Molecular Pathogens, 2025, Vol.16, No.5, 207-216 http://microbescipublisher.com/index.php/mp 214 such as backcrossing are often used in breeding to introduce resistance genes over multiple generations to eliminate adverse background effects and accumulate beneficial genes. In addition to genes, gene expression patterns in the background also play a role. The promoter methylation status and transcription level of resistance genes may be different in different genetic backgrounds, which in turn affects the strength of resistance. The developmental stage and organ identity of the host context are also critical. Many crops are more susceptible to viruses in their seedling stage and become more resistant in their mature stage, partly due to different gene expression profiles during the developmental stages. Some resistance-related genes are highly expressed in mature leaves, which enhances the resistance of adult plants. 7.3 Case analysis: study on the differences in resistance of different potato varieties under multi-virus co-infection To further illustrate the interaction of environmental and genetic factors, a case of differential resistance to multi-virus co-infection in potatoes is introduced here. In trials of late-maturing potato varieties in northern China, some studies compared the virus infection of a resistant variety A and a highly susceptible variety B under natural field conditions. The results showed that even under the natural high infection pressure of PVY, PLRV and other viruses, variety A maintained healthy growth throughout the season with no obvious symptoms and the yield was basically unaffected; while variety B showed symptoms of mosaic and curling leaves very early, and was tested to be infected with PVY, PVS and PLRV at the same time, resulting in a final tuber yield reduction of more than 50% (Figure 3). An in-depth analysis of the differences between the two varieties can be attributed to the following points: (1) different compositions of resistance genes; (2) background stress resistance; (3) differences in growth period; (4) environmental adaptability (Slater et al., 2020). Figure 3 Symptoms of Potato Virus Y infection on the cultivar Atlantic. Note the leaf mottling and the tuber necrosis (Adopted from Slater et al., 2020) Acknowledgments The authors would like to thank all teachers and colleagues who provided guidance and assistance during this research, and for the peer review's revision suggestions. Conflict of Interest Disclosure The authors confirm that the study was conducted without any commercial or financial relationships and could be interpreted as a potential conflict of interest. References Andika I., Maruyama K., Sun L., Kondō H., Tamada T., and Suzuki N., 2015, Differential contributions of plant Dicer-like proteins to antiviral defences against potato virus X in leaves and roots, The Plant Journal : for Cell and Molecular Biology, 81(5): 781-793. https://doi.org/10.1111/tpj.12770 Chen J., Mohan R., Zhang Y., Li M., Chen H., Palmer I., Chang M., Qi G., Spoel S., Mengiste T., Wang D., Liu F., and Fu Z., 2019, NPR1 promotes its own and target gene expression in plant defense by recruiting CDK81, Plant Physiology, 181: 289-304. https://doi.org/10.1104/pp.19.00124 Chen Z., Wu Q., Tong C., Chen H., Miao D., Qian X., Zhao X., Jiang L., and Tao X., 2021, Characterization of the roles of SGT1/RAR1 EDS1/NDR1 NPR1 and NRC/ADR1/NRG1 in Sw-5b-mediated resistance to tomato spotted wilt virus, Viruses, 13(8): 1447. https://doi.org/10.3390/v13081447
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