Triticeae Genomics and Genetics, 2025, Vol.16, No.4, 184-194 http://cropscipublisher.com/index.php/tgg 186 commonly used Fusarium head blight resistance gene, and some QTLs have also been found to provide partial resistance (Ma et al., 2021). Stb6 can help wheat resist leaf spot, and although Lr34 and Lr67 are not completely resistant, they can provide relatively stable, sustained, and effective partial resistance to multiple pathogens (Krattinger et al., 2016; Saintenac et al., 2018). These resistance genes were screened through traditional breeding, molecular mapping technology, and genomic methods developed in recent years (Juliana et al., 2018; Hafeez et al., 2021). 2.3 Limitations of single-gene resistance Although a disease resistance gene can sometimes play a strong role in disease prevention, this effect generally does not last long. Because pathogens change very quickly, they may be able to break through the defense line of this gene within a few years (Hao et al., 2023; Waites et al., 2025). Many disease resistance genes are "race-specific", that is, they can only protect against a certain type of pathogen and are ineffective against other types. This makes their resistance range very limited and not stable enough (Hafeez et al., 2021). In contrast, to make resistance longer, it is usually necessary to combine several different disease resistance genes together. This combination is sometimes called a "gene pyramid". It uses major and minor effect genes together to allow plants to resist different types of diseases at the same time, and the defense line is stronger (Ghimire et al., 2020; Mourad et al., 2024). Therefore, although a single disease resistance gene is important, it is not enough to deal with the complex disease problems in reality. This is why current molecular breeding emphasizes combining multiple disease resistance genes to take the route of sustainable disease resistance. 3 Principles and Methods of Gene Pyramiding 3.1 Definition and theoretical basis of gene pyramiding Gene aggregation is to combine multiple disease resistance genes into one wheat variety, so that it can produce long-term resistance to multiple diseases. The theoretical basis of this method is that different genes have different ways of disease resistance, and it will be more difficult for pathogens to break through all lines of defense at the same time. In this way, resistance is more stable and more effective (Dormatey et al., 2020). Now, scientists have also designed some mathematical models and family analysis tools to optimize hybridization plans and predict the possibility of successful combination of disease resistance genes (Servin et al., 2004). 3.2 Traditional breeding vs. molecular-assisted pyramiding In the past, breeders mainly relied on phenotypic selection and repeated hybridization to aggregate disease resistance genes. This method is relatively slow, and if the disease resistance trait is not obvious or affected by the environment, it is difficult to accurately distinguish which materials carry the target gene (Servin et al., 2004; Sivasamy et al., 2017). Now, with molecular-assisted breeding methods, breeders can use DNA markers linked to disease resistance genes to screen individuals with multiple target genes early on. Technologies such as marker-assisted selection (MAS) and CRISPR/Cas9 gene editing have greatly accelerated breeding, allowing multiple resistance genes to be introduced and confirmed simultaneously in one generation (Laroche et al., 2019; Dormatey et al., 2020; Gautam et al., 2020; Luo et al., 2021; Li et al., 2022). Moreover, these new technologies can also help avoid "linkage burden", that is, not bringing in some unwanted traits together, while also combining genes from different sources. 3.3 Criteria for selecting resistance genes for combination In order to make gene aggregation work, we must first select disease-resistant genes. When selecting genes, there are several aspects to pay attention to. It is best to choose genes with different disease resistance methods. For example, you can use both adult resistance genes and variety-specific resistance genes at the same time, so that the combination effect is better (Wang et al., 2022; Liu et al., 2020). You should also choose genes that are not alleles and are not linked. This can reduce the risk of losing the target gene during gene recombination (Laroche et al., 2019). The selected genes must be effective against common pathogens and also be able to prevent some emerging pathogens (Qie et al., 2019; Koller et al., 2023). These genes cannot have a negative impact on other traits of wheat. For example, they cannot reduce yield and quality, and they must be compatible with the genetic background of good varieties (Tyagi et al., 2014; Gautam et
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