Bioscience Evidence 2025, Vol.15, No.6, 303-312 http://bioscipublisher.com/index.php/be 305 3 Case Study One: Multi-Seasonal Field Trials of Rpi-amr1 / Rpi-amr3 Potatoes in Sweden (2018-2020) 3.1 Research background and objectives Late blight of potato, caused by oomycetes Phytophthora infestans, has long been a major threat to global potato production, causing severe economic losses and making production highly dependent on fungicides. With the increasing environmental and policy pressure to reduce chemical input, more sustainable disease management methods are becoming increasingly important. One effective direction is to introduce the resistance genes (Rpi genes) from wild potatoes into cultivated varieties. Solanum americanum is a wild species closely related to the common weed S. nigrum, and it has strong and broad-spectrum resistance to P. infestans. Researchers have cloned two genes, Rpi-amr1 and Rpi-amr3, fromS. americanumand demonstrated good resistance in both laboratory and early field trials. However, the stability of these genes under multi-year and natural disease conditions still needs further verification (Lin et al., 2022). 3.2 Resistance performance under natural infection conditions The field trial site was in southern Sweden, where the climate was suitable for the outbreak of late blight and the genetic diversity of the pathogen population was very high. During three consecutive growing seasons, transgenic Maris Piper carrying Rpi-amr1 and Rpi-amr3 was planted together with susceptible control varieties. No fungicides were sprayed throughout the entire test period to truly test the ability of the resistance gene. Researchers monitored the disease development throughout the season and collected P. infestans samples for genotype analysis (Resjö et al., 2025). The test results show that the materials carrying Rpi-amr1 and Rpi-amr3 exhibit strong resistance to late blight. Although there were occasional mild symptoms, the onset of the disease was significantly delayed, and the condition was much milder than that of the susceptible control group, which was completely infected shortly after the onset of the disease. More importantly, this resistance remained stable for three years, even when the weather conditions were different and even new genotypes with greater infectivity emerged (such as EU_41_A2). The emergence of these new genotypes did not increase the disease degree of transgenic materials (Lin et al., 2022). 3.3 Comparison with susceptible materials and single-gene materials All the susceptible controls were infected within a few weeks after the onset of the disease, the leaves completely rotted, and the yield was severely reduced. The Rpi-amr1 and Rpi-amr3 materials are almost unaffected throughout the season, and at the most severe times, only a few lesions appear at the end of the season. This distinct difference indicates that the genes derived fromS. americanumcan provide a very strong protective effect. Compared with single-gene materials, the advantages of combining multiple R genes are also more obvious. A single Rpi gene usually only provides partial resistance or the resistance lasts for a relatively short period of time. When Rpi-amr1 and Rpi-amr3 are stacked (gene stacking), the resistance is stronger and more stable. 3.4 Key finding: genes derived fromS. americanumprovide stable and strong resistance Rpi-amr1 and Rpi-amr3 can provide stable and strong resistance under natural infection conditions. Even in the face of a diverse population of P. infestans with new genotypes emerging year by year, they can effectively control the disease. The performance remained stable for three consecutive years. Although minor lesions occurred occasionally, they did not affect the health and yield of the plants (Lin et al., 2022). These prove that S. americanumis an important genetic resource for resisting late blight and is worthy of further in-depth exploration and utilization. At the same time, the importance of gene superposition was once again emphasized. Even a broad-spectrum gene like Rpi-amr3 performs better when combined with other R genes. 4 Case Study II: Field Trial of Transgenic Potatoes Resistant to Late Blight with Multiple Gene Superpositions 4.1 Gene superposition strategy (e.g. Rpi-vnt1.1 + Rpi-blb3 + Rpi-chc1) In the past, commercial potato varieties often contained only a single resistance gene (R gene), but this resistance usually only lasted for a very short time because pathogenic bacteria would quickly adapt and break through this
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