Molecular Pathogens, 2025, Vol.16, No.2, 69-76 http://microbescipublisher.com/index.php/mp 73 6 Case Studies and Field Applications 6.1 Successful integration of resistance genes in commercial maize varieties In commercial corn breeding, adding disease-resistant genes has achieved good results. For example, Htn1 is a gene that can fight Northern Leaf Blight (NCLB) and it can produce strong resistance. Now, this gene has been successfully introduced into multiple breeding materials. In addition, some studies have also tried to introduce the Lr34 gene of wheat into corn. Experiments show that this gene can help corn resist both common rust and northern leaf blight (Sucher et al., 2016). These examples show that using resistance genes can effectively reduce the loss caused by diseases and also help maintain stable yields. 6.2 Regional field trials for fungal disease-resistant maize Perform regional experiments in the field to see how effective the disease-resistant genes are in different environments. For example, in sub-Saharan Africa, several QTLs (quantitative trait sites) related to NCLB resistance were found, and these QTLs have now been used as marker targets in breeding (Ndlovu et al., 2024). In other places, it has been shown that the gene ZmWAK-RLK1 is indeed able to enhance corn's resistance to NCLB. It was also found that the content of benzooxazines in those disease-resistant varieties decreased, which may be related to increased resistance (Yang et al., 2018). These examples show that it is necessary to conduct experiments in different places. Because only genes that are adapted to multiple environments are suitable for commercial varieties. 6.3 Lessons learned from breeding programs Researchers have accumulated a lot of experience in the corn breeding program. For example, they found several stable QTL and candidate genes associated with Fusarium and Gibberia spike rot, which contributed to improving breeding efficiency (Akohoue and Miedaner, 2022). In the study of northern leaf blight resistance, scientists found that ZmWAK-RLK1 is one of the main disease-resistant sites. This gene encodes a wall-related kinase, which includes a sugar-binding domain, a transmembrane region, and a region called “non-RD-type kinase”, which are key parts of its function. In addition, different alleles (such as Ht2, Ht3 and Htn1) have some structural changes in amino acids. These changes may affect how corn recognizes the effectors secreted by bacteria, thereby triggering different immune responses. Experiments have been conducted in greenhouses and fields, and it was found that those corn with ZmWAK-RLK1 mutations responded more severely to the disease. This further demonstrates the important role of this gene in disease resistance (Figure 2) (Yang et al., 2021). These research experiences also remind us that in disease-resistant breeding, traditional methods and molecular means should be combined so that stronger and more reliable corn varieties can be bred. 7 Challenges and Opportunities in Maize Resistance Research 7.1 Overcoming genetic constraints in resistance breeding In corn breeding, disease resistance is not easy to choose. The main problem is that most disease-resistant traits are not controlled by a single gene, but are determined by many genes together. This characteristic, called "polygenetic traits", makes the breeding process more complicated. However, scientists now have new tools such as genome-assisted breeding, QTL (quantitative trait loci) analysis and marker-assisted selection. These techniques can more accurately select disease-resistant varieties (Dossa et al., 2023). If traditional breeding methods and modern technologies are combined, the breeding speed and accuracy can be improved, and corn with stronger disease resistance can be selected. 7.2 Addressing pathogen evolution and emerging threats Pathogens will continue to evolve, which is a long-term challenge to corn's disease resistance. After the germs or pests mutate, the original resistance gene may be useless. For example, when planting Bt corn, some pests (such as Western corn rootworms) have gradually developed resistance to Bt toxins, resulting in a decrease in the effectiveness of Bt corn (Andow et al., 2015). To cope with this situation, researchers recommend flexible methods, such as monitoring bacterial population changes, or combining multiple prevention and control measures, such as integrated pest management (IPM). In addition, when breeding, we cannot rely on only one
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