1- Urmia University
2- Kurdistan Agricultural and Natural Resources Research and Education Center
2- Kurdistan Agricultural and Natural Resources Research and Education Center
Abstract: (9 Views)
Abstract
Introduction and Objectives: Bread wheat, is one of the most strategic crops for providing a significant portion of the protein and energy needs for global population. Its high nutritional value, affordability, accessibility, and compatibility with the human digestive system have made this crop a staple in the diets of worldwide populations. Today, wheat has diverse industrial applications, including in the confectionery industry, biofuel production, and alcohol manufacturing, as well as playing a significant role in providing part of livestock nutrition. Drought is the most critical abiotic stress that significantly affects both the quantity and quality of wheat growth and development. Various strategies have been proposed to mitigate the effects of drought stress on plants. To develop an effective breeding program for producing drought-tolerant varieties, it is essential to identify the mode of inheritance, the magnitude of gene effects, and actions. Generation mean analysis is considered an effective method for estimating genetic parameters.
Materials and methods: Base generations derived from the cross between two wheat cultivars; Tiregan (drought-tolerant parent) and SeriM82 (drought-sensitive parent), were evaluated in a split-plot design based on randomized complete blocks with three replications under non-stress and drought stress conditions at the Pars National Agro-Industry and Animal Husbandry Company Research Farm located in Moghan Plain during the 2021-2022 cropping season. Irrigation treatments were assigned to the main plots, while base generations were arranged in the subplots. Seed sowing was carried out in late November to early December. In each experimental unit, row spacing was set at 15 cm, plant spacing at 5 cm, and row length at 1 meter. Initial irrigation was applied after sowing in both environments (non-stress and drought stress) to promote seed germination and was continued until the pollination stage. After pollination, irrigation was withheld in the drought stress plots until the end of the growing season to impose water deficit stress. Trait measurements including total plant weight, spike weight per plant, grain yield per plant, 100-grain weight, plant weight, peduncle length, main spike length, number of fertile tillers, flag leaf length and width, straw weight, harvest index, days to heading, days to maturity, greenness index (SPAD value), initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv=Fm-F0), the Fv/Fm ratio (maximum quantum efficiency of photosystem II), and the Fv/F0 ratio (photosynthetic performance) were conducted on individual plants to estimate within-generation variance. Traits measurements were taken on 10 plants per plot for the parental lines (P1, P2) and F1, 30 plants for F2, and 15 plants for each backcross generation (BC1 and BC2), in each replication. In this study, generation mean analysis was conducted based on a mixed linear model to estimate additive, dominance, and epistatic effects. In the mixed linear model framework, the estimation of genetic effects and genetic variance components was performed simultaneously using the Restricted Maximum Likelihood (REML) method.
Results: The analysis of variance (ANOVA) revealed significant inter-generational differences for most studied traits, demonstrating substantial genetic divergence between the parents and adequate genetic variability for generation mean analysis. The highly significant (P ≤ 0.01) mean effect parameter (m) for most traits under both non-stress and drought stress conditions implies shared genes between the parents and further suggests predominantly quantitative inheritance. The Wald-F test was significant for harvest index, 100-grain weight, and grain yield under both non-stress and drought stress conditions; for peduncle length, flag leaf length and width, Fm, Fv, Fv/Fm, Fv/ F0, and SPAD chlorophyll index under non-stress conditions; and for days to maturity under drought stress conditions. Therefore, the six-parameter model was employed to estimate genetic effects. Duplicate epistasis was detected for harvest index, 100-grain weight, and grain yield under both non-stress and drought stress conditions; for peduncle length, flag leaf length and width, Fm, Fv, Fv/F₀, and SPAD chlorophyll index under non-stress conditions; and for days to maturity under drought stress conditions.
Conclusion: According to the results of generation mean analysis, in addition to additive effects, dominance effects and various types of epistasis contributed to the inheritance of most traits. In many cases, dominance effects were more prominent, and due to the presence of duplicate epistasis, effective utilization of these genetic effects remains challenging. It is therefore recommended that selection be postponed until later generations of the breeding population.
