Field Crop 2024, Vol.7, No.1, 9-16 http://cropscipublisher.com/index.php/fc 12 provides new ideas for revealing crop stress response mechanisms and developing stress-tolerant varieties (Lafarge et al., 2017). For example, using GWAS analysis, scientists identified key genes associated with drought response, salt stress tolerance, and cold resistance in multiple crops. GWAS technology has also been widely used in the study of plant growth and development, secondary metabolite synthesis, resistance to pests and diseases, etc. These studies not only enrich our understanding of plant physiological and ecological functions, but also provide scientific basis for crop genetic improvement and ecological environment protection. 2 Genetic Basis of Barley Resistance 2.1 Classification and genetic characteristics of inverse tolerance In nature, plants are confronted with various biological and abiotic adversities, which seriously affect the growth, development and yield of plants. In this context, understanding plant resistance, especially for important crops such as barley, has become a key area of agricultural science research. Adverse tolerance can be divided into two main categories: abiotic and biological stress tolerance. Abiotic stresses include extreme climatic conditions such as drought, salinity, high or low temperatures, and heavy metal contamination in soil, while biological stresses involve the invasion of pathogens and pests (Singh et al., 2019). A plant's ability to respond and adapt to these adversities, known as resilience, is controlled by complex genetic mechanisms, often involving the interaction of multiple genes. The genetic characteristics of reverse tolerance are characterized by polygenic control, variable gene effect sizes, environmental dependence, epistasis and phenotypic plasticity, which imply that reverse tolerance is a quantitative trait that is jointly influenced by multiple genes and environmental factors (Andersen et al., 2016). With the development of molecular biology techniques, especially the application of advanced methods such as genome-wide association analysis (GWAS), scientists are gradually revealing the genetic basis that controls resistance to reverse-resistance. These studies not only deepen researchers' understanding of the mechanisms by which plants survive and adapt to stress conditions, but also provide important molecular markers and candidate genes for the development of more resistant crop varieties. 2.2 Genetic markers associated with reverse tolerance in barley In agricultural genetics and breeding research, identifying genetic markers associated with crop resistance is key to improving crop resilience and yield. Barley (Hordeum vulgare L.) is an important food and feed crop in the world, and its resistance to reverse-resistance has attracted extensive attention. Genetic markers related to resistance to adverse stress can not only help researchers understand the molecular mechanism of barley response to stress (Binott et al., 2017), but also provide a powerful tool for molecular-assisted breeding, especially in improving abiotic stress tolerance of barley such as drought, salinity and low temperature. With the advancement of molecular biology techniques, especially the application of genome-wide association analysis (GWAS) and gene mapping techniques, researchers have successfully identified multiple genetic markers associated with resistance in the barley genome. These markers are usually located near key stress response genes or gene clusters, covering multiple levels such as signal transduction, gene expression regulation and metabolic pathway regulation. For example, some studies have found SNP markers related to drought tolerance in barley through GWAS analysis, which are located at or near known stress response genes. For example, genes in ABA (abscisic acid) signaling pathway, as well as some antioxidant oxidase genes, etc. (Tarawneh et al., 2020). In addition to abiotic stresses, the resistance of barley to pathogens is also an important aspect in the study of resistance to reverses. By locating genetic markers associated with resistance to specific diseases, the researchers were able to identify key genes that control barley disease resistance traits, such as resistance to rust, downy mildew and leaf spot. 2.3 Key resistance genes identified in previous studies In the field of crop resistance research, previous studies have successfully identified several key genes that play a critical role in the response and adaptation mechanisms of plants in the face of abiotic and biological stresses, especially in important crops such as barley. For example, the DREB gene family, as transcription factors, plays a
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