Triticeae Genomics and Genetics, 2024, Vol.15, No.2, 100-110 http://cropscipublisher.com/index.php/tgg 103 such as drought, salinity, and extreme temperatures. For instance, the development of synthetic hexaploid, hybrid, and transgenic wheats has expanded genetic variability and improved stress resistance (Rauf et al., 2015). Genetic engineering techniques, including transgenesis and genome editing, have further enhanced wheat's tolerance to environmental stresses, ensuring high yields without increasing cultivated land (Figure3) (Trono and Pecchioni, 2022). 4.4 Yield and quality improvement Wide hybridization has also contributed to yield and quality improvements in wheat. The integration of novel genetic diversity has led to the development of high-yielding and high-quality wheat varieties. For example, the BREEDWHEAT project has provided new molecular tools to breeders, enabling the efficient analysis and structuring of genetic diversity, which is crucial for developing high-yielding varieties (Paux et al., 2022). Additionally, the use of high-throughput phenotyping, genome sequencing, and genomic selection has accelerated genetic gains, resulting in more productive wheat varieties (Mondal et al., 2016). The Xiaoyan series of wheat cultivars, developed through wide hybridization, also exhibit good adaptability and high yield potential (Li et al., 2015). Wide hybridization has significantly contributed to wheat breeding by introducing novel traits, improving disease resistance, enhancing abiotic stress tolerance, and improving yield and quality. These advancements are crucial for meeting the global demand for wheat in the face of increasing environmental challenges and population growth. Figure 1 Schematic representation of the signalling pathway leading to the plant response to abiotic stresses (Adopted from Trono and Pecchioni, 2022) Image caption: Specific receptors in the plasma membrane perceive the external stress signal and transmit the signal intracellularly through phytohormones and secondary messengers, such as calcium (Ca2+) and reactive oxygen species (ROS); The second messengers activate different classes of protein kinases, including mitogen-activated protein kinase (MAPK) cascade, calcium-dependent protein kinases (CDPKs), and calcineurin-B-like proteins-interacting protein kinases (CIPKs), and protein phosphatases, such as protein tyrosine phosphatases/dual-specificity phosphatases (PTPs/DSPs), protein phosphatases 2C (PP2Cs), and serine/threonine-specific protein phosphatases (PPPs); Subsequently, the protein kinases and phosphatases catalyze the phosphorylation/dephosphorylation of transcription factors, including APETALA2/ethylene response element-binding factors (AP2/ERF), the large NAC family, basic leucine zipper (bZIP), WRKY, and MYB; These finally regulate the expression of abiotic stress-responsive genes encoding heat shock proteins (HSPs) and other chaperones, late embryogenesis abundant (LEA) proteins, enzymes involved in the biosynthesis of osmolytes, antioxidant enzymes and enzymes involved in the biosynthesis of small antioxidant molecules, aquaporins and ion transporters, which contribute to the tolerance of wheat to abiotic stresses (Adopted from Trono and Pecchioni, 2022) 5 Methodologies in Wide Hybridization 5.1 Cross-breeding techniques Cross-breeding techniques are fundamental in wide hybridization, allowing the combination of desirable traits from different parental taxa. This process can be categorized into sexual and somatic hybridization. Sexual
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