Introduction: Barley (Hordeum vulgare L.) is the fourth most important cereal crop worldwide after wheat, maize, and rice, in terms of cultivated area and nutritional value. Its high tolerance to adverse environmental conditions has enabled wide adaptation across diverse agroecological regions. Barley grains are an important source of protein, dietary fiber, minerals, and bioactive compounds, making them valuable for both human and animal nutrition. Understanding the inheritance and genetic control of quantitative and qualitative traits is essential for selecting appropriate breeding strategies and improving yield and grain quality, particularly under abiotic stress conditions such as drought.
Materials and Methods: This study aimed to estimate genetic parameters of key agronomic and nutritional traits in barley. Ten barley cultivars with different geographic origins were evaluated using a randomized complete block design (RCBD) with three replications. The experiment was conducted over two cropping seasons (2022–2024) at a research farm located in Babil City, Al-Kifil district, southeastern Iraq. The cultivars were grown under two environmental conditions: normal irrigation and late-season drought stress, which was imposed by withholding irrigation at the anthesis stage. A total of four environments (two years × two moisture regimes) were evaluated. Twenty-seven traits were measured, including agronomic traits and grain quality attributes such as amino acid content, crude fiber, fat content, protein content, iron and zinc concentrations and water-soluble carbohydrate content. Combined analysis of variance across environments was performed, and genetic parameters were estimated.
Results and Discussion: The combined analysis of variance revealed significant differences among cultivars for all measured traits, indicating substantial genetic diversity among the evaluated barley genotypes. The cultivar × environment interaction was significant for all traits except flag leaf width, grain width, and grain iron content, suggesting differential genotypic responses to environmental conditions. The environment effect was significant for all traits except grain width, highlighting the strong influence of irrigation and drought stress on trait expression. Across the four environments, PCV and GCV values were generally close in magnitude for most traits, indicating a relatively small environmental influence and a predominant role of genetic factors. In the first year, physiological maturity showed the lowest environmental variation under both irrigation and stress conditions and exhibited the highest broad-sense heritability under irrigated conditions. In the second year, peduncle length displayed the lowest environmental variation under irrigation and the highest heritability under both moisture regimes. Spike density showed the highest genotypic and phenotypic coefficients of variation and the greatest genetic advance as a percentage of the mean in both years and under both irrigation and drought stress. Several traits, including grain filling period, flag leaf length and width, plant height, peduncle length, spike weight, grain weight per spike, number of grains per spike, number of spikes per square meter, spike density, grain yield, grain iron content, and grain fiber content, exhibited high heritability coupled with high genetic advance across years and environments. These results indicate that additive gene effects play a major role in controlling these traits, suggesting that phenotypic selection would be effective, particularly in early generations of breeding programs. In contrast, thousand-grain weight, grain zinc content, grain protein content, spike length (except in the second year under irrigated conditions), and grain length (in the first year under drought stress) showed high broad-sense heritability but low to moderate genetic advance. This pattern suggests the involvement of non-additive gene action, indicating that heterosis breeding or selection in later generations may be more effective for improving these traits.
Conclusion: The results demonstrated substantial genetic variability among barley cultivars for agronomic and grain quality traits under both irrigated and late-season drought stress conditions. Traits with high heritability and genetic advance are primarily governed by additive gene effects and can be efficiently improved through early-generation phenotypic selection. In contrast, traits influenced by non-additive gene action may benefit from heterosis-based breeding approaches. These findings provide valuable information for designing effective barley breeding programs aimed at improving yield and grain nutritional quality under water-limited environments.