Molecular Plant Breeding 2024, Vol.15, No.2, 52-62 http://genbreedpublisher.com/index.php/mpb 54 that improve growth performance in high-salt environments by enhancing the elimination mechanism of salt-ionizing molecules. Cold-resistant traits enable crops to tolerate low temperatures and frost damage. The improvement of these traits usually involves regulating the expression of antifreeze proteins in plants, the stability of cell membranes, and the regulation of plant hormone levels. For example, some rice varieties have been genetically modified to enhance their survival and yield under low temperature conditions. Disease resistance traits involve the ability of crops to resist attack by pathogens such as bacteria, viruses, fungi and insects. Through traditional breeding and modern biotechnology, researchers have developed a variety of crop varieties that are highly resistant to disease. This includes genetically modified crops, which are endowed with specific resistance genes that effectively protect against attack by specific pathogens. 2.3 Introduction to the complexity and genetic basis of crop stress resistance traits The improvement of crop stress resistance traits is an important field in agricultural scientific research, especially in the context of global climate change posing increasingly severe challenges to agricultural production. In recent years, advances in genome-wide association studies (GWAS) and molecular biotechnology have provided new tools and methods to reveal the complexity of crop stress resistance traits and their genetic basis. Crop stress resistance traits, including drought resistance, salt resistance, disease resistance, etc., are complex traits controlled by multiple genes and involve a large number of genes and regulatory networks. For example, the response of plants to salt stress involves the salt hypersensitive (SOS) signaling pathway. The SOS1, SOS2, and SOS3 genes in this pathway play a key role in the ability of plant cells to exclude Na+ ions and maintain ion homeostasis. Through genetic engineering techniques, such as overexpressing the SOS2 gene in tomato and overexpressing the SOS1 gene in tobacco and sugar beet, plants' tolerance to salt stress can be significantly improved (Wang and Chang, 2024). In addition, under drought stress, plants perform physiological and metabolic regulation by expressing specific genes such as CYP450, ZmNF-YB16, ZmbZIP33, GNAC, and CodA family genes to enhance resistance or tolerance to drought. These genes are involved in regulating various physiological processes such as photosynthesis, enzyme activity, and plant hormone accumulation in plants (Mores et al., 2021). In terms of disease resistance, crop resistance to pathogens often involves complex host-pathogen interaction mechanisms. Modern molecular breeding technologies such as marker-assisted selection (MAS), genomic selection (GS) and effector science can effectively Identify and utilize genes or quantitative trait loci (QTL) related to disease resistance to accelerate the breeding process of crop disease resistance traits (Nardana et al., 2022). Research on these complex traits not only reveals the genetic mechanisms of crop stress resistance traits, but also provides new strategies and targets for future crop breeding. For example, precisely changing specific resistance genes through transgenic technology or gene editing technology (such as CRISPR/Cas9) can directly improve the stress resistance of crops while reducing adverse impacts on the environment. The improvement of crop stress resistance traits is a complex multidisciplinary field involving genetics, molecular biology, physiology and other disciplines. Through the comprehensive use of modern biotechnologies such as genome-wide association studies (GWAS), molecular markers, and genome editing, we can accelerate the research and application of crop stress resistance traits and contribute to ensuring global food security. 3 Introduction to GWAS Strategies 3.1 Basic principles and methods of GWAS Genome-wide association studies (GWAS) are a method of studying the association between genetic variation and specific traits by searching for frequently occurring variants (usually single nucleotide polymorphisms, SNPs) across the genomes of multiple individuals), to identify genetic markers that may influence specific traits. This
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