Triticeae Genomics and Genetics, 2025, Vol.16, No.2, 63-71 http://cropscipublisher.com/index.php/tgg 64 2 Overview of Salt Stress in Barley 2.1 Physiological and biochemical effects of salinity on barley growth Under salt stress, the response of barley plants is quite intuitive - the biomass of both above-ground and underground parts decreases, the water content of leaves drops, and the level of photosynthetic pigments also decreases (Figure 1) (Eldakkak and El-Shourbagy, 2023). Meanwhile, sodium ions (Na+) often accumulate excessively, while the absorption of potassium ions (K+) is inhibited. The Na+/K⁺ ratio is disrupted, making it more difficult to maintain cellular homeostasis and metabolism (Sadiq et al., 2024). However, not all varieties are the same. Some salt-tolerant barley can still maintain a relatively high K+/Na+ ratio and relatively good moisture conditions. From a biochemical perspective, salt stress can promote the increase of osmotic regulatory substances such as proline and soluble sugar, and also enhance the activity of antioxidant enzymes such as catalase, ascorbic acid peroxidase, and peroxidase. These reactions can to some extent alleviate oxidative damage. In the salt-sensitive type, the contents of malondialdehyde (MDA) and hydrogen peroxide (H2O2) tend to increase, indicating aggravated lipid peroxidation and oxidative stress (Yildiz and Acar, 2022). Figure 1 Illustrated the variation among barley genotypes under control condition and with 100 mM and 200 mM NaCl treatments (Adopted from Sadiq et al., 2024) 2.2 Genetic complexity and heritability of salt tolerance traits Salt tolerance is not a trait that can be explained by a single gene. It involves multiple physiological and molecular mechanisms (Ouertani et al., 2021). Among barley of different genotypes, the differences in these traits are quite obvious, such as ion homeostasis, antioxidant capacity, and accumulation of osmotic protectants, which usually have high heritability and are regulated by specific genotypes. Recent studies have identified some genomic loci and candidate genes highly correlated with salt tolerance, especially those key genes directly involved in ion transport and antioxidant defense. However, the situation behind this is not simple - the interaction between genotypes and the environment, the superposition of additive and non-additive effects, all make the genetic basis of salt tolerance more difficult to fully clarify (Abdelrady et al., 2024). 2.3 Conventional breeding limitations in improving salt stress resilience It is not easy for traditional breeding to make breakthroughs in salt tolerance. Polygenic control, significant environmental influence, and complex phenotypic traits all make the screening work slow and cumbersome (Boussora et al., 2024). Coupled with insufficient molecular markers and long breeding cycles, the launch speed of salt-tolerant varieties is naturally limited (Alqudah et al., 2024). These realities also explain why more advanced genomic approaches, such as genome-wide association studies (GWAS), are particularly necessary in analyzing the genetic structure of salt tolerance and promoting the breeding process.
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