1- Horticulture Crops Research Department, Golestan Agricultural and Natural Resources Research and Education Center, AREEO, Gorgan, Iran.
2- Seed and Plant Improvement Institute, AREEO, Karaj, Iran.
2- Seed and Plant Improvement Institute, AREEO, Karaj, Iran.
Abstract: (10 Views)
Introduction and Objective: Wheat (Triticum aestivum L.) is one of the most important crops in the world, playing a key role in human nutrition and global food security. The genes function and the heritability of traits can change due to environmental changes, which is related to the complex interaction between genotype and environment. Analyzing means and variances across generations is essential in genetic and breeding studies, as it helps plant breeders to evaluate the genetic responses of crops under different environmental conditions, such as normal, saline, and drought stress. By performing generational mean analysis, researchers can estimate the additive and dominance effects and their interactions. This information is crucial for selecting optimal parents to use in crosses, aiming to enhance heterosis and improve breeding efficiency. This study aims to investigate and analyze the genetic parameters that influence key agronomic traits through the analysis of means and variances across generations derived from the crosses between Ehsan and Kavir cultivars, specifically under normal and saline stress conditions during the reproductive stage.
Material and Methods: To evaluate the genetic control of key agronomic traits in bread wheat, the parental lines and various generations from the Ehsan × Kavir cross were studied. In this study, Ehsan cultivar as the maternal line and Kavir cultivar as the paternal line played a role in producing the F1 generation. The experiment was set up as a split-plot arrangement within a randomized complete block design (RCBD), with three replications at the Gorgan Agricultural Research Station, during the 2022-2023 growing season. Two distinct irrigation conditions were applied: full irrigation and saline stress. Saline stress (10 dS m⁻¹) was introduced at two key growth stages: full spike emergence (Zadoks code 73) and early milk development (Zadoks code 60). Trait measurements were taken on 10 plants from the parent lines and the F1 generation, 30 plants for the F2 generation, and 15 plants from the backcross generations. After maturity, various agronomic traits, such as plant height, spike length, peduncle length, number of spikes per plant, number of spikelets per spike, number of grains per spike, thousand-kernel weight, and grain yield per plant, were assessed across all individuals. SAS9.4 software was used to perform analysis of variance, comparing means, and estimate genetic effects. Also, heritability and heterosis were calculated using Excel software.
Results: Variance analysis revealed that both the effects of stress and the stress × generation interaction had a significant impact on traits such as thousand-kernel weight and grain yield per plant. As a result, genetic analyses were performed separately for these traits under normal and saline stress conditions. The generation mean analysis revealed that the genetic models influencing thousand-kernel weight and grain yield differed under normal and saline stress conditions. For other traits, where stress effects and stress × generation interactions were not significant, the data were combined and analyzed together, making the results applicable to both environmental scenarios. Differences among generations were statistically significant for all traits studied. The chi-square test indicated that peduncle length, plant height, and spike length showed no significant differences. On the other hand, the chi-square test revealed significant differences for other traits, highlighting the inadequacy of the simple additive-dominance model and suggesting the involvement of epistatic effects, genetic linkage, and maternal influences in controlling these traits. The generation means analysis demonstrated that non-additive genetic effects played a more crucial role than additive effects in controlling the majority of traits, including spike length, number of grains per spike, number of spikelets per spike, number of spikes per plant, thousand-kernel weight, and grain yield per plant under both normal and saline stress conditions. Epistatic effects were particularly significant for most traits, and these traits exhibited low narrow-sense heritability. The variance analysis of generations revealed that traits such as spike length, number of grains per spike, number of spikelets per spike, number of spikes per plant, and grain yield per plant were predominantly influenced by overdominance. In contrast, for plant height and peduncle length, additive genetic effects were more influential than non-additive effects, and no epistatic effects were detected. Moreover, relatively high narrow-sense heritability was observed for plant height and peduncle length.
Conclusion: The results of this study showed that the genetic models effective on thousand-kernel weight and grain yield were different under normal and saline stress conditions. Additionally, under both environmental conditions, genetic improvement can be effectively achieved in plant height and peduncle length during the initial generations. However, for other traits, including grain yield and its components, selection should be delayed until more advanced generations to achieve more reliable gains. The offspring of the cross between Ehsan and Kavir cultivars are being selected and tracked in the bread wheat breeding program in the northern warm and humid agro-climatic zone (Iran) in order to integrate desirable alleles
Material and Methods: To evaluate the genetic control of key agronomic traits in bread wheat, the parental lines and various generations from the Ehsan × Kavir cross were studied. In this study, Ehsan cultivar as the maternal line and Kavir cultivar as the paternal line played a role in producing the F1 generation. The experiment was set up as a split-plot arrangement within a randomized complete block design (RCBD), with three replications at the Gorgan Agricultural Research Station, during the 2022-2023 growing season. Two distinct irrigation conditions were applied: full irrigation and saline stress. Saline stress (10 dS m⁻¹) was introduced at two key growth stages: full spike emergence (Zadoks code 73) and early milk development (Zadoks code 60). Trait measurements were taken on 10 plants from the parent lines and the F1 generation, 30 plants for the F2 generation, and 15 plants from the backcross generations. After maturity, various agronomic traits, such as plant height, spike length, peduncle length, number of spikes per plant, number of spikelets per spike, number of grains per spike, thousand-kernel weight, and grain yield per plant, were assessed across all individuals. SAS9.4 software was used to perform analysis of variance, comparing means, and estimate genetic effects. Also, heritability and heterosis were calculated using Excel software.
Results: Variance analysis revealed that both the effects of stress and the stress × generation interaction had a significant impact on traits such as thousand-kernel weight and grain yield per plant. As a result, genetic analyses were performed separately for these traits under normal and saline stress conditions. The generation mean analysis revealed that the genetic models influencing thousand-kernel weight and grain yield differed under normal and saline stress conditions. For other traits, where stress effects and stress × generation interactions were not significant, the data were combined and analyzed together, making the results applicable to both environmental scenarios. Differences among generations were statistically significant for all traits studied. The chi-square test indicated that peduncle length, plant height, and spike length showed no significant differences. On the other hand, the chi-square test revealed significant differences for other traits, highlighting the inadequacy of the simple additive-dominance model and suggesting the involvement of epistatic effects, genetic linkage, and maternal influences in controlling these traits. The generation means analysis demonstrated that non-additive genetic effects played a more crucial role than additive effects in controlling the majority of traits, including spike length, number of grains per spike, number of spikelets per spike, number of spikes per plant, thousand-kernel weight, and grain yield per plant under both normal and saline stress conditions. Epistatic effects were particularly significant for most traits, and these traits exhibited low narrow-sense heritability. The variance analysis of generations revealed that traits such as spike length, number of grains per spike, number of spikelets per spike, number of spikes per plant, and grain yield per plant were predominantly influenced by overdominance. In contrast, for plant height and peduncle length, additive genetic effects were more influential than non-additive effects, and no epistatic effects were detected. Moreover, relatively high narrow-sense heritability was observed for plant height and peduncle length.
Conclusion: The results of this study showed that the genetic models effective on thousand-kernel weight and grain yield were different under normal and saline stress conditions. Additionally, under both environmental conditions, genetic improvement can be effectively achieved in plant height and peduncle length during the initial generations. However, for other traits, including grain yield and its components, selection should be delayed until more advanced generations to achieve more reliable gains. The offspring of the cross between Ehsan and Kavir cultivars are being selected and tracked in the bread wheat breeding program in the northern warm and humid agro-climatic zone (Iran) in order to integrate desirable alleles
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