Triticeae Genomics and Genetics, 2025, Vol.16, No.3, 120-129 http://cropscipublisher.com/index.php/tgg 121 2 Rationale for Gene Stacking in Wheat 2.1 Overcoming pathogen evolution and resistance breakdown In the wheat fields, rust and powdery mildew are almost always present. The key issue is not just that they "come frequently", but that they "become faster". Pathogenic bacteria can constantly evolve into stronger new strains. Once a certain resistance gene is identified, the original disease-resistant variety will be quickly breached, and yield loss will follow. Relying on a single gene is often just a temporary matter. Then, is there any way to prevent pathogenic bacteria from making a move? Genetically modified superposition technology offers a direction. It is not simply adding defense lines one by one, but concentrating multiple resistance genes at one site to build a composite barrier. In this way, it becomes much more difficult for pathogens to bypass all resistance mechanisms at once. Some studies have pointed out that this strategy can indeed enable wheat strains to maintain stable resistance to a variety of highly virulent pathogenic bacteria, and the situation of resistance failure is also reduced (Aravindh et al., 2020; Jost et al., 2023; Yu et al., 2023). 2.2 Enhancing durable and broad-spectrum resistance It's not that the superposition of resistance genes is merely a quantitative accumulation; what matters is the combination. Some genes offer early recognition, while others act as a buffer layer for delayed onset. Whether it is the R gene or the resistance gene at the mature plant stage, their combination not only prolongs the resistance period but also broadens the disease resistance spectrum. Not just one disease can be prevented, such as stem rust, leaf rust and powdery mildew. Multiple "enemies" can also be caught in one net. Sometimes, when several genes come together, they can produce a stronger synergistic effect than when used alone (Figure 1). Under high disease stress conditions, the resistance performance of this combination is particularly stable. Even if the climate or region changes, the effect will not be compromised. What is even more worth mentioning is that some "rare genes" in wild relatives can also be utilized in this model to enrich the resistance resources (Singla et al., 2016; Dinglasan et al., 2022; Li et al., 2024). 2.3 Addressing environmental and agricultural demands In the past, people might have been more concerned about "whether there were disease-resistant genes", but now the question has become "whether less medicine can be taken". Climate change is becoming increasingly difficult to predict, the pressure for agricultural intensification is also growing, and chemical control is facing more and more restrictions. Against this backdrop, the superimposition of resistance becomes particularly realistic. It reduces the reliance on fungicides and also makes the breeding of disease-resistant varieties more efficient. The traditional breeding process is complex and time-consuming. However, gene superposition technology can accelerate this step and also alleviate some ecological and regulatory pressures. For farmers, this is not only related to the stability of output, but also a means to deal with the challenges of future agriculture. To some extent, it is also laying the foundation for the resilience of agricultural ecosystems (Hafeez et al., 2021; Saintenac et al., 2021; Zhao et al., 2024a). 3 Transgenic Strategies for Resistance Gene Stacking in Wheat 3.1 Direct genetic transformation techniques The Agrobacterium-mediated method and gene gun technology, these two seemingly "old-fashioned" transformation approaches, have instead played a key role in the superposition of resistance genes. In the past, people thought they were rather crude, but in fact, nowadays this kind of direct transformation method can precisely introduce multiple resistance genes at the same locus, even bringing in genes from distant species, thus bypassing the common pairing problem in traditional breeding. Especially in the application of multi-gene boxes, recent studies have shown that they can be stably transferred into wheat and exhibit good resistance to highly toxic pathogens (Camenzind et al., 2024). Moreover, the efficiency is not low. Sometimes, based on the prevalence of diseases in different regions, specific gene combinations can be selected for transformation, which is more in line with the actual planting needs.
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