Introduction and Objectives: Bread wheat, is one of the most strategic crops for providing a significant portion of the protein and energy needs for global population. Its high nutritional value, affordability, accessibility, and compatibility with the human digestive system have made this crop a staple in the diets of worldwide populations. Today, wheat has diverse industrial applications, including in the confectionery industry, biofuel production, and alcohol manufacturing, as well as playing a significant role in providing part of livestock nutrition. Drought is the most critical abiotic stress that significantly affects both the quantity and quality of wheat growth and development. Various strategies have been proposed to mitigate the effects of drought stress on plants. To develop an effective breeding program for producing drought-tolerant varieties, it is essential to identify the mode of inheritance, the magnitude of gene effects, and actions. Generation mean analysis is considered an effective method for estimating genetic parameters.
Materials and methods: Base generations derived from the cross between two wheat cultivars; Tiregan (drought-tolerant parent) and SeriM82 (drought-sensitive parent), were evaluated in a split-plot design based on randomized complete blocks with three replications under non-stress and drought stress conditions at the Pars National Agro-Industry and Animal Husbandry Company Research Farm located in Moghan Plain during the 2021-2022 cropping season. Irrigation treatments were assigned to the main plots, while base generations were arranged in the subplots. Seed sowing was carried out in late November to early December. In each experimental unit, row spacing was set at 15 cm, plant spacing at 5 cm, and row length at 1 meter. Initial irrigation was applied after sowing in both environments (non-stress and drought stress) to promote seed germination and was continued until the pollination stage. After pollination, irrigation was withheld in the drought stress plots until the end of the growing season to impose water deficit stress. Trait measurements including total plant weight, spike weight per plant, grain yield per plant, 100-grain weight, plant weight, peduncle length, main spike length, number of fertile tillers, flag leaf length and width, straw weight, harvest index, days to heading, days to maturity, greenness index (SPAD value), initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv=Fm-F0), the Fv/Fm ratio (maximum quantum efficiency of photosystem II), and the Fv/F0 ratio (photosynthetic performance) were conducted on individual plants to estimate within-generation variance. Traits measurements were taken on 10 plants per plot for the parental lines (P1, P2) and F1, 30 plants for F2, and 15 plants for each backcross generation (BC1 and BC2), in each replication. In this study, generation mean analysis was conducted based on a mixed linear model to estimate additive, dominance, and epistatic effects. In the mixed linear model framework, the estimation of genetic effects and genetic variance components was performed simultaneously using the Restricted Maximum Likelihood (REML) method.
Results: The analysis of variance (ANOVA) revealed significant inter-generational differences for most studied traits, demonstrating substantial genetic divergence between the parents and adequate genetic variability for generation mean analysis. The highly significant (P ≤ 0.01) mean effect parameter (m) for most traits under both non-stress and drought stress conditions implies shared genes between the parents and further suggests predominantly quantitative inheritance. The Wald-F test was significant for harvest index, 100-grain weight, and grain yield under both non-stress and drought stress conditions; for peduncle length, flag leaf length and width, Fm, Fv, Fv/Fm, Fv/ F0, and SPAD chlorophyll index under non-stress conditions; and for days to maturity under drought stress conditions. Therefore, the six-parameter model was employed to estimate genetic effects. Duplicate epistasis was detected for harvest index, 100-grain weight, and grain yield under both non-stress and drought stress conditions; for peduncle length, flag leaf length and width, Fm, Fv, Fv/F₀, and SPAD chlorophyll index under non-stress conditions; and for days to maturity under drought stress conditions.
Conclusion: According to the results of generation mean analysis, in addition to additive effects, dominance effects and various types of epistasis contributed to the inheritance of most traits. In many cases, dominance effects were more prominent, and due to the presence of duplicate epistasis, effective utilization of these genetic effects remains challenging. It is therefore recommended that selection be postponed until later generations of the breeding population.
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