Introduction Barley is the fourth most common cereal crop in the world after wheat, maize, and rice, which is used for animal and human feed and malt production. This plant stands out among crops due to its unexpectedly wide range of adaptation and distribution compared to other cereals, earning it recognition as a model species. Determining the variation in the morphological and physiological traits of roots and shoots in the collection of barley genotypes can provide the basis for breeding new cultivars with suitable traits for better adaptation to specific environments. So in this study, some morphophysiological characteristics of roots and shoots of commercial barley cultivars were studied to identify cultivars with a higher root-to-shoot ratio as donor parents for breeding projects. Materials and Methods In this study, 21 barley cultivars were grown in a randomized complete block design with six replications in greenhouse conditions. Morphological and physiological traits related to roots and shoots were measured during the tillering and heading stages. Also, some traits affecting photosynthesis and yield during reproductive growth and harvesting stages were measured. Analysis of variance, mean comparison by LSD test at 5% probability level, and multivariate statistical analyses including principal components analysis, cluster analysis by Ward method, correlation analysis, and path analysis were performed by JMP and R statistical software. Results and Discussion Significant genetic diversity was observed for most of the traits among cultivars (P<0.05). At the tillering stage, Behrokh and Mehtab cultivars and in the heading stage, Jolgeh cultivar showed the highest dry weight of root to shoot ratio. Reyhan variety showed the lowest dry weight of root-to-shoot ratio in both stages. The carbohydrate content of the root in the tillering stage and leaf proline, root volume, and the ratio of chlorophyll a to carotenoid in the heading stage had the highest significant correlation coefficients with dry weight of root to ©2024 The author(s). This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0), which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source. https://doi.org/10.22067/jcesc.2024.84953.1274 122 شر ژشها  ر، د 22 ، ما 2، استا 1403 shoot ratio (P < 0.05). Path analysis revealed that the root carbohydrate content in the tillering stage and the ratio of chlorophyll to carotenoids and proline in the heading stage are the most effective traits of the dry weight of root-to-shoot ratio. Principal components analysis showed that the first and second principal components explain 33.63% and the first seven principal components explain 72.66% of the total changes. Also, the first principal component showed a positive and significant correlation with root to root-to-shoot ratio in the heading stage, and the second principal component showed a negative and significant correlation with this ratio (P<0.05). The studied cultivars were classified into four groups based on cluster analysis so that the fourth and second clusters in the tillering stage and the third and second clusters in the heading stage had the highest and the first cluster in both stages had the lowest dry weight of root to shoot ratio. Conclusion Based on the results, Jolgeh and Reyhan cultivars can be used in breeding programs to improve and produce cultivars with higher root-to-shoot ratio, optimal yield, and more adapted to specific environments. These cultivars had the highest and the lowest dry weight of root-to-shoot ratio in both stages, respectively. Also, they were placed in different dimensions of the biplot drawn based on the first two principal components. In addition, these cultivars were observed in different classes based on the cluster analysis

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