Molecular Pathogens 2024, Vol.15, No.3, 106-118 http://microbescipublisher.com/index.php/mp 108 Figure 1 The regular flow charts of molecular marker-assisted breeding programs involved in wheat cultivar improvements against biotic stresses (Adopted from Luo et al., 2023) Image caption: The near-isogenic lines developed from conventional hybrid breeding programs were employed for identification and mapping the resistance genes by adopting the diverse molecular markers, and many dominant genes and QTLs had been mapped on wheat chromosomes. Following that, many candidate genes or QTL allenes had been isolated from the wheat germplasms or its donor species with map-based cloning. Most wheat resistance genes belong to the NBS-LRR family, with the Fhb7 gene encoding a protein with Glutathione S-transferase. Yrs, stripe rust resistance genes; Lrs, leaf rust resistance genes; Sr, stem rust resistance genes; Pms, powdery mildew resistance genes; Dns, Russian wheat aphid Diuraphis noxia resistance genes; Gbs, greenbug Schizaphis graminumresistance genes; Sas, English grain aphid Sitobion avenae resistance genes; QFhbs, scab resistance QTLs; QRps, bird cherry-oat aphidRhopalosiphum padi resistance QTLs; QGb, green (Adopted from Luo et al., 2023) 3 Principles of Molecular Breeding 3.1 Definition and techniques Molecular breeding refers to the application of molecular biology tools to enhance the efficiency and precision of plant breeding. This approach leverages genetic information to select desirable traits, thereby accelerating the development of new cultivars with improved characteristics. Key techniques in molecular breeding include marker-assisted selection (MAS), quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and gene editing technologies such as CRISPR/Cas9. Marker-assisted selection (MAS) utilizes molecular markers linked to specific traits to identify and select plants that carry desirable genes. This method allows for the early selection of traits at the seedling stage, significantly reducing the time and cost associated with traditional breeding methods (Miedaner and Korzun, 2021; Jabran et al., 2023). QTL mapping involves identifying regions of the genome associated with quantitative traits, which are often controlled by multiple genes. This technique is particularly useful for traits like disease resistance, which are influenced by several genetic factors (Figure 2) (Jabran et al., 2023). Genome-wide association studies (GWAS) analyze the entire genome to find genetic variations associated with specific traits. This method provides a comprehensive understanding of the genetic architecture of complex traits and helps in identifying new genes for breeding programs (Jabran et al., 2023). Gene editing technologies, such as CRISPR/Cas9, allow for precise modifications of the plant genome, enabling the introduction or removal of specific genes to enhance disease resistance and other desirable traits (Mapuranga et al., 2022; Jabran et al., 2023). 3.2 Advantages over traditional breeding Molecular breeding offers several advantages over traditional breeding methods. One of the primary benefits is the increased speed and efficiency of developing new cultivars. Traditional breeding can take many years to achieve desired traits due to the need for multiple generations of crossing and selection. In contrast, molecular breeding techniques like MAS and gene editing can significantly shorten this timeline by allowing for the direct selection of plants with the desired genetic makeup (Luo et al., 2023; Jabran et al., 2023).
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