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 124 (2005), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Yield stability is one of the main breeding objectives in breeding for stress environments, such as the semi-arid areas of Syria. The objectives of this study were to measure the effects of heterogeneity and heterozygosity on yield and yield stability by comparing doubled haploid lines (DHL) in mixed vs. pure stand (influence of heterogeneity) and F2 populations vs. corresponding DHL mixtures (influence of heterozygosity). Six barley lines from two gene pools (LR = landraces, EL = experimental lines) were used to produce nine crosses (two LR × LR, three EL × EL, four LR × EL). The F2 generation and eight DHL per cross were produced from each cross. The six parental DHL, nine F2 populations, nine 8-line mixtures and 72 DHL in pure stands were tested in five environments under drought stress in north Syria. The mean superiority of F2 populations over DHL mixtures for yield traits across environments and cross combinations ranged between 7.5 and 10%. The effect of heterogeneity was small throughout. For grain yield, harvest index, 1000-grain weight and plant height significant interactions between heterozygosity levels and environments were observed. The effect of heterozygosity for grain yield increased substantially from -1.2% in the highest-yielding environment to 45.6% in the most stressful environment. Interactions between levels of heterozygosity and cross combinations were significant for most traits. F2 populations were considerably more stable than DHL in pure stands, yet not as stable as DHL mixtures. It is concluded that heterozygosity is more important than heterogeneity in breeding for improved yield and yield stability under drought stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0523.2005.01111.x
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  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of floral characteristics of barley in the semi-arid climate of north Syria (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 122 (2003), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Previous studies have revealed that, in areas affected by severe drought, yielding ability and stability of barley (Hordeum vulgare L.) could be improved by increasing the level of heterozygosity. One possible approach to increase the heterozygosity level is to improve the outcrossing rate. In view of that, the genetic variability and phenotypic correlation coefficients involving four floral traits related to outcrossing behaviour were investigated in 274 drought adapted barley lines from the International Center for Agricultural Research in the Dry Areas (ICARDA's) current breeding programme. A significant quantitative variation existed in anther length and width, stigma length, and anther extrusion, which indicate that selection for these traits may be effective. Anther extrusion showed weak but highly significant positive correlations with anther and stigma length. Somewhat higher positive correlations were found between anther and stigma length. The results indicate that selection for high anther extrusion and longer anthers and stigmata may increase outcrossing in cultivated barley and consequently improve yielding ability through enhanced heterozygosity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1439-0523.2003.00861.x
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  • 3
    Electronic Resource
    Electronic Resource
    Variation in Ethiopian barley landrace populations for resistance to barley leaf scald and netblotch (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 117 (1998), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: One-hundred and eighty landrace populations and six-hundred single-head plants selected from 60 promising populations were evaluated for resistance to scald and netblotch at three locations in Ethiopia. Each accession was tested with and without the application of 50% of the recommended rate of fertilizer at planting. Plants were rated for disease attack two to four times during the season. Both diseases were enhanced by the application of fertilizer and were more severe at the testing sites of Holetta and Bekoji than at Sheno. The difference in disease resistance among and within populations was considerable. Moreover, populations from Arsi and Bale tend to be more susceptible to scald but more resistant to netblotch than populations from other regions. Populations collected from higher altitudes were more resistant to scald, but susceptible to netblotch, than were populations from lower altitudes. The paper illustrates approaches to the identification of valuable genotypes from landrace populations that can be incorporated into a breeding programme for the development of improved varieties with resistance to the principal diseases of barley in Ethiopia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0523.1998.tb01966.x
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of doubled haploid lines and F2 bulks for the improvement of barley in the dry areas of North Syria (1995)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 114 (1995), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Drought stress is the main factor limiting barley yields in West Asia and North Africa. This study compares the utility of doubled haploid lines (DHLs) and conventional F2 plant-derived bulks (F2Bs) in improving barley in stress environments. Double crosses were made, DHLs were developed by anther culture from double-cross F1 plants, and F2Bs were produced by bulking the offspring of F2 plants. Field tests were conducted in three drought-stressed environments. No major differences were observed in the mean performance of DHLs and F2Bs. For most traits, both the genotypic and the genotype × location interaction variances were higher in the DHL group, whereas heritabilities were similar. Higher gains from selection were predicted for the DHL group. Regression analysis of yield stability indicated a lower predictability of the DHL performance. The haploid technique can improve breeding populations from which varieties with stable yields can be developed. The costs involved are determined by the DHL production rate, which needs to be improved in many developing countries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0523.1995.tb00757.x
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  • 5
    Electronic Resource
    Electronic Resource
    Diversity for Disease Resistance in Barley Landraces from Syria and Jordan (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Plant breeding 103 (1989), S. 0 
    Details
    ISSN: 1439-0523
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A number of barley landraces collected in Syria and Jordan were evaluated for resistance to yellow rust, powdery mildew, scald and covered smut by inoculating single-head progenies with local pathogen strains during two years of field tests. A large diversity in resistance was observed for each pathogen both between populations of different collection sites as well as between head progenies within collection sites. The level of resistance varied from absolute and partial resistant types up to highly susceptible lines. No consistent association between the environmental conditions of the collection site and the level of resistance of the landrace-lines could be found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1439-0523.1989.tb00393.x
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  • 6
    Electronic Resource
    Electronic Resource
    Estimation of heritability from varietal trials data (1993)
    Springer
    Theoretical and applied genetics 86 (1993), S. 437-441 
    Details
    ISSN: 1432-2242
    Keywords: Heritability ; Standard error ; Genotype x environment interaction ; Confidence interval ; Invalid estimates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We present the estimation of heritabilities of an observed trait in situations where evaluation of several pure breeding lines is performed in a trial at a single location and in trials from several locations. For the single location situation, we evaluate exact confidence intervals, the probability of invalid estimates, and the percentage points of the distribution of heritability. Simulations were performed to numerically verify the results. Additionally, approximations to the bias and standard error of the estimate were obtained and are presented along with their simulated values and coefficients of skewness and kurtosis. For trials in several locations, explicit expressions for exact values of confidence limits are not available. Further, one would require knowledge of one more parameter, represented by the ratio of genotype x environment (G x E) interaction variance to error variance, in addition to the number of genotypes, replication and true heritability value. Approximations were made for bias and the standard error of estimates of heritability. The evaluation of the distribution of heritability and its moments was recognized as a problem of the linear function of an independent chi-square. The methods have been illustrated by data from experiments on grain and straw yield of 64 barley genotypes evaluated at three locations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00838558
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  • 7
    Electronic Resource
    Electronic Resource
    Genotype x environment interaction of crossover type: detecting its presence and estimating the crossover point (1999)
    Springer
    Theoretical and applied genetics 99 (1999), S. 988-995 
    Details
    ISSN: 1432-2242
    Keywords: Key words Crossover point ; Genotype x environment interaction ; Crossover genotype-environment interaction ; Linear regression model ; Barley
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Genotype-environment interaction (GEI) introduces inconsistency in the relative rating of genotypes across environments and plays a key role in formulating strategies for crop improvement. GEI can be either qualitative (i.e., crossover type) or only quantitative (i.e., non-crossover type). Since the presence of crossover-type interaction has a strong implication for breeding for specific adaptation, it is important to assess the frequency of crossover interactions. This paper presents a test for detecting the presence of crossover-type interaction using the response-environment relationship and enumerates the frequency of crossovers and estimation of the crossover point (CP) on the environment axis, which serves as a cut-off point for the two environments groups where different/specific selections can be made. Sixty-four barley lines with various selection histories were grown in northern Syria and Lebanon giving a total of 21 environments (location-year combinations). Linear regression of the genotypic response on the environmental index represented a satisfactory model, and heterogeneity among regressions was significant. At a 5% level of significance, 38% and 19% of the pairs showed crossover interactions when the error variances were considered heterogeneous and homogeneous, respectively, implying that an appreciable number of crossovers took place in the case of barley lines responding to their environments. The CP of 1.64 t/ha, obtained as the CP of regression lines between the genotype numbers 19 and 31, provided maximum genotype x environment-group interaction. Across all environments, genotype nos. 59 and 12 stood first and second for high yield, respectively. The changes in the ranks of genotypes under the groups of environments can be used for selecting specifically adapted genotypes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001220051406
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  • 8
    Electronic Resource
    Electronic Resource
    Estimation of heritability using variety trials data from incomplete blocks (1995)
    Springer
    Theoretical and applied genetics 90 (1995), S. 142-145 
    Details
    ISSN: 1432-2242
    Keywords: Heritability ; Incomplete block design ; Standard error ; Bias ; Genotype by environment interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An assessment of the heritability of a trait is useful in formulating a breeding strategy for crop improvement. We have considered the estimation of broad-sense heritability from a single-location trial and from multi-locational trials conducted in incomplete blocks. Using residual maximum likelihood estimates of variance components, we estimated the heritability and obtained expressions for the estimate of its bias and its standard error. The estimation procedure is illustrated for 25 barley genotypes evaluated at four locations in West Asia and North Africa during 1992.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221008
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  • 9
    Electronic Resource
    Electronic Resource
    Drought as a challenge for the plant breeder (1996)
    Springer
    Plant growth regulation 20 (1996), S. 149-155 
    Details
    ISSN: 1573-5087
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Since agriculture began, drought has been on of the major plagues affecting crop production causing famine and death. Despite many decades of research, drought continues to be a major challenge to agricultural scientists. This is due to the unpredictability of its occurrence, severity, timing and duration; and to the interaction of drought with other abiotic stresses, particularly extremes of temperature and variations in nutrients availability; and with biotic stresses. Breeding has not been as effective in improving crop production under drought-stress conditions as it has in their absence — or where the stress can be alleviated by irrigation. This paper argues that the relative lack of success of breeding for stress conditions in general, and for drought-stress conditions in particular, can be partly attributed to use of the same breeding approach that is successful for favourable environments. A different breeding approach for drought-stress conditions is discussed in relation to the environment in which selection should be conducted, the germplasm to be used, and the experimental designs and plot techniques to be employed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00024011
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  • 10
    Electronic Resource
    Electronic Resource
    Yield potential and drought tolerance of segregating populations of barley in contrasting environments (1987)
    Springer
    Euphytica 36 (1987), S. 265-273 
    Details
    ISSN: 1573-5060
    Keywords: Hordeum vulgare ; barley ; dry areas ; stress-tolerance ; stability ; bulk method ; multilocation testing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Using the traditional approach (selection for grain yield) it has been found that F3 families derived from F2's selected under unfavourable conditions were more vigorous in the early stages of growth, taller, earlier in heading and with larger yields than F3 families derived from F2's selected under favourable conditions. A high and negative correlation coefficient was found between the drought susceptibility index and grain yield at the driest site, whereas at the wettest site the correlation coefficients were lower and in some cases positive, indicating the existence of traits which are desirable under drought and undesirable under favourable conditions, or vice versa. Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment. Expected responses to selection for grain yield using different selection criteria indicated that selection under stress conditions is expected to be more efficient than selection under favourable conditions when dry areas is the target environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730673
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